Exchange coupling across the cyanide bridge: structural and DFT interpretation of the magnetic properties of a binuclear chromium(III) complex.

The reaction of [Cr(CN)6]3− with a mixture of trans-[Cr(cyclam)(OH)2]Cl, [Cr(cyclam)(OH)Cl]Cl and [Cr(cyclam)Cl2]Cl affords the cyanide bridged dimer, trans-[HO–Cr(cyclam)–NC–Cr(CN)5]−. The tetraphenylphosphonium salt of the anion crystallizes in space group P21/n and shows a bent arrangement of the Cr1–CN–Cr2 unit with the Cr1–CN bond angle at 166.9° and CN–Cr2 at 160.32°. The Cr2–O bond, trans to the hexacyanide fragment, is very short at 1.902 A. Two dimers are held together by two hydrogen bonds connecting the Cr2–OH group of each dimer with one of the NH groups of the cyclam ligand of an adjacent molecule, leading to an almost linear configuration. These dimers of dimers get packed par…