The proton spin-lattice relaxation time (T,) has been measured in methylammonium hexabromoplumbate, (CH,NH3),PbBr6, in the range 77-4503 and tetramethylammonium ("MA) hexachloroselenate, [N(CH,),I2SeCI6 in the range 77-430K In (CH3NH3)*PbBr,, TI shows a slope change at 415K, a minimum at 215K, and a discontinuous jump at 167K In [N(CH,)&SeCl6, TI shows a slope change at 340K and goes through a narrow symmetric minimum at 194K. Further, it exhibits a shoulder-like structure at 106K and goes through a broad minimum at 85K. Motional parameters such as activation energy and preexponential factor have been evaluated for the reorientational motion of CH,-NH, groups and the TMA ion in different phases.

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