Lukáš Severa, Michael Jirásek, Pavel Švec, Dr. Filip Teplý, Dr. Ágnes Révész, Dr. Detlef Schröder, Dr. Dušan Koval, Dr. Václav Kašička, Dr. Ivana Císařová and Dr. David Šaman Cover Picture: Counterion-Induced Inversion of Conformer Stability of a Helquat Dication (ChemPlusChem 8/2012) ChemPlusChem 77
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.
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