Intermolecular proton transfer in host–guest crystals: the case of pyrazole included in 1,1-di(2,4-dimethylphenyl)but-2-yn-1-ol, an X-ray and solid-state ¹³ C/ ¹⁵ N NMR study

The first example of a cyclic intermolecular solid-state proton transfer involving nitrogen and oxygen atoms is described, which takes place in a cyclic 2 :2 complex formed by inclusion of pyrazole in the host, 1,1-di(2,4-dimethylpheny)but-2-yn-1-ol; the system has been studied by a combination of X-ray crystallography and dynamic high resolution solid-state 13C/15N NMR spectroscopy.