Multinuclear Magnetic Resonance Investigation of Crystalline Alkali Molybdates

Abstract

A variety of crystalline alkali molybdate phases are characterized by (23)Na, (133)Cs, and (95)Mo magic-angle-spinning nuclear magnetic resonance (MAS NMR) to provide spectroscopic handles for studies of devitrification products in borosilicate nuclear waste glasses. The NMR parameters obtained from line-shape simulations are plotted as a function of various structural parameters to discern trends that may prove useful in the determination of unknown phases. These are applied to Cs3Na(MoO4)2, the most common precipitate found in cesium- and molybdenum-bearing model nuclear waste glasses, the crystal structure of which has not yet been determined, to provide structural constraints that may guide the refinement of powder X-ray diffraction data.

133Cs and 23Na MAS NMR Spectroscopy of Molybdate Crystallization in Model Nuclear Glasses

“…The site‐specific nature of high‐resolution NMR provides additional information about the identities of the devitrification products formed with different Mo‐loading levels and quench rates. With reference to peak assignments drawn from previous work, the 133 Cs MAS NMR data reveal that the dominant phases are CsNaMoO 4 ·2H 2 O (−70 ppm), Cs 3 Na(MoO 4 ) 2 (161, −144 ppm), and Cs 2 Mo 2 O 7 (22, 9, −14, −56 ppm), with several unidentified peaks (69, 47, −9, −78 ppm) which may belong to Cs molybdate phase(s) not yet characterized. CsNaMoO 4 ·2H 2 O is the most populous compound appearing in the 133 Cs MAS NMR spectra and is prominent also in the 23 Na MAS NMR data (Fig.…”

“…Spectra are referenced to 1 M NaCl (0 ppm). Using the previously documented unique NMR parameters for molybdate crystallization products, individual simulated subspectra were summed to fit the experimental spectra of the final materials, providing both identification and quantification of devitrification products. Quantitative peak intensities were obtained by spectral deconvolution of all transitions for 133 Cs NMR and for the central transition only for 23 Na NMR.…”

Recent progress in solid‐state nuclear magnetic resonance of half‐integer spin low‐γ quadrupolar nuclei applied to inorganic materials

“…[225] Reproduced from the reference with permission of the copyright holder T A B L E 1 1 A compilation of some experimentally determined 95 Mo NMR interaction parameters from crystalline inorganic materials since previous studies [3,14] Compound δ iso (ppm) C Q (MHz) η Q Comments Ref. [235] [232] ‡ [233] −26.0 (0. favoured for solid-state NMR observation because of its much smaller second-order quadrupolar broadening and higher receptivity (Table 1). Molybdenum has several technological materials applications, particularly in the field of catalysis.…”

“…It was demonstrated C Q is particularly sensitive to the Mo-O bond lengths and asymmetry around molybdenum, and this information was used to inform an NMR crystallography approach for Cs 3 Na(MoO 4 ) 2 . [235] The multinuclear NMR crystallography study of ZrMgMo 3 O 12 [131] included 95 Mo MAS NMR where three distinct molybdenum sites were observed, two of which have very similar NMR Note: Table S6 lists where CS interaction parameters have been experimentally determined. For the collection of molybdates reported in [232] some have additional reports in either [233] ( ‡) or [235] ( ‡ ‡)).…”

“…[235] The multinuclear NMR crystallography study of ZrMgMo 3 O 12 [131] included 95 Mo MAS NMR where three distinct molybdenum sites were observed, two of which have very similar NMR Note: Table S6 lists where CS interaction parameters have been experimentally determined. For the collection of molybdates reported in [232] some have additional reports in either [233] ( ‡) or [235] ( ‡ ‡)).…”