Isomorphous gallium substitution in the alumosilicate sodalite framework: synthesis and structural studies of chloride and bromide containing phases

Abstract

In the Na 8 [T 1 T 2 O 4 ] 6 Y 2 sodalite system (Y ¼ Cl, Br, T 2 ¼ Si) the aluminium bearing T 1 position was successively substituted with gallium. The synthesized products represent the new composition Na 8 [Al 1Ày Ga y SiO 4 ] 6 Y 2 (0 y 1), where the Al/Ga ratio is calculated from the X-ray powder data Rietveld refinements. In each composition, the gallium concentration in the framework is observed lower than that in the initial feed. The linear expansion of the lattice parameters has been observed from [AlSiO 4 ] 6 to [GaSiO 4 ] 6 in increasing gallium concentration in the framework. The position of gallium and aluminium has been refined on a single crystallographic site. This result also indicates that both aluminium and gallium are indistinguishable and statistically distributed in the T 1 -sites. The T 1 -O distance, therefore, offers an averaged magnitude of Al/Ga--O distance which increases with increasing gallium concentration. In contrast, the Si--O distance remains almost constant at 162.8 pm (2s) and 163.4 pm (3s) for chloride and bromide sodalites, respectively. The increasing average tilt of the (Al,Ga)O 4 and SiO 4 tetrahedra leads to a decrease of the six-ring window dimension as a consequence of increasing gallium incorporation in the framework. The simultaneous shortening of Na--O and Na--Cl/Br distances, with increasing gallium content, shows a direct interaction between the framework host and the enclathrated guest. Additionally, the tetragonal tetrahedron distortion and the framework oxygen s-hybridization are discussed as a function of gallium concentration in the two new sodalite series.

Gallium substitution in the alumosilicate framework: synthesis and structural studies of hydro sodalites

“…In some cases linear constraints were used for occupancy and displacement parameters as specified in the structure refinement part. Magic angle spinning nuclear magnetic resonance for the 29 Si isotopes ( 29 Si MAS NMR) measurements were recorded on a Bruker Avance ASX 400 spectrometer using standard 4 mm MAS probes at 79.49 MHz with a spinning rate of 10 KHz. Chemical shifts were determined using tetrakis-(trimethylsilyl)-silane (Si(Si(CH 3 ) 3 ) 4 , À9.885 ppm from TMS) as an external standard.…”

“…Wyckoff position 6c (space group P 4 43n) was chosen for both aluminium and gallium to be co-shared. In this regard a detailed refinement discussion is available elsewhere [29]. Similar to the sodium atoms which yield a tetrahedral configuration in the sodalite b-cage the water oxygen atoms (O(2)) are placed on the 8e position (x, x, x).…”

“…Despite the constant concentration of water (4 molecules) and sodium (3 atoms) in each sodalite cavity, it is, however, expected that the lattice parameter expands from [AlSiO 4 ] 6 to [GaSiO 4 ] 6 framework due to successive replacement of aluminium by larger gallium atoms. For instance, a linear cell expansion is observed in the Na 8 [Al 1Ày Ga y SiO 4 ] 6 (Cl/Br) 2 [29], Na 8 [AlGe y Si 1Ày O 4 ] 6 Br 2 [19] and Na 8 [Al 1Ày Ga y SiO 4 ] 6 (NO 2 ) 2 [26] (0 ! y !…”

“…In contrast, partial T-sites substitution in the sodalite frameworks [19][20][21][22] remains little explored whereas extensive commercial successes have been achieved through partial T-sites substitution in zeolites [23,24]. Recently we reported a series of partially T-site substituted halide sodalites [25][26][27][28][29]. Following those, for the first time we present here a series of hydro sodalites, Na 6 [Al 1Ày Ga y SiO 4 ] 6 (H 2 O) 8 (0 y 1).…”

Synthesis, Characterization and Crystal Structure of Gallosilicate Perchlorate Sodalite

“…Depending on the composition sodalite posses photochromic, cathodochromic, ion conducting properties and as high density optical data storage materials. Sodalites with special guest anion can be used for various technical applications like pigments, ultramarine, graphical and digital storage system, luminescence and catalytic activity (Hassan et al, 1984;Schipper et al, 1972;Van Doorn et al, 1972;Mclaughan et al, 1970;Bolwijn et al, 1972;Chang, 1974 (Piontkovskaya et al, 1970, Suzuki et al, 1985, McCusker et al, 1986, Newsam et al, 1987, Bu, Xianhui et al, 1998Gesing et al, 2000, Buhl et al, 2006, Murshed et al, 2007 Sodalites are expected to be an interesting model system for studying simple principle of perchlorate storage in small cavities of framework structure (Weitkamp et al, 1995), we extend our experimental work here on synthesis, characterization and structure of perchlorate encapsulated sodalite with gallosilicate framework. Substitution of framework by gallium is of special interest to study interactions of encapsulated ClO 4 -guest anion with a host framework of certain composition.…”