Calculation of the structure and vibrational states for anionic forms of Co-, Ni-, and Cu-porphines

Abstract

Ni-, AND Cu-PORPHINES N. V. Ivashin UDC 535.34:541.63The structure and vibrations of neutral porphine metal complexes (Me-P, Me = Co, Ni, Cu) and their d-anionic forms with an additional electron localized in vacant d x 2 −y 2 -and d z 2 -orbitals are compared based on calculations by a DFT method. It is shown that such electron population causes a significant increase of the electronic charge on the macrocycle rather than on the Me atom and is accompanied by a considerable redistribution of πand σ-electron densities (ρ π , ρ σ ). A predominant gain of ρ π (0.49e) is found for the monoanion of Co-P (Co-P -, d z 2 -monoanion); of ρ σ (0.6e), for Ni-P -(d x 2 −y 2 -monoanion). These features are reflected in both the structure of the anions and the behavior of their vibrational frequencies. The greatest frequency shifts among IR active modes when populating the d z 2 -and d x 2 −y 2 -orbitals occur for out-of-plane vibrations (>30 cm -1 ) and in-plane modes (34-46 cm -1 ) involving MeN-and C α C m -bonds, respectively. Abnormally large frequency lowering is found for B 1g -type modes (active in the resonance Raman spectrum) involving mainly C α C m -, C β C β -, C α C β -, and MeN-bonds. This is related to a change in the d π −e g interaction strength during such vibrations that contributes to a decrease in the corresponding force constants.Keywords: metalloporphyrins, anionic form, d-orbital, electronic structure, vibrational state, DFT.Introduction. Metalloporphyrins and their biologically important analogs undergo readily redox reactions and are considered promising components of molecular systems that provide effective electron phototransfer and stabilization of charge-separated states.Resonance Raman (RR) and time-resolved IR-Fourier spectroscopy are becoming more and more important for studying electron-transfer processes in native and synthetic systems. In several instances molecular vibrations appear as coherent femtosecond oscillations in excited-state spectra. An analysis of vibrational states in locally excited states and charge-separated states allow the nature of the primary electron donor and acceptor to be found [1], nuclear coordinates that facilitate charge separation to be found, and its mechanism to be proposed [2,3]. The principles characteristic of the structure and vibrational states of the oxidized and reduced forms of porphyrins must be found in order to use effectively such approaches to studying molecular systems involving them.The products from chemical reduction of Co-, Ni-, and Cu-complexes of porphyrins ( Fig. 1) have been studied using electronic [4][5][6], Raman [5,7], and IR [8,9] spectroscopy. Electronic absorption spectra of the monoanions of Co-and Ni-octaethylporphyrin (OEP) [4] and Co-etioporphyrin (Co-EP) [5] have little in common with the spectrum of π-anionic forms of Zn-complexes of porphyrins. This suggested that anions with the excess of charge localized primarily on the metal were formed. Examination of Raman spectra of the Co-EP anion found significant frequency shifts...

Electrocatalytic properties of manganese and cobalt polyporphine films toward oxygen reduction reaction

“…In conformity with expectations, demetalation process does not affect the vibrational bands in these regions (Figs. 2a and 2b) [18,31,32]. The most pronounced changes for demetalated polyporphine, pH 2 P-I, can be seen in region B: splitting of the intensive signal at ca.…”

Efficient synthesis of a new electroactive polymer of Co(II) porphine by in-situ replacement of Mg(II) inside Mg(II) polyporphine film

“…7). According to previous theoretical studies from our group [21] and from other groups [58][59], vibrational bands around 1062 cm -1 (A) and 852 cm -1 (C) correspond to the different symmetry vibrations of peripheral hydrogen atoms in the porphine plane (A) and out of it (C) while vibrational amplitudes of atoms of the carbon-nitrogen skeleton are small for both bands A and C. Therefore, the demetallation/remetallation process should not radically modify the shape of the spectrum around these bands for the series pMgP-I, pH2P-I and pCoP-I. This is experimentally verified with the spectra superimposed on Fig.…”