Thermal, FTIR and XRD study on some 1:1 molecular compounds of theophylline

Thermal stability and structural features of three newly synthesized 1:1 lattice compounds of theophylline (th) with ethylenediamine carbamate (enCO(2)), 1,10-phenanthroline (phen), and 5-sulfosalicylic acid (sa-5-SO3H) have been studied in comparison with those of the theophylline compounds with ethanolamine (ea) and salicylic acid (sa). Simultaneous TG-DTA measurements, FTIR spectroscopy and X-ray diffraction have been carried out to get information on the various structural units of these solid inclusions, especially on the actual form (molecule, anion or cation) of theophylline moieties built in. Theophyllinate and theophyllinium ions have been found in the ethanolammonium-theophyllinate (1:1) (1, eaH(+).th(-)) and the theophyllinium salicylic acid 5-sulfonate monohydrate (1: 1: 1), (5, thH(+).saSO(3)(-).H2O), respectively. Whilst the 1: 1 complexes with 1,10-phenanthroline (2, th.phen), ethylenediamine carbamate (3, th.enCO(2)), and salicylic acid (4, th.sa) contain neutral theophylline moieties associated with H-bonds. In compound (3) the zwitterion of N-(2-ammonium-ethyl)carbamate (NH3+-CH2-CH2-NH-CO2-) is present.