198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

Hydrogen-Bonded Ribbons, Tapes and Sheets as Motifs for Crystal Engineering 125
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Fig. 31 a, b. CN◊◊◊Cl mediated tapes are formed when R 1 and R 2 are small non-hydrogen
bonding groups (1 and 2). b However, as the substituents get larger, sheets start forming
ture (Fig. 31b). In the case of the dihydroxy derivative, the Cl is unable to compete
with the O-H groups and one can expect the O-H◊◊◊N interaction to dominate
in the crystal structure.
Pascal and Ho have also observed the formation of N◊◊◊Cl donor-acceptor
interactions in the formation of sheets by cyanuric chloride (48) (Fig. 32) [79].
They have also synthesized and studied molecular associations of receptors
based on these donor-acceptor forces [80].
The iodo◊◊◊nitro synthon has been used in the structures of 4-iodonitrobenzene
(49), the 1:2 complex between 1,4-dinitrobenzene and 4-iodocinnamic
acid (51) [81], and the 1:1 complex between 1,4-dinitrobenzene and 1,4-diiodobenzene
(50) [82]. The target in the work was the formation of a linear tape
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