Structures of two co-crystals of pyridine betaine with l(+)-tartaric acid

Crystal structure of pyridine betaine with l(+)-tartaric acid, crystallized from methanol, is determined by X-ray diffraction methods. The crystal 1, at the 2:1 ratio of pyridine betaine and tartaric acid, is orthorhombic, space group P21212 and contains disordered methanol guest molecules. Tartaric acid is bonded to two pyridine betaine molecules by the COOH···OOC hydrogen bonds of 2.443(2) Å. Complex 1 is situated at the special position, on twofold axis. After recrystallization of 1 from butanol crystal 2 is formed at the 3:1 ratio of pyridine betaine and semi-tartrate anion, without solvent molecules. Crystal 2 is monoclinic, space group P21 and shows an ionic character. Semi-tartrate anions form infinite chains and each anion is joined to one pyridine betaine molecule by the O–H···OOC hydrogen bonds, formed between two hydroxyl groups of semi-tartrate anion and the carboxylate oxygen atoms of pyridine betaine, of 2.772(2) and 2.738(2) Å. The counter-ion appears as a homoconjugated cation of two pyridine betaine molecules linked by the O·H·O hydrogen bond of 2.481(2) Å, using the proton transferred form tartaric acid. The FTIR and NMR spectra of 1 and 2 complexes are different. The 1H NMR spectrum in D2O confirms the presence of methanol in 1.