Characterization of the Sample Clauses

Characterization of the. [(Ar)Ru(O)(bpy)]+2 intermediate The Ru(IV)oxo complex that is assumed to be the active species in the O-O bond formation is the starting point of the investigation. The initial geometry has been generated starting from the DFT optimized coordinates of the analogous Ir based catalysts provided in Ref. [6] and by substituting the Ir atom with Xx. The geometry of the [(Ar)Ru(O)(bpy)]2+ species is optimized with different aromatic ligands and for different spin states using various functionals. The inclusion of van der Waals corrections is crucial for the structural stability of the complex, as without these corrections the Ru-Ar bond breaks during the geometry optimization. Table 4.1 shows the comparison of the relative energies for different possible multiplicities. All the functionals, both hybrid and non-hybrid, give consistently the same lowest energy spin state. In particular, the triplet is the ground-state for the benzene and hexamethylbenzene ligands, while the doublet is the ground-state for the complex with the Cp* ligand. Quantitative differences between the hybrid and non-hybrid functionals, with the latter usually giving a smaller energy splitting between the two lowest states compared to the hybrid functionals, are present. Given that all functionals considered here provide consistent results, the OPBE functional was used for the subsequent AIMD simulations, because of its superior computational efficiency (see also the computational details section). In Table 4.2 a few relevant geometrical parameters and effective RESP atomic charges [26] obtained for the most stable multiplicity using the OPBE functional are shown. These results show the effect of using different aromatic ligands on the geometric and electronic structure of the catalyst. It appears that the choice of the aromatic ring has only moderate effect on the distance between the ruthenium and the oxo ligand (Ru-O). Also the average value of the two distances between the ruthenium and the nitrogen atoms of the bipyridine (Ru-N) are reported. The distance between ruthenium and the centre of the aromatic ring (Ru-Ar) is also an interesting parameter since a weak interaction between them could be a source of instability in the catalyst. This distance becomes shorter for increasing ring size. The effective RESP charges for ruthenium, oxygen and the aromatic ring are quite sensitive to the choice of the ligand. Specifically, the oxo ligand carries a negative charge, which increases for aroma...