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(III) 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 = -2JS 1 .S 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.