Dinuclear copper(II) complexes with ferromagnetic and antiferromagnetic interactions mediated by a bridging oxalato group:structures and magnetic properties of [Cu_2L_4(mu-C_20_4)](PF_6)_2(H_20)_2 and lCu_2L_2(mu-C_2O_4)(NO_3)_2((CH_3)_2NCOH)_2] (L =

摘要

Two dinuclear Cu~(II) complexes of formula [Cu_2(dpyam)_4(mu-C_2O_4)](PF_6)_2(H_2O)_2 (1) and [Cu_2(dpyam)_2(mu-C_2O_4)(NO_3)_2(DMF)_2] (2) (dpyam = di-2-pyridylamine) have been synthesized and their spectroscopic and magnetic properties characterized.Complex (1) crystallizes in the non-centrosymmetric monoclinic space group PC,while (2) crystallizes in the non-centrosymmetric triclinic space group PI.Compound (1) involves the compressed octahedral Cu~(II) environment,whereas (2) exhibits an elongated octahedral Cu~(II) geometry.Both complexes contain six-coordinate metal centers bridged by planar bis-didentate oxalate group.The geometry,spectroscopic properties and the effective magnetic moment of (1) are very close to those of the recently published [Cu_2(dpyam)_4 (mu-C_2O_4)](C1O4)_2(H_2O)_3 and [Cu_2(dpyam)_4(mu-C_2O_4)](BF_4)_2(H_2O)_3.Thus (1) is expected to exhibit a very weak ferromagnetic interaction between the Cu~(II) centers which is confirmed by EPR spectrum.Those of (2) are comparable to those of the recently published [Cu_2(dpyam)_2(mu-C_2O_4)(NO_3)_2(DMSO)_2].Therefore a strong antiferomagnetic interaction is expected.The effective magnetic moment at room temperature of (1) was measured to be 2.55 BM/dimer,which agrees with the spin only value of Cu~(II),2.45 BM calculated for two uncoupled spin = 1/2 centers.In (2) the room temperature effective magnetic moment of 2.16 BM/dimer indicates the partial spin paring by antiferromagnetic coupling.This is confirmed by the e.p.r.spectrum and is explained as a result of the magnetic interaction between the coplanar d_(x~2-y~2) orbitals on the two copper atoms.