NQR, NMR and crystal structure studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH2)(3)](2)HgBr4 has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) angstrom, 8 = 111.67(3)degrees, and Z = 4. The crystal consists of planar [C(NH2)(3)](+) and distorted tetrahedral [HgBr4](2-) ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr4](2-) ion. In accordance with the crystal structure, two Br-81 NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH2)(3)](2)Hgl(4) yielded four (127)l NQR lines ascribable to m = +/- 1/2 <-> +/- 3/2 transitions, indicating that its crystal structure is different from the bromide complex. The H-1 NMR T-1 measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C-3 reorientations of the planar [C(NH2)(3)](+) ions gave the activation energies of 29.8 W mol(-1) for the bromide, and 30.2 and 40.0 kJ mol(-1) for the iodide.