Publication Details

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


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.



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