Spectrochimica Acta Part A 77 (2010) 219–225 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Structural characterization and electrochemical properties of novel salicylidene phosphonate derivatives Mustafa Dolaz a,∗ , Vickie McKee b , Muhammet Köse b , Ays ¸ egül Gölcü c , Mehmet Tümer c a Kahramanmaras Sutcu Imam University, Faculty of Engineering and Architecture, Department of Environmental Engineering, K.Maras, Turkey b Univ Loughborough, Dept Chem, Loughborough LE11 3TU, Leics, England, United Kingdom c Kahramanmaras Sutcu Imam University, Chemistry Department, 46100, K.Maras, Turkey article info Article history: Received 25 November 2009 Received in revised form 5 May 2010 Accepted 15 May 2010 Keywords: Salicylidene Phosphonate Schiff base X-ray Electrochemical abstract In this study, three novel salicylidene phosphonate ligands, diethyl (4-{[(1E)-(2-hydroxyphenyl)methy- lidene]amino}benzyl)phosphonate (HL 1 ), diethyl (4-{[(1E)-(2-hydroxy-3-methoxyphenyl)methyli- dene]amino}benzyl)phosphonate (HL 2 ) and diethyl (4-{[(1E)-(2,4-dihydroxyphenyl)methyli- dene]amino}benzyl)phosphonate (HL 3 ) were synthesized and characterized by the analytical and spectroscopic techniques. We obtained their single crystals from the ethanolic solution. There are intramolecular phenol-imine hydrogen bonds in all three compounds between O1 and N1 atoms. The ligand HL 3 contains a second phenol group and this is makes an intermolecular hydrogen bond with the phosphine oxide of a neighbouring molecule O2–O3 (under symmetry operation -x, 0.5 + y, 0.5 - z). In order to investigate the redox behaviours of the salicylidene phosphonate ligands (HL 1 –HL 3 ), we were studied electrochemical properties of the ligands at the different pH and scan rates. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The Schiff bases, formed by the condensation of an amine with an aldehyde [1], usually coordinate to a metal through the imine nitrogen and another group, usually oxygen, nitrogen or sulfur situated on the original aldehyde. Condensation of the carbonyl function of a -ketone with only one end of a diamine produces terdentate ligand and this can be make to undergo further conden- sation with another carbonyl function to produce unsymmetrical tetradentate Schiff base ligands. The Schiff bases are very impor- tant tools for the inorganic chemists as these are widely used to design molecular ferromagnets, in catalysis, in biological modeling applications, as liquid crystals and as heterogeneous catalysts [2]. Schiff base complexes are once again topical in connection with self-assembling cluster complexes [3]. The transition metal complexes having oxygen and nitrogen donor Schiff bases possess unusual configuration, structural lability and are sensitive to molecular environment [4]. The environment around the metal center ‘as coordination geometry, number of coordinated ligands and their donor group’ is the key factor for metalloprotein to carry out a specific physiological function [5]. About 20 Zinc enzymes are known in which Zinc is generally tetra- hedrally four coordinate and bonded to hard donor atoms such as nitrogen or oxygen [6]. Manganese plays an important role ∗ Corresponding author. Tel.: +90 344 2191460; fax: +90 344 2191052. E-mail address: mdolaz@ksu.edu.tr (M. Dolaz). in several biological redox-active system [7], a number of cop- per proteins including enzymes have been reported and proteins containing iron participate in oxygen transport [8]. The prepara- tion of model complexes having similar spectroscopic features is perhaps the most important step to understand the structure and behaviour of these biological systems. Schiff base metal complexes attract considerable interest and occupy an important role in the development of the chemistry of chelate systems [9,10] due to the fact that especially these with N 2 O 2 tetradentate ligands, such sys- tems closely resemble metallo-proteins. Survey of the literature reveals an excellent work devoted to synthesis and characteriza- tion of many metal complexes of Schiff base [11,12], furthermore the coordination compounds of phosphonic acid and their esters with transition metal ions have been the subject of several studies due to the fact that complexes of such compounds exhibit biological activity [13]. In this study, we report synthesis and structural characterization of three novel salicylidene phosphonate ligands (HL 1 –HL 3 ). In addi- tion, we also investigated the spectroscopic and electrochemical properties of the ligands. 2. Experimental 2.1. General Salicylaldehyde, 3-methoxy-2-hydroxybenzaldehyde, 2,4- dihydroxybenzaldehyde, diethyl (4-aminobenzyl)phosphonate (starting material), and organic solvents were obtained from Fluka 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.05.011