MOLECULAR MOTIONS IN FLUCTIONAL CRYSTALS - N-BASE ADDUCTS OF BIS(1,5-CYCLOOCTANEDIYLBORYL) OXIDE

The adducts of bis(1,5-cyclooctanediylboryl) oxide (1) with quinuclidine (2a) and with pyridine (2b) show an unusually large premelting endothermic phase transition. 2a has been investigated by B-11-NMR spectroscopy in the solid state and at various temperatures in its mesophase. The significant differences in the lattice packings of the molecules of the thermally stable adducts of 1 with 4-methyl-, 3-bromo-, and 4-(dimethylamino)pyridine (2c-e; X-ray structural analysis) from those of 2a and 2b suggests that it is the unique molecular arrangement in the respective lattices of the latter two adducts which allows a smooth transition to a two-dimensionally ordered mesophase. This is stabilized by intermolecular fluctuation of the N-base molecules between the boron atoms of the neighbouring molecules of 1.