Dinuclear Face‐Sharing Bi‐octahedral Tungsten(VI) Core and Unusual Thermal Behavior in Complex Th Tungstates

Abstract

Two new thorium tungstates A6 Th6 (WO4 )14 O (A=K and Rb) were synthesized by high-temperature solid-state reactions. The structures of both phases are based on a rare dinuclear confacial bi-octahedral [W2 O9 ](6-) core, encapsulated in a [Th6 W7 O46 (W2 O9 )](32-) cage showing a cross-section geometry similar to a six-leafed lily. The adjacent cages are connected in two dimensional layers by WO4 tetrahedral linkers. Due to the dissimilarities in mutual orientations of adjacent layers in these two structures, K6 Th6 (WO4 )14 O crystallizes in space group of R32 while Rb6 Th6 (WO4 )14 O stabilizes in P$\bar 6$2c. The high-temperature phase transition was observed in Rb6 Th6 (WO4 )14 O and investigated using high-temperature PXRD technique. The results demonstrate a very unusual thermal behavior of this compound. The Raman and IR spectra of both phases were analyzed with respect to their complex structures.

Crystal Growth and Structure Analysis of Ce18W10O57: A Complex Oxide Containing Tungsten in an Unusual Trigonal Prismatic Coordination Environment

“…Ternary oxides such as CaWO 4 , which adopt the common Scheelite structure, exhibit the tetrahedral coordination environment, whereas Ln 6 WO 12 (Ln = Y, Ho, Er, Yb), La 2 W 2 O 9 (Ln = La, Pr, Nd, Sm, Gd), M 2 (UO 2 )­(W 2 O 8 ) (M = Na, K), Ba 3 WO 6 , Ba 2 WO 5 , Ba 3 W 2 O 9 , Ba 3 MWO 6 (M= Mg, Zn), and Ba 3 Fe 2 WO 9 all contain tungsten in an octahedral coordination environment. The latter coordination environment is rather common in tungstates and is found as isolated, ,, corner-shared, ,− and edge-shared , motifs; very few examples, such as Ba 3 W 2 O 9 , A 6 Th 6 (WO 4 ) 14 O (A = K and Rb), and La 18 W 10 O 57 , contain tungsten in a face-shared coordination environment due to the electrostatic repulsion between the highly charged metal centers. , An exception to this generalization is found for cases where tungsten is present as W­(III), W­(IV), or W­(V), , which sufficiently reduces the tungsten–tungsten repulsion and where potential metal–metal bonding interactions can stabilize the arrangement. In a small number of reported structures, tungsten is found in other less common coordination environments that include distorted cubic coordination in Y 2 WO 6 , trigonal bipyramidal coordination in Ca 3 WO 5 Cl 2 , seven-coordinated WO 7 polyhedra in Re 10 W 22 O 81 (Ce, Nd), , and a trigonal prismatic arrangement in the oxychloride Ln 3 WO 6 Cl 3 (Ln = La, Pr). , …”

Structural Variations in Complex Sodium Thorium Arsenates

“…Such a subtle change in the ratio results in a completely different structure of Na 2 Th(AsO 4 ) 2 , which is a 3D framework structure built from the ThO 8 polyhedra and AsO 4 tetrahedra. (1) and Na 2 Th(PO 4 ) 2 significantly differ. There are five sodium atom, seven arsenic atoms and four thorium atoms in the asymmetric unit of 1, whereas, Na 2 Th(PO 4 ) 2 has four unique sodium, four phosphorus, and two thorium atoms in the asymmetric unit.…”

“…It is noteworthy that the AsO 4 groups use all of its O atoms in bonding with Th atoms and play the role of tetradentate units with Q 4 , Q 22 , or Q 21 coordination types, where Q denotes denticity and the superscripts -number of vertex-, edge-, and face-sharing (the latter are absent in these cases) neighboring ThO n polyhedra. [50] (1). A graph representation of the tetranuclear FBBs in 1 (b), Rb 7 Th 2 P 6 Se 21 [45] (c), and Cs 4 Th 2 P 6 S 18 [45] (d).…”

“…The structural chemistry of actinides is very rich due to the complex electronic structure of these elements and consequent variety of oxidation states and diversity of the actinide coordination geometries. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thorium, whose redox chemistry, unlike most other actinides, is dominated by the +4 oxidation state, shows highly variable coordination numbers (CN) in inorganic materials ranging from 6 to 15. [17][18][19][20][21][22] Coordination chemistry of Th(IV) is similar to those of highly radiotoxic and long-live transuranic element in the oxidation state +4 (e.g.…”

Thorium Chemistry in Oxo-Tellurium System under Extreme Conditions

“…The Th(1)−O bond distances range from 2.207(9) to 2.640(9) Å, and are slightly longer than those of Th(2), which range from 2.254(9) to 2.630(10) Å, but are still comparable with those in other thorium compounds. 33,46,47 These two ThO 9 polyhedra are connected with each other through common edges, resulting in corrugated Th layers that stretch along the bc plane (Figure 1b). It is of interest that such layers with the same topological linkages are also observed in a series of lanthanide-bearing tellurium compounds, M 2 Te 4 O 11 (M = La−Nd and Sm−Yb).…”