Configuration determination for chiral and polar crystals by anisotropic NMR shift

Abstract

We propose a method to perform a configuration determination for chiral and/or polar crystals by utilizing anisotropy of NMR shift. The chirality (handedness) or polarity of a crystal, that is characterized by its sign, can be extracted from the asymmetric magnetic-field angle dependence of NMR shift in the appropriate plane, as the configuration is reflected in the off-diagonal components of the shift tensor. This method is applicable to the triclinic, monoclinic, and trigonal crystal structures among 230 crystallographic space groups, and the appropriate planes to extract the asymmetric field-angle dependence are tabulated for all relevant space groups. We discuss how to determine the appropriate plane, and to identify each contribution of twin domains, and so on, by using the specific examples of Te, IrSn$_{4}$ and RhSn$_{4}$, and the spontaneous symmetry-breaking phases of URhSn. We also argue that an absolute-configuration determination is also possible in accordance with the relation between chirality or polarity of crystal and the sign of the relevant off-diagonal component of the shift tensor, provided by theoretical evaluation of internal magnetic field from surrounding ions, and/or by experimental input on the shape of the asymmetric etch pit on the cleaved face of crystal.