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 (L1) was prepared and characterized by analytical methods. Structural and spectral properties of N,N′-bis(benzimidazol-2-yl-ethyl)ethylenediamine (L1), its dianionic structure (L2), and their complexes such as [RuL1Cl(PPh3)]+ and [RuL2Cl(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 = L1 or L2) 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 [RuL1Cl(PPh3)]+ qualitatively agrees only with high energy bands (465 nm and 350 nm) of the experimental spectrum, and other visible bands (≈580 and ≈790 nm) observed in the experimental spectrum coincide with the TD-DFT of [RuL2(PPh3)Cl]+. However, electrochemical studies show existence of only [RuL1Cl(PPh3)]+ in the solution.