HYDROGEN-BONDING .49. IR AND THERMODYNAMIC STUDY OF THE HALIDE HYDRATES OF THE N,N'-DIMETHYLTRIETHYLENEDIAMMONIUM AND N,N,N',N'-TETRAMETHYLPIPERAZINIUM DICATIONS

We have studied the crystalline lower hydrates of N,N'-dimethyltriethy lenediammonium (DMTED2+) and N,N,N',N'-tetramethylpiperazinium (TMP2+) halides. The first hydrates to separate from aqueous solutions of DMT ED2+ iodide, bromide and chloride are dihydrates, which are formally h alide monohydrates. The iodide and bromide dihydrates show IR spectra assigned to extended linear rather than planar cyclic cluster HOH ... X-hydrogen bonding. The chloride shows the characteristic IR spectrum of a planar C2h(H2O.Cl-)2 cluster below about 26-degrees-C, and a line ar-type spectrum above this temperature. Equilibrium vapor pressure st udies show that the bromide forms both a dihydrate and a monohydrate, with normal DELTAH(diss)0. values of 10.00 and 13.37 kcal mol-1 respec tively. The DELTAH(diss)0 value for DMTED2+ chloride dihydrate below 2 6-degrees-C is abnormally high; this is ascribed to a positive lattice enthalpy change on dissociation. There is evidence for a chloride ses quihydrate with a normal DELTAH(diss)0 of 17.37 kcal mol-1 per mol H2O lost, but no evidence for a stable monohydrate. DMTED2+ fluoride form s a clathrate hydrate with 4.5 mol eq H2O and a dihydrate containing p lanar (H2O.F-)2 clusters. TMP2+ iodide and bromide are very insoluble in H2O and do not appear to form discrete hydrates. TMP2+ chloride for ms a monohydrate of the linear type with a rather high DELTAH(diss)0 o f 27.22 kcal mol-1. TMP2+ fluoride forms three hydrates with 6.0, 4.0 and 2.0 H2O respectively. IR spectra show that the tetrahydrate has a water-fluoride structure similar to that in tetraethylammonium fluorid e dihydrate, while the dihydrate contains planar (H2O.F-)2 clusters.