On the crystal structure of the vaterite polymorph of CaCO3: a calcium-43 solid-state NMR and computational assessment.

摘要: The vaterite polymorph of CaCO3 has puzzled crystallographers for decades in part due to difficulties obtaining single crystals. multiple proposed structures the are assessed using a combined (43)Ca solid-state nuclear magnetic resonance (SSNMR) spectroscopic and computational approach. A combination improved experimental methods, along with calibrated chemical shift scale quadrupole moment, allow insights relative our earlier work (Bryce et al., J. Am. Chem. Soc. 2008, 130, 9282). Here, we synthesize isotopically-enriched sample perform high-resolution quadrupolar SSNMR experiments including magic-angle spinning (MAS), double-rotation (DOR), multiple-quantum (MQ) MAS at field strengths 9.4 21.1T. We identify one crystallographically unique Ca(2+) site slight distribution both shifts parameters. Both electric gradient tensor isotropic compared those calculated gauge-including projector-augmented-wave (GIPAW) DFT method an attempt model that best represents crystal structure vaterite. Simulations DOR NMR spectra based on parameters computed total 18 structural models us distinguish between these models. Among 18, P3221 C2 provide simulated diffractograms agreement all data.