Estimation of stability of coordination compounds by using topological indices

Topological analysis was applied for the estimation of stability constants (β1 and β2) for sets of copper(II) mono-, ML, and bis-complexes, ML2, with bidentate ligands, namely 1,2-diaminoethanes (N = 14), aliphatic amino acids and their N-alkylated derivatives (N = 11), and naturally occurring amino acids (N = 9). A set consisting of 16 mixed (ternary) copper(II) bis-complexes with naturally occurring amino acids was also taken into account. The log β values were correlated on the connectivity index 3χv of the ligands and their mono- or bis-complexes, with or without water coordination, yielding the best results for the model with two additionally bonded water molecules. An improvement of the method was obtained by proposing an additional ligand coordination in some complexes, especially in the set of mono- (r = 0.888) and bis-complexes (r = 0.786) of naturally occurring amino acids. The error of the estimate is 0.01–0.14 and 0.01–0.33 log β units for mono- and bis-complexes, respectively. The estimation of log β2 for mixed amino acid complexes (MLA) was performed by bivariate linear regression using composite indices, obtained by addition or subtraction of the 3χv indices for two chelate rings, ML and MA. This regression gave r = 0.801 and the reproduction of experimental data 0.01–0.33 log β units.

Graphical abstractStability constants of copper(II) chelates with amino acids and diaminoethanes were correlated to the 3rd valence connectivity indices, 3χv, of the corresponding complexes. The first and second stability constants were fairly well reproduced, yielding an error of the estimate around 0.3 log K units.3χv=∑path{δ(i)δ(j)δ(k)δ(l)}-0.5Figure optionsDownload full-size imageDownload as PowerPoint slide