Structures of the alkali-metal hydrates Li(HO)Z, LiK(HO)Z, Na(HO)Z, and Rb(HO)Z, unit cell parameters for RbZ and Rb(HO)Z, and the density functional theory (DFT)-optimized structures of KZ, K(HO)Z, RbZ, Rb(HO)Z, CsZ, and Cs(HO)Z are reported (Z = BF) and compared with previously reported X-ray structures of Na(HO)Z, K(HO)Z, and Cs(HO)Z. Unusually rapid room-temperature hydration/dehydration cycles of several MZ/M(HO)Z salt hydrate pairs, which were studied by isothermal gravimetry, are also reported. Finely ground samples of KZ, RbZ, and CsZ, which are not microporous, exhibited latent porosity by undergoing hydration at 24-25 °C in the presence of 18 Torr of HO(g) to K(HO)Z, Rb(HO)Z, and Cs(HO)Z in 18, 40, and 16 min, respectively. These hydrates were dehydrated at 24-25 °C in dry N to the original anhydrous MZ compounds in 61, 25, and 76 min, respectively (the exact times varied from sample to sample depending on the particle size). The hydrate Na(HO)Z also exhibited latent porosity by undergoing multiple 90 min cycles of hydration to Na(HO)Z and dehydration back to Na(HO)Z at 23 °C. For the KZ, RbZ, and CsZ transformations, the maximum rate of hydration (rh) decreased, and the absolute value of the maximum rate of dehydration (rd) increased, as T increased. For KZ ↔ K(HO)Z hydration/dehydration cycles with the same sample, the ratio rh/rd decreased 26 times over 8.6 °C, from 3.7 at 23.4 °C to 0.14 at 32.0 °C. For RbZ ↔ Rb(HO)Z cycles, rh/rd decreased from 0.88 at 23 °C to 0.23 at 27 °C. For CsZ ↔ Cs(HO)Z cycles, rh/rd decreased 20 times over 8 °C, from 6.7 at 24 °C to 0.34 at 32 °C. In addition, the reversible substitution of DO for HO in fully hydrated Rb(HO)Z in the presence of N/16 Torr of DO(g) was complete in only 60 min at 23 °C.

No abstract

The Boron-Chalcogen Mixture method was used to obtain single crystals of the previously extremely difficult to synthesize lanthanide orthothioborates to investigate their structures and their structurally connected optical behavior, such...

Eight M­(H2O) n (Z) salt hydrates were characterized by single-crystal X-ray diffraction (Z2– = B12F12 2–): M = Ca, Sr, n = 7; M = Mg, Co, Ni, Zn, n = 6; M = Ba, n = 4, 5. Weak O–H···F hydrogen bonding between the M­(H2O) n 2+ cations and Z2– resulted in room-temperature Fourier transform infrared (FTIR) spectra having sharp ν­(OH) bands, with full widths at half max of 10–30 cm–1, which are much more narrow than ν­(OH) bands in room temperature FTIR spectra of most salt hydrates. Clearly resolved νasym(OH/OD) and νsym(OH/OD) bands with Δν­(OH) as small as 17 cm–1 and Δν­(OD) as small as 11 cm–1 were observed (Δν­(OX) = νasym(OX) – νsym(OX)). The isomorphic hexahydrates (R3̅) have two fac-(H2O)3 sets of H2O ligands and nearly octahedral coordination spheres. They exhibited four resolvable ν­(OH) bands, one νasym(OH)/νsym(OH) pair for H2O ligands with longer O­(H)···F distances and one νasym(OH)/νsym(OH) pair for H2O ligands with shorter O­(H)···F distances. The ν­(OH) bands for the three H2O molecules with shorter, slightly stronger O­(H)···F hydrogen bonds were broader, more intense, and red-shifted by ca. 25 cm–1 relative to the bands for the three other H2O molecules, the first time that such small differences in relatively weak O­(H)···F hydrogen bonds in the same crystalline hexahydrate have resulted in observable IR spectroscopic differences at room temperature. For the first time room temperature ν­(OH) values for salt hexahydrates showed the monotonic progression Mg2+ > Co2+ > Ni2+ > Zn2+, essentially the same progression as the pK a values for these metal ions in aqueous solution. A further manifestation of the weak O–H···F hydrogen bonding in these hydrates is the latent porosity exhibited by Ba­(H2O)5,8(Z), Sr­(H2O) n,m (Z), and Ca­(H2O)4,6(Z). Finally, the H2O/D2O exchange reaction Co­(D2O)6(Z) → Co­(H2O)6(Z) was ca. 50% complete in 1 h at 50 °C in N2/17 Torr H2O­(g).

Infrared spectra were recorded of organic and inorganic solids with a Fourier transform spectrometer built to operate with a photothermal beam deflection detector. No sample preparation or cells per se is needed to examine milligram quantities of powder. The total absence of sample-containing devices makes it possible to examine portions of the surfaces of objects which are very large in size. Sample heating may occur, so that care must be taken with heat-sensitive materials.

No abstract

No abstract

No abstract