Synthesis, characterization and structure of a new dinickel(II) complex as model for urease Alessandra Greatti * , Marcos Aires de Brito, Adailton Joa ˜o Bortoluzzi, Augusto Susin Ceccato LABINC Laborato ´ rio de Bioinorga ˆnica e Cristalografia, Departamento de Quı ´mica, Universidade Federal de Santa Catarina, Campus Trindade, 88040-900 Floriano ´polis-SC, Brazil Received 2 September 2003; revised 9 October 2003; accepted 9 October 2003 Abstract A new dinuclear nickel(II) complex [Ni 2 (L)(OAc) 2 (H 2 O)]·ClO 4 ·H 2 O 1 with the unsymmetrical N 5 O donor ligand 2-{[bis(2- pyridylmethyl)amino]methyl}-4-methyl-6-{[2-pyridylmethyl)amino]methyl}phenol (HL) has been synthesized and characterized by conductivity, UV – Vis – NIR and IR spectroscopy, electrochemical methods and X-ray crystallography. Complex 1 crystallizes as blue crystals in monoclinic crystal system, space group I 2=a with a ¼ 21.171(4) A ˚ , b ¼ 12.147(2) A ˚ , c ¼ 29.771(6) A ˚ , b ¼ 99.67(3)8, V ¼ 7547(2) A ˚ 3 and Z ¼ 8: In this complex both nickel ions have a distorted octahedral geometry. The nickel centers are endogenously bridged by the phenolic oxygen atom of the deprotonated ligand and also bridged by the two acetate groups as exogenous bridge. A water molecule as terminal ligand is coordinated to a Ni II ion. q 2003 Elsevier B.V. All rights reserved. Keywords: Dinickel(II) complex; Urease; Crystal structure; Phenoxo bridge; X-ray diffraction 1. Introduction Urease is a metallohydrolase that contains two proximate nickel ions in its active site and catalyzes the hydrolysis of urea to ammonia and carbon dioxide [1,2]. Recent X-ray crystallographic studies of urease isolated from two different microorganisms has provided details of the dinickel active site [1–4]. The two nickel(II) centers are bridged by a carbamylated lysine residue and a water molecule or hydroxide ion. Each nickel ion is further bonded by two histidine residues and a water molecule, and one of the Ni II ion is also coordinated by an monodentate aspartate residue. This coordination system leads one nickel center to be pentacoordinate with a square pyramidal N 2 O 3 geometry and the other having a pseudo-octahedral N 2 O 4 environment [1,4,5]. Phenol-based compartmental ‘end-off’ ligands containing N,O-donor groups can accommodate a metal and so produce binuclear complexes with coordi- nation environments resembling the urease active site [6–9]. We have interest in the synthesis of models for metalloenzymes and, in this article, we describe the synthesis, X-ray structural characterization and spectro- scopic properties of a new dinickel(II) complex of the hexadentade phenoxo bridging ligand 2-{[bis(2-pyridyl- methyl)amino]methyl}-4-methyl-6-{[2-pyridylmethyl)ami- no]methyl}phenol-HL (Chart 1). This ligand is of major interest for us due to the possibility of providing a free coordination site on one of the nickel centers allowing to coordinate with a labile group that can be easily substituted by the substrate. While this work was nearing completion Koval et al. reported the synthesis and some properties of a dicopper complex of ligand HL as model for catechol oxidase [10]. 2. Experimental Abbreviations: HL ¼ 2-{[bis(2-pyridylmethyl)amino]- methyl}-4-methyl-6-{[2-pyridylmethyl)amino]methyl}phe- nol, [TBA][PF 6 ] ¼ tetrabutylammonium hexafluorphosphate, BPMP ¼ 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4- methylphenolate, bimp ¼ 2,6-bis[(bis((1-methylimidazol- 2-yl)methyl)amino)methyl]-4-methylphenolate. 0022-2860/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2003.10.008 Journal of Molecular Structure 688 (2004) 185–190 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: þ55-21-48-331-6826; fax: þ 55-21-48- 331-6888. E-mail addresses: adajb@qmc.ufsc.br (A.J. Bortoluzzi), greatti@qmc. ufsc.br (A. Greatti), marcos@qmc.ufsc.br (M.A. de Brito).