Synthesis, crystal structure and molecular orbital investigation of the first platinum complex of piroxicam

Abstract

The first platinum complex [PtCl₂(dmso)(HL)] of the widely used anti-inflammatory drug piroxicam (HL = 4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide; dmso = dimethyl sulfoxide) was obtained from K₂[PtCl₄]. Its crystal structure reveals that the metal atom is linked to the pyridyl nitrogen atom. A Pt ⋯ H-N (amide) interaction is present and made possible by the orientation of the HL molecule which brings the N(amide)-H bond above the co-ordination plane and almost parallel to the N (pyridyl)–Pt vector. The amide hydrogen was located from the Fourier-difference-synthesis and its position refined. The Pt ⋯ H distance is 2.35 Å(0.25–0.55 Å shorter than the sum of the van der Waals radii), whereas the ν(N–H) vibration band is red-shifted by about 90 cm^–1 upon complexation. An extended-Hückel molecular orbital analysis revealed that a mixing of d_z²(Pt) and p_z[N(amide)] atomic orbitals occurs, whereas electrostatic Pt ⋯ H attractive forces can play a significant role.