organic compounds
Figure 2
A stereoview of part of the crystal structure of compound (I), showing the
formation of a complex hydrogen-bonded chain running parallel to the
[010] direction. For the sake of clarity, H atoms not involved in the motifs
shown have been omitted.
70.8 (2)ꢂ for the substituted phenyl ring at C4 and 25.1 (2)ꢂ for
the indolyl unit at C6. Accordingly, the molecule of (I) has no
internal symmetry and thus it is conformationally chiral,
although the centrosymmetric space group accommodates
equal numbers of the two conformational enantiomers. The
bond distances and angles within the molecule of compound
(I) show no unexpected values.
Figure 3
Projection of the hydrogen-bonded chains on to (010), indicating the
location of the cavities. Accordingly, the H atoms have all been included.
Three independent hydrogen bonds, one each of the
N—Hꢀ ꢀ ꢀN, C—Hꢀ ꢀ ꢀN and C—Hꢀ ꢀ ꢀꢀ(arene) types (Table 2),
link the molecules of (I) into a complex chain of rings, or
molecular ladder. The N—Hꢀ ꢀ ꢀN hydrogen bond links mol-
ecules related by translation into a C(9) (Bernstein et al., 1995)
chain running parallel to the [010] direction; this chain
formation is augmented by the C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen
bond, so forming a chain of rings along [010]. Pairs of anti-
parallel chains, related to one another by inversion, are then
linked by paired C—Hꢀ ꢀ ꢀN hydrogen bonds to form a
complex chain of edge-fused rings in which R22(14) rings
centred at (14, n + 41, 21), where n represents an integer, alternate
distribution of electron density with any plausible array of
disordered solvent molecules.
The supramolecular aggregation in compound (I) differs
markedly from that observed for compounds (II) and (III)
(Low et al., 2007), as in these structures the single N—H bond
is engaged in a hydrogen bond to the dimethylformamide
component. Thus, in compound (II), a single C—Hꢀ ꢀ ꢀꢀ(arene)
hydrogen bond links the pyrazolopyridine units into centro-
symmetric dimers from which the dimethylformamide units
are pendent, while in compound (III), a combination of
C—Hꢀ ꢀ ꢀN and C—Hꢀ ꢀ ꢀꢀ(arene) hydrogen bonds links the
pyrazolopyridine units into a chain containing two types of
ring, again with pendent solvent molecules. By contrast, the
molecules of compound (IV), where no solvent component is
present, are linked into simple C(12) chains by an N—Hꢀ ꢀ ꢀO
hydrogen bond. Hence, the hydrogen-bonding behaviour is
different in each of compounds (I)–(IV). On the other hand,
all four compounds exhibit a ꢀ–ꢀ stacking interaction invol-
ving the pyridyl rings in pairs of molecules related by inver-
sion. In compound (II), as in (I), this interaction augments the
formation of a hydrogen-bonded dimer unit, in (III) it
augments the chain formation, and in compound (IV) this
interaction links a pair of antiparallel C(12) chains.
1
1
with R44(26) rings centred at (14, n ꢁ , ), where n again
4
2
represents an integer (Fig. 2). The formation of the chain is
weakly augmented by a ꢀ–ꢀ stacking interaction involving
pairs of pyridine rings: the pyridyl rings of the molecules at (x,
y, z) and (12 ꢁ x, 21 ꢁ y, 1 ꢁ z), which form the R22(14) motif, are
˚
strictly parallel, with an interplanar spacing of 3.674 (2) A, a
˚
ring–centroid separation is 3.840 (2) A and a ring–centroid
˚
offset of 1.117 (2) A.
Four chains of this type run through each unit cell along the
lines (14, y, 0), (41, y, 21), (43, y, 0) and (43, y, 21) (Fig. 3); there are no
direction-specific interactions between adjacent chains, but
instead these chains enclose cavities, totalling ca 9% of the
unit-cell volume. There are four symmetry-related cavities per
3
˚
unit cell, each of volume ca 102 A , located on twofold rota-
1
Experimental
3
tion axes and centred close to (0, 0.335, ), (0, 0.665, ),
1
4
4
An equimolar mixture of 2-fluorobenzaldehyde, 5-amino-3-methyl-1-
phenylpyrazole and 3-(2-cyanoacetyl)indole was subjected to
microwave irradiation in the absence of solvent using a focused
microwave reaction (CEM Discover) with maximum power 300 W
for 9 min at a controlled temperature of 473 K. The reaction mixture
was allowed to cool to ambient temperature and was then extracted
with hot ethanol/dimethylformamide (2:1 v/v). The combined extracts
3
4
(12, 0.835, ) and (12, 0.165, ). Each cavity is bounded by a
4
number of aromatic C—H bonds, along with F atoms and the
N atoms belonging to nitrile units (Fig. 3). While significant
electron density is located within the cavities, calculated by the
SQUEEZE option in PLATON (Spek, 2009) as seven elec-
trons per cavity, it did not prove possible to reconcile the
ꢃ
Acta Cryst. (2009). C65, o374–o376
Quiroga et al. C28H18FN5 o375
Quiroga, Jairo
