Structure and conformation of pyridino‐ and diesterpyridino‐18‐crown‐6 complexes with primary ammonium salts in solution and crystalline states

Structures in CD3ODCDCl3 mixtures of pyridino‐18‐crown‐6 and diesterpyridino‐18‐crown‐6 complexes with primary ammonium cations containing an α‐phenyl group were found to be significantly different. The π–π overlap between the α‐phenyl group of the ammonium cation and the pyridine ring of the ligand occurs in the pyridino‐18‐crown‐6 complexes but not in the diesterpyridino‐18‐crown‐6 complexes. The solution structure of a diesterpyridino‐18‐crown‐6 complex with an α‐phenyl‐containing primary ammonium cation was also found to differ markedly from the corresponding crystal structure in that π–π overlap occurs in the crystal structure, but not in the solution structure.