Study On The Syntheses, Crystal Structures And Magnetic Properties Of Dicyanidechromate(Ⅲ)Complexes

The synthesis of molecular complexes manifesting specific structures andmagnetic properties is still one of the most challenging missions in the molecularmagneticsm research field. Cyanide-containing building blocks have attracted greatattention in the assembly of magnetic complexes for their excellent natures. In thisthesis, ten cyanide-bridged heterometallic complexes with different molecularstructures and magnetic properties have been synthesized by careful selection ofcyanidechromate(III) together with the rational design or selection of unsaturatedbuilding blocks. The structures and magnetic properties of these complexes have beeninvesitigated in detail.1) Two kind of nitrogen-containing ligands have been determined andcorresponding unsaturated nickel(II) metal building blocks have been obtained basedon1,4,8,11-tetraazacyclotetradecane. Four cyanide-bridged CrIIINiIItrinuclearcomplexes have been assembled by the reaction of these determined building blockswith dicyanidechromate(III). Magnetic investigations indicate that the existence ofoverall ferromagnetic coupling and at low temperature exhibit weak antiferromagneticcoupling in the four CrIIINiIItrinuclear complexes. The magnetic properties of thesecomplexes are close to their structures. The coupling constants (J) of cyanide bridgedCrIIINiIItrinuclear complexes increasing with the angle of Ni–Ncyanide/(o) fit therelationship of coupling constants (J) and the angle of Ni–Ncyanide/(o). Calculate andverify the theoretical calculation of the critical angle about ferromagnetic andantiferromagnetic complexes from Julve.2) Two kind of nitrogen-containing ligands have been determined andcorresponding unsaturated copper(II) metal building blocks have been obtained basedon1,4,8,11-tetraazacyclotetradecane. One cyanide-bridged CrIIICuII1D complex andthree cyanide-bridged CrIIICuIItrinuclear complexes have been assembled by thereaction of these determined building blocks with dicyanidechromate(III). Magneticinvestigations indicate that the existence of overall ferromagnetic coupling in the onecyanide-bridged CrIIICuII1D complex and three cyanide-bridged CrIIICuIItrinuclearcomplexes. The antiferromagnetic coupling strength and zero-field splitting (zfs) ofthe Cu(II) ion has been obtained by fitting the temperature-dependence magneticsusceptibilities. There exist weak antiferromagnetic and zfs effect in the CrIIICuIIion-pair complexes. 3) A cyanide-bridged CrIIICoIItwo-dimensional (2D) grid-like complex and acyanide-bridged CrIIICoIIone-dimensional (1D) chain complex have been assembledby the reaction of the [Co(L-N5)](ClO4)2with dicyanidechromate(III) andK3[Cr(CN)6]·H2O, respectively. Magnetic investigations reveal that Cr (III) and Co (II)ions of complexes9and10showed ferromagnetism to pass through the magneticcoupling of the cyano group. Due to the presence the layers of weak antiferromagneticinteraction of complexes9exhibit long-range antiferromagnetic ordering behaviorand variable magnetic changed from antiferromagnetic arrangement to ferromagneticmagnetic arrangement. Phase transition temperature TNis9.4K. Overcome theantiferromagnetic coupling between the molecules of the critical field is2000Oe.Complex10Curie temperature TCis15K. At2.0K, the hysteresis loop of complex10shows a typical soft ferromagnetic behavior, coercive field is10Oe and remanenceis about7.8N.The above results indicate that topological structures and magnetic properties ofmolecular complexes can be efficiently controlled by the careful selection of spincarriers and their coordination ligands.