New Layered Materials:  Syntheses, Structures, and Optical Properties of K₂TiCu₂S₄, Rb₂TiCu₂S₄, Rb₂TiAg₂S₄, Cs₂TiAg₂S₄, and Cs₂TiCu₂Se₄

Abstract

The new compounds K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) have been synthesized by the reactions of A(2)Q(3) (A = K, Rb, Cs; Q = S, Se) with Ti, M (M = Cu or Ag), and Q at 823 K. The compounds Rb(2)TiCu(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) are isostructural. They crystallize with two formula units in space group P4(2)/mcm of the tetragonal system in cells of dimensions a = 5.6046(4) A, c = 13.154(1) A for Rb(2)TiCu(2)S(4), a =6.024(1) A, c = 13.566(4) A for Cs(2)TiAg(2)S(4), and a =5.852(2) A, c =14.234(5) A for Cs(2)TiCu(2)Se(4) at 153 K. Their structure is closely related to that of Cs(2)ZrAg(2)Te(4) and comprises [TiM(2)Q(4)(2)(-)] layers, which are separated by alkali metal atoms. The [TiM(2)Q(4)(2)(-)] layer is anti-fluorite-like with both Ti and M atoms tetrahedrally coordinated to Q atoms. Tetrahedral coordination of Ti(4+) is rare in the solid state. On the basis of unit cell and space group determinations, the compounds K(2)TiCu(2)S(4) and Rb(2)TiAg(2)S(4) are isostructural with the above compounds. The band gaps of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), and Cs(2)TiAg(2)S(4) are 2.04, 2.19, 2.33, and 2.44 eV, respectively, as derived from optical measurements. From band-structure calculations, the optical absorption for an A(2)TiM(2)Q(4) compound is assigned to a transition from an M d and Q p valence band (HOMO) to a Ti 3d conduction band.

Hydrothermal synthesis and crystal structure of Cs6[(UO2)4(W5O21)(OH)2(H2O)2]: a new polar uranyl tungstate

“…An analytical absorption correction was applied, followed by a semi-empirical absorption correction using SADABS [33,34]. The program suite SHELXTL (v 5.1) was used for space group determination (XPREP), direct methods structure solution (XS), and least-squares refinement (XL) [35].…”

Synthesis and structure of CsCu3TiSe4

“…The new compound CsCu 3 TiSe 4 has been synthesized in greater than 85% yield from Cu, Ti, Se, and Cs 2 Se 3 in the molar ratio 3:1:4:1.2 at 923 K. Earlier [3] …”

“…These compounds are Na 2 Cu 2 ZrS 4 [1], Cs 2 Ag 2 ZrTe 4 [2], Cs 2 Cu 2 TiSe 4 [3], Cs 2 Ag 2 TiS 4 [3], and Rb 2 Cu 2 TiS 4 [3]. Here we report the synthesis and crystal structure of CsCu 3 TiSe 4 , the first example of an m = 1 compound in the A m M 4−m M Q 4 series, and contrast its structure with those with m = 2.…”

Hydrothermal synthesis and structure of K6[(UO2)4(CrO4)7]·6H2O: A layered uranyl chromate with a new uranyl sheet topology

“…An analytical absorption correction was applied, followed by a semi-empirical absorption correction using SADABS [28][29][30]. The program suite SHELXTL (v 5.1) was used for space group determination (XPREP), structure solution (XS), and refinement (XL) [31].…”