Chemistry of Gold in Molten Alkali Metal Polychalcophosphate Fluxes. Synthesis and Characterization of the Low-Dimensional Compounds A₃AuP₂Se₈ (A = K, Rb, Cs), A₂Au₂P₂Se₆ (A = K, Rb), A₂AuPS₄ (A = K, Rb, Cs), and AAuP₂S ₇(A = K, Rb)

The reaction of Au with a molten mixture of A₂Q/P₂Q₅/Q (Q = S, Se) produced the quaternary compounds A₃AuP₂Se₈ (A = K, Rb, Cs) (I-III), A₂Au₂P₂Se₆ (A = K, Rb) (IV, V), A₂AuPS₄ (A = K, Rb, Cs) (VI-VIII), and AAuP₂S₇ (A = K, Rb) (IX, X). I-III crystallize in the acentric space group Cc (No. 9): I, a = 7.122(2) Å, b = 12.527(3) Å, c = 18.666(4) Å, β= 96.06(2)°, Z = 4. IV and V crystallize in the space group C2lm (No. 12): IV, a = 12.289(2) Å, b = 7.210(1) Å, c = 8.107(1) Å, β= 115.13(1)°, Z = 2. VI and VII crystallize in the space group P2₁lm (No. 11): VI, a = 6.518(2) Å, b = 6.747(2) Å, c = 9.468(3) Å, β= 92.98(2)°, Z = 2. VIII crystallizes in the space group Pbcm (No. 57) with a = 6.904(3) Å, b = 20.093(6) Å, c = 7.025(5) Å, and Z = 4. IX and X crystallize in the space group C2lc (No. 15): IX, a = 7.917(3) Å, b = 9.247(2) Å, c = 14.968(3) Å, β= 91.84(9)°, Z = 4. Compounds I-III have a one-dimensional structure with [AuP₂Se₈]_n^3n- chains separated by A⁺ cations. The monovalent Au cation is linearly coordinated to the new ligand [P₂Se₈]^4-. IV and V possess a one-dimensional structure with [Au₂Se₆]_n^2n- chains separated by A⁺ ions. The monovalent Au cation is linearly coordinated to ethane like [P₂Se₆]^4- ligands. VI and VII have a one-dimensional structure with [AuPS₄]_n^2n- chains separated by A⁺ cations. The Au⁺ cation is linearly coordinated to alternating [PS₄]^3- tetrahedra. The structure of VIII is related to that of I-III with [AuPS₄]_n^2n- chains. The diselenide of the [P₂Se₈]^4- unit is replaced by a second, essentially linear, S-Au-S linkage leaving the structure of the chain unchanged. IX and X have the [AuP₂S₇]^n- chains with square planar Au³⁺ centers. The compounds were characterized with differential thermal analysis, far-IR, Raman spectroscopy, solid-state UV/vis diffuse reflectance spectroscopy, and single-crystal optical spectroscopy. Cs₂AuPS₄, at T > 375 °C, converts to β-Cs₂AuPS₄, which is isostructural to K₂AuPS₄.