Palladium Chemistry in Molten Alkali Metal Polychalcophosphate Fluxes. Synthesis and Characterization of K₄Pd(PS₄)₂, Cs₄Pd(PSe₄)₂, Cs₁₀Pd(PSe₄)₄, KPdPS₄, K₂PdP₂S₆, and Cs₂PdP₂Se₆

The reaction of Pd with a molten mixture of A₂Q_x/P₂Q₅/Q (A = K, Q = S, x = 3; A = Cs, Q = Se, x = 1) produced the molecular compounds K₄Pd(PS₄)₂ (I), Cs₄Pd(PSe₄)₂ (II), and Cs₁₀Pd(PSe₄)₄ (III) and the solid-state KPdPS₄ (IV), K₂PdP₂S₆ (V), and Cs₂PdP₂Se₆ (VI). Compounds I−III are air and water sensitive, while IV−VI are air and water stable. All crystals are red or dark red except those of VI, which are black. All of them exhibit a rodlike shape. Compound I crystallizes in the triclinic space group P1̄ (No. 2) with a = 6.380(1) Å, b = 6.897(1) Å, c = 8.999(1) Å, α = 87.777(8)°, β = 81.581(8)°, γ = 84.429(9)°, and Z = 1. Compound II crystallizes in the monoclinic space group P2₁/c (No. 14) with a = 7.491(2) Å, b = 13.340(2) Å, c = 10.030(3) Å, β = 92.21(2)°, and Z = 2. Compound III crystallizes in the tetragonal space group P4̄2c (No. 112) with a = b = 13.949(2) Å, c = 11.527(2) Å, and Z = 4. Compound IV crystallizes in the tetragonal space group P4₂/mnm (No. 136) with a = b = 8.5337(2) Å, c = 10.5595(5) Å, and Z = 4. Compound V crystallizes in the orthorombic space group Pnma (No. 62) with a = 15.612(2) Å, b = 7.0724(7) Å, c = 10.080(1) Å, and Z = 4. Compound VI crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.9750(4) Å, b = 8.3282(2) Å, c = 13.0568(1) Å, β = 102.940(2)°, and Z = 4. Compounds I−III contain the discrete complexes [Pd(PQ₄)₂]^4- (Q = S, Se). The mixed salt III contains additional noncoordinating [PSe₄]^3- units. The structure of IV consists of Pd(II) in square planar sulfur coordination linked by edge-sharing [PS₄]^3- tetrahedral groups to produce one-dimensional chains. The structures of V and VI feature the [P₂Q₆]^4- (Q = S, Se) group coordinated to the square planar Pd²⁺ atoms, yielding [PdP₂Q₆]_n^2n- chains. Physical characterization was performed with DTA, far-IR spectroscopy, solid-state UV/vis diffuse reflectance spectroscopy, and single-crystal optical transmission.