New perspectives on calcium environments in inorganic materials containing calcium–oxygen bonds: A combined computational–experimental 43Ca NMR approach

The potential of a combined experimental–computational 43Ca solid state NMR approach for the structural analysis of different families of inorganic compounds (calcium phosphates, silicates, aluminates and borates) has been investigated. Natural-abundance 43Ca NMR data of six crystalline calcium phosphates is reported. DFT periodic calculations of 43Ca NMR parameters of an extensive number of Ca–O inorganic species have been performed, showing that the isotropic chemical shift of calcium can accurately be predicted. A strong dependence of the isotropic chemical shift on the average Ca⋯O bond distance and on the nature of the associated oxoanion is found.