HYDROGEN-BONDING .58. INFRARED STUDY OF THE DECAMETHONIUM HALIDE DIHYDRATES, IDENTIFICATION OF AN UNEQUIVOCAL C-2H(H2O.I-)2 CLUSTER, AND ANOVERVIEW OF QUATERNARY AMMONIUM HALIDE MONOHYDRATE STRUCTURE

We have determined the infrared spectra of the dihydrates of decametho nium iodide. bromide, chloride, and fluoride. Comparison with compound s of known structure demonstrates that all four dihydrates, which are halide ion monohydrates, contain planar C2h (H2O.X-)2 monohydrate clus ters. This is the first clear and unequivocal evidence we have obtaine d for a C2h (H2O.I-)2 Cluster. The fluoride also forms a single higher hydrate with 4.5 H2O; the iodide, bromide, and chloride do not form h igher hydrates. It is likely, by analogy with hexamethonium halides, t hat these latter three halides form monohydrates (halide ion hemihydra tes); however, this possibility was not investigated. Trends in the na ture of halide monohydrate structure are summarized for a number of qu aternary ammonium halides that we have investigated.