Mononuclear and binuclear Cu(II) complexes of some tridentate aroyl hydrazones. X-ray crystal structures of a mononuclear and a binuclear complex Satyajit Mondal a , Sumita Naskar a , Ayan Kumar Dey a , Ekkehard Sinn b , Carla Eribal b , Steven R. Herron c , Shyamal Kumar Chattopadhyay a,⇑ a Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711 103, India b Chemistry Department, Western Michigan University, Kalamazoo, MI 49008-5413, USA c 10687 Logan Canyon Road, South Jordan, UT 84095, USA article info Article history: Received 22 August 2012 Received in revised form 28 November 2012 Accepted 1 December 2012 Available online 29 December 2012 Keywords: Mononuclear Cu(II) complexes Binuclear Cu(II) complexes (l-Cl) 2 -Bridge Pyridine-2-carbaldehyde hydrazone 2-Acetylpyridine hydrazone X-ray crystal structure abstract Cu(II) complexes of eight N,N,O-donor hydrazone ligands, obtained by condensation of pyridine-2-carb- aldehyde and 2-acetylpyridine with four aroyl hydrazides, are reported. Reactions of Cu(ClO 4 ) 2 6H 2 O with the pyridine-2-carbaldehyde hydrazones (L 1 H, L 2 H, L 3 H, L 4 H) in presence of Et 3 N, in 1:2:2 molar ratio, lead to isolation of mononuclear octahedral Cu(II) complexes of formula [Cu(L) 2 ] (L = L 1  ,L 2  ,L 3  ,L 4  ). However, for the 2-acetylpyridine hydrazones (L 5 H, L 6 H, L 7 H, L 8 H) reactions under similar conditions yield dichloro bridged complexes of the type [Cu 2 (l-Cl) 2 (L 0 ) 2 ] (L 0 =L 5  ,L 6  ,L 7  ,L 8  ), where each Cu(II) ion is in a square-pyramidal geometry, the chloride ions coming from the in situ reduction of perchlorate by the 2-acetylpyridine hydrazones. The X-ray crystal structures of [Cu(L 1 ) 2 ] and [Cu 2 (l-Cl) 2 (L 5 ) 2 ] are reported. The spectroscopic and electrochemical behaviors of the complexes are also reported. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Interest in the metal complexes of Schiff base ligands remains unwavering because of their applications in varied fields such as catalysis [1–3], synthesis of compounds possessing designed and controllable magnetic properties [4,5], spin-crossover materials [6], biological activities including radical scavenging ability [7], synthons for crystal engineering and materials chemistry [8–14]. Aroyl hydrazones are an important class of Schiff base ligands, coordinating through protonated/deprotonated amide oxygen and the imine nitrogen of hydrazone moiety; very often an addi- tional donor site (usually N or O) is provided by the aldehyde or ke- tone forming the hydrazone Schiff base. Aroylhydrazones have proved to be strong chelating agents for transition metals [10– 12,15–17] and lanthanides [18,19] as well as main group elements [20,21]. In our laboratory we have been investigating the structural diversity of aroylhydrazone complexes along with their redox and magneto-structural properties [10–12,15,16]. In this paper we re- port mononuclear and binuclear complexes of Cu(II) with triden- tate hydrazone ligands obtained by the condensation of four aroylhydrazides with pyridine-2-carbaldehyde and 2-acetyl pyri- dine (Scheme 1). 2. Experimental 2.1. Materials and methods The hydrazone ligands were prepared following procedure de- scribed in literature [15,22–25]. CuCl 2 2H 2 O, Cu(ClO 4 ) 2 6H 2 O and Cu(OAc) 2 H 2 O were obtained from Aldrich. The solvents for synthe- sis were of AR grade obtained from SRL (India) or Spectrochem (In- dia) and used without purification, while solvents for spectroscopic and electrochemical work were of HPLC grade from Aldrich or SRL (India). Elemental analyses were performed on a Perkin-Elmer 2400 C, H, N analyzer. Infrared spectra were recorded as KBr pellets on a JASCO FT-IR-460 spectrophotometer. UV–Vis spectra were re- corded using a JASCO V-530 spectrophotometer. Cyclic voltammo- grams were recorded in DMF solutions (for compounds 1–4) or DMSO solution (for compounds 5–8), containing 0.1 (M) TEAP as supporting electrolyte, using a CH1120A potentiostat, with Pt disc/glassy carbon working electrode, Pt wire as counter electrode and Ag,AgCl/saturated KCl as reference electrode. The ferrocene/ ferrocenium couple was observed at E 0 (DE p ) = 0.48 V (100 mV) un- der our experimental conditions. 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2012.12.018 ⇑ Corresponding author. Tel.: +91 33 2668 0521; fax: +91 33 2668 2916. E-mail address: shch20@hotmail.com (S.K. Chattopadhyay). Inorganica Chimica Acta 398 (2013) 98–105 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica