Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

摘要: Calcium is the 5th most abundant element on earth, and found in numerous biological tissues, proteins, materials, increasingly catalysts. However, due to a number of unfavourable nuclear properties, such as low magnetogyric ratio, very natural abundance, its electric quadrupole moment, development solid-state 43Ca NMR has been constrained relative similar nuclides. In this study, 12 commonly-available calcium compounds are analyzed via43Ca information which may be obtained by measurement both field gradient (EFG) chemical shift tensors (the latter extremely rare with only handful literature examples) discussed. Combined density functional theory (DFT) computations, ‘tensor interplay’ is, for first time 43Ca, illustrated diagnostic distinguishing polymorphs (e.g., formate), degree hydration CaCl2·2H2O tartrate tetrahydrate). For Ca(OH)2, we outline example 1H cross-polarization sample at abundance 43Ca. Using prior knowledge relationship between isotropic quadrupolar coupling constant (CQ) coordination number, postulate levulinate dihydrate, does not have known crystal structure. Natural samples CaCO3 (aragonite polymorph) used show that synthetic structure present nature. Gauge-including projector augmented-wave (GIPAW) DFT computations using accepted structures many these systems generally result calculated tensor parameters good agreement experimental observations. This combination measurements GIPAW ultimately allows us establish clear correlations various observables selected structural parameters, unit cell dimensions average Ca–O bond distances.