Rb<sub>3</sub>Ti<sub>3</sub>(P<sub>4</sub>S<sub>13</sub>)(PS<sub>4</sub>)<sub>3</sub> and Cs<sub>2</sub>Ti<sub>2</sub>(P<sub>2</sub>S<sub>8</sub>)(PS<sub>4</sub>)<sub>2</sub>: Two Polar Titanium Thiophosphates with Complex One-Dimensional Tunnels
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The reactions of Ti with in situ formed polythiophosphate fluxes of A2S3 (A = Rb, Cs), P2S5, and S at 500 °C result in the formation of two new quaternary titanium thiophosphates with compositions Rb3Ti3(P4S13)(PS4)3 (1) and Cs2Ti2(P2S8)(PS4)2 (2). Rb3Ti3(P4S13)(PS4)3 (1) crystallizes in the chiral hexagonal space group P63 (No. 173) with lattice parameters a = 18.2475(9) Å, c = 6.8687(3) Å, V = 1980.7(2) Å3, Z = 2. Cs2Ti2(P2S8)(PS4)2 (2) crystallizes in the noncentrosymmetric monoclinic space group Cc (No. 9) with a = 21.9709(14) Å, b = 6.9093(3) Å, c = 17.1489(10) Å, β = 98.79(1)°, V = 2572.7(2) Å3, Z = 4. In the structure of 1 TiS6 octahedra, three [PS4] tetrahedra, and the hitherto unknown [P4S13]6- anion are joined to form two different types of helical chains. These chains are connected yielding two different helical tunnels being directed along [001]. The tunnels are occupied by the Rb+ ions. The [P4S13]6- anion is generated by three [PS4] tetrahedra sharing corners with one [PS4] group in the center of the starlike anion. The P atoms of the three [PS4] tetrahedra attached to the central [PS4] group define an equilateral triangle. The [P4S13]6- anion may be regarded as a new member of the [PnS3n+1](n+2)- series. The structure of Cs2Ti2(P2S8)(PS4)2 (2) consists of the one-dimensional polar tunnels containing the Cs+ cations. The rare [P2S8]4- anion which is composed of two [PS4] tetrahedra joined by a S22- anion is a fundamental building unit in the structure of 2. One-dimensional undulated chains being directed along [100] are joined by [PS4] tetrahedra to form the three-dimensional network with polar tunnels running along [010]. The compounds are characterized with IR, Raman spectroscopy, and UV/vis diffuse reflectance spectroscopy.
