Cation effects in nuclear quadrupole resonance spectroscopy

A method for calculating the lattice contribution to the field gradient at a point in a crystal is outlined and is applied to the calculation of the chlorine N.Q.R. frequency difference between K 2 PtCl 6 and Cs 2 PtCl 6 . Closer agreement with the experimental value is obtained as compared with a previous calculation but complete agreement is not obtained using any reasonable value for the quadrupole antishielding factor. The importance of the lattice contribution to the individual N.Q.R. frequencies is also discussed.