Conformational changes in Cmethyl-resorcinarene pyridine N-oxide inclusion complexes in the solid state?

CrystEngComm Pub Date: 2016-02-26 DOI: 10.1039/C6CE00240D

Abstract

Aromatic N-oxides interact with Cmethyl-resorcinarene resulting in marked changes in the conformation of the host resorcinarene. In the solid state, 2- and 3-methylpyridine N-oxides form pseudo-capsular 2?:?2 endo host–guest complexes with Cmethyl-resorcinarene stabilized by C–H?π interactions. The Cmethyl-resorcinarene·2-methylpyridine N-oxide complex has a C4v crown conformation, while the Cmethyl-resorcinarene·3-methylpyridine N-oxide complex has a slightly open C2v boat conformation. On the contrary, other para-substituted and benzo-fused pyridine N-oxides form only exo complexes with Cmethyl-resorcinarene. In the exo complexes, the asymmetry of the guest, conformational flexibility and preferred inter-host hydrogen bonding of Cmethyl-resorcinarenes exclude endo complexation. All the exo complexes form robust 1-D hydrogen bonded chains between the host hydroxyl groups assisted by the guest N–O groups, resulting in a C2v boat conformation.

Graphical abstract: Conformational changes in Cmethyl-resorcinarene pyridine N-oxide inclusion complexes in the solid state
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