Coordination chemistry of two new tetraaza Ni(II) and Cu(II) macrocyclic and two new Co(II) and Zn(II) macroacyclic Schiff base complexes containing piperazine moiety: X-ray crystal structures of Ni(II) and Zn(II) complexes Hassan Keypour a,⇑ , Parisa Arzhangi a , Nasibeh Rahpeyma a , Majid Rezaeivala b , Yalcin Elerman c , Hamid Reza Khavasi d a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran b Department of Chemical Engineering, Hamedan University of Technology, Hamedan 65155, Iran c Department of Engineering Physics, Faculty of Engineering, University of Ankara, Besevler 06100, Ankara, Turkey d Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran article info Article history: Received 25 April 2010 Received in revised form 4 November 2010 Accepted 19 November 2010 Available online 4 December 2010 Keywords: Piperazine moiety Macroacyclic Schiff base complex X-ray crystal structure Tetraaza macrocycle abstract A new potentially tetradentate (N 4 ) Schiff base ligand (L), 1,9,12,20-tetraazatetracyclo[18.2.2.02,7.014, 19]tetracosa-2(7),3,5,8,12,14(19),15,17-octaene containing a piperazine moiety is described. Macrocyclic Schiff base complexes, [NiL](ClO 4 ) 2 (1) and [CuL](ClO 4 ) 2 (2) have been obtained from equimolar amounts of ligand (L) with nickel(II) and copper(II) metal ions. While the equilibrium reaction in the presence of cobalt(II) and zinc(II) metal ions with ligand L in a 1:1 molar ratio yielded the open-chain Schiff base complexes, [CoL 0 ](ClO 4 ) 2 (3) and [ZnL 0 ](ClO 4 ) 2 (4) containing two terminal primary amino groups. The ligand L 0 is 1,4-bis(2-(2-aminoethyliminomethyl)phenyl)piperazine. The crystal structures of (1) and (4) have been also determined by X-ray diffraction. It was shown that the Ni(II) is coordinated to the ligand L by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry. Also single crystal X-ray analysis of (4) confirmed a distorted octahedral arrangement in the vicinity of Zn atom with N 6 donor set. The spectroscopic characterization of all complexes is consistent with their crystal structures. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The Schiff base ligands are one of the most widely used ligands due to the ease of formation and remarkable versatility, and there- fore they have played an important role in the development of coordination chemistry as they readily form stable complexes with most of the transition metals. The research field dealing with Schiff base metal complexes is very broad due in part to their potential interest for a number of interdisciplinary areas that include bioin- organic chemistry, catalysis, and magnetochemistry [1–5]. Pipera- zine is a water soluble cyclic diazine with rigid preorganized cyclohexane conformation [6]. As an amine, piperazine readily undergoes nucleophilic substitution reactions with proper halides. The hexaatomic piperazine ring may exhibit a boat or a chair con- formation, the latter one is 17.2 kJ mol 1 more stable [7]. The boat conformation is stabilized when the piperazine ring coordinates one metal ion through both the nitrogen atoms forming biden- tate–chelate complexes. However, the structural character of piperazine causes some rigidity. In previous works [8–12] synthesis and characterization of some N 4 macrocyclic and macroacyclic Schiff base complexes in the presence of Co(II), Ni(II) and Cu(II) were reported. We have re- cently reported the synthesis and crystal structure study of some new macrocyclic and macroacyclic Schiff base complexes contain- ing piperazine moiety [13–19]. Herein we report the synthesis and physical properties of the complexation capability towards Ni(II), Cu(II), Co(II) and Zn(II) transition metal ions with a new 14-mem- bered N 4 macrocyclic ligand L having a piperazine moiety (Scheme 1). In addition, the X-ray crystal structures of [NiL](ClO 4 ) 2 and [ZnL 0 ](ClO 4 ) 2 are also described. 2. Experimental 2.1. Starting materials 1,4-Bis(2-formylphenyl)piperazine was obtained according to literature method [18,20]. All solvents were of reagent grade qual- ity and purchased commercially. Metal salts, piperazine, 2-fluoro- benzaldehyde and 1,2-diaminoethane were obtained from Merck and were used without further purification. 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.11.033 ⇑ Corresponding author. Tel.: +98 811 8242044; fax: +98 811 8272404. E-mail address: haskey1@yahoo.com (H. Keypour). Inorganica Chimica Acta 367 (2011) 9–14 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica