Coordination of Zn-TPHP with weak bases / nucleophiles. Method of “approximation algorithm”

The stability constants of complexes (K) Zn-TPhP with n-donor ligands, which are weak Lewis bases (alcohols, ethers, aldehyds and ketons), or low-soluble in low-polar solvents (4-nitroaniline) are examined implying “approximation algorithm” in electronic spectroscopy. К-values and thermodynamic parameters, calculated by either standard (A) method, or “approximation algorithm” (B) are very close for amines, pyridines and heteroaromatic N-oxides (K ~ 12-105000 l·mole -1). With alcohols and ethers, K-values (0,56-11,71·mole -1) display more differences the lower their values are (calculated by the (B) method have more high values, and for the ethers differ by 1,5-2,5 times). With these ligands, ΔH 0 и ΔS 0 values, calculated with (A) method, are lower, than with “approximation algorithm” (for ethers the difference in ΔH 0 reaches 4, and in ΔS 0 even 20 points, as for ethoxyethane). For the alcohols, K-values calculated with both methods demonstrate correlation lgK (B) = 1,12dgK (А) - 0,0597, between ΔH 0 and ΔS 0: (ΔH 0 (B) = 0,747 · ΔH 0 (A) - 2,10; ΔS 0 (B) = 0,775 · ΔS 0 (А) - 0,856). The authors discuss advantages of the introduced new scale of nucleophilicity as compared with the Gutman scale, and origins of incongruity of kinetic and thermodynamic constants defined by spectroscopy methods (electronic and NMR) and calorimetry.