期刊
AMERICAN MINERALOGIST
卷 97, 期 11-12, 页码 1858-1865出版社
MINERALOGICAL SOC AMER
DOI: 10.2138/am.2012.4020
关键词
Borate dimorphs; saline lakes in Tibet; B-11 NMR; Mg-25 NMR; solid-state NMR; ultrahigh field NMR; ab initio calculations; FC LAPW; NMR crystallography
资金
- One Hundred People Plan, Chinese Academy of Sciences
- Canada Foundation for Innovation
- Natural Sciences and Engineering Research Council of Canada [PGSD3]
- Government of Manitoba
- NSFC [21174039]
- Ontario Innovation Trust
- Recherche Quebec
- National Research Council Canada
- Bruker BioSpin
- Natural Sciences and Engineering Research Council of Canada (NSERC)
Borate minerals composed of [B phi(3)] triangles and/or [B phi(4)] tetrahedra (phi = O or OH) commonly exhibit complex polymerizations to form diverse polyanion groups. High-resolution solid-state magic angle spinning (MAS) B-11 and Mg-25 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, [MgB3O3(OH)(5)center dot 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 B-11 and Mg-25 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.
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