influence the secondary association of preaggregates, and therefore
the final morphologies of nanostructures. Essentially, hierarchical
intermolecular interactions may have different effects and play
different roles at different level of size regime. (i) To get organic
nanocrystalline, strong intermolecular interactions, such as p–p,
hydrogen-bonding, has to survive at supramolecular level. (ii) The
cooperation of the growth along the direction of preaggregates
with the side-by-side stacking of preaggregates is necessary to
obtain one-dimensional morphology.
This work was supported by the National Natural Science
Foundation of China (Nos 90301010, 50573084, 90606004), the
Chinese Academy of Sciences (‘‘100 Talents’’ program), and the
National Research Fund for Fundamental Key Project 973
(2006CB806200, 2006CB932101).
Fig. 4 The schematic representation for the formation processes of
nanoscale materials of compounds a, b and c, respectively. See text for
details.
Notes and references
{ Crystal data for a: C16H14N4, Mr = 262.31, monoclinic, space group
formation of an organized object requires several steps: (i)
formation of preaggregates (primary), (ii) association of preag-
gregates (secondary), and (iii) conversion into the final structure
(tertiary).11,13 Compound a forms dimers as the preaggregate,
which are quasi-spherical (see the middle image in Fig. 4A). The
weak and diffuse nature of van der Waals driving forces for the
association of dimers leads to the formation of amorphous
nanospheres. Unlike a, preaggregates for b and c should be the
zigzag and linear hydrogen-bonded chains (see the middle images
in Fig. 4B and 4C). Although aggregation numbers are unknown
in both cases, they are hydrogen-bonding open with two free sites
at each end. Therefore, association of chain-like preaggregates can
occur either by direct lock-in of existing preaggregates via
hydrogen-bonding interactions or by side-by-side stacking of
hydrogen-bonded chains via van der Waals interactions. In the
case of b, the zigzag shape of chain-like preaggregate provides
more molecular contacts as recognition sites favourable for the
latter path (see Fig. S2c and S2d{). On the one hand, side-by-side
stacking of hydrogen-bonded chains facilitates the molecules in the
preaggregates become more restricted in relative position,
necessary for the formation of organized structure, for example,
crystal structure. On the other hand, larger is the aggregate
generated by side-by-side stacking, more hydrogen-bonding sites
does the aggregate provide and thus larger is its hydrogen-bonding
association constant. Therefore, association of preaggregates for b
is a cooperative process, according to a very recent publication by
Jonkheijm and co-workers.12 The ED and XRD pattern of square
nanowires indicate that the nanowire is growing along the crystal
(010) direction, coincident with the direction of b zigzag hydrogen-
bonded chains. In the case of c, lack of recognition sites (see
Fig. S3c and S3d{) make the association of c linear chains less
cooperative, thus nanocubes rather than square nanowires are
formed. At one time, the side-by-side stacking of chain-like
preaggregates are considered to be against the direct linkage in the
assembling process of one-dimensional nanomaterials.14 Our
results indicate that the growth along the direction of preaggre-
gates has been in cooperation with the side-by-side stacking of
preaggregates to obtain one-dimensional morphology.
˚
C2/c, a = 34.919(7) b = 17.106(3) c = 14.362(3) A, b = 93.49(3)u, V =
3
8562.86(1593) A , bcalcd = 1.22076 g cm23. Crystal data for b: C16H14N4,
˚
Mr = 262.31, orthorhombic, space group Pbca, a = 10.2048(10) b =
3
15.5662(15) c = 17.4159(17) A, V = 2766.5(47) A , bcalcd = 1.25949 g cm23
Crystal data for c: C16H14N4, Mr = 262.31, monoclinic, space group
.
˚
˚
˚
P2(1)/n, a = 10.894(2) b = 9.1577(18) c = 14.177(3) A, b = 90.888(3)u, V =
1414.25(49) A , bcalcd = 1.23195 g cm23. CCDC 299563–299565. For
3
˚
crystallographic data in CIF format see DOI: 10.1039/b701327b
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In conclusion, we successfully prepared nanospheres, square
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This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 1623–1625 | 1625