Soft−Hard Acid−Base Interactions: Probing Coordination Preferences of Sulfur and Selenium in Mixed Chalcophosphates in the Family APbPS_4−xSe_x(A = K, Rb, Cs;x= 0−4)

Abstract

The synthesis and structures of the three new compounds, KPbPS(1.84)Se(2.16) (1), RbPbPS(1.56)Se(2.43) (2), and CsPbPS(3.46)Se(0.54) (3), are reported. The solid state structures of 1-3 consist of two-dimensional layers of [PbP(S/Se)(4)] separated by alkali metal ions. The structure of 1 was solved in the orthorhombic space group Pna2(1). Compounds 2 and 3 possess the CsSmGeS(4) structure type, crystallizing in the orthorhombic space group P2(1)2(1)2(1). All compounds were refined as racemic twins. All chalcogen sites around the tetrahedrally coordinated P atoms show mixed S/Se occupancy; however, there is a preference for Se binding to Pb ions and S binding to alkali ions. A (31)P magic angle spinning NMR study on 1 suggests that, in mixed seleno-/thiophosphates, all of the anions [PS(x)Se(4-x)](3-) (x = 0, 1, 2, 3, 4) are present. The different amount of sulfur and selenium present in KPbPS(1.84)Se(2.16) (1), RbPbPS(1.56)Se(2.43) (2), and CsPbPS(3.46)Se(0.54) (3) is reflected in the solid state absorption spectra from which bandgaps of 2.2 eV were determined for 1 and 2, and a blue-shift to 2.5 eV was observed because of the higher sulfur-content in 3. Thermogravimetric analysis experiments indicated that, upon heating, compound 1 decomposes forming PbSe and sulfur together with other unidentified products. A Raman spectrum of compound 1 showed more bands than are usually observed in seleno- or thiophosphate salts and is another indicator of the mixed seleno-/thiophosphate anions found in 1.

Synthesis of Alkali Metal Indium Thiophosphates Containing the Discrete Anions [In(PS4)(PS5)2]6− and [In(PS4)2(PS5)]6−

“…The four observed resonances at δ 93 ([PS 4 ] 3− ), 86, 83, and 79 ppm, respectively, indicated that the solid reaction product contains a mixture of λ-[In(PS 4 ) 2 (PS 5 )] 6− and Λλδ-[In(PS 4 )(PS 5 ) 2 ] 6− anions. The resonance at δ 93 ppm is similar to the chemical shift observed for [PS 4 ] 3− in KPbPS 4 and K 4 Ti 2 P 6 S 25 . , The remaining resonances can tentatively be assigned to [PS 5 ] 3− anions in the different chemical environments of λ-[In(PS 4 ) 2 (PS 5 )] 6− and Λλδ-[In(PS 4 )(PS 5 ) 2 ] 6− and to stereoisomers that may have formed. The presence of other potassium salts of [P y S z ] n − anions (Cs 4 P 2 S 10 containing the [S 3 P−(S) 4 −PS 3 ] 4− anion formed together with 3 ) cannot be ruled out.…”

Germanium Selenophosphates: The Incommensurately Modulated 1/∞[Ge4-xPxSe124–] and the Molecular [Ge2P2Se14]6–

“…Examples of these anions include [P 8 Se 18 ] 6– , [P 5 Se 12 ] 5– , α- and β-[P 6 Se 12 ] 4– , , 1 / ∞ [PSe 6 – ], 1 / ∞ [P 2 Se 6 2– ], [P 2 S 10 ] 4– , and [P 2 S 8 ] 4– . Addition of a second main group element to the reaction mixture can result in even more complex structures by further linking the chalcophosphate anions. − Recently, we reported on the stability of arsenic containing chalcophosphates, some of which feature novel structures . In this paper, we explore the addition of germanium to a selenophosphate flux.…”

Arsenic-Containing Chalcophosphate Molecular Anions

“…Further structural diversity is found in quaternary chalcophosphates and chalcoarsenates containing a transition-metal or main-group element. ,,, In the latter compounds, the heavier group 15 congeners such as bismuth and antimony, with their large ionic radii and flexible coordination spheres, serve to further link the chalcogenide building blocks and form new structures. − Compounds in which the chalcogen atoms are mixed have also been synthesized . Generally, these structures are described as having mixed occupancy between sulfur and selenium on the chalcogen sites, although slight preferences at specific sites have been observed. , Despite these findings, synthesis of structures containing phosphorus and arsenic have been much less explored. , In fact, no compounds comprised of A/As/P/Q have been reported. In part because of the stereochemically active lone pair typically expressed by arsenic, the oxidation state and local coordination environment of the two pnicogens tends to be different.…”