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Latent Porosity in Alkali-Metal M2B12F12 Salts: Structures and Rapid Room-Temperature Hydration/Dehydration Cycles



Dmitry V. Peryshkov, Eric V. Bukovsky, Matthew R. Lacroix, Hui Wu, Wei Zhou, W. Matthew Jones, Matic Lozinsek, Travis C. Folsom, D. Luke Heyliger, Terrence J. Udovic, Steven H. Strauss


Structures of the alkali metal hydrates Li2(H2O)4Z, LiK(H2O)4, Na2(H2O)3Z, and Rb2(H2O)2Z, unit cell parameters for Rb2Z and Rb2(H2O)2Z, and the DFT-optimized structures of K2Z, K2(H2O)2Z, Rb2Z, Rb2(H2O)2Z, Cs2Z, and Cs2(H2O)Z are reported (Z2- = B12F122-) and compared with previously reported X-ray structures of Na2(H2O)0,4Z, K2(H2O)0,2,4Z, and CsD2^(H2O)Z. Unusually rapid room-temperature hydration/dehydration cycles of several M2Z/M2(H2O^)nZ salt hydrate pairs, which were studied by isothermal gravimetry, are also reported. Finely ground samples of K2Z, Rb2Z, and Cs2Z, which are not microporous, exhibited latent porosity by undergoing hydration at 24-25 °C in the presence of 18 torr H2O(g) to K2(H2O)2Z, Rb2(H2O)2Z, and Cs2(H2O)Z in 18, 40, and 16 min, respectively. These hydrates were dehydrated at 24-25 Degree}C in dry N2 to the original anhydrous M2Z compounds in 61, 25, and 76 min, respectively (the exact times varies from sample to sample depending on particle size). The hydrate Na2(H2O)2Z also exhibited latent porosity by undergoing multiple 90 min cycles of hydration to Na2(H2O)3Z and dehydration back to Na2(H2O)2Z at 23 °C. For the K2Z, Rb2Z, and Cs2Z transformations, the maximum rate of hydration (rhmax) decreased, and the absolute value of the maximum rate of dehydration (rdmax) increased, as T increased. For K2Z - K2(H2O)2Z hydration/dehydration cycles with the same sample, the ration (rhmax)/(rddmax^) decreased 26 times over 8.6 °C, from 3.7 at 23.4 °C to 0.14 at 32.0 °C. For Rb2Z - Rb2(H2O)2Z cycles, (rhmax)/(rdmax) decreased from 0.88 at 23 °C to 0.23 at 27 °C/ For Cs2Z - Cs2(H2O)Z cycles, (rhmax)/(rdmax) decreased 20 times over 8 °C, from 6.7 at 24 °C to 0.34 at 32 °C. In addtion, the reversible substitution of D2O for H2O in fully hydrated Rb2(H2O)2Z in the presence of N2/16 torr D2O(g) was complete in only 60 min at 23 °C.
Inorganic Chemistry


alkali metal salts, B12F12, closo-dodecaborates, dehydration, hydrates, hydration, porosity, x-ray diffraction


Peryshkov, D. , Bukovsky, E. , Lacroix, M. , Wu, H. , Zhou, W. , Jones, W. , Lozinsek, M. , Folsom, T. , Heyliger, D. , Udovic, T. and Strauss, S. (2017), Latent Porosity in Alkali-Metal M<sub>2</sub>B<sub>12</sub>F<sub>12</sub> Salts: Structures and Rapid Room-Temperature Hydration/Dehydration Cycles, Inorganic Chemistry, [online], (Accessed December 1, 2023)
Created October 1, 2017, Updated October 12, 2021