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Oxalate-bridged dinuclear Cr(III)-M(II) (M = Cu, Ni, Co, Fe, Mn) complexes: Synthesis, structure, and magnetism
Abstract
The following oxalate-bridged heterodinuclear Cr(III)-M(II) (M = Cu, Ni, Co, Fe, Mn) complexes have been synthesized: [Cr(salen)(ox)Cu(acpy)] (1) (salen = N,N'-ethylenebis(salicylideneaminate), ox2- = oxalate ion, acpy = N-acetylacetonylidene-N-(2-pyridylethyl)aminate) and [Cr(salen)(ox)M(taea)](BPh4) (M = Ni (2), Co (3), Fe (4), Mn(5))(taea = tris(2-aminoethyl)amine). The [Cr(salen)(ox)Cu(acpy)]2DMF.MeOH(1') complex in the monoclinic system of the space group P2(1)/n with a = 16.429(6) angstrom, b = 25.303(14) angstrom, c = 10.191(4) angstrom, beta = 109.78(2)degrees, V = 3986(3) angstrom3, and Z = 4. The refinement converges with R = 0.079 and R(w) = 0.071 based on 3327 reflections with \F(o)\ greater-than-or-equal-to 3sigma(\F(o)\). The complex has an oxalate-bridged dinuclear Cr(III)-Cu(II) core with a Cr...Cu distance of 5.482(3) angstrom. The Cr(III) has a cis-beta octahedral geometry with the tetradentate salen in the folded form and a bidentate oxalate group. The geometry around the Cu(II) ion is square-pyramidal with the three donor atoms of acpy and one of the oxalate oxygens at the basal plane and the other oxygen of the oxalate group at the apex. Magnetic investigations of 1-5 in the 4.2-300 K temperature range reveal a ferromagnetic interaction between the Cr(III) and M(II) ions for all the complexes. On the basis of the spin Hamiltonian, H = -2JS(Cr).S(M), the values for the spin coupling constant J were estimated to be +2.8, +4.6, +1.3, +0.8, and +0.5 cm-1 for 1-5, respectively. The relative magnitude of the J values is explained by the sigma- and pi-pathways through the oxalate bridge. The correlation between the J values of 1-5 and the phase-transition temperatures, T(C), of the ferromagnetic {NBu4-[MCr(ox)3]}x (M = Cu, Ni, Co, Fe, Mn) is discussed based on Heisenberg's ferromagnet model.
... This polymer is the first structurally characterized compound in which copper(II) and chromium(III) centers are connected by bis(bidentate) oxalate group having one-dimensional arrangement [4]; only one heterotrinuclear compound with these metals has been known, prepared by using the [Cr(C2O4)3] 3-anion [46]. Two dinuclear [47,48], one trinuclear [49] and one tetranuclear [50] oxalate-bridged compounds containing copper(II) and chromium(III) atoms were found in the literature, but they were synthesized without using tris(oxalato) building block. ...
... This polymer is the first structurally characterized compound in which copper(II) and chromium(III) centers are connected by bis(bidentate) oxalate group having one-dimensional arrangement [4]; only one heterotrinuclear compound with these metals has been known, prepared by using the [Cr(C 2 O 4 ) 3 ] 3− anion [46]. Two dinuclear [47,48], one trinuclear [49] and one tetranuclear [50] oxalate-bridged compounds containing copper(II) and chromium(III) atoms were found in the literature, but they were synthesized without using tris(oxalato) building block. ...
... Ion Cr 3+ in the octahedral configuration has three unpaired electrons on the , and orbitals interacting with other occupied orbitals of the oxalate group, producing magnetic orbitals of -character. The overall superexchange interaction is expected to be ferromagnetic due to orthogonality of all these magnetic orbitals [48]. In other compounds with oxalate-bridged [Cu II Cr III ] dimer where the symmetry is such that the ferromagnetic coupling can be achieved due to orthogonality of magnetic orbitals, the ferromagnetic exchange is of comparable value [46][47][48]. ...
One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]·1.5H2O}
n
(1) (bpy = 2,2'-bipyridine) and heterodimetallic {[CrCu3(bpy)3(CH3OH)(H2O)(C2O4)4][Cu(bpy)Cr(C2O4)3]·CH2Cl2·CH3OH·H2O}
n
(2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}
n
(3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalate)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions was mediated by oxalate ligands in the chain [Mn(bpy)(C2O4)]
n
of 1, with intra-chain super-exchange interaction ? = (-3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C2O4)3]
n
n
- (Cr2-Cu4) with alternating [Cr(C2O4)3]3
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and [Cu(bpy)]2+ units mutually bridged through the oxalate group. Another chain (Cr1-Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H2O)(µ-C2O4)Cu(bpy)(CH3OH)]2+ (Cu1-Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1-Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1-Cu3 and Cr2-Cu4. A 3D polymer {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}
n
(3) comprising three different metal centers (Ca2+, Cr3+ and Cu2+) oxalate-bridged, contains Ca2+ atoms as nodes connected with four Cr3+ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (66) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [CuIICrIII], whose mutual interaction could possibly originate through the spin polarization of Ca2+ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.
... The influence of the nature of the bridging X, Y, Z and W atoms [8,14] and of the terminal ligand T [20] on the exchange interaction has been studied, as well as the exchange pathways in heterobimetallic μ-oxalato complexes, dinuclear species, [21,22] oligonuclear entities, [23] and 1D, [24] 2D or 3D systems. [25][26][27][28][29][30][31][32][33][34] Most often, the magnetic properties are in line with simple orbital models. ...
... [25][26][27][28][29][30][31][32][33][34] Most often, the magnetic properties are in line with simple orbital models. [35][36][37][38] The intramolecular ferromagnetism arising from the strict orthogonality of the magnetic orbitals in [Cu II -V IV O], [39] [Cu II -Cr III ], [22] [Ni II -Cr III ] [23] and even [Cu II -Cu II ] [40] is particularly striking. ...
... The yield was practically quantitative. C 22 [Cu 2 (bpy) 2 (NO 2 ) 2 (C 2 O 4 )] (5): An aqueous solution of copper(II) nitrite (1 mmol) was generated by a metathesis reaction between copper(II) sulfate pentahydrate and barium(II) nitrite in a 1:1 molar ratio. Solid 2,2′-bipyridine was added to the resulting green solution after the removal of the barium(II) sulfate precipitate. ...
We report the preparation, crystal structure determination, magnetic properties and DFT calculations of five oxalato-bridged dicopper(II) complexes of formula [Cu2(bpy)2(H2O)2(C2O4)](CF3SO3)2 (1), [Cu2(bpy)2(C2O4)](PF6)2 (2), [Cu2(bpy)2(C2O4)](ClO4)2 (3), [Cu2(bpy)2Cl2(C2O4)]·H2O (4) and [Cu2(bpy)2(NO2)2(C2O4)] (5) (bpy = 2,2′-bipyridine and C2O42– = oxalate). Compounds 1, 2, 4 and 5 crystallize in the monoclinic system and 3 crystallizes in the triclinic system. The oxalate ligands in 1–5 adopt the bis-bidentate coordination mode and the two bpy molecules act as terminal ligands. The coordination of the counterions and the surroundings of the copper(II) ions differentiate the five compounds. The four nearest neighbours of copper(II) in 1–4 are roughly in the plane of the CuC2O4Cu framework, whereas they are in an almost perpendicular plane in 5. Using the isotropic Hamiltonian H = –J S1·S2, where S1 and S2 are the spin quantum operators for Cu1 and Cu2; J is –384 cm–1 for 1, –392 cm–1 for 2 and –387 cm–1 for 3, slightly decreasing to –328 cm–1 for 4 and falling to –14 cm–1 for 5. The influence of the anions on the magnetic properties of this family of compounds is explained by the changes in the overlap of the magnetic orbitals through the oxalate bridge. DFT calculations reproduce well the experimental values of J and provide an illustration of the magnetic orbitals.
... The bands at 3336-3342 and 3217-3222 cm À1 are assigned to the symmetric and asymmetric NH stretch, and are obviously red-shifted relative to those of free [Fe(DABP) 3 ]SO 4 Á9H 2 O (3420 and 3340 cm À1 ), [11] indicating the formation of hydrogen bonds from amino groups to the oxalate oxygen atoms (see below). [14] Single-crystal X-ray diffraction analyses reveal that the five compounds are isomorphous, crystallizing in the space group R-3c. Thus only the compound [Cu(DABP) 3 ] 3 [Cr(C 2 O 4 ) 3 ] 2 Á 14H 2 O (1) is described in detail as a representative. ...
... In the hydrogen-bonded five-metal [Cu(DABP) 3 ] 3 [Cr (C 2 O 4 ) 3 ] 2 (A 3 B 2 ) SBU ( Fig. 1b) 14 cluster forms a six-cornered star with S 6 symmetry when the hydrogen-bonded O-O contacts from 2.69 to 3.1 Å (typical for embedded water clusters) [15] between the 14 O atoms are taken into account (Fig. 3). The star-shaped (H 2 O) 14 cluster is constructed from six corrugated six-membered rings (in the book conformation) that are mutually fused through two adjacent edges each (Fig. 3). ...
... The star-shaped (H 2 O) 14 cluster is constructed from six corrugated six-membered rings (in the book conformation) that are mutually fused through two adjacent edges each (Fig. 3). Although such a discrete water cluster cannot be given an exact motif according to Infantes' classification for (H 2 O) n clusters, [16] its structure is very similar to another (H 2 O) 14 aggregate reported recently that also features the fused, book-conformation cyclic hexamers. [17] Both tris-chelated [Cu(DABP) 3 ] 2þ and [Cr(C 2 O 4 ) 3 ] 3À units have metal-centered L or D-chirality. ...
A series of isomorphous second-sphere coordination compounds [M-II(DABP)(3)](3)[Cr(C2O4)(3)](2)center dot 14H(2)O (DABP = 5,5'-diamino-2,2'-bipyridine; M = Cu (1), Ni (2), Fe (3), Zn (4), and Mn (5)) have been constructed through multiple charge-assisted N-H-O- hydrogen-bonding interactions between the oxalate ligands in [Cr(C2O4)(3)](3-) (unit B) and the NH2 groups in the [M(DABP)(3)](2+) complex (unit A). The chiral [M(DABP)(3)](2+) cations and [Cr(C2O4)(3)](3-) anions with the same Lambda (or Delta) configuration interdigitate alternately, affording linear A(3)B(2) secondary building units. Two adjacent A(3)B(2) units adopting opposite configurations are linked by a six-cornered star-shaped 14-water cluster of S-6 symmetry (unit C) to form a racemic 1D linear chain -A(3)B(2)(Lambda)-C-A(3)B(2)(Delta)-C-. The microstructure of compound 1 shows a 3D flower-like morphology.
... It should be emphasized that the oxalate delivery process of [Nb V O(C 2 O 4 ) 3 ] 3anion was observed indirectly in the presence of chromium(III) perchlorate and bis(2,2′-bipyridyl)chromium (III) cation at room temperature, yielding molecular squares with the formulae [{Cr(dmso) 4 17 In addition to the structural interest in the oxalate ligand to design coordination polymers because of its well-known capability to adopt a great variety of bridging modes, 18 its ability to mediate significant magnetic interactions between spin carriers whose magnitude and sign can be predicted [19][20][21][22][23][24][25] is at the origin of a great number of discrete homo-and heterobimetallic compounds 18,[26][27][28][29][30] and 1D, [31][32][33][34] 2D or 3D motifs [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] exhibiting interesting magnetic properties. A remarkable feature is the occurence of intramolecular ferromagnetic coupling; this arises in the case of orthogonality between the interacting magnetic orbitals, as illustrated by the oxalate-bridged [Cu II -V IV O], 50 [Cu II -Cr III ], 27 [Ni II -Cr III ] 28 couples and even in [Cu II -Cu II ] 51 pairs. ...
... It should be emphasized that the oxalate delivery process of [Nb V O(C 2 O 4 ) 3 ] 3anion was observed indirectly in the presence of chromium(III) perchlorate and bis(2,2′-bipyridyl)chromium (III) cation at room temperature, yielding molecular squares with the formulae [{Cr(dmso) 4 17 In addition to the structural interest in the oxalate ligand to design coordination polymers because of its well-known capability to adopt a great variety of bridging modes, 18 its ability to mediate significant magnetic interactions between spin carriers whose magnitude and sign can be predicted [19][20][21][22][23][24][25] is at the origin of a great number of discrete homo-and heterobimetallic compounds 18,[26][27][28][29][30] and 1D, [31][32][33][34] 2D or 3D motifs [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] exhibiting interesting magnetic properties. A remarkable feature is the occurence of intramolecular ferromagnetic coupling; this arises in the case of orthogonality between the interacting magnetic orbitals, as illustrated by the oxalate-bridged [Cu II -V IV O], 50 [Cu II -Cr III ], 27 [Ni II -Cr III ] 28 couples and even in [Cu II -Cu II ] 51 pairs. The main goal of this synthetic route is to produce complexes with controlled molecular architectures with potential applications in fields such as magnetism, 52 catalysis, 53 optical, 54 electronics 55 and drug delivery. ...
Four compounds of formula [M2(dmphen)4(μ-C2O4)](ClO4)2 . 2dmso [M = Fe (1), Co (2) and Zn (4); dmphen = 2,9-dimethyl-1,10-phenantroline] and [Ni2(dmphen)4(μ-C2O4)]3[NbO(C2O4)3]2. 16H2O (3) have been synthesized by using the tris(oxalato)oxoniobate(V) complex anion as the source of oxalate and their structures have been determined by single crystal X-ray diffraction. X-ray quality crystals of highly insoluble oxalate-bridged species are obtained by taking advantage of the slow release of oxalate by the tris(oxalato)oxoniobate(V) complex anion.The structures of 1-4 have in common the occurrence of oxalate-bridged dimetal(II) units with didentate dmphen molecules acting as end-cap ligands, the electroneutrality being achieved by perchlorate (1-4) and oxotris(oxalate)niobate(V) (3) anions. Each divalent metal ion in 1-4 is tris-chelated in a six-coordinate distorted octahedral environment. The niobium(V) ion in 3 is seven-coordinate in a distorted pentagonal bipyramidal geometry built by one oxo group and six oxygen atoms from three didentate oxalate ligands. The values of the metal-metal separation across the bis-chelating oxalate are 5.626(1) (1), 5.575(1) (2), 5.434(1)-5.447(1) Å (3) and 5.603(1) Å (4). The cryomagnetic measurements in the temperature range 2.0-300 K for compounds 1-3 show the occurrence of antiferromagnetic interactions between the divalent metal ions across the oxalate bridge. The nature and amplitude of these magnetic interactions are rationalized by simple symmetry considerations and compared with those previously reported for related oxalate-bridged systems.
... Metal-organic frameworks (MOFs) 1 are indeed structurally diverse platforms that allow the introduction of not only a single property such as gas storage, sensors, magnetism or catalysis but of several properties leading to multifunctional materials. Since their discovery, 2 have attracted a lot of attention in that direction because the anionic network provides magnetic properties and is able to host a wide variety of functional cations, paving the way to a rational synthesis of magnetic multifunctional materials. 3 In particular, electron conduction was observed in such networks through the insertion of tetrathiafulvalene (TTF) cationic stacks between the anionic layers 4 leading to the synthesis of a molecular ferromagnetic conductor. ...
... 2nÀ/nÀ networks. 2,3 This example raised questions about (i) the metal stoichiometry and the topology of such networks and (ii) the mechanisms of the proton conduction in such high dimensional architectures. ...
The reproducible formation of a 3D oxalate based coordination compound of formula (NH4)5[Mn(II)2Cr(III)3(ox)9]·10H2O, with an unusual Mn(II)/Cr(III) ratio, is presented. The original topology of the anionic network leads to antiferromagnetic long-range ordering whereas its guests favour high humidity-dependent proton conductivity.
... The molecular-based magnetic materials have shown spectacular advances [12] in which the study of binuclear complexes has played an important and leading role. A number of binuclear complexes have been synthesized and their magnetic properties have been investigated [13][14][15]. The chemistry of multinuclear copper complexes has raised considerable interest for their possible utility to understand the fundamental science of magnetic interactions and magneto-structural correlations in molecular systems [16]. ...
AbstractA new Cu(II) dinuclear complex, Cu2L2 (1) was afforded employing the potentially pentatentate Schiff base precursor H2L, a refluxed product of o-vanillin and diethylenetriamine in methanol. Complex 1 was systematically characterized by FTIR, UV–Vis, emission and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 reveals that the copper atom exhibits a distorted square planar geometry, comprising two pairs of phenolato-O and imine-N donors from two different H2L ligands. The temperature dependent magnetic interpretation agrees with the existence of weak antiferromagnetic interactions between the bridging dinuclear Cu(II) ions. A considerable body of experimental evidence has been accumulated to elucidate the magneto-structural relationship in this dinuclear Cu(II) complex by DFT computation. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy on M. tuberculosis H37Ra (ATCC 25177) and M. tuberculosis H37Rv (ATCC 25618) strains. The practical applicability of the ligand and complex 1 has been examined in living cells (African Monkey Vero Cells). The MTT assay proves the non-toxicity of the probe up to 100 mg mL−1. Graphical abstractA new homometallic dinuclear Cu(II) complex is afforded with a tetradentate Schiff base precursor. EPR interpretation and temperature dependent magnetic studies show that complex 1 has weak antiferromagnetic coupling and DFT computation is governed to explain the magneto-structural correlation.
... 940 The syntheses of polymeric compounds of the general formula {(NR 4 )[M II -Cr(ox) 3 ]} n (a typical structural unit is represented by (183)) were first reported in 1992; 616 about 20 such complexes have been characterized since then (by X-ray crystallography and magnetic measurements). 611,[940][941][942][943][944][945][946][947][948][949][950][951][952][953][954][955][956][957] Three-dimensional architectures of the anionic assemblies are determined by the choice of counter-cations. 614 Recently, the first example of a monodentate coordination of the [Cr(ox) 3 ] 3À unit to Cu II , (184), has been reported. ...
This provides a comprehensive review of the structures and chemistry of chromium coordination chemistry from 1987 until 2003, with some refrences to structures reported in the First Edition.
... Many studies are devoted to the substitution of one or two oxalate anions in this system by a neutral or ionic ligand (L) to give new building blocks which have a significant effect on the overall structure of the supramolecular compound. In light of this, some studies have been carried out with L = N,N 0 -bis(salicylidene)ethylenediaminate (salen 2À ; Ohba et al., 1993), acetylacetonate (acac À ; Sanada et al., 1998), 2,2 0 -bipyridine (bpy; Muñ oz et al., 1998), 1,10-phenanthroline (phen; Vallejo et al., 2010), 2,2 0 -bipyrimidine (bpym; De Munno et al., 1999; Marinescu et al., 2002), 2,2 0 -dipyridylamine (dpa; Lescouë zec et al., 2001; Vivas et al., 2004 ) and 4,4 0 - dimethyl-2,2 0 -bipyridine (dmbpy; Viciano-Chumillas et al., 2010). The introduction of these organic ligands containing N-donor atoms into the metal–oxalate system not only prevents the formation of highly insoluble oxalate species but also influences the nuclearity and the topology of the metal centres and stabilizes their solid-state structure (Marinescu et al., 2004). ...
The title compound, [KCr(C2O2)2(C6H8N2)]n, was obtained from aqueous solution and analyzed with single-crystal X-ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/c and displays a three-dimensional polymeric architecture built up by bimetallic oxalate-bridged Cr(III)-K helical chains linked through centrosymmetric K2O2 units to yield a sheet-like alternating P/M arrangement which looks like that of the previously described two-dimensional [NaCr(ox)2(pyim)(H2O)]·2H2O [pyim is 2-(pyridin-2-yl)imidazole; Lei et al. (2006). Inorg. Chem. Commun. 9, 486-488]. The Cr(III) ions in each helix have the same chirality. The infinite neutral sheets are eclipsed with respect to each other and are held together by a hydrogen-bonding network involving 2-(aminomethyl)pyridine H atoms and oxalate O atoms. Each sheet gives rise to channels of Cr4K4 octanuclear rings and each resultant hole is occupied by a pair of 2-(aminomethyl)pyridine ligands with partial overlap. The shortest Cr...Cr distance [5.593 (4) Å] is shorter than usually observed in the K-M(III)-oxalate family.
Seven novel oxalate-based [CuIICrIII] compounds: [Cu4(terpy)4Cl5][Cr(C2O4)3]·9H2O (1; terpy = 2,2′:6′,2′′-terpyridine), {[Cr2Cu4(H2O)2(terpy)4(C2O4)7]·10H2O}n (2), [Cr2Cu4(H2O)2(terpy)4(C2O4)7]·12H2O (3), [Cu(H2O)3(terpy)][CrCu(H2O)(terpy)(C2O4)3]2·9H2O (4), [Cu(H2O)(terpy)(NO3)][CrCu(H2O)(terpy)(C2O4)3]·6H2O (5), [CrCu2(terpy)2(C2O4)3(NO3)]·1.5H2O·CH3OH (6) and [Cr2Cu4(H2O)4(terpy)4(C2O4)6][Cr2Cu2(terpy)2(C2O4)6]·9H2O·CH3OH (7) were obtained from the reaction of an...
An unknown manganese(II) oxalate complex [MnC2O4]•0.5H2O (1) was discovered with novel three-dimensional structure, exhibiting versatile bridging modes of oxalate ligand. Thermal and magnetic behaviors of this complex were studied and...
The review is part of a series of articles which introduce the emerging concept of inverse coordination. The article presents a panorama of inverse coordination complexes (i.e. metal compounds displaying an arrangement of acceptor and donor sites opposite to that occurring in conventional coordination complexes) built around oxalato anions and sulfur, selenium and nitrogen analogues. It covers the molecular topologies of metal complexes with oxalate, tetrathiooxalate, trithiooxalate, dithiooxalate, dithioamide, selenooxalate, oxamidine, oxamate and oxamide as coordination centers (centroligands) and illustrates the diversity and multitude of such complexes.
The dithiooxalato-bridged iron mixed-valence complex (n-C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato) undergoes a novel charge-transfer phase transition (CTPT) accompanied by electron transfer between adjacent FeII and FeIII sites. The CTPT influences the ferromagnetic transition temperature according to the change of spin configuration on the iron sites. To reveal the mechanism of the CTPT, we have synthesized the series of metal-substituted complexes (n-C3H7)4N[FeII1-xMnIIxFeIII(dto)3] (x = 0–1) and investigated their physical properties by means of magnetic susceptibility and dielectric constant measurements. With increasing MnII concentration, x, MnII-substituted complexes show the disappearance of CTPT above x = 0.04, while the ferromagnetic phase remains in the whole range of x. These results are quite different from the physical properties of the ZnII-substituted complex, (n-C3H7)4N[FeII1-xZnIIxFeIII(dto)3], which is attributed to the difference of ion radius as well as the spin states of MnII and ZnII.
Transferrin (Tf) is a key player in iron homeostasis which transports otherwise insoluble ferric ion and delivers it to cells via receptor-mediated endocytosis. Since Tf is also capable of binding a range of other metals with very high affinity, it remains in the focal point of multiple studies aiming at understanding the mechanism of biodistribution of clinically relevant non-ferric metals. The latter included toxic metals, as well as metals that can be exploited for medicinal or therapeutic benefit (e.g., radionuclides). More recently, there was a growing interest in using non-cognate metals as tracers of Tf-based therapeutics in animal-based disease models. In this work interaction of seven metal ions in their physiologically relevant oxidation states (Cr³⁺, In³⁺, Ti⁴⁺ and four lanthanides) with Tf were studied using native electrospray ionization mass spectrometry (ESI MS). Cr³⁺, In³⁺ and Ti⁴⁺ display Tf-binding properties that are similar to those of the cognate metal (Fe³⁺), while Tf association with lanthanides leads to formation of complexes that are very unstable in the gas phase, indicating the protein/metal binding mechanism and structure in this case are very different from those leading to formation of the Fe2Tf complex. Native ESI MS also allowed the receptor binding competence of Tf loaded with non-ferric metals to be evaluated. Lastly, behavior of these complexes under conditions mimicking the endosomal environment (where the release of the cognate metal actually occurs) was also evaluated. This analysis revealed striking similarities between Cr2Tf, In2Tf and Ti2Tf on one hand, and the diferric form of Tf on the other hand, strongly suggesting that Tf is indeed a critical player in homeostasis of these metals and must be considered both in the analysis of metal toxicity and in the design of metal-based therapeutics.
This chapter discusses the synthesis and specific physical properties of non-centrosymmetric molecular magnets (NCM). It describes the different strategies that have been developed to favor non-centrosymmetric magnetic metal-organic systems. The chapter concentrates on the original physicochemical properties of these compounds, in particular those arising from the interplay between magnetism and the properties related to the breaking of space inversion symmetry. It addresses the relationship between the handedness of the magnetic helices and the configuration of the structurally chiral centers. The templating activity introduction of a polar cation, namely 1-hydroxyethyl-4-(W,W-dimethylamino) pyridinium also led to the formation of a non-centrosymmetric oxalate-based coordination compound, whose properties are described. The chapter deals with molecular materials presenting (anti)ferromagnetic and (anti)ferroelectric orders and on two systems: molecular perovskites and a polar bimetallic oxalate. The most direct effect is mentioned in acentric magnets, Dzyaloshinskii-Moryia (DM) interaction is often present and gives rise to canted antiferromagnetic or even more original magnetic ordering.
A series of bimetallic oxalate-bridged one-dimensional chains with monocationic dabco derivatives, ({R-dabco}[M(solv)2][Cr(ox)3]·n(solv)) (dabco = 1,4-diazabicyclo[2.2.2]octane, H2ox = oxalate; R = H, M = Co (1); R = H, M = Zn (2); R = Bu, M = Co (3); R = Bu, M = Zn (4)) were synthesized. All compounds have one-dimensional zig-zag chain structures with R-dabco cations located between chains. Cryomagnetic studies reveal that 1 and 3 showed intrachain ferromagnetic interactions between Co(ii) and Cr(iii) ions and metamagnetic behaviour due to interchain antiferromagnetic interactions. Permittivity measurements on compound 4 indicate specific paraelectronic relaxation behaviour originating from the rotational motion of the dabco alkyl substituent.
A proposal is reviewed for using ligand design to control the sign and magnitude of the exchange-coupling constant, J, in multinuclear ions. The approach promises utility for obtaining a J of ferromagnetic sign. Its origin lies in the use of a planar array of four strongly sigma-donating ligands at a first metal ion that is bridged via two of these to a second ion [1]. Strategies are discussed for extending the local concept to complete crystals. The relationships between local site and global structural parameters are summarized for chains and helices obtained by linking D3 ions. The properties of a magnetically interesting crystalline substance consisting of stacked chains are described.
The reaction of biradical 2,6-NITpy (1) (2,6-NITpy = 2,6-bis (3’-oxide-1’-oxyl-4’,4’,5’,5’-tetramethylimidazolin-2’-yl) pyridine), 2-NIT-6-IMpy (2) (2-NIT-6-IMpy = 2-(3’-oxide-1’-oxyl-4’,4’,5’,5’-tetramethylimidazolin-2’-yl)-6-(1’-oxyl-4’,4’,5’,5’-tetra-methylimidazolin-2’-yl) pyridine), or 2,6-IMpy (3) (2,6-IMpy = 2,6-bis(1’-oxyl-4’,4’,5’,5’-tetra-methylimidazolin-2’-yl) pyridine) with M(hfac)2·XH2O (M = MnII, CoII) were investigated. These reactions were found to be related to the type of the metal ion employed. Interestingly, redox reactions involve in the synthesis process of the complexes. Structures of the five complexes were elucidated by X-ray analysis, and their magnetic properties were investigated in detail. The temperature dependence of χMT for all the five complexes at high temperature range exhibited antiferromagnetic interactions between the transition metal spin (MnII or CoII) and the nitroxide radical spin. At low temperature, the χMT curves exhibit different magnetic behaviors because of the different crystalline fields and intermolecular interactions.
The Schiff base 3-(N-2-pyridytethyl)formimidoyl)salicylic acid, H2fsaaep, is a useful ligand for the design of heterotrinuclear complexes. The synthetic approach consists in the reaction of neutral, dinuclear precursors, [M(fsaaep)]2·nH2O (M = CuII, MnII) with a transition metal perchlorate. The synthesis of the dinuclear manganese(II) derivative, [Mn(fsaaep)]2·4H2O, is first reported here. Two new heterotrinuclear complexes have been synthesized and characterized; Cu2Ni(fsaaep)2(ClO4)2·4H 2O and Mn2Cu(fsaaep)2(ClO4)2·2H 2O. The magnetic and spectral properties of all these compounds are in line with the proposed formulas.
Synthetic strategies dealing with the polymerization of either di-μ-hydroxocopper(II) complexes or 2,2′-bipyrimidine (bpym)-containing first row transition metal ions allow the preparation of polynuclear compounds whose structures and magnetic properties are presented here. The influence of structural and chemical parameters on the magnitude of the singlet-triplet energy gap (J) in di-μ-hydroxocopper(II) complexes [LCu(OH)2CuL]2+ with L = 2,2′-bipyridine (bpy) and bpym is analyzed and discussed. Special attention is devoted to nature of the counterion which allows the preparation of hydroxo-bridge copper(II) cubane and double cubane type complexes where all the intramolecular magnetic interactions are ferromagnetic. The case of the compound [Cu2(bpy)2(OH)2(CF3SO3)2] where two dimers with different values of the angle at the hydroxo bridge (θ) coexist in the unit cell is aborded here. The polymerization of the [Cu2(bpym)2(OH)2]2+ dinuclear units through bis(chelating) bpym leads to novel copper(II) chains exhibiting regular alternating ferromagnetic (through the hydroxo bridge) and antiferromagnetic (through bpym) exchange couplings within the chain. The possibility of tuning the value of J in polynuclear complexes through bis(chelating) type ligands by playing on the electronegativity of the peripheral donor atoms is analyzed and discussed. The structural changes caused by the Jahn-Teller effect in bpym-bridged copper(II) complexes appears as a potential strategy to achieve ferromagnetic coupling between copper(II) ions. Finally, the use of bis(chelating) ligands such as oxalate and bpym and transition metal ions for designing new honeycomb layered materials of formula M2(bpym)(ox)2 · nH2O (M = divalent first-row transition metal ions) is presented and their magnetic behaviour analyzed by classical Heisenberg models.
The research in the areas of molecule based-magnets and molecular conductors and superconductors has received much attention in the last decade, although most of the efforts have been devoted separately and so, the progress made in both disciplines have scarcely converged. Thus, a significant number of molecular materials exhibiting cooperative magnetic phenomena [1] or conducting and superconducting properties [2] are known. Nevertheless, the conjunction of these two areas has been very little explored so far and very few molecular materials are known in which electrical and magnetic properties coexist.
[MnIIxFeII1-x(H2O)6][LiFeIII(ox)3] (with 0 ≤ x ≤ 1) crystallizes in the space group P31c with a = 9.341(3) Å, c = 10.226(3) Å, c/a = 1.0947 and V = 772.8(5) Å3 for Z = 2. The compound has a layered structure with two enantiomeric layers per unit cell. The layers are built up by an iron and lithium oxalate framework with intercalated M(II)-water octahedra of the formula [MnIIxFeII1-x(H2O)6][MIMIII(ox)3]. The value of x cannot be specified at present. The structure displays intermolecular hydrogen bonding between the layers.
Cobalt(II) complexes of the general compositions, [CoL 2X 2] (L = NH 2NHCOOR; R = Et or Bu t; X = Cl -, Br -, I -, NO 3- and NCS -) have been synthesized and characterized by elemental analysis, molar conductance, spectroscopic techniques (UV-Vis, IR) and magnetic moment measurements. The low conductivity data of all the complexes suggest their non-electrolytic nature. The magnetic studies show the complexes to be high spin octahedral. On the basis of electronic spectral studies they are assigned tetragonally distorted octahedral stereochemistry. Various ligand field parameters have been evaluated.
X-band electron paramagnetic resonance (e.p.r.), magnetic and optical absorption spectra of the oxalato-bridged complexes [(dien)Cu-Ox-Cu(dien)] (BPh4)2, [(dien)Cu-Ox-Zn(dien)](BPh4) 2, [(dien)Cu-Ox-Ni(dien)](BPh4)2 where Ox - oxalate ion, and dien - diethylenetriamine have been described. E.p.r. spectra of the polycrystalline complexes have been studied at room temperature and also at liquid nitrogen temperature. Magnetic susceptibility measurements were carried out on a Gouy balance at room temperature. Superoxide dismutase activity have also been measured and compared with the reported complexes.
A chain-like coordination polymer with the chemical formula of {[Ni 2Mn2L2(CH3CH2OH)-(H 2O)]·CH3OH·2H2O}n has been synthesized by the assembly reaction of K2NiL·H 2O and Mn(OAC)2·4H2O with a 1:1 mole ratio in methanol, where OAC- = CH3COO- and H4L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybenzoyl)imino]ethyl}imino) methyl]benzoic acid. The crystal structure was determined by single-crystal X-ray diffraction analysis. It belongs to the triclinic system, space group P1̄, with a = 9.9464(8), b = 13.4718(11), c = 14.3877(12) Å, α = 87.1930(10), β = 85.4280(10), γ =74.6470(10)°, V= 1852.4(3) Å3, Z = 2, Dc= 1.807 g/cm3, M r= 1008.03, λ(MoKa) = 0.71073 Å, μ(MoKa) = 1.794 mm-1, F(000) = 1032, R= 0.0527 and wR= 0.1284 (I > 2σ(I)). The compound exhibits a chain-like structure formed by dissymmetrical tetranuclear units.
The structures of the mixed-valence FeII−FeIII complexes of formula [Fe(bpm)3]2[Fe2(ox)5]·8H2O (1) and Fe(bpm)3Na(H2O)2Fe(ox)3·4H2O (2) (ox = oxalate dianion) are reported here. 1 contains the first structurally characterized oxalato-bridged high-spin diiron(III) complex [Fe2(ox)5]⁴⁻. The low-spin tris-chelated [Fe(bpm)3]²⁺ unit and the high-spin [Fe(ox)3]³⁻ complex act as bidentate ligands toward a central cis (diaqua)sodium(I) unit, yielding an unprecedented FeII−NaI−FeIII assembly in 2. Significant antiferromagnetic coupling between the Fe(III) ions through the bridging oxalate occurs in 1.
Four μ- oxamido heterodinuclear complexes, [Cu (oxae) Cr (L)2 ] (NO3) 3, where oxae denotes the N, N'bis (2-aminoethyl) oxamido dianion and L represents 1,10-phenanthroline (phen); 5-nitro-1,10-phenanthroline (NO2-phen); 5-methyl-1, 10-phenanthroline (Me-phen) and 2, 2′-bipyridine (bpy), have been synthesized and characterized by elemental analyses, magnetic moments (at room temperature) and molar conductivity measurements and spectroscopy. It is proposed that these complexes have extended oxamido-bridged structures consisting of a copper (II) ion and a chromium (III) ion, which have a square planar environment and octahedral environment, respectively. The cryomagnetic properties of the [Cu(oxae)Cr(bpy)2(NO3)3(1) and [Cu(oxae)Cr(phen)2](NO3)3(2) complexes have been measured over the range of 4.2–300 K. The leastsquares fit of the experimental data based on the spin Hamiltonian, Ĥ = - 2JŜ1·Ŝ2, the exchange integrals (J) were evaluated as +36.9 cm−1 for 1 and +35.8 cm−1 for 2. The reds have connived that the spin coupling between the adjacent copper (II) and chromium (III) ions through oxamido-bridge in both 1 and 2 is ferromagnetic.
Three new μ-oxamido-bridged heterodinuclear copper (II)-chromium (III) complexes formulated [Cu(Me2oxpn)Cr-(L)2](NO3)3, where Me2oxpn denotes N,N'-bis(3-amino-2, 2-dimethylpropyl)oxamido dianion and L represents 5-methyl-1,10-phenanthroline (Mephen), 4,7-diphenyl-1,10-phenanthroline (Ph2phen) or 2,2′-bipyridine (bpy), have been synthesized and characterized by elemental analyses, IR and electronic spectral studies, magnetic moments of room-temperature and molar conductivity measurements. It is proposed that these complexes have oxamido-bridged structures consisting of planar copper (II) and octahedral chromium (III) ions. The variable temperature magnetic susceptibilities (4.2–300 K) of complexes [Cu(Me2oxpn)Cr(Ph2phen)2](NO3)3 (1) and [Cu(Me2oxpn)Cr(Mephen)2] (NO3)3 (2) were further measured and studied, demonstrating the ferromagnetic interaction between the adjacent chromium (III) and copper (II) ions through the oxamido-bridge in both complexes 1 and 2. Based on the spin Hamiltonian, Ĥ = - 2JŜ1 · Ŝ2, the exchange integrals J were evaluated as + 21.5 an−1 for 1 and + 22.8 cm−1 for 2.
In this work, we describe for first time, the structure and magnetic characterization of the one dimensional catena cis-[Ni(mu-ox)(H2O)(2)](infinity) (1), which was obtained by solvothermal synthesis. Cis-[Ni(mu-ox)(H2O)(2)]infinity crystallizes in a C2/c spatial group. The asymmetric unit contains only one type of nickel atom, oxalate ligand and water molecules. The chain backbone is constructed by the bis-chelating coordination mode of the oxalate ligand, presenting a zigzag chain in the [1 0 1] direction. The nickel ions have a distorted octahedral geometry, surrounded by six oxygens, four of them from two different oxalate ligands and the other two from the cis-coordinated water molecules. Thermal dependence of the magnetic susceptibility of (1) was studied in a temperature range of 2.5-255 K, at applied fields of 0.10 and 0.25 kOe. The plot of chi T-M(T) shows antiferromagnetic interactions between the Ni(II) centres. The experimental data were fitted between 255 and 30 K. using an empirical expression for a chain of equally spaced Ni(II) centres. The best fit of the experimental date gave a J value of -57 cm(-1), which is much higher that the obtained for the trans-analogue. Irreversibility between ZFC and FC measurements below 9 K was observed, indicating some kind of magnetic ordering. (C) 2011 Elsevier Ltd. All rights reserved.
The trimeric complexes, [{Ni(dien)}2(μ-ox){(μ-Pd(CN)4)}] (2) and [{Ni(dien)}2(μ-ox){(μ-Pt(CN)4)}] (3) were synthesised by the reaction of [{Ni(dien)(H2O)}2(μ-ox)](PF6)2·2H2O (dien=dietylenetriamine and ox=oxalate) with K2Pd(CN)4 and K2Pt(CN)4, respectively. In this reaction, water substitution and molecular reconstruction reactions take place to afford trimer complexes. These compounds are isostructural with the molecular compound [{Ni(dien)}2(μ-ox){(μ-Ni(CN)4)}] (1). In each complex, the two octahedrally coordinated Ni atoms are oxalate bridged and the sphere of coordination of each Ni is completed by three nitrogen atoms from a diethylenetriamine ligand in fac arrangement and one nitrogen atom from a bridging cyanide ligand, which belongs to the corresponding square-planar complex [M(CN)4]2−. The three compounds present antiferromagnetic behaviour. The magnetic coupling between the two nickel atoms might occur through both bridges, but the length of the exchange pathway through the bidentate tetracyanometallate ligands is large enough to predict that the magnetic interaction may take place mainly through the oxalate ligand. The values of this coupling are similar J (cm−1)=−31.2 (1), −33.5 (2) and −33.6 (3).
In the present work, a novel oxalate-bridged binuclear iron(III) complex of aminophenol derivative, (μ-ox-FeLNEM), where LNEM is deprotonated form of a tetradentate aminophenol ligand and ox stands for oxalate, was synthesized. The iron complex has been characterized by X-ray crystallography, infrared spectroscopy, UV–Vis, magnetic susceptibility studies and cyclic voltammetry techniques. X-ray structure analysis has revealed that each iron(III) is coordinated by two oxygen atoms of the oxalate group, two amine nitrogen’s and two oxygen atoms of phenolate ligand in an octahedral arrangement. The temperature variable magnetic susceptibility exhibits quite strong antiferromagnetic coupling between the two iron(III) centers. Cyclic voltammograms of the complex in dichloromethane at low temperatures showed two quasi-reversible cathodic peaks, corresponding to FeIIIFeIII to FeIIIFeII followed by FeIIIFeII to FeIIFeII process.
A new heterometallic complex, of the composition [Ni(bpy)3]2[Cr(C2O4)3]NO3·10H2O (bpy = 2,2′-bipyridine) (1), was synthesized and characterized by elemental and TG/DTA analyses, IR, UV/vis and EPR spectroscopy and by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic P21/c space group, with the unit cell parameters: a = 23.201(7), b = 13.562(4), c = 22.350(7) Å, β = 92.782(5)°, V = 7024(4) Å3 and Z = 4. The molecular structure of 1 consists of two symmetry independent [Ni(bpy)3]2+ cations, one [Cr(C2O4)3]3− anion, one nitrate anion and 10 molecules of water. Due to the rigidity of the didentate ligands, both [Ni(bpy)3]2+ and [Cr(C2O4)3]3− ions possess a trigonally distorted octahedral geometry. Analysis of crystal packing revealed the existence of a specific type of supramolecular contact comprising four bipyridine ligands from two neighbouring [Ni(bpy)3]2+ units – a quadruple aryl embrace (QAE) contact. The electronic spectrum showed superposition of bands characteristic for both nickel(II) and chromium(III) six-coordinated ions. The X-band EPR spectra were recorded on a single crystal and on a powdered sample of 1 in the temperature range 300–5 K. From the obtained spectra, the spin-Hamiltonian parameters for Cr3+ were deduced. Throughout the investigated temperature range, Ni2+ was EPR silent.
New 2,2′-bipyrimidine (bpm)-based copper(II) coordination polymers have been synthesized and characterized. The structure of [Cu(bpm)(SO4)](H2O)n (1) contains zigzag chains which are constructed of Cu-bpm-Cu units, sulfate ions and additional bridging bpms. Sulfate ions coordinate to copper(II) ions, and link the chains to form a three-dimensional bundle structure. The crystal structure of [Cu2(bpm)(suc)0.5(ClO4)2(OH)(H2O)2]n (2) consists of a chain of bpm-bridged dinuclear copper(II) units linked by a carboxylate group from the succinate anion and a hydroxo group. Coordinated perchlorate ions also bridge the adjacent chains. The chain structure of [Cu(bpm)1.5(suc)0.5](ClO4)(H2O)2n (3) consists of the bpm-bridged dinuclear copper(II) units, amphimonodentate succinate dianions and terminal bpms. The succinate dianion acts as a bridging ligand between the dimers to yield a one-dimensional zigzag chain in the crystal. The terminal bpm stacks with a nearest-neighbor terminal bpm on an adjacent chain to form a linkage for a two-dimensional sheet. The present work affords a new strategy to build multi-dimensional coordination polymers, which is based on the use of [Cu-bpm-Cu]4+ copper(II) dinuclear units as ‘building blocks’. The geometries around the pyrimidyl rings of bpm are similar to each other, whereas the geometry of the copper atoms is different. The additional linking ligand as a peripheral ligand coordinates to the dimer unit to control the plasticity of the coordination sphere of copper(II); this makes the modification of the symmetry of its magnetic orbital easy. The magnetic susceptibilities were measured from 2 to 300 K and analyzed as antiferromagnetic Heisenberg S = 1/2 alternating chains to yield J = −38.8 cm−1, α = 0.93 (1), J = −132.2 cm−1, α = 0.22 (2) and J = −4.5 cm−1, α = 0.60 (3).
Two heterometallic oxalate-bridged dinuclear anions associated with a non-H-bond donor bisamidinium cation (Cat2+), leading to compounds of formula Cat[MnII(H2O)4MIII(ox)3]2·6H2O (M = Fe (1) and Cr (2)), are presented. Their structural analysis reveals that the anion is the combination of a tris(oxalato)metallate(III) moiety with a tetra(aqua)manganese(II) entity. A 3D H-bonded network is formed between the crystallisation and coordination water molecules and the terminal and bridging oxalate ligands. The exchange interaction between both metal ions mediated by the oxalate bridge is −4.9 cm−1 for 1 and +1.6 cm−1 for 2 (H = −JS1S2).
The synthesis, structure and physical properties of the bimetallic oxalate-based molecular magnets containing MnIII of formula [NBu4][MIIMn(ox)3] (MII = Fe, Co, Ni, Zn; ox = oxalate dianion) are presented here. All compounds are isostructural, containing two-dimensional honeycomb bimetallic networks formed by alternating MII and MIII ions connected by oxalate anions. These compounds exhibit antiferromagnetic interactions that give rise to ferrimagnets or weak ferromagnets ordering at critical temperatures up to 21 K.
Four new μ-oxamido heterodinuclear complexes, [Cu(oxae)Cr(L)2]-(NO3)3, where oxae denotes the N,N′-bis(2-aminoethyl)oxamido dianion and L represents 4,7-diphenyl-l,10-phenanthroline (Ph2-phen), 5-chloro-1,10-phenanthroline (Cl-phen), 2,9-dimethyl-l,10-phenanthroline (Me2-phen) and 4,4′-dimethyl-2,2′-bipyridine (Me2-bpy), have been synthesized and characterized by elemental analyses, magnetic moments (at room temperature) and molar conductivity measurements, and by spectroscopy (IR and electronic spectra). It is proposed that these complexes have extended oxamido-bridged structures consisting of planar copper(II) and octahedral chromium(III) ions. The cryomagnetic properties of [Cu(oxae)Cr(Me2-bpy)2](NO3)3(l) and [Cu(oxae)Cr(Me2-phen)2](NO3)3 (2) have been measured over the range 4.2-300 K. From least-squares fit of the experimental data, based on the spin Hamiltonian, Ĥ = -2JŜ1 Ŝ2, the exchange integrals (J) were evaluated as +19.8 cm for(l) and +21.5 cmfor (2). The results have confirmed that the spin coupling between the adjacent copper(II) and chromium(III) ions through the oxamido-bridge in both complexes (1) and (2) is ferromagnetic.
Chiral salen ligands capable of forming polymetallic complexes have been designed. The ligands possess substituents in the 4,4′-positions, but have no substituent in the 3,3′-positions to allow a second metal ion access to the salen oxygen atoms. Ligands in which a polyether chain links the 4,4′-positions were prepared and complexed to copper. In addition, acyclic ligands with potential metal coordinating substituents in the 4,4′-positions were prepared and complexed to copper and cobalt. The crystal structure of one of the cobalt complexes shows it to be a trimetallic complex in which a Co(II)(OAc)2 group coordinates to the salen oxygen atoms of two Co(III)(salen)(OAc) units. In contrast, the crystal structure of a Co(salen) complex with tert-butyl groups attached to the 3,3′-positions is found to be mononuclear. All of the complexes were tested as asymmetric phase transfer catalysts for the asymmetric alkylation of an alanine methyl ester, forming (R)-α-methyl phenylalanine methyl ester with up to 85% ee.
Three novel tetranuclear macrocyclic complexes, [(CuL1)3Cr](ClO4)3·3H2O (1), [(CuL2)3Cr](ClO4)3·3H2O (2) and [(CuL3)3Cr](ClO4)3·3H2O (3) [L1, L2 and L3 are the dianions of three [14]N4 and [15]N4 macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene,2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene, respectively], have been prepared and characterized. These complexes are the first examples of Cu3Cr species exhibiting spin topology with all the spins parallel in the ground state. Cryomagnetic studies on (1) (2–300 K) and (3) (77–300 K) revealed that the CuII and CrIII ions interact ferromagnetically through the oxamido bridge, with the exchange integral J = 6.7 cm−1 for (1) and J = 6.3 cm−1 for (3) based on Ĥ = −2J∑Ŝ
i
Ŝ
j
. The ferromagnetic interaction has been rationalized in terms of strict orthogonality of the magnetic orbitals. The oxamido bridge is also more efficient than the oxalato bridge at propagating the ferromagnetic interaction.
A novel heterotetranuclear chromium(III)-copper(II) complex of formula {[CrIII(bpy)(ox)2]2CuII2(bpy)2(ox)}·6H2O (1) has been synthesized by the ligand exchange reaction between Ph4P[Cr III(bpy)(ox)2]·H2O and [Cu II(bpy)2(NO3)]NO3·MeOH in methanol (bpy = 2,2′- bipyridine; ox2- = oxalate dianion). The X-ray crystal structure of 1 consists of neutral oxalato-bridged CrIII2Cu 2II zigzag entities which are formed by the monodentate coordination of two [CrIII(bpy)(ox)2]- mononuclear anionic units through one of its two oxalato groups toward a [CuII2(bpy)2(ox)]2+ dinuclear cationic moiety featuring relatively long axial bonds at the square pyramidal CuII ions. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 have been interpreted on the basis of the linear tetranuclear topology of the Cr III2CuII2 entities [H = -J(S 1 · S2 + S3 · S 4)-J′ S2 · S3 with S1 = S4 = SCr = 3/2 and S2 = S3 = S Cu = 1/2]. A weak antiferromagnetic coupling occurs between the outer CrIII and inner CuII ions through the peripheral bidentate/monodentate(outer) oxalates (J = -8.7 cm-1), while a strong antiferromagnetic coupling is operative between the inner CuII ions across the central bis-bidentate oxalate (J′ = -472.2 cm-1), leading thus to a S = (SCr-SCu)-(SCr-S Cu) = 0 ground spin state for the CrIII2Cu II2 entity of 1. A simple orbital analysis of the electron exchange interaction in the oxalato-bridged CuII2 and CrIIICuII fragments identify the σ-type pathways involving the dx2-y2(Cu)/dx2-y2(Cu) and dxy(Cr)/dx2-y2(Cu) pairs of magnetic orbitals as the two main contributions responsible for the different strength of the intramolecular magnetic coupling parameters for 1. A magneto-structural correlation between the nature and magnitude of the magnetic coupling and the bending angle at the axial carbonyl-oxygen to copper bond has been established for 1 and related oxalato-bridged chromium(III)-copper(II) dinuclear complexes.
A novel heteronuclear 3d-4f compound having formula NdCu 3 L 3 ·13H 2 O (where H 3 L = Schiff base derived from 5-bromosalicylaldehyde and glycylglycine and L 3- = C 11 H 8 N 2 O 4 Br) was obtained. It was characterized by elemental and thermal analyses and magnetic measurements. The Cu(II)-Nd(III) compound is stable up to 323 K. During dehydration process the water molecules are lost in two stages. The magnetic susceptibility data for this complex change with temperature according to the Curie-Weiss law with Θ = -35 K. The magnetic moment values decrease from 5.00μ B at 303 K to 4.38μ B at 76 K.
Two heterometal assemblies, [(CuLMnII)-L-II-Mn-2(hfac)] (2) and [(CuLMnII)-L-II-Mn-3(hfac)] (3), have been synthesized by the assembly reaction of "bridging ligand-complex" Na[(CuLn)-L-II] (n = 2, 3) and [Mn-II(hfac)(2)(H2O)(2)], where H3L2 = 1-(2-hydroxy-3-methoxybenzamido) -2-(2-hydroxybenzylideneamino) ethane, H3L3 = 1-(2-hydroxy-3-methoxybenzamido)-2-(2-hydroxy-3-methoxybenzylideneamino)ethane, and Hhfac = hexafluoroacetylacetone. The temperature-dependent magnetic susceptibility and field-dependent magnetization data demonstrated that 3 was well-reproduced by a cyclic tetranuclear structure, while those of 2 indicated an infinite linear chain structure.
A novel oxalate-bridged binuclear ruthenium(III) complex, [{Ru(acac)(2)}(2)(mu-ox)] (acac(-) = acetylacetonate and ox(2-) = oxalate), has been prepared via self-dimerization of K[Ru(acac)2(OX)l in aqueous solutions containing ferric salts as catalyst. The Ru-2 III,II mixed-valence species generated electrochemically with K-c = 10(5.0) for the comproportionation constant exhibits a weak intervalence charge transfer (IVCT) band at 1430 nm. The IR spectra from spectroelectrochemistry indicate a partially localized mixed-valence state (Class II-III behavior).
Hexanuclear lanthanide(III)-chromium(III) complexes [Ln2(μ-ox){Cr(bipy)(μ-ox)(ox)}4(H2O)6]-13H2O (Ln = Pr 1, Gd 2) (bipy = 2,2′ -bipyridine and ox = oxalate dianion) have been synthesized by reaction of [Cr(bipy)(ox)2]- building blocks with Ln(III) ions. The structure of 1 has been determined by X-ray crystallography.
A novel chromium(III)-neodymium(III) heteronuclear complex has been obtained by utilizing unsym-cis-[Cr(eddp)(ox)] as a building block. From the X-ray analysis, it is revealed that this complex is tetranuclear in which the Nd(III) ion is bridged by three oxalates in the three Cr(III) units and three water molecules forming a nine-coordinate tricapped trigonal-prism geometry.
The crystal structure of ammonium bis-mu-oxalato-tinanate(III) dihydrate, NH4[Ti(C2O4)(2)].2H(2)O, is reinvestigated by careful single-crystal X-ray diffraction using Mo K alpha (room temperature and 130 K) and Ag K alpha radiation (room temperature). It crystallized in noncentrosymmetric hexagonal space group P6(4)22, with cell parameters a = 8.947 (2), c = 10.898 (1) Angstrom, Z = 3, F(000) = 423, M(r) = 278.1, D-x = 1.833, R = 0.035, wR = 0.030 for 2296 observed relections with I greater than or equal to 2 sigma(I), on Ag K alpha data. Accurate data measurement was applied using two wavelengths (0.7107 Angstrom for Mo K alpha and 0.5609 Angstrom for Ag K alpha) in order to study the charge density distribution and also to investigate the wavelength effect in such investigations. A total of 22 650 and 20 298 reflections were measured using Mo K alpha radiation. The Ti atom is coordinated by four oxalate dianions with coordination number 8 in an approximate symmetry of D-4 geometry. Each oxalato ligand is bridged between two Ti atoms and forms and infinite polymeric spiral column along the c axis. The deformation density maps, Delta rho, obtained from all three data sets are consistent and agree well. Although the formal charge of Ti in this complex is 3+, with only one electron on the 3d orbitals expected, the net atomic charge on Ti from this study is similar to 2+. Charge asphericity around the Ti atom caused by the spitting of 3d orbitals is clearly observed in the deformation density. The d-orbital population are evaluated from multipole refinement. The expected d(1) electron is mainly located in the d(z2) orbital.
An asymmetrical double Schiff-base Cu(II) mononuclear complex, HCuLp (H3Lp is N-3-carboxylsalicylidene-N′-5-chlorosalicylaldehyde-1,3-diaminopropane) and a heterometal trinuclear complex with double molecular structure (CuLp)2Co·5H2O have been synthesized and characterized by means of elemental analyses, IR and electronic spectra. The crystal structure of the heterotrinucler complex was determined by X-ray analysis. Each asymmetric unit within the unit cell of the complex contains two heterotrinuclear neutral molecules (a) [CuLpCoCuLp], (b) [(CuLpH2O)CoCuLp] and four uncoordinated water molecules. In the two neutral molecules, the central Co ions are located at the site of O6 with a distorted octahedral geometry, one terminal Cu ion (Cu(3)) at the square-pyramidal environment of N2O3, and the other three at the square planar coordination geometry with N2O2 donor atoms. Magnetic properties of the heterotrinucler complex have been determined in the temperature range 5–300 K, indicating that the interaction between the central Co ion and the outer Co ions is antiferromagnetic. The exchange integral J is equal to −34.9(7) cm.
The binuclear complex [NBun4]4[Cr2(ox)5]·2CHCl3 has been prepared by an ion-exchange procedure employing Dowex 50WX2 cation-exchange resin in the n-butylammonium form and potassium tris(oxalato)chromate(III). The dimeric complex was characterised by a crystal structure determination: monoclinic, space group C2/c, a = 29.241(7), b = 15.192(2), c = 22.026(5) Å, β = 94.07(1)°, Z = 4. The magnetic susceptibility (300–4.2 K) indicated that the chromium(III) sites were antiferromagnetically coupled (J = –3.1 cm–1).
Some dinuclear iron(III) complexes derived from two tetraaminodiphenol macrocyclic ligands, one (H2L1) contains two –NH(CH2)3NH– and the other (H2L2) one –NH(CH2)3NH– and one –NH(CH2)2NH– units, and an acyclic tetradentate ligand {H2L3N,N′-bis(2-hydroxybenzyl)-1,3-diaminopropane} have been synthesised and studied. In all of the macrocyclic complexes [Fe2(µ-OH)2(HL1)2][ClO4]21, [Fe2(µ-OH)2L12]·2H2O 2, [Fe(H2L1)(H2O)2][ClO4]3·H2O 3, [Fe2(µ-OH)2(H2L2)2]-[ClO4]4·2H2O 4, [Fe2(µ-OH)2L22]·2H2O 5 and [Fe2(µ-OH)2L32]6 only N2O2 donation to the metal centres occurs, while the two unco-ordinated amino nitrogens either remain singly protonated (2 and 5) or one (1) or both of these (3 and 4) is doubly protonated. Variable-temperature magnetic susceptibility data for 1, 4 and 6 indicate weak antiferromagnetic-exchange interactions in each case with J values of: –5.5 (1), –7.3 (4) and –11.8 cm–1(6). The isomer-shift and quadrupole-splitting values for 1 at 77 K are 0.46 and 0.43 mm s–1, respectively. The redox chemistry of 1 has been studied by cyclic voltammetry and its crystal structure has been determined: monoclinic, space group P21/c, a= 13.448(1), b= 14.847(1), c= 13.442(1)Å, β= 91.48(1)°, Z= 2, R= 0.048 and R′= 0.050. The two edge-sharing FeO4N2 octahedra are distorted and connected by a centre of inversion.
The tris-chelated [MII(bpy)3]2+ cations, where MII is a divalent transition metal and bpy is 2,2′-bipyridine, cause a remarkable crystallization of anionic three-dimensional (3D) coordination polymers of oxalate-bridged metal complexes [M2(ox)3]n2n-. With these cations, which are appropriate in charge, size, and symmetry, two types of stoichiometric units of the anionic 3D networks, with metals in different valence states, can be distinguished: [M2II(ox)3]2- and [MIMIII(ox)3]2-. Results of a structural analysis of compounds within each of the two isomorphous series are discussed: [NiII(bpy)3][Mn2II(ox)3] (3), cubic, merohedrically twinned, P4132/P4332/P4332 a = 15.579(2) Å, Z = 4; [FeII-(bpy)3][NaFeIII(ox)3] (4), cubic, P213, a = 15.507(3) Å, Z = 4; [FeII(bPy)3][LiCrIII(ox)3] (5), cubic, P212,3, a = 15.262(4) Å, Z = 4. The Mössbauer spectra of the iron-containing compounds [FeII(bpy)3] [Fe2II(ox)3] (1) and [FeII-(bpy)3][Mn2II(ox)3] (2) and type 4 but LiFeIII are consistent with the stoichiometric formula and the corresponding iron valence states. The straightforward synthetic approach and easy crystallization behavior, as well as the variety of metal combinations within the 3D networks, render these systems valuable candidates for studies in the field of molecular-based magnets. They fulfill the requirements of three-dimensional connectivity as well as accessibility to detailed structural characterization. The magnetic susceptibility data in the temperature range 2-300 K of 1, 2 and type 4 but LiFeIII are presented and the results should be taken as a starting point for more extended systematical studies. 1 and 2 reveal antiferromagnetic ordering behavior, indicated by a negative Weiss constant θ of -28 and -33 K, whereas the LiFeIII compound exhibits the expected behavior of single iron(III) ions. Further extensions to possible networks of the types [MIIMIII(ox)3]n1n- and [MIMII(ox)3]n3n- are discussed.
Preparations of the compounds [{Ni(1,3-pn)2}2C2O4](ClO4)2,H2O, [{Ni(dpt)H2O}2C2O4](ClO4)2, [{Cu(dien)}2C2O4](ClO4)2(and hydrate), [{Cu(dpt)}2C2O4](ClO4)2, [{Zn(en)2}2C2O4](ClO4)2, [{Zn(dpt)}2C2O4](ClO4)2, and [{Zn(trien)}2C2O4](ClO4)2, considered to have dimeric structures with bridging bichelate oxalate ions, are described. The pairs of compounds [{M(en)2}2C2O4](ClO4)2 and [{M(trien)}2C2O4](ClO4)2[M = Ni(II) or Zn(II)] are isostructural, whereas the pair [{M(dpt)}2C2O4](ClO4)2[M = Cu(II) or Zn(II)] are not isostructural. The racemic isomer of the cyclic tetramine 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane forms an analogous compound, [{Ni(tet b)}2C2O4](ClO4)2, whereas the meso-isomer forms only a simple oxalate, Ni(tet a)C2O4, and its trihydrate, considered to have polymeric structures with bridging, bi-unidentate oxalate ions. The compounds [Zn(1,3-pn)2](ClO4)2 and [Zn3(trien)4](ClO4)6 were also prepared. Infrared spectra and magnetic susceptibilities (µeff 3 B.M. for the nickel compounds and 1·8 B.M. for the copper compounds) are reported (en = diaminoethane; 1,3-pn = 1,3-diaminopropane; dien = diethylenetriamine; dpt = dipropylenetriamine; trien = triethylenetetramine).
The compound MnCu(obbz)·H2O [obbz = oxamido bis(benzoato)], obtained by reaction of the Mn2+ ion with the copper(II)‘brick’[Cu(obbz)]2–, orders ferromagnetically at Tc= 14 K; below Tc it exhibits a hysteresis loop characteristic of a soft ferromagnet.
The parameters in the spin Hamiltonian of isolated exchange-coupled paramagnetic ion pairs are derived through the application of the Wigner-Eckart theorem. The results are applied to two cases that have been studied experimentally.It is shown that for the axially symmetric ions, there is only one geometric configuration for a pair which will result in an isotropic ESR spectrum. The structure predicted from the ESR data of one such Cu2+ ion pair in Cu2+-Y zeolites agrees completely with X-ray findings.
Mixed-metal assemblies {NBu4[M(II)Fe(III)(ox)3]}3∞ (M = Ni (1), Fe (2), Mn, Zn) have been prepared and characterized, where NBu4+ = tetra(n-butyl)ammonium ion, ox2− = oxalate ion. Each assumes a three-dimensional network structure consisting of alternately arrayed Fe(III) and M(II) ions. The compounds 1 and 2 are shown to be ferrimagnet with a magnetic phase-transition temperature of 28 and 43 K, respectively.
Two new mononuclear complexes of formula [Hpip][M(salen)(ox)][M = CrIII(1) or FeIII(2)] and the binuclear [Fe2(salen)2(ox)]·H2O, (3) where Hpip = piperidinium, salen =N,N′-ethylenebis(saIicylideneiminate), and ox = oxalate, have been synthesized. Compounds (1) and (2) are isostructural, monoclinic, space group P21/n, Z= 4, with a= 24.425(3), b= 6.847(1), c= 14.271(2)Å, and β= 100.95(2)° for (1) and a= 24.363(4), b= 6.991(2), c= 14.105(3)Å, and β= 98.76(2)°for (2). The structure of (1) was solved by direct methods whereas that of (2) was solved by isomorphous replacement from the co-ordinates of (1). Both structures consist of [M (salen)(ox)]– mononuclear anions and piperidinium cations. The presence of the bidentate oxalate ligand in both complexes forces the salen ligand to adopt the non-planar cis-β configuration. The metal ions exhibit distorted octahedral geometry with the two co-ordinated oxygen atoms of the oxalate ligand and an oxygen and a nitrogen atom from the salen defining the best equatorial plane. The remaining two co-ordinating atoms of the quadridentate Schiff base are bent away from the oxalate ligand. The stability constant of the complex [Cr(salen)(ox)]– as well as [Cr(salen)(H2O)2]++ ox2– [graphic omitted] [Cr(salen)(ox)]–(i), [Cr(salen)(H2O)2]+ [graphic omitted] [Cr(salen)(OH)(H2O)]+ H+(ii), [Cr(salen)(OH)(H2O)] [graphic omitted] [Cr(salen)(OH)2]–+ H+(iii) the acidity constants of the complex [Cr(salen)(H2O)2]+ have been determined by potentiometry in aqueous solution: log β1= 4.80 ± 0.03, pKa1= 7.54 ± 0.01, and pKa2= 10.47 ± 0.01 (25 °C, 0.1 mol dm3 NaNO3). Complexes (1) and (2) undergo one-electron reduction at a platinum electrode in dimethyl sulphoxide solution. The reduction process is totally irreversible due to an inner-sphere redox reaction in the case of CrIII and to the dissociation of the anionic oxalate ligand in the case of FeIII A reactivity scheme is proposed to explain their different electrochemical behaviour.
Crystal and molecular structures of the title compounds are reported. In each the complex cation is dimeric with the planar oxalate group acting as a bridge by forming five-membered chelate rings with two metal centres. Co-ordination geometries are approximately octahedral in the nickel compound (I), square pyramidal in the copper compound (II)(oxalate oxygen atoms occupying one basal and one axial site), and trigonal bipyramidal in the zinc compound (III)(oxalate oxygens occupying one apical and one equatorial site). The conformations of the co-ordinated amines are discussed and their relationships with the stereochemistry of the metal centres and with the hydrogen bonding network examined.
When two paramagnetic transition metal ions are present in the same molecular entity, the magnetic properties can be totally different from the sum of the magnetic properties of each ion surrounded by its nearest neighbors. These new properties depend on the nature and the magnitude of the interaction between the metal ions through the bridging ligands. If both ions have an unpaired electron (e.g. Cu2+ ions), then the molecular state of lowest energy is either a spin singlet or a spin triplet. In the former case, the interaction is said to be antiferromagnetic, in the latter case ferromagnetic. The nature and the order of magnitude of the interaction can be engineered by judiciously choosing the interacting metal ions and the bridging and terminal ligands, and, thus, by the symmetry and the delocalization of the orbitals centered on the metal ions and occupied by the unpaired electrons (magnetic orbitals). The first success in this “molecular engineering” of bimetallic compounds was in the synthesis of a Cu2+VO2+ heterobimetallic complex in which the interaction is purely ferro-magnetic. The same strategy could be utilized for designing molecular ferromagnets, one of the major challenges in the area of molecular materials. Another striking result is the possibility of tuning the magnitude of the interaction through a given bridging network by modifying the nature of the terminal ligands, which, in some way, play the role of “adjusting screws”. By careful selection of the bridging and terminal ligands, a very large antiferro-magnetic interaction can be achieved, even if the metal ions are far away from each other. Some sulfur-containing bridges are especially suitable in this respect.
A complete treatment of the spin hamiltonian for a pair of exchange coupled metal ions is given. The results obtained through the use of the Wigner-Eckart theorem are unrestricted with respect to the relative orientation of the single-ion tensors, and appropriate for both the S1 = S2 and S1 ≠ S2 cases. The necessary constants are derived so that matrix elements within a given spin multiplet can be treated by ordinary operator algebra with the coupled representation state vectors, |SM>, as a basis set. Explicit algebraic formulae for matrix elements between spin multiplets are presented for the first time. Symmetry restrictions are discussed in general and illustrated for the simple case of two ions related by an inversion centre, pair symmetry Ci.
Three oxalate-bridged binuclear Cu(II)-Cr(III) complexes [(salen)Cr(ox)Cu(L(m))] (1, HL1 = N-salicylidene-N-(2-pyridylethyl)amine; 2, HL2 = N-acetyl-acetonylidene-N-(2-pyridylethyl)amine; 3, HL3 = N-salicylidene-N',N'-diethyl-ethylenediamine) have been prepared and the cryomagnetic susceptibility measurements(4.2-300 K) revealed that the spin-coupling is ferromagnetic with the J values +2.8, +2.2, and +2.7 cm-1 for 1, 2, and 3, respectively, based on H = -2JS(Cu)S(Cr). The J values are well compatible with J = +2.9 cm-1 of {NBu4-[CuCr(ox)3]}x evaluated from the equation Tc = nJ/3k[S(Cr)(S(Cr) + 1)S(Cu)(S(Cu) + 1)]1/2 (Tc = 7 K, n = 3) based on Heisenberg's theory of ferromagnetism.