VERSATILITY IN INCLUSION HOSTS - UNUSUAL CONFORMATION IN THE CRYSTAL-STRUCTURE OF THE PARA-TERT-BUTYLCALIX[8]ARENE - PYRIDINE (1-8) CLATHRATE

Crystal structure analysis proves that the p-t-butylcalix[8]arene host sits around a symmetry center in the P1BAR crystal lattice. The triclinic cell parameters and calculated volume are: a = 10.034(2), b = 17.434(2), c = 18.321(2) angstrom, alpha = 113.86(1)degrees, beta = 93.08(1)degrees, gamma = 92.62(1)degrees, V = 2919(2) angstrom 3. For Z = 1 and F.W. = 1834.6 the calculated density is 1.04 g/cm3. It is shown that the host macrocycle is in an open chairlike conformation and virtually leaves no cavity to be occupied by the guest molecule. Consequently the pyridine guest molecules are enclathrated through steric barriers into the crystal lattice, having only one of the guests in the asymmetric unit bound to the host. The open conformation of the host is facilitated by a break in the ring of O...O hydrogen bonds on the rim of the would-be calix. This structure also conveys essential information on the possible solution conformations of the host in pyridine.