CRYSTAL-STRUCTURE AND VIBRATIONAL-SPECTRUM OF THALLIUM(I) EUROPIUM(II) TETRATHIOPHOSPHATE(V), TLEU[PS4]

TLEu[PS4] was synthesized from the elements in a sealed quartz ampoule at 1150 K. The compound forms transparent orange needles, stable in air and moisture. It crystallizes in the orthorhombic system, space group Pnma (No. 62), with cell dimensions a = 12.157(2), b = 6.581(1), c = 8.802(2) Angstrom, Z = 4. The crystal structure consists of discrete [PS4](3-) anions irderconnected by Tl+ and Eu2+. The tetrahedral [PS4](3-) groups are slightly distorted with P-S bond lengths in the range, 2.028 to 2.043 Angstrom. These tetrahedral anions are arranged in such a way that the sulfur atoms form columns of distorted trigonal S-6 prisms along [001]. The columns are condensed via common edges to puckered layers parallel to (100). The interlayer region consists of empty distorted half-cubes and tetrahedral holes, half of them filled by P atoms. The trigonal prisms in the columns are centered alternately by Tl+ and Eu2+. In this way, the structure can be regarded as an ordered superstructure of the InNi2 type, where half of the tetrahedral holes are filled by phosphorus atoms: InInNi4 square(2)(tet) = TlEuS4P square(1)(tet). TlEu[PS4] is a centrosymmetric variant of the TlSn[PS4] structure type (space group Pna2(1)). The vibrational spectrum is in accordance with the X-ray crystal structure, the Raman and infrared vibrations are assigned on the basis of [PS4](3-) units with C-2v symmetry.