An N₂O₄ isomer as a model for the examination of the origin of the antiferro magnestism of the copper acetate monohydrate dimer

Abstract

Some results of VESCF molecular orbital calculations, with configuration interaction, are reported for an N₂0₄ isomer having the geometry of (see diagram in article) This isomer can mimic the two copper ions and the oxygen atoms of two acetate ligands of Cu₂(O₂CCH₃)₄,2H₂O. The calculations suggest that the primary factor responsible for the singlet-triplet separation (J ≈ 286 cm^-1) for the copper acetate is the simultaneous overlap which occurs between two lone-pair oxygen atomic orbitals of each acetate ligand with each other and with the singly occupied orbitals of the copper(11) ions. The relevance of five-electron three-centre bonding for the interpretation of the magnetic properties of two classes of binuclear transition metal complexes is indicated.