Ternary Coordination Complexes of Chromium(III) with Glycine and Some Dicarboxylic Acids—Potentiometric, Spectral and Ion-Exchange Studies

Central Leather Research Institute, Adyar, Madras-600 020

Reliable stability constants for the CrAH, CrA, CrA₂, CrA₃, Cr(OH) and Cr₂,A₄- (OH)₂ have been obtained at 50 ± 0.1º and I- 0.1 mol dm^-3 in the Cr(III)-glycine system by the computer based analysis of the potentiometric data. Ternary complexation of Cr(III) with glycine as the primary ligand (A) and malefic, maleic, or succinic acids as the secondary ligand (B) gives rise to CrAB, CrAB, and CrA₂B (only in the systems with B -malonic or maleic acid) types of ternary complexes. The results suggest the marked stabilities of these ternary complexes over the corresponding binary analogues which may probably be accounted for by considering the charge neutralization and interligand inter­actions in the ternary systems. The results indicate the preferred formation of Cr(III) ternary chelates containing five and six membered rings rather than those with five and seven membered rings. The enhanced stability of the unsaturated mixed complexes, CrAB, over the saturated complexes of the type CrA₂B or CrAB₂ is evident from the results. Ion exchange and spectroscopic evidence have been obtained to support the existence of CrAB, CrA₂B and CrAB₂ ternary species in the Cr(III)-glycine(A)-malonic acid(B) system.