We reported the synthesis of the quaternary alkali metal chromium thiophosphate compounds using reaction of the elements with eutectic alkali metal halide fluxes (KCl/LiCl or RbCl/LiCl or CsCl/LiCl). The crystal structures of the these compounds have been structurally characterized by single crystal X-ray diffraction techniques.
The quaternary alkali metal chromium thiophosphate compounds have dark brownish color and a similar shape.
First polyhedron-shaped dark brown colored crystal of Cs2CrPS6 crystallizes in the space group P21/n of the monoclinic system with a unit cell parameter ; a = 14.454(5), b = 8.972(3), c = 9.029(3) Å, β = 102.74(3)˚. The structure of contain of molecular cluster, [Cr2P2S12]4-. The molecular cluster of [Cr2P2S12]4- is composed of isolated edge sharing [CrS6] octahedra and [PS4] tetrahedra. This cluster is stabilized through the electrostatic interaction with cesium ions. In conclusion, Cs2CrPS6 compound has zero dimensional character.
The ACrPS5(A = Rb, Cs) crystals have dark brown color polyhedra shaped. These compounds crystallized in the monoclinic space group P21/c. The crystal structures of the compounds comprise one dimensional [CrPS5 −] chains separated from one another by alkali metal cations (Rb+, Cs+). The linear chains are built up from the basic repeating unit, [Cr2(PS4)2S2]2-, which is composed of isolated edge sharing [CrS6] octahedra and [PS4] tetrahedra. These repeating units are linked together sharing two μ-S atoms to from the one dimensional [CrPS5 −] chains. The alkali cations spread between chains and there are only van der Waals interactions between them. The classical charge valence can be [A+][Cr4+][P5+][S2-]5(A = Rb, Cs).
The ACrP2S7(A = K, Rb, Cs) crystals have needle-plate shaped and dark brown color. These compounds crystallized in the monoclinic space group C2 . The
crystal structures of the compounds comprise two dimensional described as [CrP2S7 −] layers separated from one another by alkali metal cations (K+, Rb+, Cs+). The two dimensional structures of ACrP2S7(A = K, Rb, Cs), built from bitetrahadral [P2S7] units sharing edges and corner with [CrS6] octahedra. The [P2S7] unit is comprised of two [PS4] units sharing common corner. The ACrP2S7(A = K, Rb, Cs) structures are isostructural with RbVP2S7 and KMP2S7 (M = Cr, V and In). The classical charge valence if the compound can be written as [A+][Cr3+][[P5+]2[S2-]7 (A = K, Rb, Cs).
Finally, the compound of Rb2CrP2S6 crystals have plate shape and dark brown color. Rb2CrP2S6 crystallizes in the space group Pbca. These [CrS6] octahedral units are linked by sharing three μ-S atoms of [P2S6]4− anions to form the infinite two-dimensional [CrP2∞2S6 −] layers. The classical charge valence of these compounds should be represented by [Rb+][Cr3+][P2S64-].
