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

26,27,28-tetrakis(diethylcarbamoylmethoxy)calix[4] arene (L(1)) has be en synthesised in the 1,3-alternate conformation for the first time. P roton NMR complexation studies suggest that this molecule forms 1:1 an d 2:1 complexes with potassium cations. A crystal structure determinat ion has been performed on the 2:1 complex [K(2)L(1)][CuCl2][l(3)], [mo noclinic, space group P2(1)/n, a = 13.972(6), b = 23,373(12), c = 25.2 71(12) Angstrom, beta = 102.5(1)degrees, Z = 4, R = 0.092 for 6501 'ob served' reflections]. The structure of the 1:1 potassium complex of th e related diamide, etra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy) -26,28-dihydroxycalix[4]arene (L(2)), [KL(2)][l(3)], has also been elu cidated [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), g amma = 88.87(1)degrees, Z = 2, R = 0.091 for 4976 'observed' reflectio ns]. Remarkably, the calixarene is again found in the 1,3-alternate co nformation, 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 hither to unobserved combination of close contacts to four oxygen atoms, and to two phenyl rings of the respective calix[4]arenes, Molecular mechan ics calculations have been carried out to investigate the relative sta bilities of the calixarene conformations.