An investigation of the structure and properties of layered copper thiolates

Copper(I) n-alkane thiolate systems have been characterized using powder X- ray diffraction, IR spectroscopy, X-ray photoelectron spectroscopy and ther mal analyses. The diffraction pattern is composed of a series of peaks, whi ch are indexed to (0k0) reflections of a layered structure. The tilt angle, theta, of the alkyl chains is estimated to be 13 degrees, distinctly diffe rent from the silver thiolates, where the chains are near normal to the sil ver plane. The layers interpenetrate to a small (or negligible) extent. The alkyl chain assembly is different from that of crystalline alkanes. An inc rease in the alkyl chain order with increase in chain length is evident in the infrared spectra. The chains are essentially all-trans, but gauche conf ormations are seen near the sulfur end. Upon cooling, an orientational tran sition occurs resulting in the freezing of the local symmetry around the me thyl group. The materials show high thermal stability and desorption is see n only above 500K. High temperature phase transitions of the materials have been studied by variable temperature powder XRD, variable temperature IR a nd differential scanning calorimetry. Two distinct transitions; one from an original gauche-trans (g-t) to a gauche (g) phase and another subsequent o ne, to a columnar mesophase, have been identified. The transitions are not fully reversible, conformational changes are observed upon heating and cool ing. Thiolates appear to be model systems for the investigation of molecula r self-assembly on copper surfaces.