COMPARATIVE SPECTRAL AND STRUCTURAL-ANALY SES OF TISOPURINE AND ITS PROTONATED FORM 4-THIOXO-2,5H,7H(-PYRAZOLO[3,4-D]PYRIMIDINIUM CHLORIDE IN THE CRYSTALLINE STATE())

The molecular structure of the protonated form of tisopurine, 4-thioxo -2,5H,7H(+)-pyrazolo [3,4-d] pyrimidinium chloride, C5H5N4SCl (TPH+Cl- ), was determined by x-ray diffraction methods. The crystals are monoc linic, space group P2(1)/a, with a = 7.332(5), b = 10.911(9) and c = 9 .423(8) Angstrom, beta = 104.99(6)degrees, V = 728(2) Angstrom(3) and Z = 4. The structure was refined to R = 0.043. TPH+Cl- was found to be in the thione form with hydrogen atoms bonded to the N-1, N-3 and N-8 atoms. A comparison between tisopurine base in the monoclinic form (f orm I) and the chloride (TPH+Cl-) is proposed. The Raman and infrared spectra of the crystalline powders of the tisopurine bases [monoclinic (form I) and orthorhombic (form II)] and deuterated (TD) and chloride (TPH+Cl-) forms were investigated from 4600 to 20 cm(-1). The two pol ymorphic base forms of the tisopurine were identified by spectral anal ysis. The assignments of the fundamental vibrations involved in interm olecular H-bonds as N-H(D)... N and N+-H(D)... Cl- are discussed. (C) 1998 John Wiley & Sons, Ltd.