Synthesis of platinum(II)–piroxicam compounds. Crystal structure of trans-dichloro(η2-ethene)(piroxicam)platinum(II) ‡

Autor: Renzo Cini, Francesco Berrettini, Daniela Di Leo
Rok vydání: 1998
Předmět:
Zdroj: Journal of the Chemical Society, Dalton Transactions. :1993-2000
ISSN: 1364-5447
0300-9246
DOI: 10.1039/a709280f
Popis: The reaction of Zeise’s salt K[PtCl3(η2-C2H4)]·H2O and piroxicam [4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide, Hpir] in ethanol at room temperature produced crystalline trans-[PtCl2(η2-C2H4)(Hpir)]·0.5C2H5OH 1·0.5C2H5OH. Crystals of 1·0.5C6H6 obtained from a benzene solution of 1·0.5C2H5OH were studied via X-ray diffraction techniques. The neutral piroxicam ligand co-ordinates through pyridyl N(1′) and has an EZE conformation typical for the neutral form. The pyridyl system of piroxicam is significantly twisted (20°) around the C(2′)–N(16) vector with respect to the rest of the ligand molecule. A comparison with previously investigated metal–piroxicam complexes shows that the C(2′)–N(16) bond is ‘more flexible’ than the N(16)–C(14), C(14)–C(13) and C(3)–C(4) ones. The co-ordination environment has the usual square-planar geometry for platinum(II) complexes if the middle point of the ethene C–C bond (CM) is considered. The Pt–N bond [2.093(6) A] is longer than most PtII–N(sp2) bond distances, because of the high trans influence of ethene. There is an attractive interaction between the H(N) amide atom and the Pt. The 1H NMR spectrum of 1·0.5C2H5OH recorded from CDCl3 solution at 22 °C shows that the signal of H(N) undergoes a shift to lower field as much as 1.98 ppm upon complexation; no 1H–195Pt coupling could be revealed. The 1H (ethene)–195Pt coupling constant is 64 Hz and spectra recorded in the temperature range –50 to 40 °C show that a fast rotation of co-ordinated ethene around the Pt–CM vector takes place at 22 °C. The reaction of potassium tetrachloroplatinate(II) with piroxicam in water at pH 8.5 gives a yellow precipitate whose formula is Pt(pir)2·3H2O, 2·3H2O. 1H NMR data from CDCl3 solutions at 22 °C are in agreement with the presence of two isomers which have been tentatively assigned to cis- and trans-[Pt(pir)2] complexes of N(1′)–O(15) chelating piroxicamate.
Databáze: OpenAIRE
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