A unified ²³Na NMR chemical shift correlation with structural parameters in multicomponent silicate‐based glasses

Abstract

From a large ensemble of 34 silicate‐based glasses from the borosilicate, phosphosilicate, and borophosphosilicate systems that comprise either Na as a sole glass‐network modifier or when mixed with Ca, we established a good correlation between the 23Na average isotropic chemical shift (δ¯iso) and the average coordination number of Na and the mean Na–O distance. The latter parameters were obtained by atomistic molecular dynamics simulations. We also demonstrated that δ¯iso is essentially independent on the precise network forming (Si, B, P) species but depends primarily on the net molar fraction of Na and Ca, thereby offering a straightforward 23Na chemical shift prediction from the glass composition alone.

The Carbonate and Sodium Environments in Precipitated and Biomimetic Calcium Hydroxy-Carbonate Apatite Contrasted with Bone Mineral: Structural Insights from Solid-State NMR

“…The half-integer spin (S = 3/2) quadrupolar nature of 23 Na coupled with distributions of both isotropic chemical shifts and quadrupolar coupling constants (C Q = e 2 qQ/h) 114 render the NMR responses broad and featureless. 51,52,65 As noted previously, 63,65,115 the comparably Figure 10. 23 Na NMR spectra recorded at 14.1 T and 14.00 kHz MAS from the as-indicated samples of synthetic and biogenic HCA.…”

“…Figure displays the 23 Na MAS NMR spectra acquired at B 0 = 14.1 T and ν r = 14.00 kHz from the set of synthetic and biogenic HCA specimens. The half-integer spin ( S = 3/2) quadrupolar nature of 23 Na coupled with distributions of both isotropic chemical shifts and quadrupolar coupling constants ( C Q = e 2 qQ / h ) render the NMR responses broad and featureless. ,, As noted previously, ,, the comparably modest C Q values (see below) of the 23 Na sites in HCA implies that the chemical-shift distribution mainly governs the width of the near-Gaussian shaped 23 Na NMR peak from these structurally disordered CaP phases at B 0 = 14.1 T; see Figure . The 23 Na NMR parameters of each HCA structure were extracted by fitting numerically simulated MAS NMR spectra to the experimental counterpart of Figure using the Czjzek C Qη -distribution model and assuming one 23 Na site in the structure.…”

Correlating Sulfur Solubility with Short-to-Intermediate Range Ordering in the Structure of Borosilicate Glasses

“…Compared to the connectivity with trigonal B 3 units, linking to Si 4 units produces a shift toward more negative frequencies, whereas linking to anionic B 4 units produces a shift toward more positive values. Based on empirical chemical shift trends on sodium borosilicate glasses, as well as the whole body of structural information available in this system, − ,,,− we further infer that connectivity to other anionic species such as B 2 and Si 3 units will also produce chemical shift changes toward more positive values. In general, although a given B 4 unit may simultaneously participate in different linkages with varying numbers from one site to the next (e.g., B 4B 4 , B 1Si3B 4 , B 2Si2B 4 , etc.…”

Structural Role and Spatial Distribution of Carbonate Ions in Amorphous Calcium Phosphate

“…Whereas all ACP w specimens with carbonate contents up to 10 wt % manifest 23 Na NMR responses typical for 23 Na in structurally disordered environments (Figure ), ,, the 23 Na NMR spectrum from ACP14 merely suggests the presence of two Na-bearing CaP components: a broad and dominating resonance with (presumably) similar NMR characteristics as for the other ACP w samples, along with a significantly narrower component centered at δ Na max = −5.9 ppm (Table ) that reflects 23 Na sites in a markedly more ordered structure. We have no fully satisfactorily explanation for the origin of the latter: a 3QMAS , 23 Na NMR spectrum recorded at 14.1 T and 24.00 kHz MAS (not shown) only revealed the broad 23 Na NMR peak component, while the powder XRD pattern recorded from the ACP14 specimen after the NMR experimentation did not suggest any crystalline phase (Figure S2).…”