How the change of the ligand from L = porphine, P2−, to L = P4-substituted porphine, P(P)42−, affects the electronic properties and the M-L binding energies for the first-row transition metals M = Sc-Zn: Comparative study

We performed comparative DFT study, including Natural Bond Orbitals (NBO) analysis, of the binding energies between all the first-row transition metals Mn+ (M = Sc-Zn) and two ligands of the similar type: porphine, P2−, and its completely P-substituted counterpart, P(P)42−. The main findings are as follows: (i) complete substitution of all the pyrrole nitrogens with P-atoms does not affect the ground spin state of metalloporphyrins; (ii) generally, for the MP(P)4 compounds the calculated HOMO/LUMO gaps and optical gaps are smaller than for their MP counterparts; (iii) the trends in the change of the binding energies between Mn+ and P(P)42−/P2− are very similar for both ligands. The complete substitution of the pyrrole nitrogens by the P-atoms decreases the Mn+-ligand binding energies; all the MP(P)4 compounds studied are stable according to the calculated Ebind values and therefore can be potentially synthesized.