Coordination Properties of Sterically Stressed Zincporphyrins

Abstract

Spectrophotometric titration and computer simulation were used to study how the nature of porphyrin and extra ligand affect the formation of extra complexes of zincporphyrins in o-xylene. The compounds under study were zincporphyrins (ZnP) with different substituents and phenyl radicals in meso-positions (zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetraethylporphyrin (ZnP1), zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphyrin (ZnP2), zinctetraphenylporphine (ZnP3), and zinc complexes with overlapped porphyrin (ZnP4). N-Methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide were used as extra ligands (L). The strength of Zn–L bonding was found to decrease in extra complexes (L)ZnP in the series of ZnP as follows: ZnP4> ZnP1> ZnP2> ZnP3. It was established that the stability constant (logKst) for sterically nonstressed complexes (L)ZnP4linearly increases with growth in the extra ligand basicity (log \(K_{BH^ + } \)) and is proportional to the shift of the main absorption bands (Δλ) in the electronic spectra of extra complexes of zinctetraphenylporphine. For spatially distorted (L)ZnP1, (L)ZnP2, and (L)ZnP3, the values of logKstand log \(K_{BH^ + } \), as well as logKstand Δλ, change symbatically. The geometric structure and energy characteristics of pentacoordinated zincporphyrins were calculated by quantum-chemical methods. Correlations were established between the calculated values of the energy of the interaction of the central metal atom with the extra ligand molecule and the stability of the extra complexes of zincporphyrins.