The FT-IR spectra were recorded in a VERTEX 70 (Bruker). The IR spectra were acquired using the attenuated total reflectance (ATR) mode in a range of 4000 -600 cm -1 . For this, roughly 2 mg of the sample were placed on the diamond of the ATR unit. Prior to every measurement, a background spectrum was recorded and subtracted from the spectra of the material.