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An unusually flexible expanded hexaamine cage and its CuII complexes: variable coordination modes and incomplete encapsulation

Journal Article


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Abstract


  • The bicyclic hexaamine "cage" ligand Me 8tricosaneN 6 (1,5,5,9,13,13,20,20-octamethyl-3,7,11,15,18, 22-hexaazabicyclo[7.7.7]tricosane) is capable of encapsulating octahedral metal ions, yet its expanded cavity allows the complexed metal to adopt a variety of geometries comprising either hexadentate or pentadentate coordination of the ligand. When complexed to Cu II the lability of the metal results in a dynamic equilibrium in solution between hexadentate- and pentadentate- coordinated complexes of Me 8tricosaneN 6. Both [Cu(Me 8tricosaneN 6)](ClO 4) 2 (6-coordinate) and [Cu(Me 8tricosaneN 6)](S 2O 6) (5-coordinate) have been characterized structurally. In weak acid (pH 1) a singly protonated complex [Cu(HMe 8tricosaneN 6)] 3+ has been isolated that finds the ligand binding as a pentadentate with the uncoordinated amine being protonated. vis-NIR and electron paramagnetic resonance (EPR) spectroscopy show that the predominant solution structure of [Cu(Me 8tricosaneN 6)] 2+ at neutral pH comprises a five-coordinate, square pyramidal complex. Cyclic voltammetry of the square pyramidal [Cu(Me 8tricosaneN 6)] 2+ complex reveals a reversible Cu II/I couple. All of these structural, spectroscopic, and electrochemical features contrast with the smaller cavity and well studied "sarcophagine" (sar, 3,6,10,13,16,19-hexaazabicyclo[6.6. 6]eicosane) Cu II complexes which are invariably hexadentate coordinated in neutral solution and cannot stabilize a Cu I form. © 2011 American Chemical Society.

Authors


  •   Qin, C-J (external author)
  •   James, Lloyd
  •   Chartres, J D. (external author)
  •   Alcock, Leighton (external author)
  •   Davis, Kimberley J.
  •   Willis, Anthony C. (external author)
  •   Sargeson, Alan M. (external author)
  •   Bernhardt, Paul V. (external author)
  •   Ralph, Stephen Frederick.

Publication Date


  • 2011

Citation


  • Qin, C., James, L., Chartres, J. D., Alcock, L. J., Davis, K. Jane., Willis, A. C., Sargeson, A. M., Bernhardt, P. V. & Ralph, S. F. (2011). An unusually flexible expanded hexaamine cage and its CuII complexes: variable coordination modes and incomplete encapsulation. Inorganic Chemistry: including bioinorganic chemistry, 50 (18), 9131-9140.

Scopus Eid


  • 2-s2.0-80052717537

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=6550&context=scipapers

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/3208

Has Global Citation Frequency


Number Of Pages


  • 9

Start Page


  • 9131

End Page


  • 9140

Volume


  • 50

Issue


  • 18

Abstract


  • The bicyclic hexaamine "cage" ligand Me 8tricosaneN 6 (1,5,5,9,13,13,20,20-octamethyl-3,7,11,15,18, 22-hexaazabicyclo[7.7.7]tricosane) is capable of encapsulating octahedral metal ions, yet its expanded cavity allows the complexed metal to adopt a variety of geometries comprising either hexadentate or pentadentate coordination of the ligand. When complexed to Cu II the lability of the metal results in a dynamic equilibrium in solution between hexadentate- and pentadentate- coordinated complexes of Me 8tricosaneN 6. Both [Cu(Me 8tricosaneN 6)](ClO 4) 2 (6-coordinate) and [Cu(Me 8tricosaneN 6)](S 2O 6) (5-coordinate) have been characterized structurally. In weak acid (pH 1) a singly protonated complex [Cu(HMe 8tricosaneN 6)] 3+ has been isolated that finds the ligand binding as a pentadentate with the uncoordinated amine being protonated. vis-NIR and electron paramagnetic resonance (EPR) spectroscopy show that the predominant solution structure of [Cu(Me 8tricosaneN 6)] 2+ at neutral pH comprises a five-coordinate, square pyramidal complex. Cyclic voltammetry of the square pyramidal [Cu(Me 8tricosaneN 6)] 2+ complex reveals a reversible Cu II/I couple. All of these structural, spectroscopic, and electrochemical features contrast with the smaller cavity and well studied "sarcophagine" (sar, 3,6,10,13,16,19-hexaazabicyclo[6.6. 6]eicosane) Cu II complexes which are invariably hexadentate coordinated in neutral solution and cannot stabilize a Cu I form. © 2011 American Chemical Society.

Authors


  •   Qin, C-J (external author)
  •   James, Lloyd
  •   Chartres, J D. (external author)
  •   Alcock, Leighton (external author)
  •   Davis, Kimberley J.
  •   Willis, Anthony C. (external author)
  •   Sargeson, Alan M. (external author)
  •   Bernhardt, Paul V. (external author)
  •   Ralph, Stephen Frederick.

Publication Date


  • 2011

Citation


  • Qin, C., James, L., Chartres, J. D., Alcock, L. J., Davis, K. Jane., Willis, A. C., Sargeson, A. M., Bernhardt, P. V. & Ralph, S. F. (2011). An unusually flexible expanded hexaamine cage and its CuII complexes: variable coordination modes and incomplete encapsulation. Inorganic Chemistry: including bioinorganic chemistry, 50 (18), 9131-9140.

Scopus Eid


  • 2-s2.0-80052717537

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=6550&context=scipapers

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/3208

Has Global Citation Frequency


Number Of Pages


  • 9

Start Page


  • 9131

End Page


  • 9140

Volume


  • 50

Issue


  • 18