HYDROGEN-BONDING .48. IR AND THERMODYNAMIC STUDY OF THE LOWER HYDRATES OF N-METHYLQUINUCLIDINIUM IODIDE, BROMIDE, CHLORIDE, FLUORIDE, AND HYDROXIDE - EVIDENCE FOR A TEMPERATURE-DEPENDENT REARRANGEMENT OF HYDROGEN-BONDS IN THE CHLORIDE MONOHYDRATE

Below 28-degrees-C the IR spectrum of N-methylquinuclidinium chloride shows the characteristic absorptions of a C2h (H2O . Cl-)2 Planar clus ter; however, above this temperature this spectrum is replaced with an entirely different spectrum tentatively assigned to extended ''linear '' hydrogen bonding. The bromide and iodide show only the linear type of IR spectra. Dissociation vapor pressure measurements of the low tem perature form of the chloride give an unreasonably high value for DELT AH(dis)-degrees (27.56 kcal mol-1), while the high temperature form sh ows a normal value (14.70 kcal mol-1). The high value for the low temp erature form is ascribed to an unfavorable lattice enthalpy change. Th e bromide gives a normal DELTAH(dis)-degrees of 11.58 kcal mol-1. The first material to separate on dehydration of an aqueous fluoride solut ion is a pentahydrate; there is also a fluoride 3.50 H2O hydrate and a fluoride monohydrate. The IR spectrum of the fluoride monohydrate sup ports the presence of a C2h (H2O . F-)2 cluster similar to that found in tetramethylammonium fluoride monohydrate. N-Methylquinuclidinium hy droxide forms a dihydrate and a monohydrate; the monohydrate appears t o contain planar (H2O . OH-)2 clusters.