2014
DOI: 10.1039/c4ce01749h
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Density functional theory study of the magnetic shielding mechanism for11B in pentaborate minerals: ulexite and probertite

Abstract: Nuclear magnetic resonance (NMR) parameters of 11 B in borates and borosilicates, unlike those of many other nuclei such as 29 Si and 27 Al, vary only in limited ranges for a given polyhedral geometry, but mechanisms for such insensitivity to local structural environments remain poorly understood. In this contribution, ulexite and probertite, with the IJ[B 5 O 6 IJOH) 6 ] 3− ) pentaborate polyanion as the fundamental building block, have been investigated in detail by ab initio theoretical calculations of the de… Show more

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Cited by 7 publications
(9 citation statements)
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“…Two approaches can be used to calculate isotropic chemical shifts (δ iso ) from the absolute magnetic shieldings (σ iso = (σ xx + σ yy + σ zz )/3, where σ ii represent the principal components of the shielding tensor) predicted by WIEN2k: (1) using a reference taken from an unconstrained (slope different from −1) linear fit of the calculated absolute shieldings, , and (2) scaling to the absolute magnetic shielding of a reference compound: δ iso = −(σ iso – σ ref ). In this study, we adopted the second approach with sassolite (triclinic H 3 BO 3 ) as the reference, which has a measured δ iso ( 11 B) = 19.61 ppm , and an average absolute magnetic shielding of 74.21 ppm calculated for its two [3] B sites.…”
Section: Materials and Methodologiesmentioning
confidence: 99%
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“…Two approaches can be used to calculate isotropic chemical shifts (δ iso ) from the absolute magnetic shieldings (σ iso = (σ xx + σ yy + σ zz )/3, where σ ii represent the principal components of the shielding tensor) predicted by WIEN2k: (1) using a reference taken from an unconstrained (slope different from −1) linear fit of the calculated absolute shieldings, , and (2) scaling to the absolute magnetic shielding of a reference compound: δ iso = −(σ iso – σ ref ). In this study, we adopted the second approach with sassolite (triclinic H 3 BO 3 ) as the reference, which has a measured δ iso ( 11 B) = 19.61 ppm , and an average absolute magnetic shielding of 74.21 ppm calculated for its two [3] B sites.…”
Section: Materials and Methodologiesmentioning
confidence: 99%
“…A notable deviation from the common [Bϕ 3 ] planar triangles and [Bϕ 4 ] tetrahedra is the presence of highly distorted, four-coordinated boron oxyanions, which contain three normal B–O bonds of ∼1.48 Å ,, and one anomalously long B–O bond from 1.54 to 1.69 Å. These boron oxyanions deviate significantly from the tetrahedral symmetry and are best described as approximate trigonal pyramids (hereafter denoted as [OBO 3 ]). ,, Previous solid-state 11 B nuclear magnetic resonance (NMR) studies ,, showed, on the one hand, that the [Bϕ 4 ] groups in borates are characterized by 11 B isotropic chemical shifts (δ iso ) close to 0 ppm and the nuclear quadrupole parameter C Q invariably less than 0.5 MHz, reflecting the approximately tetrathedral symmetry. The [Bϕ 3 ] groups, on the other hand, have a somewhat wide range of δ iso ( 11 B) values from 15 to 25 ppm, but the C Q ( 11 B) values are clustered around 2.5 MHz. ,, The δ iso ( 11 B) variations of the [Bϕ 3 ] groups in borates and borosilicates have been correlated with various structural characters of both the first and outer shells (e.g., FBBs, next-nearest-neighbor cations, hydrogen bonding, etc. ). However, the reported δ iso ( 11 B) values of four-coordinated boron oxyanions in borates vary by less than 2 ppm, ,,,,, making their NMR resolution difficult.…”
Section: Introductionmentioning
confidence: 99%
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“…The structural model built from X-ray diffraction results underwent a geometrical optimization prior to carrying out NMR calculations. In our previous borate studies, ,,,, this approach was necessary to improve the calculated results because it is difficult to accurately locate the positions of light elements such as H, B, and F, via X-ray diffraction. ,, As such, a comparison of the theoretically calculated NMR parameters (chemical shielding and EFG tensors) with the experimentally measured NMR parameters (δ iso , C Q , η) may provide refinements of the structural models obtained via diffraction methods.…”
Section: Theoretical Backgroundmentioning
confidence: 99%
“…Laskowski and Blaha developed another formalism to compute nuclear shielding tensors within the LAPW and APW+lo frameworks [13,14] (APW+lo approach uses local orbitals for an improved convergence according to the number of PWs). Although recent, the few applications of this formalism have demonstrated a result quality almost equivalent to that of GIPAW for various nuclei [13,14,15]. 93 Nb is a 9/2 spin nucleus with 100% natural abundance and a relatively large gyromagnetic ratio.…”
Section: Introductionmentioning
confidence: 96%