SUPERSTRUCTURE CONTROL IN THE CRYSTAL-GROWTH AND ORDERING OF UREA INCLUSION-COMPOUNDS

A template-directed mechanism of crystal growth is demonstrated for ur ea inclusion compounds (UICs). For UICs containing n-alkanone or alpha +1,omega-1-alkanedione guests, x-ray diffraction revealed superstructu re relations between host and guest repeats along the channel axis for guests containing 8 to 14 carbons, For a favorable structural match b etween host and guest, UICs typically grow as flat hexagonal plates, a nd atomic force microscopy of {001} surfaces revealed molecularly smoo th terraces differing in height by multiples of the guest repeat, If t he match is poor, protrusion of guests from the {001} surfaces nucleat es growth along the channel axis to form hexagonal needles.