• conformers;
  • density functional calculations;
  • dications;
  • helical molecules;
  • ion pairs;
  • mass spectrometry
Thumbnail image of graphical abstract

The cover picture shows different approaches used by chemists in Prague to investigate the conformations of a pentacyclic bispyridinium ion in the gas phase, in solution, and in the solid state. The title heterocycle has two conformers of which one is helical (helquat, HQ2+) and the other looks like a horse-saddle (saddlequat, SQ2+). For the free dication in the gas phase, the neutral salt in solution, and the crystal, the helical form is preferred. However, in the singly charged binary ion pairs [HQ2+ ⋅ X] and [SQ2+ ⋅ X], subtle effects of the counterions X determine the relative stabilities of conformers, and with several counterions the saddle forms are in fact more stable than the helical ones. A full account can be found in the Full Paper by D. Schröder and co-workers on page 624 ff.