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Structures, hostguest chemistry and mechanism of stepwise self-assembly of M 4 L 6 tetrahedral cage complexes

Hall, Benjamin R. ; Manck, Lauren E. ; Tidmarsh, Ian S. ; Stephenson, Andrew ; Taylor, Brian F. ; Blaikie, Emma J. ; Griend, Douglas A. Vander ; Ward, Michael D.

Dalton Transactions, Dalton Transactions, 2011, Vol.40(45), pp.12132-12145 [Rivista Peer Reviewed]

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  • Titolo:
    Structures, hostguest chemistry and mechanism of stepwise self-assembly of M 4 L 6 tetrahedral cage complexes
  • Autore: Hall, Benjamin R. ; Manck, Lauren E. ; Tidmarsh, Ian S. ; Stephenson, Andrew ; Taylor, Brian F. ; Blaikie, Emma J. ; Griend, Douglas A. Vander ; Ward, Michael D.
  • Note di contenuto: The ligand L bip , containing two bidentate pyrazolylpyridine termini separated by a 3,3-biphenyl spacer, has been used to prepare tetrahedral cage complexes of the form [M 4 (L bip ) 6 ]X 8 , in which a bridging ligand spans each of the six edges of the M 4 tetrahedron. Several new examples have been structurally characterized with a variety of metal cation and different anions in order to examine interactions between the cationic cage and various anions. Small anions such as BF 4 and NO 3 can occupy the central cavity where they are anchored by an array of CHF or CHO hydrogen-bonding interactions with the interior surface of the cage, but larger anions such as naphthyl-1-sulfonate or tetraphenylborate lie outside the cavity and interact with the external surface of the cage via CH interactions or CHO hydrogen bonds. The cages with M = Co and M = Cd have been examined in detail by NMR spectroscopy. For [Co 4 (L bip ) 6 ](BF 4 ) 8 the 1 H NMR spectrum is paramagnetically shifted over the range 85 to +110 ppm, but the spectrum has been completely assigned by correlation of measured T 1 relaxation times of each peak with CoH distances. 19 F DOSY measurements on the anions show that at low temperature a [BF 4 ] anion diffuses at a similar rate to the cage superstructure surrounding it, indicating that it is trapped inside the central cage cavity. Furthermore, the equilibrium step-by-step self-assembly of the cage superstructure has been elucidated by detailed modeling of spectroscopic titrations at multiple temperatures of an acetonitrile solution of L bip into an acetonitrile solution of Co(BF 4 ) 2 . Six species have been identified: [Co 2 L bip ] 4+ , [Co 2 (L bip ) 2 ] 4+ , [Co 4 (L bip ) 6 ] 8+ , [Co 4 (L bip ) 8 ] 8+ , [Co 2 (L bip ) 5 ] 4+ , and [Co(L bip ) 3 ] 2+ . Overall the assembly of the cage is entropy, and not enthalpy, driven. Once assembled, the cages show remarkable kinetic inertness due to their mechanically entangled nature: scrambling of metal cations between the sites of pure Co 4 and Cd 4 cages to give a statistical mixture of Co 4 , Co 3 Cd, Co 2 Cd 2 , CoCd 3 and Cd 4 cages takes months in solution at room temperature.
  • Fa parte di: Dalton Transactions, Dalton Transactions, 2011, Vol.40(45), pp.12132-12145
  • Soggetti: Anions ; Cage ; Cations ; Entropy ; Holes ; Mathematical Models ; Self Assembly ; Superstructures ; Miscellaneous Sciences (So) ; Magnetism (Ea)
  • Tipo: Articolo
  • Identificativo: ISSN: 1477-9234 ; E-ISSN: 1477-9242 ; DOI: 10.1039/c1dt10781j

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