Copper(II) complexes of thioether containing an azoimidazolyl system. X-ray structure of Cu(SEtaaiNEt)Cl 2 (SEtaaiNEt = 1-ethyl-2-{(o-thioethyl)phenylazo}imidazole) Debasis Banerjee a , Umasankar Ray a , Sk. Jasimuddin a , Jian-Cheng. Liou b , Tian-Huey Lu b , Chittaranjan Sinha a, * a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India b Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, ROC Received 19 March 2005; accepted 25 August 2005 Available online 7 November 2005 Abstract The arylthioether diazonium ion is coupled with imidazole to synthesize tridentate imidazolylazothioether-based NN 0 S ligands. The reaction of CuCl 2 Æ 2H 2 O with NN 0 S ligands has synthesized penta-coordinated Cu(NN 0 S)Cl 2 compounds. The structure has been con- firmed by an X-ray diffraction study in one case and also by other spectroscopic and magnetic properties. a-Diimine (N,N) ligands react with Cu(NN 0 S)Cl 2 to prepare ternary complexes, [Cu(NN 0 S)(N,N)] 2+ . Cu(NN 0 S)Cl 2 show a Cu II /Cu I couple (0.2 V versus Ag/AgCl). Ternary complexes show a Cu II /Cu I potential at 0.3 V versus Ag/AgCl. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Copper(II)-imidazolylazothioether complexes; Spectra; Electrochemistry; X-ray structure 1. Introduction The structure and stereochemistry of copper complexes have largely been influenced by the electronic configura- tion of the metal ion. Copper(I), a d 10 configuration pre- fers a tetrahedral orientation; copper(II) complexes, a d 9 system, exhibit coordination number dependent struc- tures: 4 coordination prefers square planar, the 5 coordi- nated system is square pyramid or trigonal bipyramidal and 6 coordinated complexes are distorted octahedral [1–4]. The structural flexibility is more versatile in penta- coordinated copper(II) complexes than hexa-coordinated ones. The structural change has been associated with the large reorganization effects observed for Cu(II)/Cu(I) interconversion and the energy associated with this change has been utilized by the majority of biochemical systems with copper containing metallo-enzymes [5–8]. Research in diimine complexes of copper(II) has been attracting great interest for their stereochemistry, magne- tism, photophysical and biochemical properties [9–11]. The design of conjugated polydentate imidazolyl based chelates, isoelectronic with the diimine system, is a chal- lenging task. The use of imidazole containing thioether bulky ligands having N x S y donor centers has been of continuing interest to ensure the stability of Cu(II) and Cu(I) [12–18]. The imidazole (N) and thioether (S) donor atoms are both weakly p-accepting but of different soft- ness so that both Cu(I) and Cu(II) complexes can be synthesized [19]. For the last few years, we have been engaged in the development of chemistry of 2-(arylazo)imidazoles [20– 33]. The functionalization of a pendant aryl group by a suitable donor center may make a bidentate ligand into a potentially tridentate chelating ligand. The prospect of an 0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.08.053 * Corresponding author. Tel.: +91 033 2414 6666x2453; fax: +91 033 2414 6584. E-mail address: c_r_sinha@yahoo.com (C. Sinha). www.elsevier.com/locate/poly Polyhedron 25 (2006) 1299–1306