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Published: Kem. Ind. 56 (9) (2007) 449–455
Paper reference number: KUI-23/2007
Paper type: Review
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Estimation of Stability Constants of Complex Compounds

A. Miličević and N. Raos


The stability constant of a complex generally depends on the electronic, stereochemical and steric factors, as well as on the chelate effect and interaction of the complex, metal and ligand with water. In the first part of the paper we discuss the Irving-Williams order of stability of bivalent transition metal ion complexes from Mn2+ to Zn2+, along with the HSAB model (hard and soft acids and bases) of stability. The second part describes three kinds of models for the estimation of the stability constants of complex compounds. First are those based on molecular mechanics, which were used mainly for the estimation of the enantioselectivity effect, i. e. Gibbs energy differences between MLL and MDL isomers. The second kind of models are mechanistic, that rest on the presumption of linear dependence of measured stability constants of the complexes with the same ligand (stability constants of mono- and bis-complexes, protonation constants, etc.). The third kind of models are heuristic (QSPR), which encompass molecular descriptors calculated by the method of overlapping spheres (OS), as well as topological indices. Among the variety of topological indices, connectivity indices proved best. They were calculated for the ligand and various representations of the coordination compound structure.

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QSPR, overlapping spheres, molecular mechanics, topological indices