Crystal structure and vibrational spectra of the 1:1 and 1:2 complexes of pyridine betaine with pentachlorophenol

Crystalline complexes of pyridine betaine (PBET) with pentachlorophenol (PCP) have been synthesized and characterized by X-ray diffraction and FTIR spectroscopy: PBET .(PCP)(2) (space group P (1) over bar with a=8.748(4), b=11.855(6), c=13.221(6) Angstrom, alpha=66.70(5), beta=74.06(4), gamma=77.97(4)degrees), PBET . PCP . H2O (space group P2(1)/c with a=8.616(2), b=27.610(6), c=7.0760(10), a=90, beta=104.82(3), gamma=90 degrees), PBET . PCP . HOMe and PBET . PCP. In PBET .(PCP)(2) the betaine carboxylate group is linked to two phenol molecules by hydrogen bonds of 2.582(6) and 2.611(6) Angstrom. In PBET . PCP . H2O a centrosymmetric molecular complex is formed by two formula units, where two carboxylate groups are bridged by two water molecules to form an eight membered ring with four O-H ... O hydrogen bonds of 2.703(4) and 2.715(5) Angstrom, respectively; each water molecule, in rum, forms a hydrogen bond of 2.580(4) Angstrom to PCP. The IR spectrum of PBET . PCP . HOMe is consonant with a structure in which the betaine carboxylate group accepts both PCP and HOMe. (C) 1997 Elsevier Science B.V.