Antiferromagnetically coupled chromium(III)-chromium(III) binuclear complexes with tris(oxalato)chromate(III)

Three new binuclear chromium(III) complexes bridged by tris(oxalato)chromate(III), [Cr(ox)(3)](3-) and end-capped with 2,2'-bipyridine (bpy); 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy) or 5-methyl-1,10-phenanthroline (Mephen), have been synthesized and characterized, namely [Cr-2(ox)(3)(bpy)(2)] (1), [Cr-2(ox)(3)(Me(2)bpy)(2)] (2) and [Cr-2(OX)(3)(Mephen)(2)] (3). At present, the three complexes have not yet been isolated in crystalline form, suitable for X-ray structure analysis, but based on elemental analyses, molar conductance and magnetic moments of room-temperature measurements, and spectroscopic studies, extended ox-bridged structures consisting of two chromium(Ill) ions, each in an octahedral environment are proposed for these complexes. The complexes [Cr-2(ox)(3)(bpy)(2)] (1) and [Cr-2(ox)(3)(Me(2)bpy)(2)] (2) were further characterized by variable temperature magnetic susceptibility (4.2-300 K) measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, (H) over cap = -2J (S) over cap (.) (S) over cap (2), giving the exchange integrals J = -9.73 cm(-1) for (1) and J = -5.29 cm(-1) for (2). This result indicates the presence of weak antiferromagnetic spin-exchange interaction between the metal ions within each molecule. The influence of the methyl substituents in the terminal ligand on magnetic interactions between the metals is also discussed.