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Organic ferromagnetic chain in the yttrium diphthalocyanine [YPc2]·CH2Cl2: X-ray structure and magnetic behavior
Abstract
The yttrium diphthalocyanine [YPc2]·CH2Cl2 has been synthesized and its structure and magnetic properties are reported. They are compared to those of the nonsolvated derivative αYPc2, which is isostructural to NdPc2. In [YPc2]·CH2Cl2, the phthalocyanine macrocycles are packed above each other in order to form infinite chains parallel to the c axis of the crystal. One macrocycle is rotated relative to the other 45°, so that the coordination of yttrium is a distorted square antiprism. One-dimensional ferromagnetism is emphasized for the first time in a pure organic system. αYPc2 which presents a different packing of Pc rings, exhibits on the contrary an antiferromagnetic behavior. A model, based on the influence of orbital degeneracy of [Pc-Pc2-] radicals in the exchange mechanism, is developed. Starting from the “extended” Anderson approach, an effective exchange Hamiltonian is proposed, taking into account spin-spin, orbit-orbit and spin-orbit like contributions. Such a model is shown to stabilize a ferromagnetic ground-state. Competing effects, such as the overlap between magnetic orbitals of adjacent radical species, and the degeneracy of involved orbitals, are discussed to explain the different behaviors of the solvated and nonsolvated derivatives.
... In the solid phase, the complexes exhibit a unique intrinsic conductivity owing to the unpaired electron [3][4][5]. Static behavior of the p hole as a magnetic spin has been reported in single crystals of Y(Pc) 2 , in which either ferromagnetic or antiferromagnetic interactions are observed depending on the crystal morphology [6]. Because of these interesting properties, the bis(phthalocyaninato) lanthanide complexes are expected to be functional building blocks for supramolecular (SM) structures functioning as molecular conducting wires or molecule-based magnets. ...
... From the plot and the experimentally obtained zfs constant (D= 0.00407 cm − 1 ), the center-to-center distance is estimated at about 7.0 A , . This value is about 0.5 A , larger than the distance [17] in crystals of unsubstituted lanthanide bis(phthalocyaninato) complexes: 6.5 A , in Lu(Pc) 2 ·CH 2 Cl 2 [18,19], 6.47 A , in Y(Pc) 2 ·CH 2 Cl 2 [6], and 6.58 A , in Nd(Pc) 2 [20]. ...
This paper reviews the authors’ attempts to create novel supramolecular structures composed of bis(phthalocyaninato)lanthanides and the analysis of their geometric and electronic structures. We synthesized tetra- and mono-crown-substituted bis(phthalocyaninato)lutetium, which show different aggregate forms under various conditions. The aggregate structures fall into three categories: (1) a D4h vertically stacked structure formed from the tetra-crown complex and cations such as K+ or NH4+; (2) a sliding form composed of tetra-crown complexes in methanol/chloroform mixed solvent; and (3) a pivoted form constructed from mono-crown substituted complexes with cations such as K+. The electronic structure of the supramolecular structures and magnetic interactions within are discussed.
... The calculated bent angles [177] clearly indicate that the two Pc ligands have different conformations. Several tetrabutylammonium salts of the [LnPc 2 ] 1− complexes were prepared, and the crystal structures were analysed [166,[177][178][179][180][181][182][183][184]. The analysed structures showed that the conformations of [LnPc 2 ] − are not only staggered but also eclipsed if the Ln(III) ions are exchanged. ...
Magnetic phenomena and magnetic materials are everywhere. Since the invention
of the compass, a great number of magnetic materials including frictionless bearings,
medical devices, magnetic separators, loudspeakers, microphones, switches,
sensors, data storage devices, motors and generators are used in daily life. In
contrast to these traditional magnetic materials, nano-scaled magnetic molecules
are at the scale of a billionth of a metre and they provide a unique opportunity to
observe the coexistence of classical and quantumproperties. Integrating them into
electronic circuits opens the possibility of processing or of storing information at
the single-molecule level.Therefore, the search for molecular species with unusual
magnetic properties which could lead to molecular devices is currently an important
field of study in chemistry and physics called molecular spintronics.
New conception of spin-tautomery was developed based on the results of quantum chemical investigation of the endohedral Y@C60 complex. The embedding energies of yttrium into the fullerene cavity, dipole moments, polarizabilities, and IR spectra in the doublet and quartet spin states were calculated by the density-functional theory quantum chemical methods. The degeneracy degree of the state of the complex is retained upon doublet–quartet excitation, since a twofold increase in the number of electron spin projections is compensated by a twofold decrease in the number of equivalent potential energy minima. The non-conservation of spin by an endohedral complex with a heavy atom makes it possible to interpret the interconversion of doublet and quartet states as a non-degenerate spin-tautomery.
FID-detected nutations of the antiferromagnetic crystal form of [Y(pc)2]• demonstrated that its radical spin can be coherently driven in the its magnetically condensed undeuterated phase and at room temperature. Liquid-helium...
A tris(alkoxo)pyridine-augmented Wells-Dawson polyoxometalate (nBu4N)6[WD-Py] (WD = P2V3W15O59(OCH2)3C, Py = C5H4N) was functionalized with phthalocyaninato metal moieties (MPc where M = Y or Yb and Pc = C32H16N8) to afford (nBu4N)4[HWD-Py(MPc)] compounds. High-resolution mass spectrometry was used to detect and identify the hybrid assembly. The magnetism studies reveal substantial differences between M = Yb (monomeric, single-ion paramagnetism) and M = Y (containing dimers, radical character). The results of electronic paramagnetic resonance spectroscopy, SQUID magnetometry, and magnetochemical calculations indicate the presence of intramolecular charge transfer from the MPc moiety to the polyoxometalate and of intermolecular charge transfer from the MPc moiety of one molecule to the polyoxometalate unit of another molecule. These compounds with identified VIV ions represent unique examples of transition-metal/lanthanide complex-POM hybrid compounds with nonphotoinduced charge transfer between electron donor and acceptor centers.
For Abstract see ChemInform Abstract in Full Text.
The reaction of rare earth silylamides Ln[N(SiHMe2)2]3(thf)n [n = 1 for Sc (1a); n = 2 for Y (1b), La (1c), Nd (1d)] with trans-1,2-bis(2,4,6-triisopropylbenzenesulfonamido)cyclohexane (H2L, rac-2) in toluene at ambient temperature proceeds via an extended silylamide route, affording highly soluble complexes Sc(L)[N(SiHMe2)2] (3) and Ln(L)[N(SiHMe2)2](thf) (4a-c) in excellent yields. An X-ray crystallographic study performed on the solvent-free, dinuclear yttrium derivative 5 revealed an unusual μ2,η4:η1-coordination of the disulfonamide ligand, involving bridging S=O groups. In solution, equilibria between dimeric and monomeric forms, dependent on the presence of a donor molecule, were observed by NMR techniques.
Four crystal structures of the title complexes have been analyzed by X-ray crystallography. 1: C80H68N17Nd, a = 17.0545(6) Å, c = 22.807(3) Å, tetragonal, P4/ncc, Z = 4. 2: C80H68N17Gd, a = 17.399(8) Å, c = 11.377(6) Å, tetragonal, P4212, Z = 2. 3: C80H70N17OHo, a = 18.096(5) Å, c = 11.079(6) Å, tetragonal, P4212, Z = 4. 4: C80H70N17OLu, a = 18.171(3) A, c = 10.987(4) Å, tetragonal, P4/nmm, Z = 2. The [LnIIIPc2]- and [NBu4n]+ ions in each crystal stack alternately in a column along the 4-fold axis. The Ln(III) cation of each [LnIIIPc2]- is eight-coordinated by two phthalocyanato dianions (Pc). The interplanar distances between the two Pc rings have a linear relationship to the ionic radii of the central Ln(III) cations. The skew angles between the two Pc rings are 6.2, 34.4, 43.2, and 45.0° for the Nd, Gd, Ho, and Lu complexes, respectively. The skew angle seems to depend on the strength of the π-π interaction between the two Pc rings.
The single-crystal X-ray diffraction analysis of the title compound, the pyrene-substituted unsymmetrical bis(phthalocyaninato)terbium(III) Single-Molecule Magnet (SMM) [Pc–Tb–Pc*]0 (1) (Pc = dianion of phthalocyanine, P* = dianion of phthalocyanine decorated with six flexible hexyl chains and one 4-pyren-1yl-butoxy group), was carried out. Both phthalocyaninato ligands in 1 are distorted from planarity and, therefore, adopt a biconcave shape. Effective π–π interactions between the molecules lead to the formation of head-to-tail π dimers. These dimers are stacked in the crystal, forming adjacent, parallel columns, the axes of which are tilted by 30° with respect to the C4 axes of the macrocycles. Herein, we also report the synthesis and characterization of the new isostructural Dy (compound 2) and Ho (compound 3) analogues of 1.
The crystal structure of four bis(phthalocyaninato) rare earth tetrabutylammonium salts are reported (RE = Nd, Gd, Ho, Lu) as determined by X-ray crystallography. Each crystallizes in a tetragonal lattice. Structural data for all determinations are reported with special focus on the skew angle between the phthalocyanine rings in the compounds.
For Abstract see ChemInform Abstract in Full Text.
The molecular structures of a series of nine mixed (2,3-naphthalocyaninato)(octaethylporphyrinato) double-decker complexes of lanthanide(III), M(Nc)(OEP)
(M=La, Pr, Nd, Tb, Dy, Ho, Er, Tm, Yb), have been determined by single-crystal X-ray diffraction analysis. All these compounds together with the Sm, Eu, Gd, Y, Lu and Ce analogues, whose structures have been solved previously, crystallize in the same orthorhombic system, Pnma, Z=4. The molecular structures of all these compounds are isostructural, exhibiting a slightly distorted square antiprismatic geometry with two domed ligands. The metal centre of M(Nc)(OEP) is coordinated by eight nitrogen atoms from the isoindole and pyrrole of the Nc and OEP rings, respectively. The ring-to-ring separation between the two domed ligands, as defined by the two N4 mean planes, decreases monotonically from 3.056 to 2.652 Å along the series of La to Lu as a result of lanthanide contraction. This interplanar distance as well as the average M–N(Nc) and M–N(OEP) bond lengths of M(Nc)(OEP)
(except M=Ce) show a linear relationship with the ionic radius of the metal centre. The skew/twist angle between the two macrocyclic rings remains almost unchanged, ca. 45°, for the whole series of lanthanide complexes, regardless of the size of the metal centre.
Density functional theory calculations were carried out to study the charge transfer properties of bis(phthalocyaninato) yttrium and lanthanum double-decker complexes M(Pc)2 (M = Y, La) for organic field effect transistors. The results indicate that the intrinsic delocalized hole in M(Pc)2 (M = Y, La) induces the high energy level of highest occupied molecular orbital and low energy level of lowest unoccupied molecular orbital in the sandwich double-decker molecules as well as the small ionization potential and large electronic affinity. These factors lead to very small injection barrier relative to Au source-drain electrode of these two double-deckers for both hole and electron and render them as good potential ambipolar semiconductor. Associated with the very small reorganization energy for hole and electron and large transfer integral in crystal, these two complexes M(Pc)2 (M = Y, La) display intrinsic charge transfer mobility of 0.034 and 0.17 cm2 V−1 s−1 for hole and 0.031 and 0.088 cm2 V−1 s−1 for electron in crystal according to the calculation results. The high intrinsic mobility for both hole and electron in these double-deckers was rationalized by examining the changes of geometric and electronic structures upon reduction and oxidation and charge transfer integral of different transfer modes in crystal. Charge transfer integrals in all the possible dimers composed of two Y(Pc)2 molecules were systematically studied to simulate the molecular arrangement of bis(phthalocyaninato) rare earth complexes in thin solid films.
Geometric structures of three types of supramolecular aggregates composed of bis(phthalocyaninato)lutetium (Lu(Pc)2) radicals are investigated by means of ESR measurements and theoretical calculations. The tetra-crown-substituted complex, Lu(CR4Pc)(Pc) (CR4Pc = tetra-15-crown-5 substituted Pc), forms an aggregate showing an ESR signal of electronic triplet state on addition of cations such as K+ and NH4+, which have a radius large enough to form a 2:1 sandwich-type complex with 15-crown-5. Addition of Na+ cation, which forms a 1:1 complex with 15-crown-5, did not give rise to such ESR signal. By comparison of the observed zero-field-splitting (zfs) constant D and theoretical calculation on the spin−spin interaction, the assumption that the aggregate has D4h symmetry is confirmed to be reasonable. The center-to-center distance between the two Lu(Pc)2 sites is estimated at 7.0 Å. When no cation is added, Lu(CR4Pc)(Pc) gives another type of aggregate in methanol/chloroform mixed solvent. This also gives a triplet-state ESR signal with a zfs constant D which is 0.71 times that of the cation-induced ESR. From the theoretical calculation, we concluded that two Lu(Pc)2 sites are placed parallel with a horizontal displacement in the Pc plane. The amount of the displacement is estimated at about 5 Å. The mono-crown substituted complex, Lu(CR1Pc)(Pc) (CR1Pc = mono-15-crown-5 substituted Pc), forms a structure linked with one bridge on addition of K+. The bridge acts as a pivot around which two radical sites can rotate. The zfs constant D obtained from the triplet ESR spectrum is 0.66 times that of the cation-induced system of Lu(CR4Pc)(Pc). The rotation angle is estimated at about 30−40°. It is suggested, by the calculation of the exchange coupling in the three cases, that spin multiplicity of the ground state can be switched between triplet and singlet depending on the amount of slide or rotation of the Lu(Pc)2 units in the xy plane, in which the Pc planes lie.
The present review should be seen far beyond pure homage to organometallic lanthanide amide chemistry. The class which is settled between the alkyl and alkoxide counterparts has claimed its own importance within the family of organolanthanide compounds during the last ten years. Meanwhile compound design can fall back on an extensive reservoir of sterically and electronically tailored ligands. Of course, the lanthanide dilemma requires special emphasis on structural chemistry, although, encouraging applications should highlight this review. The thermal stability and kinetic lability of the Ln-N bond make this class of lanthanide compounds not only a valuable synthetic precursor. The article covers the literature until mid-1995 and seeks to uncover the current trends in this field.
Magnetism and electronic structure of two types of phthalocyanine-based magnets, “ferromagnets” and “single-molecule magnets,”
both of which exhibit spontaneous magnetization but by different mechanism, are reviewed.
KeywordsElectronic structure-Ferromagnet-Phthalocyanine-Single molecule magnet
Cofacial and planar homo- and heteroleptic dimers and oligomers of phthalocyanine (Pc) and its analogues reported to date have been reviewed.
Density functional theory (DFT) calculations were carried out to describe the molecular structures, molecular orbitals, atomic charges, UV-vis absorption spectra, IR, and Raman spectra of bis(phthalocyaninato) rare earth(III) complexes M(Pc)(2) (M = Y, La) as well as their reduced products [M(Pc)(2)](-) (M = Y, La). Good consistency was found between the calculated results and experimental data. Reduction of the neutral M(Pc)(2) to [M(Pc)(2)]- induces the reorganization of their orbitals and charge distribution and decreases the inter-ring interaction. With the increase of ionic size from Y to La, the inter-ring distance of both the neutral and reduced double-decker complexes M(Pc)(2) and [M(Pc)(2)](-) (M = Y, La) increases, the inter-ring interaction and splitting of the Q bands decrease, and corresponding bands in the IR and Raman spectra show a red shift. The orbital energy level and orbital nature of the frontier orbitals are also described and explained in terms of atomic character. The present work, representing the first systemic DFT study on the bis(phthalocyaninato) yttrium and lanthanum complexes sheds further light on clearly understanding structure and spectroscopic properties of bis(phthalocyaninato) rare earth complexes.
Quantitative bulk ferromagnetic behavior (spontaneous magnetization) has been established for the organic-like molecular solid [FeIII(C5Me5)2] •+[TCNE]•-. It exhibits a Curie temperature, Tc, of 4.8 K, saturation magnetization of 16 300 (emu G)/mol, and a 2 K coercive field of 1 kG. Above 16 K the dominant magnetic interactions are along a chain (1-D) and near Tc 3-D bulk effects, as evidenced by the values of the critical exponents, dominate the susceptibility. The extended McConnell model has been developed, and it provides the synthetic chemist guidance for making new molecular materials to study cooperative magnetic coupling in systems. Assuming the electron-transfer excitation arises from the POMO, to achieve ferromagnetic coupling in a molecular solid via the McConnell mechanism, a stable radical (neutral, cations/anions, or ions with small diamagnetic counterions) must possess a degenerate POMO that is not half-filled, and the lowest excited state formed via virtual charge transfer (retro or forward) possesses the same spin multiplicity and mixes with the ground state. This requirement limits the structure of a radical to D2d, C3, or higher symmetry where symmetry-breaking distortions do not occur. Intrinsic doubly and triply degenerate orbitals are not necessary and accidental degeneracies suffice. To achieve bulk ferromagnetism, ferromagnetic coupling must be established throughout the solid. A microscopic model that accounts for the observations to data has been discussed. These requirements for ferromagnetism are met by [FeIII(C5Me5)2] •+[TCNE]•+. Additionally, this model predicts that the NiIII and CrIII analogues should be respectively antiferromagnetic and ferrimagnetic, as preliminary data suggest. Extensive chemical syntheses of cleverly designed radicals, as well as physical, experimental, and theoretical insight, are necessary to test and extend these concepts and establish a deeper understanding of cooperative phenomena in molecular solids.
We show how the partition functions for finite clusters with spin- 1/2 Heisenberg interactions may be computed efficiently and generally to any desired number of powers in reciprocal temperature. As an example, we have expanded the zero-magnetic-field free energy to the twenty-first power for the linear Heisenberg model and for nonzero magnetic field give an expression good through the tenth power. We introduce the concept of the two-point Padé approximant and use it to analyze the energy for the linear Heisenberg model.
The crystal and molecular structure of bis-phthalocyaninatouranium(IV), the first complex of an actinide element with the phthalocyaninato-ion, has been determined by X-ray diffraction analysis.
Cyclic 4n pi electron conjugated systems with C3 or greater symmetry can have triplet ground states. If stable examples of such systems can be prepared they can serve as the most important components of ferromagnetic organic compounds, a hitherto unknown class of substances. The theory of how triplets can be used to prepare ferromagnets is outlined. Synthetic approaches to stable triplets, and to the ferromagnetic systems themselves, are also described.
A comparison was made between the infrared, electronic, and electron spin resonance spectroscopic properties of lutetium and ytterbium diphthalocyanines, in the solid state as analytically pure powders, and after vacuum sublimation as thin deposited films. No significant differences were observed. Spectroscopic analysis of the sublimed films during electrochromic changes showed that the lutetium and ytterbium complexes behaved in a similar manner. Both gave identical variations in their electronic spectra with potential. Electron spin resonance data demonstrated that the oxidative color change is not associated with a change in paramagnetism, although the shape of the signal from the lutetium complex was altered upon oxidation. The ytterbium complex displayed no ESR signal before or after electro‐oxidation.
Lutetium diphthalocyanine can be electrolyzed reversibly in dimethylformamide to give four different colored solutions: violet, blue, green, and yellow‐red. Two of these solutions, the violet and the green, also exhibit electron paramagnetic resonance (EPR) signals indicative of organic‐free radicals. The blue and the yellow‐red solutions are EPR silent. The oxidation state of the phthalocyanine nucleus is responsible for the electrochromism of this rare‐earth complex. The EPR signal of the violet form, which is produced by electrolytic reduction and which is probably the anion radical of the complex, has a . The signal of the green form, which is the initially prepared material and which is probably a salt containing the cation radical of the complex, has a . The optical absorption spectra and extinction coefficients of three of the forms are also reported.
A method for location of the peak in a step-scan-measured Bragg reflexion profile is described. It leads to a ratio between the standard deviation of the intensity and the intensity, σ(I)/I, which is near minimum. The method is based on the observation that if σ(I)/I is calculated for all possible peak widths for a given profile then σ(I)/I is minimum near the true value of the peak width, and minimal σ(I)/I can thus be used as a criterion for correct location of the peak. The intensity determined this way is however in general slightly underestimated, and the bias as well as possible corrections are discussed. In addition a simple function resembling σ(I)/I, which has proved to be useful for practical applications, is given.
Absorption effects usually present the most serious source of systematic error in the determination of structure factors from single-crystal X-ray diffraction measurements if the crystal is not ground to a sphere or cylinder. A novel method is proposed for the correction of these effects for data collected on a diffractometer. The method works from the premise that the manifestation of systematic errors due to absorption, unlike most other sources of systematic error, will not be evenly distributed through reciprocal space, but will be localized. A Fourier series in the polar angles of the incident and diffracted beam paths is used to model an absorption surface for the difference between the observed and calculated structure factors. Knowledge of crystal dimensions or linear absorption coefficient is not required, and the method does not necessitate the measurement of azimuthal scans or any extra data beyond the unique set. Moreover, application of the correction is not dependent upon the Laue symmetry of the crystal or the geometry of the diffractometer. The method is compared with other commonly used corrections and results are presented which demonstrate its potential.
The problem of exchange interaction between two Ti3+ (d1) ions in a binuclear unit (Ti2Cl9)3- is investigated from a microscopic description of the exchange mechanisms. With the use of pseudofermion operators, the effective Hamiltonian between the orbitally degenerate ground terms 2T2g is determined with the various excited configurations being taken into account. Further, local trigonal distortion, spin-orbit coupling, and covalency effects are introduced for describing the real magnetic behavior of the entity. Thus it is shown that the use of the Heisenberg Hamiltonian for distorted systems is often a poor approximation. Lastly, a least-squares fitting of the experimental data of Cs3Ti2Cl9 is proposed from the developed model.
Rare-earth phthalocyanine sandwich compounds and their iodine analogues have been synthesized. Single crystals were obtained by electrochemical means, and magnetic susceptibility measurements on the polycrystalline samples follow the Curie-Weiss law. Room temperature and 77 K EPR spectra at X-band for undoped lutetium phthalocyanine indicate the presence of a free-radical phthalocyanine unit. Doped complexes also show a narrow signal with a g-value of 2.00.D.C. conductivity measurements on pellets in the temperature range 20 to 300 K yielded values on the order of 10−5 to 10−7 s cm−1 for the undoped phthalocyanines, and 10−2 to 10−4 s cm−1 for the doped ones. The conductivity behavior may be explained in terms of the variable-range hopping mechanism for heavily-doped semiconductors.
A new and simple model is presented for an organic ferromagnet containing segregated stacks of radical ions. This new model gives a conceptual framework for selecting candidate molecules, and hence appears to be a promising, general guide for designing new organic ferromagnetic materials. The discovery of the first organic ferromagnet is reported. It is based on a polymer obtained from reacting s-triaminobenzene with iodine. The reaction is complex and the resulting polymer is not very reproducible. Nevertheless, on a number of occasions a ferromagnet material has been obtained. This material remains ferromagnetic to high temperatures, until it decomposes near 400°C.
Thin films of bisphthalocyaninatolutetium derivatives (Pc2Lu) have been doped using a co-sublimation technique with an electron acceptor (dichlorodicyanoquinodimethane, DDQ) and an electron donor (tetraphenyldithiapyranylidene, DIPSΦ4). The conduction properties of Pc2Lu and of p- and n-type doped materials have been determined and correlated with the optical characteristics of the films. Pc2Lu is the first molecular semiconductor that satisfies the following three criteria: (i) it is a molecular material, (ii) its intrinsic conductivity is in the range 10−6−10−1Ω−1cm−1, (iii) it can be doped with both electron acceptors and electron donors.
The exchange interaction between two orbitally degenerate ground-state ions is analyzed on the basis of Anderson's model. These ions are supposed to be in octahedral environment with a 2T2g or 3T1g crystal-field ground term. We inspect the situation where they interact through a common corner (D4h) of their coordination octahedra. The suggested treatment differs from the previously developed ones by the distinction which is introduced between the various excited-state configurations with definite spin quantum numbers; the assumption is made that l-l and l-s intraionic coupling terms are negligible compared to the s-s one. Finally, from the results obtained, we are able to predict both the form of the exchange Hamiltonian describing these systems and the number of independent parameters. They are given in an explicit manner and discussed in the peculiar case of two t2g1 ions showing the D4h molecular symmetry.
The problem of exchange interaction between two Ti3+ (d1) ions in a binuclear unit (Ti2Cl9)3- is investigated from a microscopic description of the exchange mechanisms. With the use of pseudofermion operators, the effective Hamiltonian between the orbitally degenerate ground terms 2T2g is determined with the various excited configurations being taken into account. Further, local trigonal distortion, spin-orbit coupling, and covalency effects are introduced for describing the real magnetic behavior of the entity. Thus it is shown that the use of the Heisenberg Hamiltonian for distorted systems is often a poor approximation. Lastly, a least-squares fitting of the experimental data of Cs3Ti2Cl9 is proposed from the developed model.
: Single crystal X-ray diffraction analysis and X-ray photoelectron spectroscopy have been employed to investigate a bis(phthalocyaninato)-neodymium(III) compound which exhibits electrochromism. A neodymium ion occupies a central position between two parallel but staggered phthalocyanine ligands. An acidic hydrogen may play an important role in electrochromism of the compound, but apparently does not bind strongly to any of the pyrrole nitrogen atoms, in opposition to the structure proposed by Nicholson and Galiaridi. However, a weak interaction between the hydrogen and nitrogen atom(s) cannot be excluded. (Author)
The three compounds MnCu(obbz) {times} 5H{sub 2}O, MnCu(obbz) {times} 1H{sub 2}O, and NiCu(obbz) {times} 6H{sub 2}O, hereafter abbreviated as MnCu {times} 5H{sub 2}O, MnCu {times} 1H{sub 2}O, and NiCu respectively, have been synthesized. obbz stands for oxamidobis(benzoato). The crystal structure of NiCu has been determined. NiCu crystallizes in the monoclinic system, space group P2{sub 1}/n, with a = 7.764 (1) {angstrom}, b = 12.559 (3) {angstrom}, c = 20.083 (3) {angstrom}, {beta} = 97.56{degree}, and Z = 4. The structure consists of isolated heterodinuclear units with octahedral Ni(II) and square-planar Cu(II) ions bridged by an oxamido group. NiCu is not isomorphous to MnCu {times} 5H{sub 2}O or to MnCu {times} 1H{sub 2}O, neither of which has been obtained in the form of single crystals suitable for X-ray work. To get information on their structure, they have studied their XANES and EXAFS spectra at both Mn and Cu edges, as well as their powder X-ray patterns. MnCu {times} 5H{sub 2}O and MnCu {times} 1H{sub 2}O have very similar structures, with four noncoordinated water molecules in the former compound. Cu(II) is in elongated tetragonal surroundings and Mn(II) in octahedral surroundings. The radius of the first shell around Mn(II) is equal to 2.17more » (2) {angstrom} for MnCu {times} 5H{sub 2}O and 2.16 (2) {angstrom} for MnCu {times} 1H{sub 2}O. Those data are consistent with the following structure: Mn(II) would be surrounded by six oxygen atoms; two of these atoms MnCu {times} 1H{sub 2}O belong to an oxamido group, one to a carboxylato group, and one to a water molecule in the equatorial plane; the oxygen atoms in the apical positions would belong to other carboxylato groups, forming a two- or three-dimensional network. The magnetic properties of NiCu were studied in the 4.2-300 K temperature range.« less
The reaction of hydrazine with copper(II) chloride in acidic aqueous solution has been shown to produce at least four distinct complexes. Hydrazine behaves as a reducing agent, leading to the white, diamagnetic copper(1) complex (N 2H 4)CuCl and the black paramagnetic mixed-valence tricopper(2I,II) complex (N 2H 5) 2Cu 3Cl 6. Blue and green copper(II) complexes (N 2H 5) 2CuCl 4·2H 2O and (N 2H 5)CuCl 3 are also formed. Infrared spectra establish the presence of coordinated hydrazinium ions in the blue, green, and black compounds. Structures are proposed for all of these materials on the basis of spectroscopic and magnetic measurements Significant exchange interactions are present in the chloride-bridged linear-chain complex (N 2H 5)CuCl 3. The structure of the complex (N 2H 5)CuCl 3 has been determined from single-crystal X-ray counter data. The complex crystallizes in the orthorhombic space group Pnma with four molecules in a cell of dimensions a = 14.439 (2), b = 5.705 (1), and c = 6.859 (1) Å. The structure has been refined by full-matrix least-squares techniques to a conventional R factor (on F) of 0.042 using 538 independent observations. The entire formula unit (with the exception of some of the hydrogen atoms) is constrained to lie on a mirror plane. The structure consists of infinite chains of dichloro-bridged dimers, in which one chloride ligand serves to propagate the chain in both directions while the other two chloride ligands do not. Thus, one chloride ligand is coordinated to three copper atoms with an in-plane distance of 2.297 (1) Å and two out-of-plane separations of 2.8560 (5) Å, while the other two chloride ligands are each coordinated to only a single copper center with bond lengths of 2.280 (1) and 2.298 (2) Å. The Cu-Cu′ separation and the bridging Cu-Cl-Cu′ angle in the chain are 3.751 (1) Å and 9279 (3)°, respectively.
The molecular configuration of stannic phthalocyanine, Sn(C32H16N8)2, has been determined by three-dimensional X-ray analysis. The orthorhombic cell dimensions (at 22°) and space group are a = 10.547 ± 0.001, b = 50.743 ± 0.004, and c = 8.9046 ± 0.0009 Å; Z = 4; dc = 1.59, dm = 1.60 ± 0.01 g/cm3; and P212121. The final parameters were determined from 2168 independent reflections measured by counter methods. The least-squares fitting of the data refined to R1 = 6.8%. The two phthalocyanine ring systems form a sandwich-type compound with the tin atom in the center. The cores of the phthalocyanine moieties are separated from each other by 2.70 ± 0.04 Å and are rotated 42° with respect to each other. The eight isoindole nitrogen atoms form an antiprism about the tin atom with Sn-N distances (individually ± 0.02 Å) ranging from 2.32 to 2.37 Å and the average Sn-N distance being 2.347 ± 0.007 Å.
Two novel compounds formed by nickel(II) hexafluoroacetylacetonate and nitronyl nitroxide radicals NITR = 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide, with R = methyl, Me, and phenyl, Ph, were synthesized. The compound Ni(hfac) 2(NITPh) 2 crystallizes in the monoclinic system, space group P2 1/c, with a = 12.243 (4) Å, b = 15.237 (4) Å, c = 22.310 (8) Å, β = 100.68 (2)°, and Z = 4. The nickel ions are octahedrally coordinated to two hfac molecules and to the oxygen atoms of two different radicals. The magnetic properties indicate the presence of a strong antiferromagnetic coupling between the nickel and the radicals, which has been roughly estimated to be on the order of 400 cm -1. Even if the structure of Ni(hfac) 2NITMe is not available, we suggest an infinite chain structure, with each radical bridging two Ni(hfac) 2 units, on the basis of analogies with other M(hfac) 2NITR compounds. In agreement with the proposed structure, the magnetic susceptibility shows a divergence in the χT product at low temperature. A numerical fit, with a model previously used for Mn(hfac) 2NITR ferrimagnetic chains, yields an antiferromagnetic coupling of 424 cm -1. The fast divergence of the susceptibility at very low temperature indicates the presence of a phase transition to three-dimensional order. Low-field (0-1 Oe) magnetic measurements show that the system undergoes a phase transition at ca. 5.3 K. The nature of the transition is presumably ferromagnetic and is driven by the dipolar interaction between chains, as in the analogous manganese-radical systems.
The bis(phthalocyaninato)lutetium(III) derivative LuPc2·CH2Cl2 (1, LuC65H34N16Cl2) and the (phthalocyaninato)lutetium(III) complex [LuPc(OAc)(H2O)2]·H2O·2CH 3OH (2, LuC36H33N8O7) were synthesized in boiling 1-hexanol with use of lutetium(III) acetate and 1,2-dicyanobenzene in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene and purified by chromatography. The visible spectroscopic properties are reported for both complexes. 1 crystallizes in the orthorhombic system with a = 28.242 (9) Å, b = 22.877 (8) Å, c = 8.050 (4) Å, Z = 4, and space group Pnma. 2 belongs to the monoclinic system with a = 12.033 (3) Å, b = 20.807 (6) Å, c = 14.011 (3) Å, β = 95.34 (2)°, space group P21/n, and Z = 4. 1 is a sandwich type complex in which the lutetium atom is eightfold coordinated by the isoindole nitrogens (Niso) of two staggered phthalocyanine rings. The mean value of the Lu-Niso bond distances with one ring is 2.387 (4) Å whereas the average value for the four Lu-Niso bond lengths with the other ring is 2.372 (3) Å. Both rings are convex. In 2, the lutetium atom is also eightfold coordinated to the four isoindole nitrogens of one phthalocyanine ring, to two oxygens of one acetato anion, and to two water molecules. The mean value of the four Lu-Niso bond distances with the nitrogens of the phthalocyanine ring is 2.345 (2) Å. The structure and the magnetic properties of 1 are consistent with a nonprotonated, ligand-oxidized [LuPc2] formulation.
Quantitative bulk ferromagnetic behavior (spontaneous magnetization) has been established for the organic-like molecular solid [FeIII(C5Me5)2] •+[TCNE]•-. This complex exhibits magnetic behavior characterized by a Curie-Weiss constant (θ) of +30 K, a Curie temperature (Tc) of 4.8 K, a saturation magnetization of 16700 (emu G)/mol, and a coercive field of 1 kG at 2 K. Above 16 K the dominant magnetic interactions are along a chain (1-D) and near Tc 3-D bulk effects as evidenced by the value of the critical exponents dominate the susceptibility. Additionally, six-line zero applied magnetic field Zeeman-split 57Fe Mössbauer spectra with large internal fields (>400 kG) are observed. The structural requirements necessary to prepare molecular ferromagnetic compounds are evolving. The only structure type reported to date possesses parallel ⋯D•+A•-D•+A •-⋯ linear chains where both the donor (D) and acceptor (A) are radicals. The best studied systems possess decamethylmetallocenium donors; however, replacement of the C5Me5 ligand with C5H5 does not lead to materials exhibiting ferromagnetic behavior. Preliminary data suggest that C6 ligands can be utilized to prepare charge-transfer complexes exhibiting ferromagnetic behavior. Substitution of [TCNE]•- with [DDQ]•-, [C4(CN)6]•-, or [TCNQI2]•- leads to similarly structured complexes exhibiting dominant ferromagnetic behavior. In contrast, the [TCNQ]•- salt exhibits metamagnetic behavior with a Neel temperature of 2.55 K and critical field of ∼1.6 kG. The planar [TCNQF4]•- salts, [M(S2C2(CN)2]- salts (M = Ni, Pt), and three polymorphs of the 1:1 [C6(CN)6]•- salts as well as the tetrahedral [FeX4]- (X = Cl, Br) salts possess different structural motifs and do not exhibit ferromagnetic behavior. Alternate first-row (3d) metallocenes as the [TCNE]•- salt lead to differing magnetic behaviors; i.e., S = 0 CoIII is paramagnetic, S = l/2 NiIII is antiferromagnetic, and S = 3/2 CrIII is ferrimagnetic. Analogous complexes based on second-row (4d) and third-row (5d) RuIII and OsIII donors have yet to be prepared. The extended McConnell model was developed and provides the synthetic chemist with guidance for making new molecular materials (organic, organometallic, main group, polymer, and/or inorganic coordination complex) to study cooperative magnetic coupling in systems. Assuming the electron-transfer excitation arises from the POMO, to achieve ferromagnetic coupling in a molecular solid via the McConnell mechanism a stable radical (neutral, cations/anions, or ions with small diamagnetic counterions) must possess a degenerate POMO that is not half-filled and the lowest excited state formed via virtual charge transfer (retro or forward) possesses the same spin multiplicity and mixes with the ground state. This requirement limits the structure of a radical to D2d, C3, or higher symmetry where symmetry-breaking distortions do not occur. Intrinsic doubly and triply degenerate orbitals are not necessary and accidental degeneracies suffice. To achieve bulk ferromagnetism, ferromagnetic coupling must be established throughout the solid, and a microscopic model based on the intra- and interchain configurational mixing of excited states was discussed. These requirements are met by [FeIIIC5Me5)2]•- [TCNE]•-, [FeIII(C5Me5)2] •+[C4(CN)6]•-, etc. Addition-ally, this model suggests that the NiIII and CrIII analogues should be respectively antiferromagnetic and ferrimagnetic, as preliminary data suggest. The bulk nature of the magnetic behavior emphasizes the importance of not only the primary and secondary, but the tertiary structure in this class of materials. We are probing these effects via acceptor substitution and studying the structure/property relationship. We are looking toward the development of computational methods to aid in the understanding of the structure/magnetic behavior. Extensive chemical syntheses of cleverly designed radicals as well as physical, experimental, and theoretical insight are necessary to test these concepts and establish a deeper understanding of cooperative phenomena in molecular solids.
The multiplicity and the full spin of the ground state of large alternate molecules with conjugated bonds are considered. It is strictly shown that if the numbers of starred and unstarred atoms (say, carbon) differ from each other the full spin of the molecule is more than zero. Some possible planar and linear molecules having the full spin to be proportional to their sizes are presented. Particularly, they would be ferromagnets at infinite sizes.
Linear chains (and rings) of S=1 / 2 spins with the anisotropic (Ising-Heisenberg)
Hamiltonian H=-2JSUM [under i=1][over N][SizSi+1z+ gamma (SixSi+1x+SiySi+1y)]-g
beta SUM [under i=1][over N][H·Si] have been studied by exact machine
calculations for N=2 to 11, gamma =0 to 1 and for ferro- and antiferro-magnetic
coupling. The results reveal the dependence on finite size and anisotropy
of the spectrum and dispersion laws, of the energy, entropy, and
specific heat, of the magnetization and susceptibilities, and of
the pair correlations. The limiting N--> [infinity] behavior is accurately
indicated, for all gamma , in the region kT / |J| >= 0.5 which includes
the maxima in the specific heat and susceptibility. The behavior
of thermal and magnetic properties of infinite chains at lower temperatures
is estimated by extrapolation. For infinite antiferromagnetic chains
the ground-state degeneracy, the anisotropy gap, and the magnetization,
perpendicular susceptibility, and pair correlations at T=0 are similarly
studied. Estimates of the long-range order suggest that it vanishes
only at the Heisenberg limit gamma =1 and confirm the accuracy of
Walker's perturbation series in gamma .
The Enraf-Nonius CAD4-SDP
- Frenz