Second-sphere Coordination of [Pt(bipy)(NH3)2]2+ by Dibenzo-crown Ethers. Solution Spectroscopic Studies and the Crystal and Molecular Structures of [Pt(bipy)(NH3)2.dibenzo-30-crown-10] [PF6]2.0.6 H2O and [Pt(bipy)(NH3)2.dibenzo-24-crown-8] [PF6]2 |
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| Authors: | Howard M Colquhoun Simon M Doughty John M Maud J Fraser Stoddart David J Wllliams John B Wolstenholme |
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| Affiliation: | 1. New Science Group, Imperial Chemical Industries PLC, Runcorn WA7 4QE, UK;2. Department of Chemistry, The University, Sheffield S3 7HF, UK;3. Chemical Crystallography Laboratory, Imperial College, London SW7 2AY, UK |
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| Abstract: | In addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between Pt(bipy)(NH3)2] 2+ and a series of dibenzo-3n-crown-n (n = 6–12) ethers as evidenced by 1H NMR and UV-visible spectra in solution and by X-ray crystal structures (for n = 8 and 10) in the solid state. Mutual diamagnetic (ring current) shielding by the aromatic systems of host and guest results in dramatic upfield shifts of certain aromatic proton resonances on adduct formation, especially when n = 10 or 11. A broad charge-transfer absorption band at 350 nm attains its maximum intensity at n = 11 though stability constant measurements indicate optimum binding when n = 10. X-ray diffraction studies reveal that, when n = 8, only one of the crown ether benzo-rings interacts with the bipyridyl ligand in a charge-transfer sense. However, when n = 10, the macrocycle is sufficiently large and flexible to allow both benzo-rings to enter into stabilising interactions with the bipyridyl ligand such that the platinum complex is encapsulated by the host in a U-shaped cavity. |
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