Interactions of Coinage-Group Cations with the Tetraselenotungstate Anion: Multinuclear NMR Spectroscopic Results and Crystal Structures of (μ-WSe₄)[(PMe₂Ph)₂Cu]₂, (μ-WSe₄)[(PMePh₂)Au]₂, and (μ₃-Cl) (μ₃-WSe₄)[(PPh₃)Cu]₃

Reaction of a CH₃CN solution of [NPr₄]₂[WSe₄] with 2 equivalents of Cu⁺, Ag⁺, or Au⁺ in the presence of excess PMe₂Ph affords (μ-WSe₄)[(PMe₂Ph)₂M]₂ (M = Cu (1), Ag (2), or Au (3)). (μ-WSe₄) [(PMe₂Ph)₂Cu]₂ crystallizes with four formula units in the monoclinic space group C⁶_2h-C2/c in a cell of dimensions a = 19.315(7) Å, 6 = 15.575 (4) Å, c = 16.829 (7) Å, and β = 127.99 (1)° (T = 113 K). Full anisotropic refinement of the structure led to a value of R(F) = 0.032 (R_W(F) = 0.042) for 196 variables and 4047 unique reflections. The molecule possesses a crystallographic 2-fold axis; the W center is tetrahedrally coordinated to four Se atoms that bridge to the Cu atoms; coordination of each Cu atom to two P atoms completes the distorted tetrahedral geometry about each Cu atom. Substitution of PMePh₂ for PMe₂Ph with M = Au⁺ affords (μ-WSe₄) [(PMePh₂)Au]₂ (4). This compound crystallizes with four molecules in the monoclinic space group P2₁/c in a cell of dimensions a = 14.647 (5) Å, b = 14.161 (5) Å, c = 15.319 (6) Å, and β = 106.65 (1)° (T= 113 K). A value of R(F) = 0.088 (R_W(F) = 0.081) for 186 variables and 5859 unique reflections was obtained from anisotropic refinement of the heavy atoms. The structure is similar to that of 1, except that the geometry around the Au atoms is distorted trigonal planar. The ⁷⁷Se NMR spectra of solutions of 1-4 exhibit a single peak; for 1-3 this peak shifts to lower field with increasing atomic number of the coinage metal. The ³¹P NMR spectra also consist of a single resonance. Reaction of [NPr₄]₂[WSe4] with [(PPh₃)₂Cu(BH₃)(CN)]₂ in CH₂C1₂ in the presence of NH₄Cl affords the cubane-like compound (μ₃-Cl) (μ₃-WSe₄)[(PPh₃)Cu]₃ (5). Its structure, which has analogues in the MoSe₄^2- and the WS₄^2- systems, is that of a cubane in which each Cu center is bonded tetrahedrally to a P atom, a Cl atom, and two Se atoms and the W center is bonded tetrahedrally to four Se atoms. Consistent with this solid-state structure, the ⁷⁷Se NMR spectrum of a solution of 5 displays two resonances at δ 1651 and 1232 ppm. The compound crystallizes with four molecules in the orthorhombic space group D₂⁴-P2₁2₁2₁ in a cell of dimensions a = 12.88 (1) Å, b = 17.72 (1) Å, and c = 22.59 (1) Å (T = 113 K). The structure has been refined anisotropically to a value of R(F) = 0.063 (R_W(F) = 0.069) for 570 variables and 8950 observations.