CRYSTAL-STRUCTURE AND INVESTIGATION OF PHASE-TRANSITIONS IN DI(TETRAETHYLAMMONIUM)PENTACHLOROANTIMONATE(III) [N(C2H5)(4)]2SBCL5

The investigation of phase transitions in [N(C2H5)(4)]2SbCl5 was carried out in the temperature range 100-400 K by the DSC method and by temperature dependencies of lattice parameters. The presence of two phase transitions at 218 K from monoclinic to orthorhombic, of second order, and at 347 K from orthorhombic to tetragonal, of first order, was revealed. The crystal structures of [N(C2H5)(4)]2SbCl5 at 298 K and at 353 K were determined. At 298 K [N(C2H5)(4)]2SbCl5 crystallizes in an orthorhombic Pcnn space group with a = 14.271 (4), b = 14.173 (4), c = 12.745 (2) Angstrom, V = 2578 Angstrom(3), Z = 4. The anionic sublattice consists of isolated SbCl52- units. The antimony atom has square pyramidal co-ordination with stereochemically active lone pairs of electrons. It has 4 Sb-Cl contacts in the 2.598-2.605 Angstrom range and one is equal to 2.346 Angstrom. One of two crystallographically inequivalent tetraethylammonium cations is disordered. The disorder is realized by presence of two positions for all methylene carbon atoms (CH2) with the occupancy factor equal to 0.5. The transition at 347 K to P4/mnc space group (a = 10.138(3), c = 12.816(3) Angstrom, V = 1317 Angstrom(3), Z = 2) was attributed to triggering of overall rotation of the second tetraethylammonium cation.