Coordination properties of sterically stressed zincporphyrins

Spectrophoiometric titration and computer simulation were used to study how the nature of porphyrin and extra ligand affect the formation of extra com plexes of zincporphyrins in o-xylene. The compounds under study were zincpo rphyrins (ZnP) with different substituents and phenyl radicals in meso-posi tions (zinc-5,15-(p-butyloxyphenyl)-2,8, 12,18-tetramethyl-3,7,13,17-tetrae thylporphyrin (ZnPl), zinc-5,15-(p-butyloxyphenyl)-2,8, 12,18-tetramethyl-3 ,7,13,17-tetrabutylporphyrin (ZnP2) zinctetraphenylporphine (ZnP3), and zin c complexes with overlapped porphyrin (ZnP4). N-Methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide were used as extra l igands (L). The strength of Zn-L bonding was found to decrease in extra com plexes (L)ZnP in the series of ZnP as follows: ZnP4 > ZnP1 > ZnP2 > ZnP3. I t was established that the stability constant (logK(st)) for sterically non stressed complexes (L)ZnP4 linearly increases with growth in the extra liga nd basicity (log KBH+) and is proportional to the shift of the main absorpt ion bands (Delta lambda) in the electronic spectra of extra complexes of zi nctetraphenylporphine. For spatial ly distorted (L)ZnP1, (L)ZnP2, and (L)Zn P3, the values of logK(st) and log KBH+, as well as logK(St) and Delta lamb da, change symbatically. The geometric structure and energy characteristics of pentacoordinated zincporphyrins were calculated by quantum-chemical met hods. Correlations were established between the calculated values of the en ergy of the interaction of the central metal atom with the extra ligand mol ecule and the stability of the extra complexes of zincporphyrins.