Iron(II) and nickel(II)-thiocyanato complexes of 1-alkyl-2-(arylazo)imidazole: single crystal X-ray structure of [Fe(MeaaiEt) 2 (NCS) 2 ] (MeaaiEt = 1-ethyl-2(p-tolylazo)imidazole) and [Ni(MeaaiMe)(NCS) 2 (H 2 O) 2 ] Æ 2DMF (MeaaiMe = 1-methyl-2(p-tolylazo)imidazole) Umasankar Ray a , Debasis Banerjee a , Jian-Cheng Liou b , Chun-Nan Lin b , Tian-Huey Lu b , Chittaranjan Sinha c, * a Department of Chemistry, The University of Burdwan, Burdwan 713 104, India b Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan, PR China c Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India Received 31 July 2004; accepted 10 November 2004 Available online 11 February 2005 Abstract The reaction of green vitriol (FeSO 4 ,7H 2 O) with 1-alkyl-2-(arylazo)imidazoles [RaaiR 0 where R = H (a), Me (b); R 0 = Me (1/3/5), Et (2/4/6)] and NH 4 SCN in 1:2:2 mole proportion affords mononuclear bis-chelated [Fe(RaaiR 0 ) 2 (SCN) 2 ](3, 4) complexes. Reaction of NiSO 4 Æ 6H 2 O with 1-alkyl-2(arylazo)imidazole and ammonium thiocyanate (1:2:2 molar ratio) in methanol solution forms mononuclear monochelated thiocyanato complexes of the type [Ni(RaaiR 0 )(H 2 O) 2 (SCN) 2 ] Æ 2H 2 O(5, 6). Slow diffusion of DMF solution of [Ni(MeaaiMe)(H 2 O) 2 (NCS) 2 ] in methanol has isolated the X-ray quality crystals. All the complexes are characterized by elemental, UV–Vis, IR, thermal and magnetic studies. In both cases, the distorted octahedral structure was confirmed by single crystal X-ray diffraction study of [Fe(MeaaiEt) 2 (NCS) 2 ](4b) and [Ni(MeaaiMe)(H 2 O) 2 (NCS) 2 ] Æ 2DMF (7). Variable temperature susceptibility measurements of [Fe(MeaaiEt) 2 (NCS) 2 ](4b) do not exhibit spin crossover property, which may be due to high struc- tural distortion. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Arylazoimidazole; Iron(II), Nickel(II)-complexes; X-ray structure, electrochemistry 1. Introduction There has been a continuous interest in the chemistry of metal complexes of imidazole and related heterocy- cles [1–5]. Imidazole and its derivatives have been widely used in chemistry and biology due to their appearance in biomolecules, metalloproteins and their versatility in the production of polymetallic complexes of magneto- chemical interests. We have been interested to design functionalized imidazole ligands like arylazoimidazoles. For the past several years, we [6–17] and others [18–20] have been engaged in the exploration of the chemistry of arylazoimidazoles. The molecule bears azoimine, – N@N–C@N–, functional group. This is an efficient p-acid system for the stabilization of low oxidation me- tal ions. The platinum chemistry of this function is known in more detail [10–20] than 3d transition metals [6–9]. Present work stems from our continued interest 0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2004.11.020 * Corresponding author. Tel.: +91 909830632450; fax: +91 033 24146584. E-mail address: c_r_sinha@yahoo.com (C. Sinha). www.elsevier.com/locate/ica Inorganica Chimica Acta 358 (2005) 1019–1026