2013. 54, 2 – UDC 541.6:547.12:546.17:546.21 4-HYDROXY-2H-1,2-BENZOTHIAZINE-3-CARBOHYDRAZIDE 1,1-DIOXIDE-OXALOHYDRAZIDE (1:1): X-RAY STRUCTURE AND DFT CALCULATIONS M.N. Arshad1, O. ahin2, M. Zia-ur-Rehman3, I.U. Khan4 , A.M. Asiri1, H.M. Rafique 5 1Department of Chemistry & Center of Excellence for Advanced Materials Research (CEAMR) Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 2Scientific and Technological Research Application and Research Center, Sinop University, Sinop, Turkey E-mail: onurs@omu.edu.tr sity of the Punjab, Lahore, Pakistan Received November, 18, 2011 3Applied Chemistry Research Center, PCSIR, Laboratories Complex Ferozpur Road, Lahore, Pakistan 4Materials Chemistry Laboratory, Department of Chemistry, GC University, Lahore, Pakistan 5X-ray Diffraction and Crystallography Laboratory, Department of Physics, School of Physical Sciences, UniverRevised — June, 2, 2012 The title compound, 4-hydroxy-2H-1,2-benzothiazine-3-carbohydrazide 1,1-dioxide-oxalohydrazide (1:1), is determined using X-ray diffraction techniques and the molecular structure is also optimized at the B3LYP/6-31G(d,p) level using density functional theory (DFT). <...> The asymmetric unit consists of four independent molecules. <...> The oxalohydrazide molecules have the centre of symmetry at the mid-point of the central C—C bond. <...> Each thiazine ring adopts a half-chair conformation. <...> An extensive three-dimensional supramolecular network of N—H…N, N—H…O, C—H…O and O—H…O hydrogen bonds is responsible for crystal structure stabilization. <...> Keywords: X-ray diffraction analysis, benzothiazine, oxalohydrazide, DFT, Mulliken atomic charge, molecular electrostatic potential. <...> Synthesis and structural characterization of carbohydrazides and their derivatives is much focused in the recent literature due to their applications in biochemistry as well as in materials synthesis via complexation [ 1, 2 ]. <...> As part of a research program regarding the synthesis of new derivatives of benzothiazine 1,1-dioxides [ 9, 10 ], the synthesis and crystal structure of 4-hydroxy-2H-1,2-benzothiazine-3-carbohydrazide 1,1-dioxide-oxalohydrazide (1:1) is reported here. <...> The title compound was synthesized from commercially available saccharin, which was converted to methyl 4-hydroxy-2H-1,2-benzothiazine-3-carboxylate 1,1-dioxide by a reported procedure [ 11 ] and was subsequently subjected to hydrazinolysis in methanol along with equimolar dimethyl oxalate. <...> V, Е3 Z calc, g/cm3 T, K Radiation; y <...>