Analysis of vibrational spectra (FT-IR and VCD) and nonlinear optical properties of [Ru(L)₃]²⁺ complexes

Abstract

Density functional theory calculations were performed on [Ru(L)₃]²⁺ (L = 1,10-phenanthroline, 2,2′-bipyridine, 2,2′-bipyrimidine, 2,2′-bipyrazine) complexes by employing B3PW91 functional and LAN2DZ basis set to predict their spectra and nonlinear optical response. The geometrical and coordination energy studies explained that the stability of [Ru(L)₃]²⁺ metal complexes depends on the extent of interaction of the dπ orbitals of Ru²⁺ with the π* ligand orbitals, which is maximum for 1,10-phenanthroline. The two enantiomers of the [Ru(L)₃]²⁺ show IR absorption peaks in the region of 1100–1800 cm⁻¹, and a slight shift occurs to lower frequency by solvent. The vibrational circular dichroism peaks of [Ru(phen)₃]²⁺ had major contribution from out-of-phase stretching of 1,10-phenanthroline rings and a minor contribution from H–C=C–H wagging and C=C stretching of rings. Maximum hyperpolarizability was observed for [Ru(phen)₃]²⁺ due to stronger anharmonicity in the π-electron system. Among the [Ru(L)₃]²⁺ (L = bpy, bpm, and bpz) complexes, [Ru(bpm)₃]²⁺ shows enhanced hyperpolarizability due to increase in the dipole along the X-direction. In derivative Ru²⁺ complexes, we found that hyperpolarizability depends on electron-donating capability of the substituent. As per FMOs study, the HOMO is predominantly metal fragment based, the LUMO is primarily ligand based, and the larger value of hyperpolarizability corresponds to the lower E_LUMO–E_HOMO gap, reflecting that nonlinear optical response is a consequence of additive dipolar responses of charge transfer and hyperpolarizability.

Graphical Abstract

Keywords:

• Ruthenium
• Density function theory
• Coordination energy
• Enantiomers
• Hyperpolarizability

Acknowledgements

We are thankful to the Head, Department of Chemistry, University of Kashmir, for providing the necessary laboratory facility for carrying out this work. A.H.P thanks the University Grants Commission (UGC), Government of India for research grant [F.No. 42-305/2013(SR)].