PMR studies of molecular motions, phase transitions and quantum tunnelling in $NH_{4}$$SnCl_{3}$ and $N(CH_{3})$$_{4}$$SnCl_{3}$

Molecular reorientation and low temperature relaxation effects of NH4+ ion and the effect of CH3 substitution (in place of H) are investigated by proton spin lattice relaxation time (T-1) measurements at 10 MHz in NH4SnCl3 and N(CH3)(4)SnCl3 in the temperature range 4.2 K upto the melting points of the compounds (approximate to 440 K). Phase transitions around 360 K in NH4SnCl3 and around 361 and 116 K in N(CH3)(4)SnCl3 have been observed. In NH4SnCl3, the high temperature minimum at 330.5 K is attributed to the translational diffusion of the NH4+ ions, while the other T-1 minima at 103.5, 60 and 50 K are ascribed to the reorientations of the NH4+ ion about the C-2 and C-3 axes. The low temperature minimum at 13.5 K is attributed to rotational tunnelling of the NH4+ ions. In N(CH3)(4)SnCl3, in addition to the high temperature minima at 212.2 and 182.6 K due to N(CH3)(4) tumbling and CH3 reorientation, a temperature independent T-1 behaviour between 83 and 31 K is observed, below which T-1 decreases and tends to go through a minimum around 5 K. This low temperature minimum is attributed to rotational tunnelling of the CH3 groups. The motional parameters and tunnel frequencies are estimated