STRUCTURES OF POTASSIUM ENCAPSULATED WITHIN THE 1,3-ALTERNATE CONFORMATION OF CALIX[4]ARENES

5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrakis(diethylcarbamoylmethoxy)calix[4] arene (L(1)) 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 [K(2)L(1)][CuCl2][l(3)], [monoclinic, space group P2(1)/n, a = 13.972(6), b = 23,373(12), c = 25.271(12) Angstrom, beta = 102.5(1)degrees, 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-dihydroxycalix[4]arene (L(2)), [KL(2)][l(3)], has also been elucidated [triclinic, space group P (1) over bar, a = 14.160(8), b = 16.326(10), c = 16.540(10) Angstrom, alpha = 65.83(1), beta = 67.37(1), gamma = 88.87(1)degrees, Z = 2, R = 0.091 for 4976 'observed' reflections]. Remarkably, the calixarene is again found in the 1,3-alternate conformation, although C-13 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 calix[4]arenes, Molecular mechanics calculations have been carried out to investigate the relative stabilities of the calixarene conformations.