Syntheses, structures, spectroscopic, electrochemical properties and DFT calculation of Ru(II)–thioarylazoimidazole complexes T.K. Mondal a , J.-S. Wu b , T.-H. Lu b , Sk. Jasimuddin c , C. Sinha a, * a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India b National Tsing Hua University, Hsinchu, Taiwan 300, ROC c Assam University, Silchar, Assam, India article info Article history: Received 16 February 2009 Received in revised form 15 June 2009 Accepted 18 June 2009 Available online 24 June 2009 Keywords: Ruthenium(II)–azoimidazoles X-ray structure Electrochemistry and DFT calculation abstract The reaction of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles (SRaaiNR) (2a/2b) with Ru(II) has synthe- sized [Ru(SRaaiNR) 2 ](ClO 4 ) 2 (3a/3b) in 2-methoxyethanol. The reaction in methanol, however, has synthesized [Ru(SRaaiNR)(SRaaiNR)Cl](ClO 4 )(4a/4b). The solid phase reaction of SRaaiNR and RuCl 3 on silica gel surface upon microwave irradiation has synthesized [Ru(SRaaiNR)(SaaiNR)](PF 6 )(5a/5b) [SRaaiNR represents tridentate N,N 0 ,S-chelator; SRaaiNR is N,N 0 -bidentate chelator where S does not coor- dinate and SaaiNR refers N,N 0 ,S-chelator where S refers to thiolato binding]. The structural characteriza- tion of [Ru(SEtaaiNEt)(SEtaaiNEt)Cl](ClO 4 ) (4b) and [Ru(SEtaaiNEt)(SaaiNEt)](PF 6 ) (5b) has been confirmed by single crystal X-ray diffraction study. The IR, UV–Vis, and 1 H NMR spectral data also support the stereochemistry of the complexes. The complexes show metal oxidation, Ru(III)/Ru(II), and ligand reductions (azo/azo  , azo  /azo @ ). The molecular orbital diagram has been drawn by density functional theory (DFT) calculation. Normal mode of analysis has been performed to correlate calculated and exper- imental frequencies of representative complexes. The electronic movement and assignment of electronic spectra have been carried out by TDDFT calculation both in gas and acetonitrile phase. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The coordination complexes of transition metals with azo-li- gands are of current attraction due to the interesting physical, chemical, photophysical and photochemical, catalytic, biological and different material properties. The p-acidity and metal binding ability of azo nitrogen have drawn attention to the exploration of the chemistry of metal complexes incorporating azo-ligands [1– 8]. Notable examples of these ligands are arylazobenzene [9], arylazooxime [10], arylazophenol [11], arylazopyridine [7,8,12], arylazoimidazole [13], arylazopyrimidine [14], arylazoaniline [15], azoantipyrene [16] and related ligands. We are engaged for last decade in the designing of azo-conjugated ligands and their metal complexes [13,14]. The synthesis of ligands in the framework of dii- mine (–N@C–C@N–) [17,18] and azoimine functions (–N@N–C@N–) [13] are of interest in the recent years of chemical research. Re- cently we have synthesized thioarylazoimidazoles (1 and 2 in Scheme 1) [19], a tridentate N(imidazole), N(azo) and S(thioether) chelating molecule. In this work we report ruthenium(II) com- plexes of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles (SRaaiNR) and their reactions. We observe also ruthenium mediated selective C–S bond cleavage when reaction is carried out on silica surface un- der microwave irradiation. Metal mediated cleavage of carbon–sul- fur bonds into carbon–hydrogen or carbon–carbon bonds under homogeneous or heterogeneous condition have diverse application in synthetic chemistry, bioinorganic chemistry and petroleum industry [20–22]. The reaction condition has influenced the effi- ciency, rate and nature of the products. The electronic structures of the precursor and product have been calculated by density func- tional theory (DFT). The spin-allowed singlet–singlet electronic transitions of the studied compounds have been calculated with the time dependent DFT method (TDDFT method), and a good agreement with the experimental spectra has been observed. 2. Results and discussion 2.1. Synthesis and formulation Thioarylazoimidazole belongs to tridentate N,N 0 ,S donor system. They are synthesized (Scheme 1) by coupling o-(thioalkyl)phen- yldiazonium ions with imidazole in aqueous sodium carbonate and purified by solvent extraction and chromatographic process [19]. The alkylation is carried out by adding alkyliodide (MeI, EtI) in dry THF solution to the corresponding 2-{o-(thioalkyl)phenyl- azo}imidazole (2) in the presence of sodium hydride. They are abbreviated as SRaaiNR. The donor centres are N(imidazole), (N), N(azo) (N 0 ) and thioether (S). 0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2009.06.021 * Corresponding author. Fax: +91 033 2413 7121. E-mail addresses: tkmondal_ju@yahoo.com (T.K. Mondal), c_r_sinha@yahoo.com (C. Sinha). Journal of Organometallic Chemistry 694 (2009) 3518–3525 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem