Crystal structures of seven mixed-valence gold compounds of the form [(R1R2R3PE)2AuI]+[AuIIIX4]− (R = tert-butyl or isopropyl, E = S or Se, and X = Cl or Br)

The ligands at the Au^I atoms are anti­periplanar to each other across the S⋯S vectors. Residues are linked by various contacts of the types C—H⋯X, E⋯X and Br⋯Br.

During our studies of the oxidation of gold(I) complexes of tri­alkyl­phosphane chalcogenides, general formula R¹R²R³PEAuX, (R = tert-butyl or isopropyl, E = S or Se, X = Cl or Br) with PhICl₂ or elemental bromine, we have isolated a set of seven mixed-valence by-products, the bis­(tri­alkyl­phosphane chalcogenido)gold(I) tetra­halogenidoaurates(III) [(R¹R²R³PE)₂Au]⁺[AuX₄]⁻. These corres­pond to the addition of one halogen atom per gold atom of the Au^I precursor. Com­pound 1, bis­(triiso­propyl­phosphane sulfide)­gold(I) tetra­chlorido­aur­ate(III), [Au(C₉H₂₁PS)₂][AuCl₄] or [(ⁱPr₃PS)₂Au][AuCl₄], crystallizes in space group P2₁/n with Z = 4; the gold(I) atoms of the two cations lie on twofold rotation axes, and the gold(III) atoms of the two anions lie on inversion centres. Compound 2, bis­(tert-butyl­diiso­propyl­phosphane sulfide)­gold(I) tetra­chlorido­aurate(III), [Au(C₁₀H₂₃PS)₂][AuCl₄] or [(^tBuⁱPr₂PS)₂Au][AuCl₄], crystallizes in space group P1 with Z = 4; the asymmetric unit contains two cations and two anions with no imposed symmetry. A least-squares fit of the two cations gave an r.m.s. deviation of 0.19 Å. Compound 3, bis­(tri-tert-butyl­phosphane sulfide)­gold(I) tetra­chlorido­aurate(III), [Au(C₁₂H₂₇PS)₂][AuCl₄] or [(^tBu₃PS)₂Au][AuCl₄], crystallizes in space group P1 with Z = 1; both gold atoms lie on inversion centres. Compound 4a, bis­(tert-butyl­diiso­propyl­phosphane sulfide)­gold(I) tetra­bromi­doaurate(III), [Au(C₁₀H₂₃PS)₂][AuBr₄] or [(^tBuⁱPr₂PS)₂Au][AuBr₄], crystallizes in space group P2₁/c with Z = 4; the cation lies on a general position, whereas the gold(III) atoms of the two anions lie on inversion centres. Compound 4b, bis­(tert-butyl­diiso­propyl­phosphane selenide)gold(I) tetra­bromido­aurate(III), [Au(C₁₀H₂₃PSe)₂][AuBr₄] or [(^tBuⁱPr₂PSe)₂Au][AuBr₄], is isotypic with 4a. Compound 5a, bis­(tri-tert-butyl­phosphane sulfide)­gold(I) tetra­bromido­aurate(III), [Au(C₁₂H₂₇PS)₂][AuBr₄] or [(^tBu₃PS)₂Au][AuBr₄], is isotypic with compound 4a. Compound 5a, bis­(tri-tert-butyl­phosphane sulfide)­gold(I) tetra­bromido­aurate(III), [Au(C₁₂H₂₇PS)₂][AuBr₄] or [(^tBu₃PS)₂Au][AuBr₄], crystallizes in space group P1 with Z = 1; both gold atoms lie on inversion centres. Compound 5b, bis­(tri-tert-butyl­phosphane selenide)gold(I) tetra­bromido­aurate(III), [Au(C₁₂H₂₇PSe)₂][AuBr₄] or [(^tBu₃PSe)₂Au][AuBr₄], is isotypic with 5a. All Au^I atoms are linearly coordinated and all Au^III atoms exhibit a square-planar coordination environment. The ligands at the Au^I atoms are anti­periplanar to each other across the S⋯S vectors. There are several short intra­molecular H⋯Au and H⋯E contacts. Average bond lengths (Å) are: P—S = 2.0322, P—Se = 2.1933, S—Au = 2.2915, and Se—Au = 2.4037. The complex three-dimensional packing of 1 involves two short C—H_methine⋯Cl contacts (and some slightly longer contacts). For 2, four C—H_methine⋯Cl inter­actions combine to produce zigzag chains of residues parallel to the c axis. Additionally, an S⋯Cl contact is observed that might qualify as a ‘chalcogen bond’. The packing of 3 is three-dimensional, but can be broken down into two layer structures, each involving an S⋯Cl and an H⋯Cl contact. For the bromido derivatives 4a/b and 5a/b, loose associations of the anions form part of the packing patterns. For all four compounds, these combine with an E⋯Br contact to form layers parallel to the ab plane.