Astatistical aspects of the stabilities of ternary complexes of cobalt(II), nickel(II), copper(II) and zinc(II) involving aminopolycarboxylic acids as primary ligands and salicylaldoxime as a secondary ligand

Summary Stability constants of binary (ML, ML₂) and ternary (MAL) complexes, where M=Co^II, Ni^II, Cu^II and Zn^II; A-iminodiacetic acid (ida),N-methyliminodiacetic acid (Me-ida), anthranilatediacetic acid (ada), nitrilotriacetic acid (nta); LH₂=salicylaldoxime have been determined at 25° C at 0.1M KNO₃ ionic strength by the Irving-Rossotti technique. K_MAL^MA is always lower than K_ML^M and KMI₂^ML. In the ternary systems studied, the K_MAL^ML values lie in the sequence: K_M(ida)L^M(ida)>K_M(Me-ida)L^M(Me-ida)>K_M(nta)L^M(nta)>K_M(ada)L^M(ada). For Cu^II, the K_Cu(nta)L^Cu(nta) and K_Cu(ada)L^Cu(ada) values are significantly reduced compared to all other primary ligands. For different primary ligands, the K_MAL^MA sequence is reversed compared to K_MA^M, but for A=ada and nta their relative positions remain unaltered in both binary and ternary systems. The results have been explained in the light of different astatistical factors such as electrostatic effects, steric hindrance, change of electronegativity of the central metal and stereochemical factors.