Synthesis, molecular structure and spectral analysis: DFT-TDDFT computational study of ruthenium complex of tetradentate N,N′-bis(benzimidazole-2yl-ethyl)-ethylenediamine

Ruthenium complex of N,N'-bis(benzimidazol-2-yl-ethyl)ethylenediamine (L-1) was prepared and characterized by analytical methods. Structural and spectral properties of N,N'-bis(benzimidazol-2-yl-ethyl)ethylenediamine (L-1), its dianionic structure (L-2), and their complexes such as [(RuLCl)-Cl-1(PPh3)](+) and [(RuLCl)-Cl-2(PPh3)](+) were studied by DFT. In the structures, the ruthenium ion is positioned in an equatorial plane formed by amine, benzimidazole nitrogens in a distorted octahedral geometry, and chloride and triphenylphospine are axially coordinated. Furthermore, the molecular orbital of [Ru(L)Cl(PPh3)]Cl (L = L-1 or L-2) proves that the HOMOs are localized over the benzimidazole and amine moieties, favoring a strong bond with the metal. DFT-TDDFT was used to analyze the molecular orbitals contribution to MLCT bands that were observed in the visible region: interestingly, the calculated spectrum of [(RuLCl)-Cl-1(PPh3)](+) qualitatively agrees only with high energy bands (465 nm and 350 nm) of the experimental spectrum, and other visible bands (approximate to 580 and approximate to 790 nm) observed in the experimental spectrum coincide with the TD-DFT of [RuL2(PPh3)Cl](+). However, electrochemical studies show existence of only [(RuLCl)-Cl-1(PPh3)](+) in the solution. (c) 2011 Elsevier B.V. All rights reserved.