Binuclear Carbonato-complex of Chromium (II)

Abstract

WITH few exceptions, chromium (II) complexes can be simply classified according to their colours and magnetic moments. Most are blue or purple with magnetic moments which correspond to four unpaired electrons for each metal ion, but some salts of carboxylic acids are red or brown in colour and diamagnetic. Chromous acetate has been shown to possess a dinuclear structure with a short metal–metal bond¹. One species which seems to fall outside this classification is the product of the interaction of chromium (II) and carbonate ion. The simple colourless carbonate is soluble in excess aqueous carbonate media to give yellow solutions, from which yellow-brown complexes can be crystallized, such as Na₂Cr(CO₃)₂.10H₂O, Na₂Cr(CO₃)₂.H₂O, K₂Cr(CO₂)₂.3H₂O, (NH₄)₂Cr(CO₃)₂.H₂O (ref. 2). We have examined the yellow complex in aqueous solution by a spectrophotometric method and have shown that it contains two atoms of chromium per complex ion.