On the Enclathration of NaB(OH)₄ in the β-Cages of Sodalite: Crystallization Kinetics and Crystal Structure

Abstract

The hydrothermal formation of sodium hydroxyborate enclathrated sodalite synthesized from an initial ternary mixture of mullite, cristobalite and corundum has been investigated. Depending on temperature and pressure the compound Na7.5[AlSiO4]6[B(OH)4]1.5 · 2H2O could be synthesized in form of polycrystalline powder as well as in form of single crystals. The kinetics of the sodalite growth could be determined at 423 K and 473 K. 29Si-and 27Al MAS NMR was shown to be the preferred method to describe the conversion into sodalite quantitatively. Evidence for the first formation of polycrystalline sodalite has been found after the total dissolution of mullite and cristobalite. Single crystal X-ray diffraction data were used for the structure determination and refinement. The position and orientation of the hydroxyborate anions within the sodalite's /β-cages could only be found in the course of a "rigid body" refinement with constraints for the B(OH)4 tetrahedron. The boron atoms are located in an off-centre position within the sodalite cages. One out of the four oxygen atoms of the hydroxyborate group is positioned near the centre of a face of the sodium tetrahedron, whereas the three remaining oxygen atoms are near to the middle of its edges.

Structure, Vibrational Spectra and 11B-NMR Chemical Shift of Na8[AlSiO4]6(B(OH)4)2: Comparison of Theory and Experiment

“…The positions of the hydrogen atoms are not given in the experimental reference (cf. Tables S1 and ). , Therefore, standard values were assumed for initial O–H distances and B–O–H angles. A B–O distance of 1.48 Å, an O–H distance of 0.95 Å, and an O–B–O angle of 109.47° were set.…”

“… Experimentally, NaB­(OH) 4 -SOD has been identified as an intermediate product using 11 B-NMR spectroscopy. We compare our calculations to experimental IR, Raman, and 11 B-NMR spectra of directly synthesized NaB­(OH) 4 -SOD. − …”

“…NaB­(OH) 4 -SOD could be synthesized as a micro crystalline powder as well as larger single crystals. The structure has been solved using X-ray powder diffraction (XRD). , The cubic phase of NaB­(OH) 4 -SOD crystallizes at 295 K in space group (SG) P 4̅3 n with a lattice constant of a = 9.024 Å and a chemical composition of Na 7.6 [AlSiO 4 ] 6 (B­(OH) 4 ) 1.7 ·1.9 H 2 O (cf. Table S1).…”

“…Table S1). Since XRD cannot locate the hydrogen positions, vibration spectroscopy can be employed to gain information on the molecular structure of the B­(OH) 4 – ions. The measured IR vibrational spectrum of NaB­(OH) 4 -SOD can be separated into five significant regions.…”

Enclosure of Sodium Tetrahydroborate (NaBH4) in Solidified Aluminosilicate Gels and Microporous Crystalline Solids for Fuel Processing

“…Those guests are enclathrated during synthesis according to the chlathralite like properties of sodalites [46]. As known for other salt-filled sodalites the thermal reactivity of the enclathrated guests can differ from the behaviour of the pure salt according to special interactions of the guest-complex with the sodalite host-framework [47][48][49][50]. The toc-unit of the sodalite structure is a common building unit in other zeolites like LTA, LSX, X and Y.…”