Reversible Transformation between a [PdL2]2+ “Figure-of-Eight” Complex and a [Pd2L2]4+ Dimer: Switching On and Off Self-Recognition |
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Authors: | Dr Dan Preston Prof Paul E Kruger |
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Institution: | MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Christchurch, 8041 New Zealand |
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Abstract: | Structural changes to metallosupramolecular assemblies resulting in the release or uptake of guests are currently well established, whereas transformations turning on and off specific self-recognition are far less developed. We report a novel ligand (2,6-bis(1-(3-pyridin-4-yl)phenyl-1H-1,2,3-triazol-4-yl)pyridine) possessing a tridentate central metal-binding site flanked by two pendant pyridyl arms. In a 2:1 ratio with PdII metal ions, a spiro-type PdL2]2+ “Figure-of-eight” complex forms with the central tridentate binding pocket unoccupied. The introduction of an additional one equivalent of PdII metal ion results in the conversion to a dimeric Pd2L2]4+ molecule with the tridentate pocket occupied. There is site-specific self-recognition between dimers in solution with strong NOE peaks between adjacent molecules. The self-recognition between dimers can be turned off in two ways: firstly, adding another equivalent of PdII metal ion brings about binding to the previously uncoordinated pyridyl arms that are key to the self-recognition event, and; secondly, addition of sufficient ligand to return the stoichiometry to 2:1 regenerates the PdL2]2+ complex. Hence, the self-recognition event can be turned on or off through simple variation of L:PdII stoichiometry. |
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Keywords: | molecular recognition palladium self-assembly spiro compounds structural transformation |
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