Nuclear-resonance techniques are used to determine the magnetic and electric quadrupole interactions of the nuclei of all ions (except O 2−) in the two compounds. The magnetic behaviour of these compounds, including the direction of the spontaneous magnetization and the occurence of spontaneous magnetostriction effects in zero field below T c, is quite analogous to that observed for the isomorphous Rb and Cs compounds. In the paramagnetic state in an external field a finestructure on some of the chlorine resonance lines has been observed. Experimental results on the field and temperature dependence of these line splittings are given.