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

76 A. Nangia · G.R. Desiraju
bonds in the three-point array with isolated hydrogen bonds; and lastly (4) to
demonstrate the construction of supramolecular architectures using the synthon
concept.
The crystal structure of the 1:2 complex 46 of dibenzylidene ketone 40 and
trinitrobenzene 43 showed the expected DAD:ADA motif 49 constituted with
C-H◊◊◊O hydrogen bonds (Scheme 10) [49]. The overall structure is fortified by
additional C-H◊◊◊O hydrogen bonds from the acidic vinyl and phenyl hydrogen
atoms to the nitro oxygen atom on the other side of the carbonyl group. The 1:2
complex 47 between dibenzylidene cyclopentanone 41 and 43 contains the triply
hydrogen bonded array 49 along with C-H◊◊◊O hydrogen bonds between the
allylic H-atoms of 41 and the nitro O-atoms of 43. The additional fortification
from bifurcated C-H◊◊◊O hydrogen bonds on the hydrocarbon side of the molecule
is present in complexes 46 and 47 but not in 48. This may be ascribed to
acidity effects. A comparison of the three crystal structures 46–48 reveals also
that the C-H◊◊◊O hydrogen bonds that constitute synthon 49 are shorter and
more linear compared to the isolated C-H◊◊◊O hydrogen bonds elsewhere in the
structure. This strengthens the idea that C-H◊◊◊O hydrogen bonds which are part
of a multipoint array are more significant (see also the article by J.P. Glusker in
this volume).
The idea of robustness of a synthon has been alluded to earlier. The ability of
synthon 49 in controlling self-assembly within this family of crystal structures
was evidenced in the related complexes with picryl chloride 44 where it was
found that the chloro group does not interfere with the formation of the
DAD:ADA array. However, when the -Cl was replaced with an -OH group, the
multipoint recognition motif is absent. This suggests that the strongly hydrogen
40
41
42
49
43
44
45
46:40.43
47:41.43
48:42.43
Scheme 10. DAD:ADA complexes 46–48 of dibenzylidene ketones and trinitrobenzene
(see [49])
11