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 degrees C, followed by dissolution of the mixture in water and addition of PF6-, led to the isolation of the fir st Cr(III)-nicotinamide complex [Cr3O(O2CCH3)(6)(na)(3)](+) (1). Crystals o f the compound 1 . PF6. 3CH(3)CN were subjected to a detailed X-ray structu ral analysis. The three N-bonded na ligands, which occupy axial positions a t the corners of the triangular basic chromium acetate, are nearly co-plana r with the Cr3O system. The three Cr-N(na) bond distances are in the range 2.121(8)-2.128(8) Angstrom. Two of the na ligands on each cluster form four hydrogen bonds with two ligands from a neighboring cluster, via their amid e ends with N...O distances of 2.88(1)-2.92(1) Angstrom. Magnetic susceptib ility measurements of a powdered sample of 1 . PF6. 3CH(3)CN over the range 2-300 K showed that the three Cr(III) ions were antiferromagnetically coup led with J -10.4 cm(-1). There was no evidence for intermolecular magnetic exchange between the two Cr3O centers which are connected via hydrogen bond s. (C) 2000 Elsevier Science S.A. All rights reserved.