Metalloporphyrins with all the pyrrole nitrogens replaced with phosphorus atoms, MP(P)4 (M = Sc, Ti, Fe, Ni, Cu, Zn)

• First systematic DFT study of the MP(P)4 compounds with increasing number of d-electrons.
• Complete substitution of pyrrole nitrogens by P-atoms does not change the ground spin state.
• Complete substitution of pyrrole nitrogens by P-atoms results in a bowl-like shape.
• Significant stabilization of the MP(P)4 LUMOs compared to the MP counterparts.
• MP(P)4 HOMO/LUMO gaps are smaller than the MP HOMO/LUMO gaps.

We performed first systematic DFT study of the structures and electronic features (frontier orbitals energies, HOMO/LUMO and optical gaps, IPs and EAs) of the MP(P)4 compounds, with increasing number of d-electrons: 3d14s2 (Sc) → 3d24s2 (Ti) → 3d64s2 (Fe) → 3d84s2 (Ni) → 3d104s1 (Cu) → 3d104s2 (Zn). We performed systematic comparison with the tetrapyrrole MP counterparts. Complete substitution of the pyrrole nitrogens by P-atoms does not change the calculated ground spin state of the compound. All the MP(P)4 species adopt a bowl-like shape, compared to generally planar or slightly distorted shapes of their MP counterparts. Significant positive charge accumulates on P-atoms in MP(P)4. Positive charges on the metals in MP(P)4 are noticeably lower than in the MP counterparts. The calculated MP(P)4 HOMO/LUMO gaps and optical gaps are noticeably smaller than the corresponding gaps in their MP counterparts, which is explained by stabilization of the MP(P)4 LUMOs.

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