CRYSTAL-STRUCTURE AND INVESTIGATIONS OF PHASE-TRANSITIONS OF A NEW MEMBER OF THE FAMILY OF HALOGENOANTIMONATES - [C(NH2)(3)]2SBCL5-CENTER-DOT[C(NH2)(3)]CL

The room temperature structure of ([C(NH2)(3)]2SbCl5.[C(NH2)(3)]Cl) (GHCA) was solved. It crystallizes into the monoclinic P2(1)/c space group with a = 9.734(2), b = 21.865(4), c = 8.564(2), beta = 91.48(3), V = 1821, Z = 4, d(c) = 1.878, d(m) = 1.87(1). The structure consists of polyanionic (SbCl52-), chains built of deformed SbX(6)(3-) octahedra connected to each other by corners. The polyanionic chains, extended along the c axis, form cavities in which isolated chlorine ions Cl- are located. The guanidinium C(NH2)(3)(+) (Gu) cations are connected to chlorine atoms by rather weak N-H...Cl hydrogen bonds. The anionic sublattice of GHCA is compared, in a short review, with sublattices of other halogenoantimonates and bismuthates. The temperature X-ray scattering experiments were carried out to study the nature of phase transitions of GHCA. Temperature dependencies of lattice parameters between 100 K and 380 K were determined. The presence of three phase transitions at T-c1 = 146 K, T-c2 = 162 K and T-c3 = 370 K was confirmed. Discontinuous changes of lattice parameters corresponding to the first-order phase transitions were revealed at T-c1 and T-c3. The transition at T-c2 is of second order.