Structure-spectroscopy correlations in silver thiolates: Application to the structure of silver 1,5-pentanedithiolate

A variety of spectroscopic methods have been used to deduce the solid-state structure of Ag-2[S(CH2)(5)S] (1), the yellow compound formed by mixing of Ag+ and 1,5-pentanedithiol. Solid-state reflectance UV-vis, X-ray diffraction, cross-polarization magic angle spinning (CPMAS) C-13 NMR, and CPMAS Ag-109 NMR spectra of 1 were compared to corresponding spectra for two crystallographically-characterized homoleptic Ag thiolates, the cluster Ag-5{mu(2)-S(CH2)(3)N(CH3)(2)}(3){mu(2)-S(CH2)(3)NH(CH3)(2)}(3)(ClO4)2 (2) and the infinite strand AgSC(CH2CH3)(2)CH3 (3). Two limiting geometries for 1 are considered: a linear polymer and a layered geometry similar to that adopted by neutral Ag thiolates with primary, unbranched alkane chains. All spectroscopic data are consistent with the latter structure. Information about alkane chain orientation and Ag-S vibrational modes in 1 was obtained by comparison of low-wavenumber Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectra with those for all-trans AgS(CH2)(3)CH3 (T) and the C(1)-C(2) gauche isomer (G). The spectra show that the majority of alkane chains in 1 adopt a fully extended, all-trans geometry, but that gauche conformers are clearly present. These experiments demonstrate that sensitive structure elucidation can be achieved by combination of solid-state spectroscopic methods, when appropriate standards are available. Although isostructural layered, neutral compounds of the form AgSR exhibit liquid crystalline behavior upon melting, 1 does not, a consequence of covalent attachment between layers.