High T_c Ferrimagnetic Organic-Inorganic Hybrid Materials with Mn~(II)-L-Mn~(II) and Mn~(II)-NC-Nb~(IV) Linkages (L = Pyrazine,Pyrazine-N,N'-dioxide,Bipyrimidine)

摘要

A series of heterobimetallic,cyano-bridged 3D inorganic-organic hybrid networks with Mn~(II)-L-Mn~(II) and Mn~(II)-NC-Nb~(IV) linkages are reported.Reaction of [Mn(H2O)6]~(2+) with [Nb(CN)8]4~- in the presence of organic linker L (pyrazine (pyz),pyrazine-N,N'-dioxide (pzdo),and 2,2'-bipyrimidine (bpym)) in H2O affords {Mn_2~(II)(pz)2(H2O)4[Nb~(lv)(CN)8]} centre dot pz-3H2O (1),{Mn~(II)2(pzdo)(H2O)4[Nb~(IV)(CN)8]} centre dot 5H2O (2),and {Mn~(II)2(bpym)(H2O)2[Nb~(IV)(CN)8]} (3),respectively.1-3 were examined by X-ray crystallography and vibrational and magnetochemical studies.1 is characterized by the coexistence of 3D inorganic cyano-bridged and 1D organic [Mn-(mu-pyz)]_n~(2n+) sublattices along with the presence of monocoordinated and crystallization molecules of pyrazine.Assemblies 2 and 3 exhibit dimeric {Mn~(II)_2-(mu-L)}~(4+) coordination motifs.The magnetic behavior of heterobimetallic 1-3 complexes is dominated by antiferromagnetic coupling between Wn~(II) and Nb~(lv) centers mediated by cyano bridges,resulting in long-range ferrimagnetic ordering with a high T_c of 27 (1),37 (2),and 50 K (3).The magneto-structural correlation leads to the conclusion that the magnitude of T_c is related to the type of coordination polyhedra of [Nb(CN)8] moieties (SAPR (1),intermediate between SAPR and DD (2),and DD (3)),the relative number of cyano bridges per Mn2Nb unit,and coexistence of inorganic and organic connectivity.FC/ZFC responses appear to be sensitive to the degree of organic connectivity.The discussion of magneto-structural correlation is based on the spin-density properties of adequate heterobimetallic systems containing octacyanometalates.