BR-81 NQR AND CRYSTAL-STRUCTURE OF ETHYLAMMONIUM TRIBROMOMERCURATE (II), CH3CH2NH3HGBR3

The Br-81 NQR triplet spectrum of (CH3CH2NH)3+(HgBr3)- was measured in the range 77 K to near the m.p. (99 approximately 106-degrees-C). Nu1 decreases strongly with increasing temperature, exhibiting 136.784 MHz at 77 K and 128.129 MHz at 298 K. Nu2 decreases from 82.060 MHz at 77 K to 76.322 MHz at 298 K. Nu3 increases with temperature, showing nu3=81.292 MHz at 77 K and 84.903 MHz at 298 K. Replacement of the ammonium hydrogens by deuterium produces a negative shift of nu1 and positive ones of nu2 and nu3 at high temperatures. These shifts change with temperature from \approximately 0\ up to \approximately 200\ kHz. The crystal structure of the title compound was determined at room temperature: P2(1)/m, Z = 2, a = 1021.6(8) pm, b = 643.0(6) pm, c = 691.8(6) pm, beta = 96.96(4)-degrees. The coordination of the mercury atom by the bromines is trigonal bipyramidal; by formation of bridges Hg...Br...Hg by one of the three bromines (Br(2)) of the planar HgBr3- ions a double chain of trigonal bipyramids is formed, running along the b-axis of the crystal. Br(1) and Br(3) are single bonded to Hg. The hydrogen bonds NH...Br(2) and NH...Br(3) (twice), connect the Hg Br chains to planes lying parallel to the bc plane at x = 0. The relations between the Br-NQR spectrum and the structure are discussed.