The interferograms were averaged over 512 scans, Happ–Genzel-apodized and Fourier-transformed using a zero filling factor of 2 to give spectra in the 100–3700 cm−1 range at a resolution of 8 cm−1. Under such conditions it took approximately 10 min to obtain the spectrum.UV–vis spectra were recorded using a Carry-5 Varian spectrometer. The density of samples at 20 °C was measured using an Ecolab MG-2 densimeter.