Co-crystallization with acetylene. Part III. Molecular complexes with aromatic azacycles

Using C–H⋯N interactions, acetylene can be introduced at increased pressure to form molecular complexes with azacyclic N-acceptors which can be crystallized and investigated by X-ray methods. With pyridine, we expected dumbbell-like 2∶1 complexes with acetylene in the middle, instead a 1∶1 zigzag chain is formed where each of the N-atoms accepts two hydrogen atoms from two acetylene molecules. The same happens with 2,5-dimethylpyridine which, together with water, results in a complex having the water chains networked by acetylene molecules. With 2,5-dimethylpyrazine, linear chains are found which are additionally stabilized by sp3 and sp2 C–H⋯N interactions. 2,6-Di-tert-butylpyridine forms a clathrate with acetylene.