TETRAGUANIDIUM HEXABROMOCADMATE, [C(NH2)3]4[CDBR6] - CRYSTAL-STRUCTURE AND BROMINE NUCLEAR-QUADRUPOLE RESONANCE

The Br-79, Br-81 NQR spectra of tetraguanidinium hexabromocadmate, [C(NH2)3]4[CdBr6] have been studied as a function of temperature from 77 K to 390 K and the crystal structure of the compound was determined at room temperature. The title compound crystallizes monoclinic, P2(1)/c, with four formula units in the unit cell, a = 839.2(3) pm, b = 1895.8 (6) pm, c = 1527.4(5) pm, beta = 108.14(1)-degrees. The anion [CdBr6]4- is an isolated octahedron, with bond lengths 275 less-than-or-equal-to d (Cd - Br)/pm less-than-or-equal-to 281, and bond angles 88 less-than-or-equal-to (Br-Cd-Br)/-degrees less-than-or-equal-to 95, slightly distorted by hydrogen bonds N-H ... Br. The Br-81 NQR sextet, in dependence from temperature, shows positive and negative temperature coefficients. At 77 K the Br-81 NQR frequencies have been found between 42.42 MHz and 31.99 MHz; the Br-79 NQR at the frequencies expected from the nuclear quadrupole moment ratio Q(Br-79)/Q(Br-81). Relations between the Br-81 NQR spectrum, the crystal structure, and the hydrogen bonds are discussed.