Enhancing the Magnetic Anisotropy of Cyano-Ligated Chromium(II) and Chromium(III) Complexes via Heavy Halide Ligand Effects

A method of increasing the axial zero-field splitting parameter for transition metal complexes of utility in the assembly of magnetic clusters is demonstrated through the use of heavy atoms as auxiliary ligands. The octahedral complexes [Cr(dmpe)2(CN)X]+ (dmpe = 1,2-bis(dimethylphosphino)ethane, X = Cl, Br, I) and Cr(dmpe)2(CN)X (X = Cl, I) are synthesized and structurally characterized. Variable-field magnetization measurements show the magnitude of D for these complexes to increase significantly as the halide ligand varies from chloride to iodide, ranging from 0.11 cm−1 for [Cr(dmpe)2(CN)Cl]+ to 6.26 cm−1 for Cr(dmpe)2(CN)I.