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EPR and H NMR spectroscopy and DFT study of pentaammineruthenium(III)phenylcyanamide complexes |
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| Authors: | Lubna Mahmoud Wolfgang Kaim Robert J. Crutchley |
| Affiliation: | a Chemistry Department, Carleton University, Ottawa, Canada ON K1S 5B6 b Centre for Catalysis Research, Department of Chemistry, University of Ottawa, Ottawa, Canada ON K1N 6N5 c Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany |
| Abstract: | The EPR and 1H NMR spectroscopy of seven [Ru(NH3)5L]2+ complexes, where L = 3,5-dimethoxyphenylcyanamide (MeO2pcyd), 3,4,5-trimethoxyphenylcyanamide (MeO3pcyd), 4-nitrophenylcyanamide (NO2pcyd), 2,3-dichlorophenylcyanamide (Cl2pcyd), 2,4,6-trichlorophenylcyanamide (Cl3pcyd), 2,3,5,6-tetrachlorophenylcyanamide (Cl4pcyd) and pentachlorophenylcyanamide (Cl5pcyd), was performed. EPR spectra of the complexes showed an axial signal with g|| and g⊥ at high and low field, respectively. The g|| axis is suggested to lie along the Ru-cyanamide bond. Gas-phase DFT calculations of [Ru(NH3)5 phenylcyanamide]2+ showed spin density localized mostly on the phenylcyanamide ligand, in disagreement with EPR data. DFT/polarizable continuum model (PCM, water solvation) calculations shifted spin density towards ruthenium so that spin density was shared between ruthenium and phenylcyanamide ligand. Proton contact shifts were determined from NMR and EPR data and were used to estimate spin density distributions on phenyl ring carbons. The results showed that the DFT/PCM calculation overestimated spin density on phenyl ring carbons by approximately one order of magnitude. Donor-acceptor interactions between the solute and solvent that are not fully accounted for in the DFT/PCM method are suggested to stabilize the Ru(III) oxidation state. |
| Keywords: | Paramagnetic NMR EPR DFT Pentaammineruthenium(III) Phenylcyanamide |
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