Diverse Supramolecular Architectures Having Well-Defined Void Spaces Formed from a Pseudorotaxane Cation: Influential Role of Metal Dithiolate Coordination Complex Anions

This
paper describes the influence of a group of classical inorganic
coordination complex anions on assembling a particular pseudorotaxane
cation (the crown ether, dibenzo-24-crown-8 threaded by an axle, 1,2-bis­(4,4′-bipyridinium)
ethane) resulting in a series of supramolecular
ion pair compounds, namely, [pseudorotaxane]­[Cu­(mnt)2] (1), [pseudorotaxane]­[Ni­(mnt)2] (2), [pseudorotaxane]­[Pd­(mnt)2] (3), and [pseudorotaxane]­[Zn­(dmit)2] (5) of varying dimensions in terms of their topology; dithiolene =
mnt2–(1,2-dicyanoethylenedithiolate) and dmit2–(1,3-dithiole-2-thione-4,5-dithiolate). The shapes
of supramolecular framework void spaces of diverse dimensions, that
are observed in the crystal structures of compounds 1–3, are influenced by the geometry of particular
coordination complex anions, used in the relevant synthesis, and the
concerned coordination complex gets encapsulated in the void spaces
of respective supramolecular pseudorotaxane frameworks. The platinum
compound [pseudorotaxane]­[Pt­(mnt)2] (4) is found to be an exception in forming well-defined void spaces.
The crystal structure of compound [pseudorotaxane]­[Zn­(dmit)2] (5) reveals an interesting aggregation of supramolecular
ladders, in which each compartment of the ladders accommodates the
complex anion Zn­(dmit)2]2–. The shape
of this coordination complex anion seems to be responsible for such
ladderlike arrangement in the relevant crystals. Compounds 1 through 5 have been characterized by routine analysis,
such as IR, 1H NMR, UV–Vis–NIR, and electron
paramagnetic resonance spectroscopic techniques including elemental
analysis, and unambiguously by single crystal X-ray crystallography.
The stabilization of such cationic supramolecular pseudorotaxane architectures
having well-defined grid-type void spaces is achieved through hydrogen
bonding interactions that include C–H···S, C–H···N,
and C–H···O, and π–π stacking
interactions. The exchange of the complex anion in one of these ion
pair compounds (compound 1) with Br– anions (in a solid-to-solid transformation through solid–liquid
interface reaction) results in the formation compound [pseudorotaxane]­Br2 whose X-ray powder pattern is different than that of 1 indicating a new phase formation in the crystals of [pseudorotaxane]­Br2.