Solid state 13C-NMR and X-ray studies on the structure of tetraethylpyrazabole

DSC measurements of 4,4,8,8-tetraethylpyrazabole (2) show a high enthalpy phase transition in the solid state (ΔH=28.61 kJ mol−1) at 69.0°C, far from its melting point at 106°C with ΔH=3.22 kJ mol−1. 13C-CP/MAS spectra of 2 show that at 69°C the ethyl groups attached to boron atoms start to rotate around the CB bond and the whole molecule starts to rotate and to move changing its conformation from one boat to another. X-ray studies confirm its boat conformation in the solid state at room temperature.