Tin(IV) porphyrin complexes. Crystal structures of meso-tetraphenyl-porphyrinatotin(IV) diacetate, bis(dichloro-acetate), bis(trifluoroacetate) and diformate, and structural correlations for tin(IV) porphyrin complexes with O-bound anionic ligands

Abstract

Structures of four tetraphenylporphyrinatotin(IV) bis(carboxylato) complexes [Sn(tpp)(OCOR)2] have been determined by single crystal X-ray diffraction. All complexes have typical octahedral geometry. The average Sn-N bond lengths for R = CH3, CHC12, CF3, and H are 2.091 A, 2.084 A, 2.082 A, and 2.086 A, respectively. The Sn-0 bond lengths are 2.096 A, 2.091 A, 2.109 A, and 2.090 A respectively. These bond lengths and those of all other reported Sn(tpp) complexes of O-bound anionic ligands are compared. There is an inverse correlation between the Sn-N and Sn-O bond lengths, indicating that stronger electron donation by the axial anionic ligand results in an expansion of the porphyrin core. Correlation of the Sn-O bond lengths with the pKa of the conjugate acids of the axial ligands shows that the stronger the acid, the longer the Sn-0 bonds, indicating that the bonding is dominated by electrostatic effects.