Synthesis, Structure, and Properties of Cs4Th4P4Se26:  A Quaternary Thorium Selenophosphate Containing the (P2Se9)6- Anion

• Published in: Inorganic chemistry Vol. 40; no. 19; pp. 4871 - 4875
• Main Authors: Briggs Piccoli, Paula M, Abney, Kent D, Schoonover, Jon D, Dorhout, Peter K
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10-09-2001
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic001103l

Orange crystals of Cs4Th4P4Se26 were grown from the reaction of 232Th and P in a Cs2Se3/Se molten salt flux at 750 °C. Cs4Th4P4Se26 crystallizes in the orthorhombic space group Pbca with the unit cell parameters:  a = 12.0130(6), b = 14.5747(7), c = 27.134(1) Å; Z = 8. The compound exhibits a three-dimensional structure, consisting of dimeric [Th2Se13] polyhedral units. The two crystallographically independent, nine-coordinate, bicapped trigonal prismatic thorium atoms share a triangular face to form the dimer, and each dimer edge-shares two selenium atoms with two other dimers to form kinked chains along the [010] direction. While this structure shares features of the previously reported Rb4U4P4Se26, including phosphorus in the 5+ oxidation state, careful inspection of the structure reveals that the selenophosphate anion that knits the structure together in three directions in both compounds is a unique (P2Se9)6- anion. The formula may be described best as [Cs2Th2(P2Se9)(Se2)2]2. The (P2Se9)6- anion features a nearly linear Se−Se−Se backbone with an angle of 171° and Se−Se distances that are approximately 0.2−0.3 Å longer than the typical single Se−Se bond. Magnetic studies confirm that this phase contains Th(IV). Raman data for this compound is reported, and structural comparisons will be drawn to its uranium analogue, Rb4U4P4Se26.