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

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journal contribution
posted on 07.05.2014 by Vedichi Madhu, Samar K. Das
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 13, 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.