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The surprisingly high ligation energy of CO to Ruthenium porphyrins


A combined theoretical and experimental approach has been used to investigate the binding energy of a ruthenium metalloporphyrin ligated with CO, ruthenium tetraphenyl porphyrin [RuII TPP] in the RuII oxidation degree. Measurements made by VUV ionization with the DESIRS beamline at Synchrotron SOLEIL lead to adiabatic ionization energies of [RuII TPP] and its complex with CO, [RuII TPP-CO], to be 6.48±0.03 eV and 6.60±0.03 eV, respectively while the ion dissociation threshold of [RuII TPP-CO]+ is measured at 8.36±0.03 eV from the ground state neutral complex. These experimental data are used to derive binding energies of the CO ligand in the neutral and cationic complex (1.88±0.06 eV and 1.76±0.06 eV, respectively) using a Born-Haber cycle. Density Functional Theory calculations, in very satisfactory agreement with the experimental results, help to get insights into the metal-ligand bond. Notably, the high ligation energies can be rationalized in terms of the ruthenium orbital structure, which is singular from that of the iron atom. Thus, beyond indications of a strengthening of the Ru-CO bond from the decrease in the CO vibrational frequency in the complex as compared to the Fe-CO bond, high level calculations are essential to describe accurately the metal ligand (CO) bond and show that the Ru-CO bond energy is strongly affected by the splitting of triplet and singlet spin states in uncomplexed [Ru TPP].

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Publication details

The article was received on 21 Feb 2018, accepted on 02 Apr 2018 and first published on 03 Apr 2018

Article type: Paper
DOI: 10.1039/C8CP01190G
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    The surprisingly high ligation energy of CO to Ruthenium porphyrins

    N. Shafizadeh, S. Boyé-Péronne, S. Soorkia, S. Chen, A. de la Lande, B. Cunha de Miranda, G. A. Garcia, L. Nahon, L. Poisson and B. SOEP, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01190G

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