Crystallographic and computational studies of a tartaric acid amide linked zinc bisporphyrinate

Abstract

A chiral zinc bisporphyrinate ([Zn2(D-BTABis)]) showed a bisignate CD signal in the Soret band region. In order to understand the origin of this CD spectrum, we have done crystallographic and computational studies. The crystal structure shows this bisporphyrin is composed of two zinc porphyrin subunits with a tartaric acid amide linker. There are π-π interactions between the phenyl substituents in the linker and porphyrin planes. Bisporphyrin adopts syn-conformation in the crystal structure, but that cannot rationalize the solution CD. Density function theory (DFT) calculations reveal that the conformation of the optimized structure is different from that of the crystal structure. Based on the optimized structure, TDDFT calculations provide the simulated CD spectrum consistent with the observed CD. Our studies suggest the comprehensive understanding of the CD origin should rely on the combination of crystal structure and theoretical calculations.