Density functional theory study on the geometric, electronic and vibrational structures of alkali metal porphyrin complexes

The ground-state geometry, electronic structures and vibrational frequencies of alkali metal porphyrin complexes, M2P (M=Li, Na, K), have been studied using B3LYP/6-31G(d) method. The computed structures were compared with the crystallographic data of related compounds. The Na2P and K2P molecules have D4h symmetry with the two alkali metal atoms locating on the different sides of the porphyrin plane. For Li2P, the energy of D4h structure is higher than the symmetry broken C2h structure, but the energy difference is very small. Natural population analysis suggests a significant charge transfer from the alkali metals to the porphyrin ring.The vibrational frequencies of M2P (M=Li, Na, K) were calculated and the results were compared with zinc porphyrin (ZnP).