Chromium(II) chemistry. Part V. Ethylenediamine complexes

Abstract

The chromium(II) complexes of ethylenediamine (en): Cr en₃Cl₂,H₂O, Cr en₃Br₂, Cr en₃SO₄, Cr en₂SO₄, Cr en₂Br₂, and Cr en₂I₂, have been found to be high-spin with temperature-independent magnetic moments of about 4·8 B.M. Reflectance spectra show the tris-compounds to have distorted octahedral structures in spite of the presence of equivalent ligands, and the bis-compounds to have trans-octahedral structures with co-ordinated anions. The trans-structures are confirmed by i.r. investigations of the ligand vibrations in these and related copper(II) complexes. However, correlations between structure and ligand absorptions found valid for bis(ethylenediamine)–cobalt(III) complexes do not hold for the chromium(II) complexes. The distortion increases as the axial donor atoms change: N < O < Br < I. The ions Cr en₃²⁺ are stable only in the solid with certain anions; in solution an ethylenediamine molecule is readily lost because of the distortion arising from the high-spin d⁴ configuration.