Hydrogen bonding Part 57. Stoichiometry and IR spectra of the lower hydrates of N, N'-dimethyltriethylenediammonium, decamethonium, hexamethonium, and (attempted) N, N, N', N'-tetramethylpiperazinium hydroxides

We have examined the lower hydroxide hydrates of the dipositive quaternary ammonium ions N, N'-dimethyltriethylenediammonium (DMTED ²⁺), decamethonium (DMO ²⁺), hexamethonium (HMO ²⁺), and (attempted) N, N, N', N'-tetramethylpiperazinium (TMP ²⁺). TMP(OH) ₂ cannot be prepared; the cation is destroyed by concentrated aqueous OH ^- through E ₂ reactions. Since TMPF ₂·2H ₂O can be prepared, this demonstrates the greater facility of OH ^- over F ^- in such eliminations. DMTED(OH) ₂ forms a hexahydrate (OH ^-·3H ₂O) and a tetrahydrate (OH ^-·2H ₂O), DMO(OH) ₂ forms a hexahydrate and a dihydrate (OH ^-·H ₂O), and HMO(OH) ₂ forms a hexahydrate, a trihydrate (OH ^-·1.5H ₂O), a dihydrate, and possibly a fourth hydrate, HMO(OH) ₂·4.5H ₂O. The two hydroxide hydrates of DMTED(OH) ₂ give poorly resolved IR spectra which shows that free (not hydrogen bond donor) OH ^- is present in the tetrahydrate and H ₂O…HOH…OH ₂ bridges are present in both. The four hydroxide hydrates of HMO(OH) ₂ all contain very tightly bound H ₂O with no H ₂O…HOH…OH ₂ bridges. Free OH ^- is present in all four hydrates. The hexahydrate appears to contain a water—hydroxide structure similar to that found in tetraethylammonium hydroxide trihydrate, while the trihydrate shows a modified form of this structure. The IR spectrum of the dihydrate is consonant with the presence of planar (H ₂O·OH ^-) ₂ clusters. The hexahydrate of DMO(OH) ₂ has a generic framework clathrate spectrum, while the dihydrate has spectral properties similar to those of HMO(OH) ₂·2H ₂O.