Conformational analysis of the nonplanar deformations of cobalt porphyrin complexes in the Cambridge structural database

Principal component analysis, cluster analysis, and various structural parameters have been used to differentiate the nonplanar deformations of cobalt(III) porphyrins. The results were compared with normal-coordinate structural decomposition analysis. Cobalt(III) porphyrins discussed in this paper do not undergo large wav, dom, and pro deformations and they were not considered in our analysis. The cis C alpha -N-N-C-alpha, dihedral angle is the best structural measure of ruffling and it is the only structural parameter that does not overestimate the extent of ruffling due to the presence of saddling. The average distance between the C-beta carbons and the plane comprising the four nitrogens, the four meso carbons and the cobalt ion is the best structural measure of saddling. No structural parameters were found that could be used in principal component analysis to find PC's that quantified the nonplanar deformations in cobalt(III) porphyrins. Cluster analysis was able to separate the sad, ruf, and planar structures, however, the preparation and symmetry adaptation of all the structures was complicated and was no more informative than the use of some of the univarient structural parameters. The NSD deformations are related to the vibrational energies and motions of the macrocycle and are thus the preferred description, but the more easily obtained structural parameters are useful measures of the normal coordinate deformations whenever a full NSD analysis is not possible.