Supramolecular recognition. Terpyridyl palladium and platinum molecular clefts and their association with planar
Andrew J Goshe1, Ian M Steele, B Bosnich
1Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Illinois 60637, USA.
Abstract:
Molecular receptors, consisting of either two parallel cofacially disposed terpyridyl-Pd-Cl+ or terpyridyl-Pt-Cl+ units, are described. Concerted rotation of these units about the molecular spacer can alter their separation between 6.4 and 7.2 A to accommodate the dimensions of molecular guests. Neutral and anionic planar complexes of platinum(II) were investigated as guests to determine if metal-metal interaction between the host and guest metals could stabilize host-guest association. With a neutral guest, it was found that host-guest formation is signaled by a color change from light yellow to deep red. For one of the anionic guests, a visible absorption band appears upon host-guest formation with the platinum receptor that is ascribed to transitions associated with a Pt-Pt interaction. The association constants found for the neutral guest with the palladium and platinum receptors are large, suggesting that metal-metal interaction contributes to the molecular recognition. The structures of the host-(neutral)guest complexes in solution have been determined by 1H NOESY spectra. A crystal structure of the platinum host-(neutral)guest complex is the same as that found in solution and confirms the presence of a Pt-Pt interaction. Temperature-dependent (195)Pt NMR spectra in solution provide a quantitative estimate of the conformational interconversions of the free platinum receptor.
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