8-(2-Pyridylmethoxy)quinoline: a new N,O,N ?-tridentate ligand and X-ray crystal structures of its mononuclear palladium(II), copper(II) and nickel(II) complexes Muna R.A. Al-Mandhary a , Peter J. Steel b, * a College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khod 123, Oman b Department of Chemistry, University of Canterbury, Christchurch, New Zealand Received 5 August 2002; accepted 22 January 2003 Abstract The synthesis of the new N,O,N ?-tridentate ligand 8-(2-pyridylmethoxy)quinoline (2) is described. X-ray crystal structures of its mononuclear complexes with palladium(II) chloride, copper(II) chloride and nickel(II) nitrate are reported. The ligand acts as a flexible bidentate or tridentate ligand, according to the requirements of the coordinated metal. # 2003 Elsevier B.V. All rights reserved. Keywords: X-ray crystal structures; Palladium complexes; Copper complexes; Nickel complexes; N -ligands 1. Introduction 2,2?-Bipyridine (bpy) has been used for over a century [1] as the classical N ,N ?-bidentate ligand in coordina- tion, organometallic and analytical chemistry [2]. Whereas other N ,N ?-biheterocyclic ligands have often been employed as analogues of bpy [3], N,O -chelating ligands are somewhat less common. Of these, by far the most well studied is 8-hydroxyquinoline (1) (oxine), which also has a long history as a versatile bidentate ligand [4]. Oxine acts as uninegative ligand with a pyridine-like donor and an alkoxo donor. Numerous related N,O -bidentate ligands have been studied in recent years [5], including ether derivatives of oxine, such as 8-methoxyquinoline [6]. N ,N ?,N ƒ-Tridentate ligands are also much used, the most common being 2,2?:6?,2ƒ-terpyridine, which acts as a T-shaped ligand for meridional coordination to octahedral transition metals [7]. Equally popular as facially coordinating N ,N ?,N ƒ-ligands are the tripyrazolylborates (scorpio- nates) [8] and the tripyrazolylmethanes [9]. Mixed donor tridentate ligands are considerable less well studied. We are currently engaged in a study of the synthesis of a diverse group of new ligands, which incorporate one or more quinoline units linked via ether linkages through the hydroxyl group of (1). In this context, we now describe the preparation of a new ligand, 8-(2- pyridylmethoxy)quinoline (2), which is potentially a doubly chelating N,O,N ?-tridentate ligand with two pyridine-like donors and an ether donor. Ether deriva- tives of (1) have been used in other more complex multidentate ligands [10], but not in simple N,O,N ?- tridentate ligands. Surprisingly few N,O,N ?-doubly chelating ligands have been used in coordination chemistry, the simplest being di-2-aminoethyl ether and its N ,N ,N ?,N ?-tetramethyl derivative [11]. We further report the preparations, and X-ray crystal structures, of three mononuclear complexes of 2 with representative transition metal adducts and show that 2 can act as either an N ,N ?-bidentate or N,O,N ?-triden- tate ligand. * Corresponding author. Tel.:  /64-3-3642432; fax:  /64-3-3642110. E-mail address: p.steel@chem.canterbury.ac.nz (P.J. Steel). Inorganica Chimica Acta 351 (2003) 7  /11 www.elsevier.com/locate/ica 0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0020-1693(03)00188-9