Blue-Colored, Linear Rigid-Axle [2]Pseudorotaxanes: Metal-Binding Properties, Crystal Structures, and Blue/Red Dichroism

Rare blue-colored [2]­pseudorotaxanes based on the previously
unexplored
[N,N′-bis­(4-pyridyl)-4,4′-bipyridinium]2+ axle and bis­(1,5-naphtho)-32-crown-8 (BN32C8) or bis­(1,5-naphtho)-38-crown-10
(BN38C10) wheels have been synthesized and characterized by UV–vis, 1H NMR spectroscopy,
and electrochemistry, and their metal-binding properties toward CdI2 and HgCl2 have been studied by optical absorption
in solution and X-ray crystallography in the solid state. We report
contrasting structures of the same metal and different wheels or the
same wheel and different metals. We also show for the first time that
a simple metal complex, such as Hg2Cl62–, can induce a blue/red linear dichroism by organizing the [2]­pseudorotaxane
units into a columnar arrangement in the crystal.