Hisashi Okawa's research while affiliated with Kyushu University and other places

Proton-conductive magnetic metal-organic frameworks (MOFs), {NR3(CH2COOH)}[MaIIMbIII(ox)3] (abbreviated as R-MaMb: R = ethyl (Et), n-butyl (Bu); MaMb = MnCr, FeCr, FeFe), have been studied. The following six MOFs were prepared: Et-MnCr∙2H2O, Et-FeCr∙2H2O, Et-FeFe∙2H2O, Bu-MnCr, Bu-FeCr and Bu-FeFe. The structure of Bu-MnCr was determined by X-ray crystallography. Crystal data: trigonal, R3c (#161), a = 9.3928(13) Å, c = 51.0080(13) Å, Z = 6. The crystal consists of oxalate-bridged bimetallic layers interleaved by {NBu3(CH2COOH)}+ ions. Et-MnCr∙2H2O and Bu-MnCr (R-MnCr MOFs) show a ferromagnetic ordering with TC of 5.5-5.9 K, and Et-FeCr∙2H2O and Bu-FeCr (R-FeCr MOFs) also show a ferromagnetic ordering with TC of 11.0-11.5 K. Et-FeFe∙2H2O and Bu-FeFe (R-FeFe MOFs) belong to the class II of mixed-valence compounds and show the magnetism characteristic of Néel N-type ferrimagnets. The Et-MOFs (Et-MnCr∙2H2O, Et-FeCr∙2H2O and Et-FeFe∙2H2O) show high proton conduction while the Bu-MOFs (Bu-MnCr, Bu-FeCr and Bu-FeFe) show moderate proton conduction. Together with water adsorption isotherm studies, the significance of the carboxyl residues as proton carriers is revealed. The R-MnCr MOFs and the R-FeCr MOFs are rare examples of coexistent ferromagnetism and proton conduction, and the R-FeFe MOFs are the first examples of coexistent Néel N-type ferrimagnetism and proton conduction.

A series of one-dimensional heterotrimetallic assemblies, [Cu2Ln(L)2(H2O)4][M(CN)6]·nH2O [Ln = Gd, M = Co (1), Fe (2), Cr (3), and Ln = La, M = Co (4), Fe (5), Cr (6)], were prepared by the reaction of a Cu2Ln precursor complex, [Cu2Ln(L)2(NO3)3], with K3[M(CN)6] in water. All of the assemblies were isomorphous and formed a 1D zigzag chain, in which the [Cu2Ln(L)2(H2O)4]3+ and [M(CN)6]3– units were alternately positioned and were linked in a Cu–NC–M–CN–Cu manner. Compound 1 showed magnetic behaviour similar to that of the discrete precursor complex, [Cu2Gd(L)2(NO3)3], owing to the diamagnetic nature of the [CoIII(CN)6]3– unit. In the case of 2, a simple summation of the magnetic behaviour of the [Cu2Gd(L)2(H2O)4]3+ and [Fe(CN)6]3– units was observed, whereas ferromagnetic interactions were found to be operative between the Cu2+ and Cr3+ ions in compound 3. The same magnetic interactions between Cu2+ and M3+ were confirmed in compounds 4 to 6, which included the diamagnetic La3+ ion. The differences in the magnetic behaviours of 2 and 3 can be explained by the overlap of the d(Cu)–pπ(CN) orbitals in the bent Cu–N≡C linkage and the spin-density on the cyanide nitrogen of the [Cr(CN)6]3– unit.

This paper discusses coordination-position isomeric MIICuII and CuIIMII complexes, using unsymmetric dinucleating macrocycles (Lm;n)2− ((L2;2)2−, (L2;3)2− and (L2;4)2−) that comprise two 2-(N-methyl)-aminomethyl-6-iminomethyl-4-bromo-phenonate entities, combined through the ethylene chain (m = 2) between the two amine nitrogens and through the ethylene, trimethylene or tetramethylene chain(n = 2, 3 or 4) between the two imine nitrogens. The macrocycles have dissimilar N(amine)2O2 and N(imine)2O2 metal-binding sites sharing the phenolic oxygens. The reaction of the mononuclear CuII precursors, [Cu(L2;2)], [Cu(L2;2)] and [Cu(L2;2)], with a MII perchlorate and a MII acetate salt formed (acetato)MIICuII complexes: [CoCu(L2;2)(AcO)]ClO4·0.5H2O] (1), [NiCu(L2;2) (AcO)]ClO4 (2), [ZnCu(L2;2) (AcO)]ClO4 (3), [CoCu(L2;3)(AcO)]ClO4·0.5H2O (4), [NiCu(L2;3)(AcO)]ClO4 (5), [ZnCu(L2;3)(AcO)]ClO4·0.5H2O (6), [CoCu(L2;4)(AcO)(DMF)]ClO4 (7), [NiCu(L2;4) (AcO)]ClO4·2DMF (8) and [ZnCu(L2;4)(AcO)]ClO4 (9) (the formulation [MaMb (Lm;n)]2+ means that Ma resides in the aminic site and Mb in the iminic site). The site selectivity of the metal ions is demonstrated by X-ray crystallographic studies for 2·MeOH,3,5,7, and9. An (acetato)CuIIZnII complex, [CuZn(L2;3)(AcO)]ClO4 (10), was obtained by the reaction of [PbCu(L2;3)]-(ClO4)2 with ZnSO4·4H2O, in the presence of sodium acetate. Other complexes of the CuIIMII type were thermodynamically unstable to cause a scrambling of metal ions. The Cu migration from the iminic site to the aminic site in the synthesis of10 is explained by the ‘kinetic macrocyclic effect’. The coordination-position isomers,6 and10, are differentiated by physicochemical properties.

We controlled the hydrophilicity of metal-organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR(3)(CH(2)COOH)}[MCr(ox)(3)]·nH(2)O (abbreviated as R-MCr, where R = Me (methyl), Et (ethyl), or Bu (n-butyl), and M = Mn or Fe): Me-FeCr, Et-MnCr, Bu-MnCr, and Bu-FeCr. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR(3) residue to decrease with increasing bulkiness of the residue: {NMe(3)(CH(2)COOH)}(+) > {NEt(3)(CH(2)COOH)}(+) > {NBu(3)(CH(2)COOH)}(+). The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, Me-FeCr, adsorbed a large number of water molecules and showed a high proton conductivity of ~10(-4) S cm(-1), even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions.

The observed magnetic data for two isosceles trico-balt(II) complexes have been successfully analyzed, considering the axial distortion around each cobalt(II) ion, the local spin-orbit coupling, the anisotropic ex- change interactions, and the intermolecular exchange interactions. The complexes each contains two types of octahedral high-spin cobalt(II) ions (CoA and CoB) in the shape of an isosceles triangle (CoA1-CoB-CoA2), and the contribution of the orbital angular momen- tum is significant. The exchange interaction between the CoA and CoB ions is practically negligible (J = ~ 0), whereas the interaction between the CoA1 and CoA2 ions is ferromagnetic (J’ > 0) for both complexes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The structures and magnetism of complex-based metal assemblies derived from [M(CN)6]n- (M = Cr3+, Mn3+, Fe3+, Co3+, Fe2+; n = 3, 4) and coordinatively unsaturated [MA(L)x]m+ (MA = Mn2+, Ni2+, Cu2+, Mn3+, Fe3+; L = polyamine ligand, salen2- derivatives) are reviewed. The reaction of the constituents in different ratios, in the absence or presence of an appropriate cation or anion and by the change of ligand L provides multi-dimensional bimetallic assemblies of various networks extended through M-CN-MA-NC- linkages. The magnetic properties of the assemblies are discussed with respect to their network structures and MA/M combinations. These assemblies provide significant insights into magnetostructural correlation and design of magnetic materials.

The oxalate-bridged bimetallic complexes {NH(prol)(3)}[M(II)Cr(III)(ox)(3)] (M(II) = Mn(II), Fe(II), Co(II)) with hydrophilic tri(3-hydroxypropyl)ammonium (NH(prol)(3)(+)) were prepared by a new synthetic procedure, and the effects of the NH(prol)(3)(+) ion upon the structure, magnetism, and electrical conduction were studied. An X-ray crystallographic study of the MnCr dihydrate, {NH(prol)(3)}[MnCr(ox)(3)].2H(2)O, was performed. Crystal data: hexagonal, P6(3), a = b = 9.3808(14) A, c = 15.8006(14) A, Z = 2. The structure comprises oxalate-bridged bimetallic layers interleaved by NH(prol)(3)(+) ions. The ions assume a tripodal configuration and are hydrogen bonded to the bimetallic layers together with water molecules, giving rise to a short interlayer separation (7.90 A) and unsymmetrical faces to the bimetallic layer. Cryomagnetic studies demonstrate ferromagnetic ordering with transition temperature of 5.5 K for the MnCr complex, 9.0 K for the FeCr complex, and 10.0 K for the CoCr complex. The interlayer magnetic interaction is negligibly weak in all of the complexes despite the short interlayer separation. A slow magnetization is observed in all the complexes. This is explained by spin canting associated with the unsymmetrical feature of the bimetallic layer. The complexes show proton conduction of 1.2 x 10(-10) to 4.4 x 10(-10) S cm(-1) under 40% relative humidity (RH) and approximately 1 x 10(-4) S cm(-1) under 75% RH. On the basis of water adsorption/desorption profiles, the conduction under 40% RH is mediated through the hydrogen-bonded network formed by the bimetallic layer, NH(prol)(3)(+) ions, and water molecules (two per MCr). Under 75% RH, additional water molecules (three per MCr) are concerned with the high proton conduction. This is the first example of a metal complex system exhibiting coexistent ferromagnetism and proton conduction.

A di-mu-fluoride mixed-valent tetrairon(II,II,III,III) complex, [{Fe-2(L)(dnba)}(2)(mu-F)(2),](BF4)(2), was synthesized and characterized by X-ray structural analysis, UV-vis-NIR spectroscopy, and Mossbauer measurement.