Hydrogen bonding Part 51. Thermodynamic, IR, and solubility studies of the iodide hydrates of N-methylhexamethylenetetramine cation, N-methylquinuclidinium ion, N-methyltriethylenediamine cation, hexamethonium ion, and N, N′-dimethyltriethylene-diammonium ion; evidence for a possible (H 2O·I −) 2 planar cluster

Abstract

We have carried out dissociation vapor pressure measurements on N-methylhexamethylenetetramine cation iodide monohydrate, N-methylquinuclidinium iodide monohydrate and hemihydrate, N-methyltriethylenediamine cation iodide monohydrate and hemihydrate, N, N′-dimethyltriethylenediammonium iodide monohydrate and hexamethonium iodide dihydrate and monohydrate. Six of these hydrates have similar values for Δ H° dis with an average of 10.2 kcal mol −1 per mol of H 2O lost, or a minimum value of about 5.1 kcal mol −1 per HOH ⋯ I − hydrogen bond.broken. N-methylquinuclidinium and N-methyltriethylenediamine cation iodide hemihydrates have essentially identical Δ H° dis values of 15.8 kcal mol −1, or 7.9 kcal mol −1 per HOH ⋯ I − hydrogen bond. These two hemihydrates also have similar and much higher values of Δ S° dis than the other hydrates, and their IR spectra suggest that they may contain Type I planar (H 2O·I −) 2 cluster ions. The IR spectra of all of the other iodide hydrates studied show Type II extended linear HOH ⋯ I − hydrogen bonding. The solubilities of quaternary ammonium iodides in H 2O vary over an extremely large range, even for cations of similar size and charge. Possible reasons for these solubility effects are discussed.