Synthesis and crystal structure of a new microporous silicate with a mixed octahedral-tetrahedral framework: Cs₃ScSi₈O₁₉

Abstract

a new, unusual microporous compound, Cs 3 ScSi 8 O 19 , was synthesized as colourless plates from a CsF-MoO 3 flux. The crystal structure was determined from single-crystal X-ray diffraction data (Mo-Ka radiation, CCD area detector). The compound is orthorhombic, space group Pnma, with a = 11.286(2), b = 7.033(1), c = 26.714(5) Å , and Z = 4 (R1(F) = 2.6% and wR2 all (F 2 ) = 7.3%, using 3066 'observed' reflections with F o > 4s(F o )). The crystal structure of Cs 3 ScSi 8 O 19 represents a new microporous framework structure type ('MCV-1'), and the compound is exceptional in being the first representative of a mixed octahedral-tetrahedral framework structure, in which the [TO 4 ]: [MO 6 ] ratio is >6:1. The structure is based on isolated, nearly regular ScO 6 octahedra [d av (ScÀO) = 2.112 Å ] sharing corners with SiO 4 tetrahedra to form an open framework with four-, six-and eight-membered rings; the latter are formed by SiO 4 tetrahedra only. Two fully occupied Cs positions are located in large framework voids close to the six-membered rings, whereas four partly occupied and disordered Cs positions are close to very large framework voids bordered by the puckered eight-membered rings. The cavities are linked into channels parallel to [100] and [010]. The structure is compared with that of Cs 2 TiSi 6 O 15 and related microporous scandium-, REE-, titano-and zirconosilicate minerals and compounds. Cs 3 ScSi 8 O 19 or derivatives may be important in the context of immobilization of radioactive 137 Cs waste, cationic conductivity or catalysis.

Crystal structures of shlykovite and cryptophyllite: comparative crystal chemistry of phyllosilicate minerals of the mountainite family

“…2c). Corrugated double silicate layers similar to those described in rhodesite were found in the structure of synthetic microporous silicate Cs 3 ScSi 8 O 19 (Kolitsch & Tillmanns, 2004).…”

(3+1)-Incommensurately modulated crystal structure of Cs3ScSi6O15

“…The only other CsSc silicate known to date, Cs 3 ScSi 8 O 19 (Kolitsch & Tillmanns, 2004), has a unique microporous framework structure. Although the coordination environment of Sc and of the fully occupied Cs positions is very similar in (Huang et al, 2005), Cs 3 DySi 6 O 15 (Zhao et al, 2010) and Cs 1.86 K 1.14 DySi 6 O 15 (Wierzbicka-Wieczorek et al, 2015) Bond-valence sum of Cs as a function of t calculated up to a distance of 3.5 Å .…”

“…S1. Additional crystals of less frequent occurrence and distinctly different platy form have been identified as Cs 3 ScSi 8 O 19 (Kolitsch & Tillmanns, 2004) on the basis of determining their lattice parameters and a search for the lattice parameters in the ICSD database (Belsky et al, 2002).…”

“…On the other hand, quite a number of caesium-bearing synthetic oxosilicates containing trivalent rare earth element (REE) cations that can be potentially used as host lattices for luminescence have been disclosed in the literature. Examples include Cs 3 NdSi 8 O 19 and CsNd 2 Si 21 O 48 (Schä fer & Schleid, 2009), Cs 3 EuSi 6 O 15 (Huang et al, 2005), Cs 3 DySi 6 O 15 ( (Kolitsch et al, 2009) as well as Cs 3 ScSi 8 O 19 (Kolitsch & Tillmanns, 2004).…”

Novel synthetic alkali‐yttrium silicates with a new microporous mixed framework topology: (Rb,Cs)9Y7Si24O63 and isotypic Rb9Y7Si24O63

“…They were mainly studied because of their large topological diversity and potential applications in the fields of catalysis, gas and ion adsorption, ionexchange and environmental protection [1][2][3]. However, recently also the microporous mixed-framework silicates containing octahedrally coordinated M 3+ -cations became an increasingly studied subject of research [4][5][6][7]. Various investigations have shown that the lanthanide-containing materials are of great interest for a wide range of photonic applications, such as tuneable (UV and visible) lasers, light-emitting diodes, lowenergy scintillators, amplifiers for optical communications and optical storage devices [8][9][10][11][12][13].…”