Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations

Abstract

Borate minerals composed of [Bφ 3 ] triangles and/or [Bφ 4 ] tetrahedra (φ = O or OH) commonly exhibit complex polymerizations to form diverse polyanion groups. High-resolution solid-state magic angle spinning (MAS) 11 B and 25 Mg NMR spectroscopy at moderate to ultrahigh magnetic fields (9.4, 14.1, and 21.1 T) allows for very accurate NMR parameters to be obtained for the borate dimorphs, inderite, and kurnakovite, [MgB 3 O 3 (OH) 5 ·5H 2 O]. Improved agreement between experimental results and ab initio density functional theory (DFT) calculations using Full Potential Linear Augmented Plane Wave (FP LAPW) with WIEN2k validates the geometry optimization procedures for these minerals and permits refinements of the hydrogen positions relative to previous X-ray diffraction crystal structures. In particular, the optimized structures lead to significant improvements in the positions of the H atoms, suggesting that H atoms have significant effects on the 11 B and 25 Mg NMR parameters in inderite and kurnakovite. This study shows that combined high-resolution NMR spectroscopy and ab initio theoretical modeling provides an alternative method for the refinement of crystal structures, especially H positions.

Density functional theory study of the magnetic shielding mechanism for11B in pentaborate minerals: ulexite and probertite

“…4,5 As such, the popularity of DFT calculations has in recent years formed a link between NMR and crystallography, leading to the formalization of "NMR crystallography". [9][10][11][12][13] For example, high-resolution 11 B magic angle spinning (MAS) NMR spectra of borate minerals such as ulexite and probertite have been obtained at high and ultrahigh magnetic fields (14 and 21 T). 7,8 Due to recent advances in NMR techniques as well as progress in quantum mechanical theoretical calculations, interest in 11 B NMR for determination of local structural characteristics in borates has been rekindled.…”

“…3-6 11 B NMR parameters in borates and borosilicates, however, generally show limited variations and, hence, have been thought to be incapable of providing structural information beyond the first shell. [11][12][13] Although these borates with the ijB 5 O 6 IJOH) 6 ] 3− polyanion as the fundamental building block (FBB) (Fig. [9][10][11][12][13] For example, high-resolution 11 B magic angle spinning (MAS) NMR spectra of borate minerals such as ulexite and probertite have been obtained at high and ultrahigh magnetic fields (14 and 21 T).…”

“…[9][10][11][12][13] For example, high-resolution 11 B magic angle spinning (MAS) NMR spectra of borate minerals such as ulexite and probertite have been obtained at high and ultrahigh magnetic fields (14 and 21 T). [11][12][13] On the other hand, the 21 T spectra clearly resolve the two threefold-coordinated B ( [3] B) sites compared with their 14 T counterparts due to the reduction of second-order QI and therefore the full width at the higher field. 1) have three crystallographically distinct fourfold-coordinated B ( [4] B) sites, 14,15 their 11 B NMR spectra are characterized by a single broad resonance centered at~1 ppm in both fields of 14 and 21 T, with the latter having a hint of asymmetry in the [4] B peak attributable to the greater chemical shift dispersion at the higher field.…”

Hydrogen bonding system in euchroite, Cu2(AsO4)(OH)(H2O)3: low-temperature crystal-structure refinement and solid-state density functional theory modeling

“…It is worth noting here that theoretical studies of hydrogen bonding can provide important information with a higher degree of precision then that available from X-ray diffraction measurements, especially for minerals that do not form high-quality crystals (Milman and Winkler 2001;Zhou et al 2012). It is also the task of the present work to compare the results of experimental and theoretical studies of the hydrogen bonding system in euchroite in order to investigate their complementarity and reliability.…”

Effect of Dissolved Silica on Immobilization of Boron by Magnesium Oxide

“…In general, the chemical shift for the tetra-coordinated boron resonance reflects the distribution of the second-nearest neighbor cation (B or Si). [29], borosilicate glass [30] and tourmaline [31] have been reported as 1.29, 0.0, and −0.1 ppm, respectively. Angeli et al [30] and Lin-Shu et al [32] have been reported that tetra-coordinated boron in borosilicate glass has a chemical shift near 0 ppm and a structure of BO-B*-(OSi) 3 .…”