The influences of the packing ligand on spin state and magnetic interactions in new oxalates with 3d-transition metals

Two new hetero tri-nuclear oxalates (NH4)8[Fe2Co(C2O4)8]·6H2O and [Fe2Co(C2O4)2(OH)4]·2H2O have been synthesized. The compound presented opposite behaviour in ac-susceptibility measurements, different frustration level and spin–orbit coupling in magnetization ones. The Mössbauer approach pointed to local interactions governed by metal-oxalate strongly coupled unit. The data were interpreted in terms of role of positive (NH4) or negative (OH) bridging ligands on general magnetic properties.