K₃(Sc_0.875Nb_0.125)Nb₂O₉H_1.75: a new scandium niobate with a unique cage structure

Abstract

Potassium scandium niobate hydroxide, K(3)(Sc(0.875)Nb(0.125))Nb(2)O(9)H(1.75), is a new scandium niobate with a unique cage structure. The structure contains two non-equivalent K(+) sites (3m and 6m2 site symmetry), one disordered Sc(3+)/Nb(5+) site (3m site symmetry), one Nb(5+) site (3m site symmetry), two O(2-) sites (m and mm2 site symmetry) and one H(+) site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube-like cage built of seven octahedra, while the other K atom is encapsulated by an eight-membered trigonal face-bicapped prism. The cages form sheets that extend along the ab plane.

Hydrogen bond-assisted crystallization: structure, growth and characterization of a new mixed-anion transition metal fluoride Na3NH4(TiF6)(SO4)·H2O

“…To the best of our knowledge, NTS is the first mixed-anion TM fluoride containing [MF 6 ] xÀ anions. Furthermore, unlike the typical type of mixed-anion TM fluorides whose different types of anions were connected via bridging oxygen atoms to form 0D large limited polyanions, 14 1D infinite chains, 27b 2D layers, 30 or a 3D network, 16 NTS features isolated [TiF 6 ] 2À and [SO 4 ] 2À anions, and can be described as a new type of mixed-anion TM fluoride.…”

“…Such a synthetic route is widely applied in the fields of molecular sieves (aluminophosphate 5 and aluminosilicates 6 ), catalysts (polyoxometalates 7 ), nonlinear optical materials (borophosphates, 8 borosilicates, 9 borocarbonates 10 and boronitrates 11 ), etc. Based on these ideas, a lot of efforts were made to apply these design routes to TM fluoride systems and a series of mixed-anion TM fluorides 12 were obtained successively, for instance, KCu(CO 3 )F 13 with mixed [CuO 2 F 2 ] 4À and [CO 3 ] 2À anions, K 16 [Ti 10 (PO 4 ) 4 F 44 ] 14 with mixed [TiOF 5 ] 3À , [TiO 2 F 4 ] 4À , [TiO 3 F 3 ] 5À and [PO 4 ] 3À anions, Tavorite-type fluorides LiM(SO 4 )F (M = Co, Ni) 15 with mixed [MO 4 F 2 ] 8À and [SO4] 2À anions, Ba 2 [Ti 2 F 2 O 2 (Si 2 O 7 )] 16 with mixed [TiO 5 F] 7À and [SiO 4 ] 4À anions, etc. These compounds feature the connection of different types of anions via bridging oxygens and can be viewed as typical mixed-anion TM fluorides.…”

Hydrothermal Chemistry and Growth of Fergusonite-type RENbO4 (RE = La–Lu, Y) Single Crystals and New Niobate Hydroxides

“…The alkali rare earth niobate hydroxides are a relatively limited class of compounds. To our knowledge, the only other reported single crystal structure in this class that exhibits a unique alkali metal site and a coordinated hydroxide group is K 3 (Sc 0.875 Nb 0.125 )­Nb 2 O 7 (OH) 1.75 , reported previously by our group . In that structure, some of the niobium ions were substitutionally disordered with scandium ions, and the blue color of the crystals was indicative of some reduction of Nb 5+ to Nb 3+ (compensated by a partial vacancy of the OH site).…”

“…To our knowledge, the only other reported single crystal structure in this class that exhibits a unique alkali metal site and a coordinated hydroxide group is K 3 (Sc 0.875 Nb 0.125 )Nb 2 O 7 (OH) 1.75 , reported previously by our group. 39 In that structure, some of the niobium ions were substitutionally disordered with scandium ions, and the blue color of the crystals was indicative of some reduction of Nb 5+ to Nb 3+ (compensated by a partial vacancy of the OH site). The compounds K 3 YNb 2 O 7 (OH) 2 and K 3 LuNb 2 O 7 (OH) 2 are isostructural with that potassium scandium niobate hydroxide, but extend our understanding of the structure type in several ways.…”