David J. Williams

Host–Guest Chemistry Aids and Abets a Stereospecific Photodimerization in the Solid State

A bis(dialkylammonium ion)-substituted stilbene derivative cocrystallizes with bisparaphenylene[34]crown-10 to form, in the solid state, a 2:2 host-guest complex wherein the stilbene double bonds are aligned with a relative geometry suitable for a stereospecific photochemical [2+2] cycloaddition. When irradiated with white light, this crystalline complex forms a single diastereoisomer of the corresponding cyclobutane derivative, the stereochemistry of which has been determined unambiguously in the solid state by X-ray crystallography to be syn-anti-syn.

THE GENESIS OF A NEW RANGE OF INTERLOCKED MOLECULES

Secondary dialkylammonium ions self-assemble with suitably sized macrocyclic polyethers, such as the well-known dibenzo-24-crown-8 and bis-p-phenylene-34-crown-10, into pseudorotaxane superstructures in (a) solution, (b) the solid state and (c) the ‘gas phase’.

THIAMACROCYCLIC CHEMISTRY : SYNTHESIS OF A NOVEL OXADITHIACROWN AND ITS COPPER IODIDE COMPLEX

A mixed oxa–thia macrocycle incorporating a rigid n‘horseshoe-shaped’ aromatic moiety, n1,11,21-trioxa-8,14-dithia[2,9,2]paracyclophane, L, has been nsynthesised. The molecular structures of L and of its copper iodide ncomplex have been determined by single-crystal X-ray diffraction nmethods. There are two independent conformations observed in the solid nstate for the macrocycle, L. Its copper iodide complex n[Cu n 2 nI n 2 n(L)]·1.25MeCN, crystallises, nin a 2∶1 metal∶crown ratio, as a one-dimensional infinite narray of cubane-like units consisting of four copper atoms, four iodine natoms and four sulfur atoms from four different macrocycles.

Cyclophanes with self-recognising components

High dilution techniques have been employed to construct a series of charged flexible cyclophanes comprised of π-electron-rich hydroquinone and π-electron-deficient bipyridinium residues linked by polyether spacer units of varying length: significant conformational changes, leading to intramolecular and intermolecular interactions between the π-donors and π-acceptors, have been observed—as evidenced by X-ray crystallographic and variable temperature 1H NMR and 2D ROESY spectroscopic investigations—within the series of the cyclophanes both in the solid and solution states as a result of increasing the lengths of the polyether spacer units.