Hydrogen bonding Part 56. IR spectra and stoichiometry of the hydrates of N-methyltriethylenediamine cation halides and hydroxide

We have prepared the N-methyltriethylenediamine cation bromide hemihydrate, chloride monohydrate, fluoride monohydrate and hydroxide dihydrate. These salts show no propensity to form higher crystalline hydrates. There is no indication of H ₂O to cage nitrogen hydrogen bonding, as was previously observed for the iodide monohydrate. Combination of IR and thermodynamic information demonstrates that the bromide and iodide hemihydrates have the same water—halide structure. Since the bromide hemihydrate does not contain (H ₂O·Br ^-) ₂ clusters, we conclude that the iodide hemihydrate does not contain (H ₂O·I ^-) ₂ clusters, as previously postulated. Both the bromide and iodide hemihydrates are presumed to contain C_2v X ^- ⋯ HOH ⋯ X ^- groupings. The chloride and fluoride monohydrates contain planar (H ₂O·X ^-) ₂ clusters. The hydroxide monohydrate could not be prepared; the dihydrate decomposes slowly on further dehydration, presumably by S _N2 attack of OH ^- on the methyl group.