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.