Simultaneous endo and exo Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests

Abstract

The formation of complexes between hexafluorophosphate (PF ) and tetraisobutyloctahydroxypyridine[4]arene has been thoroughly studied in the gas phase (ESI-QTOF-MS, IM-MS, DFT calculations), in the solid state (X-ray crystallography), and in chloroform solution ( H, F, and DOSY NMR spectroscopy). In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of a PF anion within a pyridine[4]arene dimer was observed. While similar ternary complexes are often observed in the solid state, this is a unique example of such behavior in the gas phase.

Ion mobility–mass spectrometry of supramolecular complexes and assemblies

“…3b). 47 An X-ray structure of pyridine [4]arene crystals obtained from CHCl3 solution in the presence of n Bu4NPF6 showed that the amide tautomer predominates, with each pyridine [4]arene binding one PF6 − anion in an exo fashion by means of CHanion and ArH-anion interactions with the alkyl groups. Two pyridine [4]arenes then come together to sandwich CHCl3, which is bound in an endo mode.…”

“…First observed in the solid phase, such interactions evidently persist in the gas phase. Calculated from the CCS assuming a spherical conformation Obtained from molecular modelling.Table 1| A comparison of ionic diameters from IM, 1 H DOSY NMR, X-ray diffraction and molecular modelling 47,60,63. The collission cross-section (CCS) values were each obtained using an N2filled drift tube ion mobility (IM) spectrometer.Self-interlocked structures such as catenanes and [1]rotaxanes are special examples of host-guest systems.…”

Thermodynamically driven self-assembly of pyridinearene to hexameric capsules

“…Despite their obvious structural similarities, pyridinearenes display different binding properties due to amide-iminol tautomerism and electronic properties arising from the pyridine ring. 6 From the two tautomeric forms, dihydroxy and hydroxy-oxo, only the latter has been observed in crystal structures. 6 Recently, conformational analysis for the tautomers also revealed that the hydroxy-oxo tautomer (Scheme 1) is ∼150 kJ mol −1 lower in energy than the dihydroxy tautomer.…”

“…6 From the two tautomeric forms, dihydroxy and hydroxy-oxo, only the latter has been observed in crystal structures. 6 Recently, conformational analysis for the tautomers also revealed that the hydroxy-oxo tautomer (Scheme 1) is ∼150 kJ mol −1 lower in energy than the dihydroxy tautomer. 7 The cavity of pyridinearene was earlier considered electron deficient and suitable to bind anionic guests.…”

“…In fact, pyridinearenes bind anions, but outside the cavity, in exo position between the lower rim alkyl chains via CH⋯anion interactions. 6 Although the cavity of pyridinearenes is most suitable for neutral guests, also anion-driven encapsulation of cations inside the pyridinearene dimers was recently demonstrated. 7 In one of the earliest reports concerning the self-assembly of pyridinearene, two species were observed in chloroform solution which were initially erroneously assigned as a mixture of monomers and dimeric assemblies.…”