IONIC MOTION OF PHENETHYLAMMONIUM ION [C6H5CH2CH2NH3](2)PBX4 (X=CL, BR, I) AS STUDIED BY H-1-NMR

The temperature dependences at 110 to 400 K of the H-1 spin-lattice re laxation time (T-1) of the phenethylammonium ion in phenethylammonium lead(II) halides, [C6H5CH2CH2NH3](2)PbX4 (X=Cl, Br, I), revealed that this ion slows reorientation of the NH3 moiety around the three-fold a xis and torsional motion of the alkyl chain (CH2CH2). Below room tempe rature, the chloride and the bromide yielded two minima of H-1 T-1 ori ginating from NH3 reorientation, whereas the iodide yielded only one m inimum. These findings indicate that there are two kinds of NH3 sites in the chloride and bromide but only one in the iodide. The T-1 minimu m observed below room temperature gave similar activation energies of the NH3 reorientation, E-a = 15.7, 15.1 and 15.5 kJ mol(-1) for the ch loride, bromide and iodide, respectively, suggesting that the correspo nding NH3 groups are located at similar environments. Above room tempe rature, the T-1 minimum in the chloride and bromide gave larger E-a va lues of the NH3 reorientation: E-a = 23.6 and 20.2 kJ mol(-1) for the chloride and bromide, respectively. These findings suggest that the NH 3 groups form stronger hydrogen bonding with halogen atoms (N-H...X). Furthermore, the amplitude of the CH2CH2 motion is discussed, using th e two sites jump model. The activation energies for the CH2CH2 motion in these compounds are almost equal (E-a = 29.1, 30.0 and 28.2 kJ mol( -1) for the chloride. bromide and iodide. respectively), but that the torsional angles become Larger in the order iodide much less than brom ide < chloride.