All C MAS NMR spectra were acquired using the 13 C{ 1 H} cross-polarization experiment, and at room temperature without temperature control if not stated otherwise. kHz. H NMR spectra were recorded using a 90° pulse sequence at νr=3 and 10 kHz spinning speed with τP( 1 H) = 5.0 µs at a recycle delay of 2 s. C and 1 H chemical shifts were referenced using adamantane to 38.5 ppm (tertiary carbon, left-hand resonance) and 1.8 ppm.