Abstract
Density functional theory (DFT) calculations were employed to study a series of complexes of general formula [Ru(salen)(X)(CO)](0/-1) (X = Cl(-), F(-), SCN(-), DMSO, Phosphabenzene, Phosphole, TPH, CN(-), N(3)(-), NO(3)(-), CNH(-), NHC, P(OH)(3), PF(3), PH(3)). The effect of ligands X on the Ru-CO bond was quantified by the trans-philicity, Δσ(13)C NMR parameter. The potential of Δσ(13)C to be used as a probe of the CO photodissociation by Ru(II) transition metal complexes is established upon comparing it with other trans-effect parameters. An excellent linear correlation is found between the energy barrier for the Ru-CO photodissociation and the Δσ(13)C parameter, paving the way for studying photoCORMs with the (13)C NMR method. The strongest trans-effect on the Ru-CO bond in the [Ru(salen)(X)(CO)](0/-1) complexes are found when X = CNH(-), NHC, and P(OH)(3), while the weakest for X = Cl(-), NO(3)(-) and DMSO trans-axial ligands. The Ru-CO bonding properties were scrutinized using Natural Bond Orbital (NBO), Natural Energy Decomposition Analysis (NEDA) and Natural Orbital of Chemical Valence (NOCV) methods. The nature of the Ru-CO bond is composite, i.e., electrostatic, covalent and charge transfer. Both donation and backdonation between CO ligand and Ru metal centre equally stabilize the Ru(II) complexes. Ru-CO photodissociation proceeds via a (3)MC triplet excited state, exhibiting a conical intersection with the T(1)(3)MLCT excited state. Calculations show that these complexes show bands within visible while they are expected to be red emitters. Therefore, the [Ru(salen)(X)(CO)](0/-1) complexes under study could potentially be used for dual action, photoCORMs and theranostics compounds.