Note Structures and properties of trans -dichloro{tetrakis (5-chloro-2(1H)- pyridone-O )}M(II) [M /Mn, Fe, Co, Ni, Cu]; formation of quasi- macrocyclic metal complexes through hydrogen bonding Tomoyuki Mochida a,b, *, Mikio Ueda a , Chigusa Aoki a , Hatsumi Mori c a Department of Chemistry, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba 274-8510, Japan b PRESTO, Japan Science and Technology Corporation (JST), Japan c Institute for Solid State Physics, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8581, Japan Received 19 November 2001; accepted 30 January 2002 Abstract The reaction of 5-chloro-2(1H)-pyridone (HL) with M(II)Cl 2 (M/Mn, Fe, Co, Ni, Cu) in ethanol solution results in the formation of octahedral complexes represented as [M(II)(HL) 4 Cl 2 ], X-ray structure determination of the Mn(II) and Ni(II) complexes revealed that the four ketone ligands are O bonded in the equatorial positions, which are arranged in a quasi-macrocyclic fashion through N  /H /ÁÁÁ /O hydrogen bonds. The packing arrangements of the complexes are symmetrical and show three- dimensional (3-D) p  /p stacking structures, though these complexes are paramagnetic with negligible intermolecular interactions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Crystal structures; Hydrogen bonds; Pyridone complexes; Mononuclear complexes 1. Introduction The versatile ligands of 2-pyridone (or 2-hydroxypyr- idine) and its derivatives have been shown to form a large number of complexes with various metals, afford- ing mononuclear, dinuclear and polynuclear com- pounds, as extensively investigated by Cotton et al. [1]. These ligands exhibit a variety of bonding modes and, in particular, have played an important role in the under- standing of metal  /metal multiple bonds, as summarized by Rawson and Winpenny in their extensive review [2]. However, studies on monodentate pyridone metal com- plexes are relatively fewer than those on 2-pyridi- nethione (or 2-mercaptopyridine) derivatives [3]. Recently, molecular magnetism and redox activities of transition metal complexes have attracted attention [4]. This led us to the present study of basic aspects of coordination schemes, packing structures, and magnetic properties of monodentate pyridone complexes with a series of transition metals. Another interesting aspect of the 2-pyridone derivatives is the formation of hydrogen bonding in the solid state, due to the presence of N /H and O / hydrogen bonding sites [5]. Here we describe the synthesis, structure, and properties of the complexes of a 5-chloro-2(1H)-pyridone ligand (abbreviated as HL, Scheme 1) with transition metals M /Mn(II), Fe(II), Co(II), Ni(II), and Cu(II). 2. Experimental 2.1. General methods All chemicals and solvents used for the synthesis were commercially available. Infrared spectra were recorded in compressed KBr pellets on a JASCO FT-IR230 spectrometer. 1 H NMR spectra were measured on a Bruker AC-300 FT spectrometer in methanol-d 4 or dimethylsulfoxide-d 6 (DMSO-d 6 ) solutions. Magnetic moments were measured at room temperature (r.t.) using a Sherwood Scientific Gouy magnetic balance. Temperature dependence of the magnetic susceptibilities was collected from 300 to 2 K using a Quantum Design * Corresponding author. Tel./fax:  /81-47-472 4406. E-mail address: mochida@chem.sci.toho-u.ac.jp (T. Mochida). Inorganica Chimica Acta 335 (2002) 151  /155 www.elsevier.com/locate/ica 0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0020-1693(02)00817-4