Structure and IR Vibrational Spectra of Na₈[AlSiO₄]₆(BH₄)₂: Comparison of Theory and Experiment

Abstract

The structure and IR vibrational spectra of tetrahydroborate sodalite (Na8[AlSiO4]6(BH4)2) were calculated using density functional theory (DFT) methods. The calculations, performed at the GGA hybrid DFT level yield a close agreement with XRD refinements of the structure and allow interpretation of observed bands of the enclosed BH4(–) and the framework and, in particular, a verification of hydrogen positions (Buhl, J.-C., Gesing, T. M., and Rüscher, C. H. Microporous Mesoporous Mater. 2005, 80, 57−63). In a first step, different basis sets and functionals were tested on NaBH4 and Na8[AlSiO4]6Cl2. We show that accurate treatment of B–H stretching modes requires anharmonic corrections, while lattice vibrations are well described within the harmonic approximation.

Lattice Vibrations to Identify the Li/Na Ratio in Li x Na2−x Ti6O13 (x = 0…2)

“…2a and c. framework is often not affected by such an exchange [31,32]. Thus, for a detailed analysis of the Li/Na ratio, the spectral region up to 350 cm Figure 4 shows the theoretical prediction of Raman modes for Na 2 Ti 6 O 13 (Figure 4a) and Li 2 Ti 6 O 13 (Figure 4b tions between theory and experiment are in the range observed for other compounds in a previous study on Na 8 [AlSiO 4 ] 6 (BH 4 ) 2 [27]. Small deviations could arise from the fact that a powder is measured and its surface is not perfectly plain.…”

“…Standard basis sets of triple-zeta (Ti) and triple-zeta plus polarization (Na, Li, O) quality were taken from the CRYSTAL website [25]. The generalized gradient approximation (GGA) functional according to Perdew, Burke and Ernzerhof (PBE) [26] was applied as it has provided accurate results for spectroscopic properties in a previous study [27] and has been tested for Raman intensities in CRYSTAL14. For Li 2 Ti 6 O 13 and Na 2 Ti 6 O 13 the crystal lattice parameters for calculation were taken from experiment [13] and kept fixed while the atomic positions were fully relaxed in order to obtain a stationary point for the vibration analysis.…”

Energetics of Salt-Bearing Sodalites, Na8Al6Si6O24X2 (X = SO4, ReO4, Cl, I): A Treatment Option for Pertechnetate-Enriched Nuclear Waste Streams

“…Since the late 1970s it has been recognized that the vibrational features of sodalites vary with cell parameters, which are strongly influenced by the size of the anion hosted within the sodalite β-cage. , These structure–spectra relationships have since been highlighted many times within the literature − ,− and continue to provide insight into sodalite materials with novel compositions. ,− While sodalite vibrational features are generally compared directly against cell parameters determined using XRD, it is also possible to relate these features to the ionic radius of the anion for sodalites with identical cation composition. The frequencies for the major Raman and FTIR peaks as a function of the anion radius are shown in Figure , where it is observed that the two major Raman and four major infrared peak frequencies display a strong linear relationship with anion radius ( R 2 values all >0.9).…”

Identification of Intermediates during the Hydration of Na8[AlSiO4]6(BH4)2: A Combined Theoretical and Experimental Approach

“…Therefore, in the present work we compare experimental IR spectra and 11 B NMR chemical shifts with calculated results obtained at DFT level for selected intercalated species. The starting material BH 4 –SOD was synthesized as described in our previous study . In the present study the same theoretical setup was used that has been recently applied to BH 4 –SOD and B­(OH) 4 –SOD .…”