Synthesis, structural characterization, magnetic and EPR studies of heterometallic Cu2Cr2 and Cu2Ga2 complexes

Two heterometallic complexes [{Cu(phen)2}2{Cr2(μ-OH)2(nta)2}][Cr2(μ-OH)2(nta)2]·8H2O (I) and [{Cu(phen)2}2{Ga2(μ-OH)2(nta)2}][Ga2(μ-OH)2(nta)2]·dmf·16H2O (III), where nta is the nitrilotriacetate ligand and dmf is dimethylfomamide, phen is ο,ο′-phenanthroline, have been prepared and structurally characterized by single-crystal X-ray crystallography. Both compounds display an ionic type structure, with close geometric parameters, containing {Cr2(μ-OH)2(nta)2} and {Ga2(μ-OH)2(nta)2} entyties for I and III, respectively. These dimeric di-μ-hydroxy units exhibit different coordination functions. In the tetranuclear Cu2Cr2 and Cu2Ga2 complex cations they are involved in a bidentate bridging form being linked to the cooper atoms through two symmetrically related oxygen atoms of the carboxylate groups. The anionic forms [Cr2(μ-OH)2(nta)2]2− and [Ga2(μ-OH)2(nta)2]2− are non-coordinating and only involved in a multiple hydrogen bonds architecture.Comparative analysis of the temperature dependence of EPR spectrum and magnetic susceptibility of compound I and III, showed that the magnetic properties of tetranuclear cluster [{Cu(phen)}2Cr2(OH)2(nta)2] are dominated by strong antiferromagnetic interaction between chromium ions (JisoCrCr = −13.4 cm−1). The interaction between chromium(III) and copper(II) ions via syn–anti carboxylic groups has a small antiferromagnetic values (JisoCrCu = −0.23 cm−1). The small anisotropy of the exchange interaction between chromium ions manifests itself only in the EPR spectra.

Heterometallic complexes [{Cu(phen)2}2{Cr2(μ-OH)2(nta)2}][Cr2(μ-OH)2(nta)2]·8H2O and [{Cu(phen)2}2{Ga2(μ-OH)2(nta)2}][Ga2(μ-OH)2(nta)2]·dmf·16H2O have been prepared and structurally characterized by single-crystal x-ray crystallography. The temperature dependence of EPR spectrum and magnetic susceptibility showed that the magnetic properties of the tetranuclear cluster are dominated by strong antiferromagnetic interaction between chromium ions (JisoCrCr = –13.4 cm –1).Figure optionsDownload as PowerPoint slide