NQR, NMR and crystal structure studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH2)(3)](3)Sb2Br9 was determined at 143 K: monoclinic, space group C2/c, Z=4, a=15.695 (3), b=9.039(2), c=18.364(3) angstrom, beta=96.94(1)degrees. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb2Br93-) in which SbBr6 octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb2Br93-)(n) layer with statistical disorder, while the other situates between the layers without disorder. Three Br-81 NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the Br-81 NQR resonance lines Were subjected to fade-out at low temperatures. The temperature dependence curve of 1(H) NMR T-1 showed well defined two minima, which were explained by postulating the C-3 reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.