Crystal structure determination of bis(tetraphenylphosphonium) heptasulfide, (Ph₄P)₂S₇

The S₇^2- anion has been obtained by the reaction of MoS₉^2- with an excess of the sodium salt of the diethyldithiocarbamate anion in acetonitrile solution. The tetraphenylphosphonium salt of S₇^2-, (Ph₄P)₂S₇ (I), crystallizes in the triclinic space group P1 with Z = 2 and lattice parameters a = 11.041 (3) Å, b = 18.589 (4) Å, c = 12.040 (3) Å, α = 74.58 (3)°, β = 69.05 (3)°, γ = 87.76 (4)°, and V = 2220.18 ų. Diffraction data (Mo Kα radiation, 2θ_max = 50°) were collected with a Picker FACS-I automated diffractometer, and the structure was solved and refined by direct methods and full-matrix least-squares procedures to R_F = 5.8% and R_wF = 8.7% with use of 5102 unique reflections. The S₇^2- ion is found to be a right-handed nonbranched S(1)S(2)S(3)S(4)S(5)S(6)S(7) helix with very short terminal sulfur-sulfur bonds of 1.990 (2) and 1.995 (2) Å for S(1)-S(2) and S(6)-S(7), respectively. The internal bond distances are as follows (in Å): S(2)-S(3), 2.036 (2); S(3)-S(4), 2.062 (2); S(4)-S(5), 2.062 (2); S(5)-S(6), 2.037 (2). The torsion angles in the chain are as follows (in degrees): S(2)-S(3), 73.28 (10)°; S(3)-S(4), 74.41 (10)°; S(4)-S(5), 65.22 (10)°; S(5)-S(6), 79.86 (10)°. The (Ph₄P)₂S₇ salt dissolves in polar solvents to give blue solutions with adsorption bands at 610, 470, 345 (sh), and 304 nm.