Synthesis, characterization, and reactions of tetrakis(nitrile)chromium(II) tetrafluoroborate complexes †

Abstract

Reaction of chromium(II) acetate with HBF4 in nitrile solutions led to air-sensitive, paramagnetic complexes of the general formula [Cr(NCR)4][BF4]2 (R = Me, But or Ph). In contrast to an earlier report of the synthesis of [Cr(NCMe)4][BF4]2 by electrochemical methods, these compounds are blue. The crystal structure of [Cr(NCMe)4][BF4]2 has been determined. The chromium(II) cation is surrounded by nitrile ligands in a square-planar manner. The BF4– counter ions are located at the apical positions of an elongated octahedron. Magnetic susceptibility measurements yielded µeff = 4.9 µB at 300 K which is characteristic for a d4 high-spin complex. The paramagnetic complexes [Cr(NCR)4][BF4]2 are easy to prepare and can be used for the high-yield synthesis of several other chromium derivatives in low oxidation states like [Cr(py)4][BF4]2, [Cr(C5H5)2], [Cr(dppe)2][BF4]2 and [Cr(NO)(NCMe)5][BF4]2.