FULL PAPER DOI: 10.1002/ejic.200900423 Thioether Bonded Nickel(II)-Azoimidazole Complexes: Structures, Spectra and Electrochemical Oxidation to the Nickel(III) State Soumendranath Nandi, [a] Debashis Bannerjee, [a] Jian-Sung Wu, [b] Tian-Huey Lu, [b] Alexandra M. Z. Slawin, [c] John Derek Woollins, [c] Joan Ribas, [d] and Chittaranjan Sinha* [a] Keywords: Nickel / Electrochemistry / Magnetic properties / Ferromagnetic coupling / Density functional calculations Nickel(II) complexes of 1-alkyl-2-[(o-thioalkyl)phenylazo]- imidazole (SRaaiNR') are described in this article. SRaaiNR' has imidazole-N, azo-N and thioether-S donor centres. Counter ions ClO 4 – , pseudohalides [azide (N 3 – ), thiocyanate (CNS – )] are used in the syntheses of complexes. One of the structures of [Ni(SRaaiNR') 2 ](ClO 4 ) 2 has suggested meridio- nal binding of tridendate chelator with cis-trans-cis configu- ration in the sequence of cis-N(imidazole), trans-N(azo) and cis-S(thioether). Structural study of Ni II -azido-SRaaiNR' de- 1. Introduction The coordination chemistry of N,S donor ligands have received great attention for their stability, chemical and elec- trochemical activities, and biological relevance. [1,2] Thio- ether (-SR) forms very stable complexes with soft metal ions and has been employed in analytical chemistry for the extraction of toxic heavy metals like Cd II , Hg(II/I), Pb II etc. [3] Design of ligands with thioether donor center in a chelated environment with N and/or O donors in which one of N centres is coming from imidazole is important in coor- dination chemistry to synthesise good working models, [4–8] in view of their soft-hard character, excited state properties, chemoselective organic transformation, generation of anti- cancer drugs with reduced nephrotoxicity, regulatory tran- scription ability etc. The use of imidazolyl based polychel- ate or bulky ligands having N x S y donor centres has been of continuing interest. [1,2] We have synthesized thioether func- tionalized azoimidazoles, 1-alkyl-2-[(o-thioalkyl)phenylazo]- imidazoles (SRaaiNR')(1, 2), where the donor centres are imidazole-N, azo-N and thioether-S. [9] Nickel(II) complexes of SRaaiNR' are reported in this work. The counterions [a] Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700032, India Fax: +91-033-2413-7121 E-mail: c_r_sinha@yahoo.com [b] Department of Physics, National Tsing-Hua University, Hsinchu-300, Taiwan, ROC [c] Department of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, UK [d] Departament de Química Inorgánica, Universitat de Barcelona, Diagonal 6487, 08028 Barcelona, Spain Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.200900423. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2009, 3972–3981 3972 fines μ 1,1 -N 3 bridged Ni II dimer, [Ni(NNS)(N 3 ) 2 ] 2 and thus show interesting intramolecular ferromagnetic coupling. The best fit gave the results: J = 38.13  0.6 cm –1 , g = 2.24  0.002, D = 8.1  0.4 cm –1 and R = 2.1  10 –4 . DFT computation has attempted to explain spectral, redox and magnetic properties of the complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) like, ClO 4 – , bridging anions like azide (N 3 – ), thiocyanate (CNS – ) are used in the syntheses of complexes. The struc- tures are confirmed by single-crystal X-ray diffraction study in representative cases. Electronic structure, spectra, redox and magnetic properties are explained by DFT calculation of optimized geometry of the complexes. 2. Results and Discussion 2.1. Synthesis and Formulation Imidazolylazothioether (1) is generally a tridentate imid- azole-N (N), azo-N (N'), thioeher-S donor ligand. [9] They are synthesized by coupling o-(thioalkyl)phenyldiazonium ions with imidazole in aqueous sodium carbonate solution and purified by solvent extraction and chromatographic process. The alkylation is carried out by adding alkyliodide (MeI, EtI) in dry THF solution to the corresponding 2-[o-(thioal- kyl)phenylazo]imidazole in the presence of sodium hydride. They are abbreviated as SRaaiNR' (1). The reaction between methanolic solution of Ni(ClO 4 ) 2 · 6H 2 O and appropriate ligand, SRaaiNR' in 1:2 mol ratio has isolated shining dark crystals upon slow evaporation. The composition of the complex, [Ni(SRaaiNR') 2 ](ClO 4 ) 2 (2) is supported by microanalytical data. Upon addition of aqueous solution of NaN 3 or NH 4 CNS (2 equiv.) to the mixture of NiCl 2 and SRaaiNR' (1:1 mol ratio) in MeOH has isolated brown-yellow crystalline compound. The com- position is established as [Ni(SRaaiNR')(X) 2 ] 2 {Scheme 1 X=N 3 – (3) and CNS – (4)} The complexes are sufficiently soluble in common organic solvents viz., methanol, etha-