Thermal Behavior of a Self-Assembled Silver n-Dodecanethiolate Layered Material Monitored by DSC, FTIR, and ¹³C NMR Spectroscopy

The thermal behavior of a self-assembled silver alkanethiolate layered material (AgSC n, n = 12) has been explored using two spectroscopic techniques: 13 C CPMAS NMR ( 13 C cross-polarization magic angle spinning NMR) and FTIR (Fourier transform infrared) spectroscopy. The goal was to correlate structural changes monitored by spectroscopy with the phase transition detected by DSC (differential scanning calorimetry). Variable-temperature 13 C CPMAS NMR was used for the first time to study silver alkanethiolates in order to obtain conformational and structural information about each of the C positions in the alkyl chain as a function of the temperature. In the low-temperature domain, a subtle change in the chain packing is observed, as evidenced by the chemical shift of the internal methylenes in the 13 C CPMAS NMR spectra. A remarkable degree of conformational order is observed, which is retained up to 120 °C. A sharp phase transition between 125 and 130 °C is associated with conformational changes, from all-trans to gauche containing bonds, as detected by IR and 13 C CPMAS NMR. The complete reversibility of these structural changes indicates that the alkyl chains remain anchored to the Ag−S backbone above the transition. The key determinants of the thermal behavior of the layered system are the strong Ag−S bonding and the high conformational degree of order conferred by the polymeric character of the compound.