Crystal structure of 2,5-di(4-methoxycarbonyl-phenyl)-1,3,4-oxadiazole characterized by AFM and IR-spectroscopy

Low molecular aromatic 1,3,4-oxadiazoles are of interest for scientists dealing with biologically active or photochemically active materials. They are also of interest as model compounds for thermostable polymers. Here, for the first time the characterization of the crystal structure of 2,5-di(4- methoxycarbonyl-phenyl)-1,3,4-oxadiazole by Atomic Force Microscopy (AFM) and IR-spectroscopy is presented. Additionally, the experimental data are interpreted by molecular modelling results. The crystallographic data known from X-ray investigations can be determined from the molecular resolved AFM pictures too. The molecular parameters of the organic crystal were also calculated by molecular modelling and agree with all experimental results. The modelling was carried out without any assumptions about the molecular or crystal structure of the oxadiazole molecule. The oxadiazole crystal was also characterized by FTIR-spectroscopy using polarized radiation. A distinct dichroism was observed for several bands as well as of the oxadiazole ring, the phenylene group and the carboxylic group. On the contrary the dichroism for the methylene bands is lower. All IR-data support the crystal structure deduced from AFM, X-ray investigations and molecular modelling.