Synthesis, spectroscopic properties, structural characterization and electrochemistry of mixed ligand complexes of copper(I) halide with PPh 3 and naphthylazoimidazole G. Saha a,1 , K.K. Sarkar a,2 , P. Datta a , P. Raghavaiah b , C. Sinha a, * a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India b School of Chemistry, National Single Crystal X-ray Diffractometer Facility, University of Hyderabad, Hyderabad 500 046, India article info Article history: Received 3 December 2009 Accepted 5 April 2010 Available online 14 April 2010 Keywords: Copper(I)–naphthylazoimidazole-halide X-ray structure Electrochemistry DFT computation abstract The reaction of CuX (X = Cl, Br, I) with a mixture of PPh 3 and 1-alkyl-2-(naphthyl-a/b-azo)imidazole has synthesized mixed ligand complexes of the composition, [Cu(a/b-NaiR)(PPh 3 )X]. The spectroscopic char- acterization (IR, UV–Vis, 1 H NMR) supports this formulation. The single crystal X-ray diffraction study of [Cu((a-NaiMe)(PPh 3 )I] (7a)(a-NaiMe = 1-methyl-2-(naphthyl-a-azo)imidazole) shows a distorted tetra- hedral geometry about Cu(I). Cyclic voltammograms of the complexes show a high potential Cu(II)/Cu(I) couple and azo reductions. The [Cu(a/b-NaiR)(PPh 3 )I] complexes show an additional oxidative response at 0.4 V that is assigned to I/I  A sharp anodic peak at 0.2 V is assigned to the oxidation of metallic Cu, deposited on electrode surface upon scanning to the negative side of the SCE. DFT and TD-DFT computa- tions of [Cu((a-NaiMe)(PPh 3 )I] (7a), [Cu((a-NaiMe)(PPh 3 )I] + (7a + ) and [Cu((a-NaiMe)(PPh 3 )I]  (7a  ) were carried out to examine the electronic configuration and to explain the spectral and redox properties of the complexes. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Imidazole is ubiquitous in chemistry and biology [1]. The syn- thesis of polydentate ligands using imidazole and their metal com- plexes are of interest [2–4]. We have been engaged in the synthesis of azo functionalized imidazoles such as 1-alkyl-2-(arylazo)imid- azole for several years [5–12]. The arylazoheterocycle stabilizes metals in their lower oxidation state [8–12], such as Cu(I), Ag(I), Fe(II), Co(II), Ru(II), Os(II). The azoimine function, –N@N–C@N– is the chelating group contributing to the chemical, spectral and elec- trochemical properties of the molecules. It has been proposed that the stability, visible spectra and Cu(II)/Cu(I) redox potential of Cu(I)-arylazoheterocycles are due to dp(Cu(I)) ? p * (ligand orbital) transitions [10–12]. The presence of p-acidic co-ligands, like PPh 3 and CO, may assist the azoimine function to stabilize the lower oxi- dation state more efficiently [8,9] compared to the azoimine func- tion alone. In this work, we report mixed ligand complexes of copper(I) halide with PPh 3 and 1-alkyl-2-(naphthyl-a/b-azo)imida- zoles (a/b-NaiR). The complexes are oxidized by chlorine in methanol and the copper(II) complexes thus obtained are reduced by ascorbic acid to the copper(I) derivatives. A theoretical calcula- tion using the DFT computation technique is used to define the electronic configuration of the molecules and to give an explana- tion of their electronic properties. We have attempted this proce- dure to correlate the electronic and redox properties of the complexes. The calculation was carried out using the neutral, oxi- dized and reduced compound. 2. Experimental 2.1. Materials Imidazole, naphthyl amines, CuX (X = Cl, Br, I) and triphenyl phosphine were purchased from E. Merck India. All other chemi- cals and solvents were of reagent grade and were used as received. The 1-alkyl-2-(naphthyl-azo)imidazoles were prepared by the reported procedure [10]. 2.2. Physical measurements Microanalytical (C,H,N) data were obtained from a Perkin– Elmer 2400 CHNS/O elemental analyzer. Spectroscopic data were obtained using the following instruments: UV–Vis, Perkin–Elmer Lambda-25; IR (KBr disc, 4000–200 cm 1 ), Perkin–Elmer RX-1 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.04.007 * Corresponding author. E-mail address: c_r_sinha@yahoo.com (C. Sinha). 1 Present Address: Department of Chemistry, Mahadevananda Mahavidyalaya, Barrackpore, Monirampore, Kolkata 700 120, India. 2 Present Address: Department of Chemistry, Barrackpore Rastraguru Surendranath College, Barrackpore, Kolkata 700 120, India. Polyhedron 29 (2010) 2098–2104 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly