¹¹B Chemical Shift Anisotropies in Borates from ¹¹B MAS, MQMAS, and Single-Crystal NMR Spectroscopy

Abstract

11B chemical shift anisotropies (CSAs) have been obtained for tetrahedral and trigonal boron sites in tetraphenyl borates, datolite (CaBSiO4(OH)), danburite (CaB2Si2O8), colemanite (CaB3O4(OH)3·H2O), borax (Na2B4O7·10H2O), and Li2B4O7 from solid-state 11B NMR spectra recorded at 14.1 T. These parameters along with 11B quadrupole couplings and the relative orientation of the quadrupole coupling and CSA tensors have been determined from either the manifold of spinning sidebands observed for the satellite transitions in 11B MAS NMR spectra or single-crystal NMR spectra of the satellite transitions. Furthermore, the potential of the MQMAS experiment for determination of small 11B CSAs is illustrated for the trigonal boron site in Li2B4O7. The 11B single-crystal NMR spectra of the satellite transitions are strongly dominated by the first-order quadrupolar interaction, which may prevent a direct determination of small CSAs. However, an improved precision of the CSA parameters and the Euler angles, describing the relative orientation of the CSA and quadrupole coupling tensors, are achieved from analysis of rotation plots for the sum frequencies of the m = 1/2 ↔ m = 3/2 and m = −/2 ↔ m = −3/2 transitions, which are influenced only by the first-order CSA and the second-order quadrupolar interactions. The 11B CSA parameters determined in this work show that tetrahedrally coordinated boron in borates possess shift anisotropies (δσ = δiso − δ zz ) of magnitude |δσ| less than 10 ppm.

Correlations between 11B NMR parameters and structural characters in borate and borosilicate minerals investigated by high-resolution MAS NMR and ab initio calculations

“…2, 3, 4, 5), which also is verified by the consistency between the spectra acquired at 14 and 21 T. In addition, our NMR parameters are in high congruence with available results obtained by single-crystal NMR experiments for minerals such as colemanite (Hansen et al 2004(Hansen et al , 2005. The accuracy and confidence are also highlighted by the consistency between theoretically calculated and NMR experimental results (Table 2).…”

“…These polyhedra in borates and borosilicates commonly show complex polymerization to give rise to diverse fundamental building blocks (FBB;Clark 1959;Christ and Clark 1977;Burns 1995;Hawthorne et al 1996;Grice et al 1999;Yuan and Xue 2007;Filatov and Bubnova 2008). Although 11 B is a suitable isotope for NMR experiments due to its natural abundance and intermediate quadrupolar interaction (QI), the d iso values of 11 B for borates and borosilicates vary only in narrow ranges (i.e., 17.0-20.0 ppm for [3] B and -0.5 to 2.0 ppm for [4] B, Kroeker and Stebbins 2001;Turner et al 1986;Hansen et al 2004Hansen et al , 2005. This is in contrast to the large ranges of 29 Si d values in silicates, where adding one bridging oxygen atom (BO) or the next-nearest-neighbor (nnn) Si can shield 29 Si by more than 10 ppm.…”

Effects of T2-relaxation in MAS NMR spectra of the satellite transitions for quadrupolar nuclei: a 27Al MAS and single-crystal NMR study of alum KAl(SO4)2·12H2O

“…Finally, we note that a 11 B MAS NMR spectrum of NH 4 B(C 6 H 5 ) 4 , recently recorded in our laboratory [24], indicates a variation in T 2 values for the two 11 B (I = 3/2) satellite transitions for this compound, although the effect on the spectrum is less apparent when compared to the 27 Al MAS NMR spectra of alum in Figs. 1 and 2.…”

Contribution of first-principles calculations to multinuclear NMR analysis of borosilicate glasses

“…The number of CSA values reported in literature for borates [48,71] is so far insufficient for a systematic assessment of the GIPAW method. Additionally, at the magnetic field used in this work (11.72T), a homonuclear 11 B-11 B dipolar broadening of the same order of MAS and static spectra of boron atoms in three-membered rings ( [3] B ring species) are also displayed in dashed lines.…”