ORIGINAL PAPER Spectroscopic Studies and Crystal Structure of 4-(2-Hydroxy- 3-Methoxybenzylideneamino)-N-(5-Methylisoxazol-3-yl) Benzenesulfonamide Mustafa Yıldız • Hu ¨seyin U ¨ nver • Dig ˘dem Erdener • Nazan Ocak _ Iskeleli Received: 11 February 2008 / Accepted: 11 February 2010 / Published online: 13 March 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Schiff base 4-[(2-hydroxy-3-methoxybenzylidene- amino)-N-(5-methylisoxazol-3-yl)benzene-sulfonamide has been synthesized from the reaction of 4-amino-N-(5-meth- ylisoxazol-3-yl)benzenesulfonamide(sulfamethoxazole) with 2-hydroxy-3-methoxybenzaldehyde. It has been characterized by elemental analysis, MS, IR, 1 H NMR, 13 C NMR, HET- COR and UV–Visible techniques. The structure of it also has been examined crystallographically. For the compound exist as dominant form of enol-imines in both the solid state and the solutions. It crystallizes in the monoclinic space group P2 1 /c with a = 8.2694(7), b = 8.3453(5), c = 26.260(2) A ˚ , b = 97.142(7) °, V = 1798.1(2) A ˚ 3 , D x = 1.431 g cm -3 , R 1 = 0.0529 and wR 2 = 0.1370 [I [ 2r(I)], respectively. Keywords Schiff base Á Spectroscopy Á Crystal structure Á Tautomerisim Á Hydrogen bonds Introduction The tautomerism in the Schiff base ligands plays an important role for distinguishing their photochromic and thermochromic characteristics [1–3]. It has been proposed that molecules showing thermochromism are planer, while those showing photochromism are non-planer [4], both appearances being associated with a proton transfer [5]. In conclusion, it is evident that a closely related phenomenon of interest is the possibility of tautomeric isomerism in orthohydroxy Schiff bases. In particular, we are interested in the study of 3-methoxysalicylaldehyde. Therefore the structures of this kind of compounds, which are showed as tautomeric form, are relevant due to the possibility of finding them in the solid state or in solution as keto-amine or phenol-imine forms. In the solid state, salicylaldimine compounds tend to form two (NÁÁÁH–O or N–HÁÁÁO) types of hydrogen bonding, respectively [6]. In many cases in solution, both types of hydrogen bonds have been observed indicating enol-imine, O–HÁÁÁN, keto-amine, OÁÁÁH–N tau- tomerism [7–17]. Knowing the structures of free Schiff bases in solution and in the solid state is important in view of the intramolecular hydrogen bonding and comparison with the structure of their complexes. In this study, we have synthesized new Schiff base and investigated by using elemental analysis, MS, IR, 1 H NMR, 13 C NMR, HETCOR, UV–Visible and X-ray crystallo- graphic techniques in order to study the hydrogen bonding and tautomeric equilibrium in both the solution and solid states (Scheme 1). Experimental Reagents and Techniques The 1 H and 13 C NMR spectra were recorded on a Bruker AVANCE DPX NMR spectrometer operating at 400 and 101.6 MHz. Infrared absorption spectra were obtained from a Perkin Elmer BX II spectrometer in KBr discs and M. Yıldız(&) Á D. Erdener Department of Chemistry, Faculty of Science and Arts, C ¸ anakkale Onsekiz Mart University, 17100 C ¸ anakkale, Turkey e-mail: myildiz@comu.edu.tr H. U ¨ nver Department of Physics, Faculty of Science, Ankara University, 06100 Tandog ˘an, Ankara, Turkey N. O. _ Iskeleli Department of Physics, Faculty of Science and Arts, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey 123 J Chem Crystallogr (2010) 40:691–695 DOI 10.1007/s10870-010-9723-9