Beer, Paul D., Drew, Michael G.B., Gale, Philip A., Leeson, Philip B. and Ogden, Mark I.
Structures of potassium encapsulated within the 1,3-alternate conformation of calixarenes
Journal of the Chemical Society Dalton Transactions, (23), . (doi:10.1039/dt9940003479).
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5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrakis(diethylcarbamoylmethoxy)calixarene (L1) has been synthesised in the 1,3-alternate conformation for the first time. Proton NMR complexation studies suggest that this molecule forms 1:1 and 2:1 complexes with potassium cations. A crystal structure determination has been performed on the 2:1 complex [K2L1][CuCl2][I3], [monoclinic, space group P21/n, a= 13.972(6), b= 23.373(12), c= 25.271(12)Å, ?= 102.5(1)°, Z= 4, R= 0.092 for 6501 ‘observed’ reflections]. The structure of the 1:1 potassium complex of the related diamide, 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-dihydroxycalixarene (L2), [KL2][I3], has also been elucidated [triclinic, space group P, a= 14.160(8), b= 16.326(10), c= 16.540(10)Å, ?= 65.83(1), ?= 67.37(1), ?= 88.87(1)°, Z= 2, R= 0.091 for 4976 ‘observed’ reflections]. Remarkably, the calixarene is again found in the 1,3-alternate conformation, although 13C NMR studies suggest that, in this case, the conformation is not maintained in solution. The co-ordination spheres of the potassium cations in both structures are similar, with a hitherto unobserved combination of close contacts to four oxygen atoms, and to two phenyl rings of the respective calixarenes, Molecular mechanics calculations have been carried out to investigate the relative stabilities of the calixarene conformations.
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