Molecular Structure, Electronic Structure, Properties and Analyses of Five Azopyridine Ruthenium Complexes α-Cl, β-Cl, γ-Cl, δ-Cl and ε-Cl of RuCl 2 (4,6-Dimethyl-Phenylazopyridine) 2 as Potential Cancer Drugs: DFT and TD-DFT Investigations

Abstract

Ground state geometries, natural bond orbital (NBO), analysis of frontier molecular orbitals (FMOs), analysis and spectral (RMN and UV-Visible) properties of five azopyridine ruthenium (II) complexes α-Cl, β-Cl, γ-Cl, δ-Cl and ε-Cl of RuCl2(Dazpy)2 have been theoretically studied by the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) methods using two basis sets: Lanl2DZ and a generic basis set in gas or in chloroform solvent. Dazpy stands for 4,6-dimethyl-phenylazopyridine. Optimized geometry shows that, except β-Cl, all the other four isomers α-Cl, γ-Cl, δ-Cl and ε-Cl are C2 symmetrical. Otherwise, a good agreement was found between experimental and the calculated geometry and NMR data. Moreover, Lanl2DZ effective core potential basis set provides good chemical shifts and geometric properties. Furthermore, the prediction of the frontier orbitals (Highest Occupied Molecular Orbital or HOMO and Lowest Unoc-cupied Molecular Orbital or LUMO) shows that the most active isomer suita-ble for electronic reactions is admitted to be δ-Cl. Besides, the NBO analysis indicates that the Ru-N is formed by the electron delocalization of lone pair atomic orbital of N2 and Npy to Ru. Also, the strongest interactions between LP(N) with LP*(Ru) and LP(Cl) with LP*(Ru) stabilize the molecular struc-ture. In addition, NBO shows that the five d orbitals of Ru in the complex are organized so that there is no order of priority from one complex to another. Therefore, the transition LP(Ru) → π*(N1 = N2) corresponding to Metal to Li-gand Charge Transfer (MLCT) is in reality no more than d → π*. Besides, TDDFT prediction in chloroform solvent reveals that all the five isomerics complexes absorb in the visible region as well as efficient photosensitizers. What’s more, δ-RuCl2(dazpy)2 can potentially act as the excellent sensitizer with a large band of absorption in visible region and a small excited energy. This study can help design and find out the ability or properties of the com-plex to behave as sensitizer or potential cancer drugs.