Research Article Quantum Chemical Study of Mixed-Ligand Monometallic Ruthenium(II) Complex of Composition [(bpy) 2 Ru(H 3 Imbzim)](ClO 4 ) 2 ⋅2H 2 O Mohsin Yousuf Lone and Prakash Chandra Jha School of Chemical Sciences, Central University of Gujarat, Sector 30, Gandhinagar, Gujarat 382030, India Correspondence should be addressed to Prakash Chandra Jha; prakash.jha@cug.ac.in Received 29 November 2013; Revised 24 February 2014; Accepted 11 March 2014; Published 19 May 2014 Academic Editor: Yinghong Sheng Copyright © 2014 M. Y. Lone and P. C. Jha. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. On the basis of density functional theoretical approach, we have assessed the ground state geometries and absorption spectra of recently synthesized monometallic ruthenium (II) complex of composition [(bpy) 2 Ru(H 3 Imbzim)](ClO 4 ) 2 ⋅2H 2 O where bpy = 2,2  - bypyridine and H 3 Imbzim = 4,5-bis(benzimidazol-2-yl)imidazole. he all diferent kinds of charge transfers such as ligand-ligand, and metal-ligand have been quantiied, compared, and contrasted with the experimental results. In addition, the efect of solvent on excitation energies has been evaluated. In spite of some digital discrepancies in calculated and observed geometries, as well as in absorption spectra, the density functional theory (DFT) seems to explain the main features of this complex. 1. Introduction In recent times, the importance of inorganic complexes has been reported extensively keeping in mind the wide range of applicability these complexes possess in diferent domains of life. hanks to the synthetic chemists for synthesizing, char- acterizing, and demonstrating the wide range of applicability of these complexes. Among the entire applicability domain, the recognition and sensing of anions is one of the recently emerged and challenging areas in the ield of research. his is due to the important role played by anions in the ield of biological, industrial, agricultural, and environmental processes [1–8]. his importance can be visualized from the facts that majority of enzymes bind anions as either substrate or cofactor and many act as ubiquitous nucleophiles, bases, redox agents, and phase transfer catalysts [9, 10]. Diseases like cystic ibrosis and Alzheimer’s are induced by the malfunction of natural anion regulation processes [11, 12]. Even, from environmental point of view, the eutrophication of water is an important issue which is caused by phosphate and nitrate ions and used in agriculture fertilizers [13–16]. he advantage of the transition metal complex of composition [(bpy) 2 Ru(H 3 Imbzim)] 2+ where bpy = 2,2  -bypyridine and H 3 Imbzim = 4,5-bis(benzimidazol-2-yl)imidazole to act as a sensor is that it contains three potent NH bonds that can be donated for the hydrogen bonding to the anions. Given this importance, it is not surprising that extensive experimental studies have been dedicated to design of simple artiicial anion receptors and sensors [17–20]. However, there is not very clear understanding about the guiding principles about the selection of right kind of moiety as a chromophore and ligand as an anion sensor. In such situation, quantum chemical based electronic structure calculations can be expected to provide us valuable information about its structural features which in turn could be further used for better understanding of structural features and hence for enhanced appreciative of the factors responsible for such properties. Recently, Debasish et al. [21] have synthesized and characterized monometallic ruthenium (II) complex of composition [(bpy) 2 Ru(H 3 Imbzim)](ClO 4 ) 2 ⋅2H 2 O using standard analytical and spectroscopic techniques. On the basis of their study, they have proposed molecular struc- ture from single crystal X-ray measurements. Furthermore, they have experimentally explored in detail the electronic absorption and emission behavior in diferent solvents. In this work, our aim is to complement experimental work Hindawi Publishing Corporation Journal of Quantum Chemistry Volume 2014, Article ID 149380, 8 pages http://dx.doi.org/10.1155/2014/149380