TY - JOUR
T1 - An unusually flexible expanded hexaamine cage and its CuII complexes
T2 - Variable coordination modes and incomplete encapsulation
AU - Qin, Chang Jin
AU - James, Lloyd
AU - Chartres, Jy D.
AU - Alcock, Leighton J.
AU - Davis, Kimberley J.
AU - Willis, Anthony C.
AU - Sargeson, Alan M.
AU - Bernhardt, Paul V.
AU - Ralph, Stephen F.
PY - 2011/9/19
Y1 - 2011/9/19
N2 - The bicyclic hexaamine "cage" ligand Me 8tricosaneN6 (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 CuII the lability of the metal results in a dynamic equilibrium in solution between hexadentate- and pentadentate- coordinated complexes of Me8tricosaneN6. Both [Cu(Me 8tricosaneN6)](ClO4)2 (6-coordinate) and [Cu(Me8tricosaneN6)](S2O6) (5-coordinate) have been characterized structurally. In weak acid (pH 1) a singly protonated complex [Cu(HMe8tricosaneN6)] 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(Me8tricosaneN6)]2+ at neutral pH comprises a five-coordinate, square pyramidal complex. Cyclic voltammetry of the square pyramidal [Cu(Me8tricosaneN6)]2+ complex reveals a reversible CuII/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) CuII complexes which are invariably hexadentate coordinated in neutral solution and cannot stabilize a CuI form.
AB - The bicyclic hexaamine "cage" ligand Me 8tricosaneN6 (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 CuII the lability of the metal results in a dynamic equilibrium in solution between hexadentate- and pentadentate- coordinated complexes of Me8tricosaneN6. Both [Cu(Me 8tricosaneN6)](ClO4)2 (6-coordinate) and [Cu(Me8tricosaneN6)](S2O6) (5-coordinate) have been characterized structurally. In weak acid (pH 1) a singly protonated complex [Cu(HMe8tricosaneN6)] 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(Me8tricosaneN6)]2+ at neutral pH comprises a five-coordinate, square pyramidal complex. Cyclic voltammetry of the square pyramidal [Cu(Me8tricosaneN6)]2+ complex reveals a reversible CuII/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) CuII complexes which are invariably hexadentate coordinated in neutral solution and cannot stabilize a CuI form.
UR - http://www.scopus.com/inward/record.url?scp=80052717537&partnerID=8YFLogxK
U2 - 10.1021/ic201326d
DO - 10.1021/ic201326d
M3 - Article
SN - 0020-1669
VL - 50
SP - 9131
EP - 9140
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 18
ER -