A Facile Trans to Gauche Conversion in Layered Silver Butanethiolate

Abstract

Raman, X-ray diffraction (XRD), UV−visible reflectance, and 13 C and 109 Ag CPMAS NMR studies have been carried out on three different forms of the layered solid AgS(CH 2 ) 3 CH 3: a white all-trans compound, a bright yellow gauche C(1)−C(2) conformational isomer, and a phase containing both species. The structure of these compounds comprises a slab of Ag and S atoms, alkyl chains extending in both directions, and layer stacking. Raman spectroscopy and 13 C NMR show that the all-trans species is less stable, converting cleanly to the gauche form. This transformation ( E a ≈ 60 kJ/mol) is accompanied by a color change from white to yellow, a phenomenon previously observed upon melting of mesogenic AgSR (R = alkyl) compounds. XRD shows that the 15.56 Å interlayer spacing in the trans form increases to 16.88 Å in the gauche form. On the basis of 109 Ag NMR data and bond lengths from structurally-characterized Ag thiolate model compounds, S−S spacings of 4.4−4.8 Å were found, which agree with those reported for two-dimensional self-assembled monolayers of organothiols (SAMs) on well-defined Ag surfaces. These findings shed light on the molecular origins of AgSR mesogenic behavior and reinforce the idea that Ag−S interactions play a dominant role in self-assembly of organothiols on Ag.