Journal of Physics and Chemistry of Solids 68 (2007) 45–52 Synthesis, crystal structure, Cu 2+ doped EPR and voltammetric studies of bis[N-(2-hydroxyethyl)ethylenediamine]zinc(II) squarate monohydrate I ˙ brahim Uc - ar à , Bu¨nyamin Karabulut, Ahmet Bulut, Orhan Bu¨yu¨kgu¨ngo¨r Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, Kurupelit, 55139, Samsun, Turkey Received 17 May 2006; received in revised form 4 August 2006; accepted 12 September 2006 Abstract Crystal structure of [Zn(hydet-en) 2 ]  C 4 O 4  H 2 O (ZHES) (hydet-en is N-(2-hydroxyethyl)ethylenediamine) complex has been synthesized and characterized by analytical, spectroscopic (IR, UV/Vis) and voltammetric techniques. After doping Cu 2+ ion, its magnetic environment has been identified by electron paramagnetic resonance (EPR) technique. The title complex crystalizes in monoclinic system with space group P2 1 /c and with Z ¼ 4. Each hydet-en ligand acts as a tridentate ligand through the two N atoms and the hydroxyl O atom, resulting in a six coordinate Zn(II) ion. The EPR spectra were recorded in three perpendicular planes of Cu 2+ doped ZHES single crystal. The calculated g and A values indicated that the paramagnetic center is rhombic symmetry with the Cu 2+ ion having distorted octahedral environment. The molecular orbital bond coefficients of the Cu(II) ion in d 9 state is also calculated by using EPR and optical absorption parameters. The dianion SQ 2 is oxidized reversibly in two consecutive steps to the corresponding radical monoanion and neutral form. r 2006 Elsevier Ltd. All rights reserved. Keywords: D. Electron paramagnetic resonance (EPR) 1. Introduction Increasing attention has been devoted to the study of the coordination chemistry of the squarate ligand, C 4 O 4 2 , by both inorganic and bioinorganic chemists during the past few years [1]. Squarate acts as a bridge between two or more metal atoms in mono or polydentate coordination modes when acting as a ligand towards first row transition metal ions [2,3]. It coordinates to Fe(II), Fe(III), Ni(II), and Cu(II) complexes in a m-1,3 fashion, giving binuclear [4,5] and chain structures [6,7], whereas the m-1,2 coordina- tion mode has been reported for binuclear complex of Cu(II) [8]. It is also observed that the squarate anion, with Cu(II) and Ni(II), acts as a tetramonodentate ligand and forms polynuclear compounds [9]. The chelating and bis- chelating coordination modes are only possible in com- plexes with larger metal ions, such as alkaline and rare earth cations [10–12]. In all the cases reported so far, metal- squarate complexes have been found interesting in terms of the structural relationships between their respective solid- state architectures [13]. In our ongoing research on squaric acid, we have synthesized some mixed-ligand metal(II) complexes of squaric acid, and their structures have been reported [14–17]. In these compounds, squaric acid behaves as a monodentate ligand [18,19] or acts as both a monodentate and a bidentate ligand [20], while in ZHES, reported in the study, it has not coordinated to Zn(II) ion and acts as a counter anion. It is also aimed in this study to see the magnetic properties of the compound by electron paramagnetic resonance (EPR) technique. In order to achieve these, transition metal ions should be doped in the diamagnetic host lattice of ZHES as an impurity. It is now well known that the transition metal ions as a probe can be used to determine the symmetry environments of the complexes in host lattices by EPR technique [21,22]. When these ions form paramagnetic centers then one can get information ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2006.09.008 à Corresponding author. Tel.: +90 362 3121919 E-mail address: iucar@omu.edu.tr (I ˙ . Uc - ar).