Tuning one dimensional chiral channel interior in mixed ligand Cu(II) complexes of L-histidine derivative and substituted pyridine Rik Rani Koner, Md. Serajul Haque Faizi, Manabendra Ray ⇑ Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati-781039, Assam, India article info Article history: Available online 23 March 2011 Dedicated to Prof. S.S. Krishnamurthy Keywords: Chiral channel Amino acid Histidine Molecular assembly Cu(II) complex abstract Four pentacoordinated square-pyramidal Cu(II) complexes with the general formula [Cu(L)(X)], where L is a L-histidine derived tetradentate ligand and X is either 3-hydroxypyridine or 2-methylpyridine, has been synthesized. Structural analysis showed that the presence of water filled one dimensional chiral channel in the lattices. The interiors of the channels were varied using aromatic ring substitution on the ligand as well as on the monodentate ligand. The dimensions of the channels range from 7 to 9 Å. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The reduced Schiff-base of L-histidine and salicylaldehyde (H 2 L 1 ) belongs to a class of ligands which are known for versatility in forming extensive H-bonded network because of their flexible conformation and multiple H-bonding capability [1]. The ligand H 2 L 1 showed formation of octameric chiral capsule with Cu(II) [1a], binuclear Fe(III) complexes with refillable one dimensional channels [1b] in the lattice and the formation of heptanuclear iron cluster [1d]. Advantage of H-bonding capability of H 2 L 1 is somewhat coun- terbalanced with unpredictability in the crystallization of the metal complexes as the resulting complexes can incorporate hydrogen bond capable solvent and assemble in multiple different ways [2]. Thus designing molecular assembly with this ligand remains challenging. Earlier, we have explored an alterna- tive design by reducing number of H-bonds and introducing hydrophobic groups within the ligand [3]. Thus predictability of solid state structure could be improved at the expense of useful multinuclear species formation [3]. In the present manu- script, we have modified a reported complex [Cu(L 1 )(imidazole)] by changing the imidazole to hydroxypyridine. Both imidazole and hydroxypyridine are monodentate ligand with one H-bond donation site differing only in length and angle (Scheme 1). The effect of this minor change and aromatic ring substitution on the crystal lattice has been investigated with the hope that this small perturbation may result in clues leading to useful architecture. 2. Results and discussion 2.1. Synthesis and characterization All the complexes were synthesized from the ligand by deprotonation of the ligand using base followed by addition Cu(II) salt and excess of either 3-hydroxypyridine (3-Hpy) or 2-methylpyridine (2-Mepy). The complexes [Cu(L 1 )(3-Hpy)]3H 2 O (1a), [Cu(L 2 )(3-Hpy)]3H 2 O(2a) and [Cu(L 3 )(3-Hpy)]4H 2 O(3a) were crystallized from slow evaporation of methanolic solution. The complex [Cu(L 2 )(2-Mepy)]3H 2 O (2b) was crystallized by slow diffusion of diethyl ether into solution of the complex in 2-methylpyridine. The complexes 1a, 2a, 2b and 3a showed vibrational stretches at 1600 and 1380 cm 1 which were identified as asymmetric and symmetric carboxylate stretches, respectively [1a,3,4]. Except C% of 2b, the elemental analyses of all the complexes were satisfactory. The thermo gravimetric analysis (TGA) between 50 and 80 °C shows weight loss of 11.09%, 11.10%, for 1a and 2b against the calculated values of 11.46% and 10.80%, respectively, for 3H 2 O. The conductance val- ues in DMF revealed non-electrolyte nature of the complexes [5]. The room temperature magnetic moments of 1a, 2a, 2b and 3a are found to be 1.73, 1.78, 1.80, 1.85 B.M., respectively, which 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.03.044 ⇑ Corresponding author. E-mail address: manabray@iitg.ernet.in (M. Ray). Inorganica Chimica Acta 372 (2011) 367–373 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica