Synthesis and characterization of nickel(II) complexes with three potentially hexadentate Schiff-base ligands and polyamines: X-ray crystal structure determination of one nickel(II) complex Hassan Keypour Æ Reza Azadbakht Æ Hadi Amiri Rudbari Æ Alireza Heydarinekoo Æ Hamidreza Khavasi Received: 22 May 2009 / Accepted: 19 August 2009 / Published online: 30 August 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Three new potentially hexadentate N 4 O 2 Schiff- base ligands (H 2 L 1 ,H 2 L 2 and H 2 L 3 ) were prepared from the reaction of the polyamines N,N 0 -bis(2-aminophenyl)-1, 2-ethanediamine (L 1 ), N,N 0 -bis(2-aminophenyl)-1,3-pro- panediamine (L 2 ) and N,N 0 -bis(2-aminophenyl)-1,4-butane- diamine (L 3 ), respectively with salicylaldehyde. Reaction of the Schiff bases with Ni(II) salts in the presence of N(Et) 3 gave the neutral complexes [NiL 4 ], [NiL 5 ] and [NiL 6 ]. Ni(II) complexes of the polyamines were also prepared. One of complexes [Ni(L 1 )(MeCN) 2 ](ClO 4 ) 2 ÁMeCN has been char- acterized through X-ray diffraction methods. Introduction The chemistry of metal complexes with chelate ligands containing nitrogen or oxygen donors has been studied extensively in order to mimic reactions in the redox func- tion of various metalloenzymes, as well as the coordination and reactivity of dioxygen in synthetic, industrial and biological processes. Metalloenzymes have several func- tions, including redox as in superoxide dismutase-like activity [1–6], structural and catalytic roles [7–11]. Therefore, for many years, there has been great interest in the study of complexes able to mimic the active sites of metalloproteins. These model complexes are generally obtained from bulky polydentate ligands in order to get an environment similar to those found in proteins. In the present paper, we have prepared and characterized three new potentially hexadentate N 4 O 2 Schiff-base ligands (H 2 L 1 ,H 2 L 2 and H 2 L 3 ) derived from the polyamines [N,N 0 -bis(2-aminophenyl)-1,2-ethanediamine (L 1 ), N,N 0 -bis- (2-aminophenyl)-1,3-propanediamine (L 2 ) and N,N 0 -bis(2- aminophenyl)-1,4-butanediamine (L 3 )] and salicylaldehyde. During the course of this work, we have prepared and characterized nickel(II) complexes of both the polyamines and their Schiff-base derivatives. Experimental NMR spectra were recorded using a Jeol FX-Q 90 spec- trometer. The IR spectra were recorded as KBr discs, using a Perkin–Elmer FTIR GX spectrophotometer (4000– 400 cm -1 ). Salicylaldehyde and Ni(ClO 4 ) 2 Á6H 2 O were obtained from Merck and used without further purification. N,N 0 -bis(2-aminophenyl)-1,2-ethanediamine (L 1 ), N,N 0 -bis(2- aminophenyl)-1,3-propanediamine (L 2 ) and N,N 0 -bis(2- aminophenyl)-1,4-butanediamine (L 3 ) were prepared according to a literature method [12, 13]. Crystal structure determination Vapor diffusion of diethyl ether into a solution of [Ni(L 1 )(MeCN) 2 ](ClO 4 ) 2 in acetonitrile afforded crystals suitable for study by X-ray crystallography. X-ray data were measured on a STOE IPDS-II two circle diffrac- tometer at 293 K, using graphite monochromated Mo-Ka H. Keypour (&) Á H. Amiri Rudbari Á A. Heydarinekoo Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran e-mail: haskey1@yahoo.com R. Azadbakht Department of Chemistry, Payame Noor University, Hamedan, Iran H. Khavasi Department of Chemistry, Shahid Beheshti University, Tehran, Iran 123 Transition Met Chem (2009) 34:835–839 DOI 10.1007/s11243-009-9271-3