Thermal and photochemical characteristics of silver 4-(4-nitrophenyl)butyrate revealed by infrared and Raman spectroscopy

We have investigated the thermal and photochemical characteristics of silver 4-nitrophenylbutyrate (Ag-4NPB) by means of infrared and Raman spectroscopy, coupled with X-ray diffraction (XRD) and thermogravimetry. XRD analysis indicated that Ag-4NPB consisted of a layered structure. Upon heating the sample, structural changes took place, particularly at two specific temperatures. The binding state of the carboxylate group changed from bridging to unidentate at 363 K. A second dramatic change occurred at 536 K, producing 4NPB-capped Ag nanoparticles. The latter transition temperature for Ag-4NPB is about 18 K higher than that for silver stearate (Ag-STA), but nearly 57 K lower than that for silver 4-nitrobenzoate (Ag-4NBA). The thermal stability of aromatic silver carboxylate is thus lowered by the incorporation of a short alkane chain between the benzene ring and the carboxylate group. On the other hand, Ag-4NPB was readily subjected to photolysis even by the 632.8-nm radiation. Initially, silver nanoparticles appeared to be generated, followed by the nitro-to-amine group conversion. Although silver particles could also be generated from Ag-4NBA, the nitro-to-amine group conversion did not take place by the 632.8-nm light. The photochemical stability thus seemed to be lowered, parallel to the thermal stability, by the incorporation of a short alkane chain between the benzene ring and the carboxylate group.