Synthesis, structure and magnetic properties of a chromium(III)-nicotinamide complex [Cr₃O(O₂CCH₃)₆(na)₃]⁺ (na = nicotinamide)

The reaction between [Cr₃O(O₂CCH₃)₇(H₂O)] ('basic chromium acetate') and an excess of nicotinamide (na) at 120°C, followed by dissolution of the mixture in water and addition of PF₆^-, led to the isolation of the first Cr(III)-nicotinamide complex [Cr₃O(O₂CCH₃)₆(na)₃]⁺ (1). Crystals of the compound 1·PF₆·3CH₃CN were subjected to a detailed X-ray structural analysis. The three N-bonded na ligands, which occupy axial positions at the corners of the triangular basic chromium acetate, are nearly co-planar with the Cr₃O system. The three Cr-N(na) bond distances are in the range 2.121(8)-2.128(8) Å. Two of the na ligands on each cluster form four hydrogen bonds with two ligands from a neighboring cluster, via their amide ends with N···O distances of 2.88(1)-2.92(1) Å. Magnetic susceptibility measurements of a powdered sample of 1·PF₆·3CH₃CN over the range 2-300 K showed that the three Cr(III) ions were antiferromagnetically coupled with J = -10.4 cm^-1. There was no evidence for intermolecular magnetic exchange between the two Cr₃O centers which are connected via hydrogen bonds. (C) 2000 Elsevier Science S.A.