Research Articles

Superstructure Control in the Crystal Growth and Ordering of Urea Inclusion Compounds

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Science  06 Sep 1996:
Vol. 273, Issue 5280, pp. 1355-1359
DOI: 10.1126/science.273.5280.1355


A template-directed mechanism of crystal growth is demonstrated for urea inclusion compounds (UICs). For UICs containing n-alkanone or α+1,ω−1-alkanedione guests, x-ray diffraction revealed superstructure relations between host and guest repeats along the channel axis for guests containing 8 to 14 carbons. For a favorable structural match between host and guest, UICs typically grow as flat hexagonal plates, and atomic force microscopy of {001} surfaces revealed molecularly smooth terraces differing in height by multiples of the guest repeat. If the match is poor, protrusion of guests from the {001} surfaces nucleates growth along the channel axis to form hexagonal needles.