Structures of Diethynyl Sulfide and Bis(phenylethynyl) Sulfide

Rotational transitions for four isotopomers of diethynyl sulfide, S(CCH) 2, were observed by using a pulsed nozzle Fourier transform microwave spectrometer. Vibration−rotation interaction constants obtained from ab initio calculated force fields were used to convert the ground-state rotational constants to equilibrium values. The latter were used to derive structural parameters, several of which are not in good agreement with those obtained from high level ab initio calculations. The structure has planar C 2 v symmetry with the following parameters: d (S C) = 1.708(20) Å, d (C⋮C) = 1.211(10) Å, d (C H) = 1.061(10) Å, ∠(C S C) = 100.5(5)°, ∠(S C⋮C) outside angle = 174.4(15)°, ∠(C⋮C H) inside angle = 177.0(25)°. The structure of bis(phenylethynyl) sulfide, S(C⋮CC 6 H 5 ) 2, was determined by X-ray crystallography. The unit cell contains two inequivalent molecules. The structural parameters are (average of both species; uncertainties represent 1σ) d (S C) = 1.695(4) Å, d (C⋮C) = 1.198(2) Å, d (C C phenyl ) = 1.440(4) Å, ∠(C S C) = 101.4(9)°, ∠(S C⋮C) = 176.4(19)°, and ∠(C⋮C C phenyl ) = 178.2(8)°. The phenyl groups are twisted out of the C−S−C plane from 20 to 85° such that each phenyl ring is oriented nearly 90° to its intramolecular mate. The structural parameters are compared with several other sulfides and with hydrocarbons containing acetylenic linkages. The nonlinearity about the acetylenic bond follows a pattern seen in other similar species, although it is more pronounced in S(CCH) 2 than in hydrocarbons. These data constitute the first experimental structural studies on uncomplexed diethynyl sulfides.