A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

作者：Widdifield Cory M; Bryce David L^*

来源：Canadian Journal of Chemistry, 2011, 89(7): 754-763.

DOI：10.1139/V11-009

• solid-state NMR
• chlorine
• (35)Cl
• (37)Cl
• (43)Ca
• CaCl(2)
• polymorphism
• hydrates
• C(Q)
• chemical shift anisotropy (CSA)
• electric field gradient

The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a (35/37)Cl and (43)Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl(2). The (35)Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl(2)center dot 2H(2)O. Chlorine-35 SSNMR spectra are also presented for CaCl(2)center dot 6H(2)O, and when taken in concert, the SSNMR observations for CaCl(2), CaCl(2)center dot 2H(2)O, and CaCl(2)center dot 6H(2)O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of delta(iso) decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl(2)center dot 2H(2)O, and to explore the isostructural relationship between CaCl(2) and CaBr(2). Finally, the (43)Ca CS tensor span is measured to be 31(5) ppm for anhydrous CaCl(2), which represents only the fifth CS tensor span measurement for calcium.

• 出版日期2011-7