Calculation of the structure and vibrational states for anionic forms of Co-, Ni-, and Cu-porphines |
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Authors: | N V Ivashin |
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Institution: | 1.B. I. Stepanov Institute of Physics,National Academy of Sciences of Belarus,Minsk,Belarus |
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Abstract: | The 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 dx2 -y2 - d_x^2 -_y^2 - and dz2 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 π- and σ-electron densities (ρπ ρσ). A predominant gain of ρπ (0.49e) is found for the monoanion of Co-P (Co-P–, dz2 d_z^2 -monoanion); of ρσ (0.6e), for Ni-P–( dx2 -y2 - 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 dz2 d_z^2 - and dx2 -y2 - 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 CαCm-bonds, respectively. Abnormally large frequency lowering is found for B1g-type modes (active in the resonance Raman spectrum) involving mainly CαCm-, CβCβ-, CαCβ-, and MeN-bonds. This is related to a change in the dπ-eg interaction strength during such vibrations that contributes to a decrease in the corresponding force constants. |
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