Macro-rings designed for uncharged molecule complexation. Synthesis, complex formation, and structural studies of new pyridino crowns incorporating resorcinol and hydroquinone building blocks. X-Ray crystal and molecular structure of a 22-membered pyridino crown

Abstract

The crystal structure of the pyridino crown (2) containing a resorcinol group is reported. Two crystallographically independent molecules of compound (2) with considerably different conformations are present in the crystal. Both molecules provide a potential cavity, but have other steric factors highly unfavourable for complex formation. Also, there is no free space in the crystal lattice for accommodation of a guest molecule. Based on this result, three pyridino crowns of different ring size incorporating two resorcinol units in different positions (5a–c) have been synthesized, together with the hydroquinone-group-containing analogues (6a–c). The host properties of the new macro-rings were determined. It was found that compound (6c) forms crystalline inclusion complexes with a number of dipolar aprotic and rather apolar organic guests such as nitromethane, acetonitrile, DMF, or dioxane, while the other compounds are inefficient. Host–guest relationships are discussed and conclusions for future host design are drawn.