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 a ir and moisture. It crystallizes in the orthorhombic system, space gro up 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 su ch a way that the sulfur atoms form columns of distorted trigonal S-6 prisms along [001]. The columns are condensed via common edges to puck ered 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 squa re(1)(tet). TlEu[PS4] is a centrosymmetric variant of the TlSn[PS4] st ructure type (space group Pna2(1)). The vibrational spectrum is in acc ordance with the X-ray crystal structure, the Raman and infrared vibra tions are assigned on the basis of [PS4](3-) units with C-2v symmetry.