organic compounds
provide some evidence for the polarization of its molecular
structure, such that the potential for electronic delocalization
is optimized when the carbaldehyde groups are coplanar with
the heterocyclic system, and this may thus be the dominant
factor controlling the orientation of the carbaldehyde groups.
Firstly, the C31—O31 and C61—O61 bonds are both long for
chain, and the combination of all these hydrogen bonds
generates an S(6)C(6)C(9)[R22(5)] chain of rings (Fig. 2). In
this chain, the R22(5) motif actually contains three hydrogen
bonds, but atoms H4 and O31 act, respectively, as a double
donor and a double acceptor. Four chains of this type pass
through each unit cell, but there are no direction-specific
interactions between the chains.
˚
their type (mean literature value = 1.192 A; Allen et al., 1987),
while the C3—C31 and C6—C61 bonds are both short (mean
It is interesting to note that, despite the large excess in (I) of
potential hydrogen-bond donors in the form of aromatic C—H
bonds over potential hydrogen-bond acceptors, the O atoms of
the nitro group play no part in the hydrogen bonding. Nor are
there any dipolar nitro–nitro interactions (Garden et al., 2006;
Glidewell et al., 2006), analogous to the well documented
dipolar carbonyl–carbonyl interactions (Allen et al., 1998).
The action of the hydrogen bonds in (I) differs from that in
(II) (Low et al., 2006). While (II) also contains an asymmetric
N—Hꢀ ꢀ ꢀ(O)2 system, the shorter component generates a
centrosymmetric dimer containing an R22(12) motif, rather
than a C(6) chain as in (I). There are two C—Hꢀ ꢀ ꢀO hydrogen
bonds in the structure of (II), which link the R22(12) dimers
into sheets, but both of these donor atoms are components of
the unsubstituted phenyl ring, which is absent from the
constitution of (I). Hence, the supramolecular aggregation in
compounds of this type is very markedly influenced by the
nature of the peripheral substituents.
˚
literature value = 1.464 A). Secondly, the C5—C6 bond is long
˚
for its type (mean literature value = 1.331 A), and the C3a—
N4 and N4—C5 bonds have almost identical lengths. These
observations, taken all together, indicate that polarized forms
such as (Ia)–(Ic) (see the second scheme) are contributors to
the overall molecular–electronic structure. The molecular
dimensions of compound (II) were not discussed in the
original report (Low et al., 2006), but re-examination of the
structure of (II) shows that it exhibits exactly the same pattern
of intramolecular distances as found here for (I), pointing to a
similar interpretation of the carbaldehyde conformations.
Experimental
A mixture of 5-amino-3-(4-chlorophenyl)-1H-pyrazole, (C) (1.9 mmol),
and 1-(4-nitrophenyl)propenone, (B) (1.9 mmol), in dimethylform-
amide (1 ml) was heated under reflux for 20 min to afford the
intermediate 2-(4-chlorophenyl)-5-(4-nitrophenyl)-4,7-dihydropyra-
zolo[1,5-a]pyrimidine, (A). The reaction mixture was cooled to
ambient temperature and the intermediate was collected by filtration,
washed with ethanol and dried, and then purified by chromatography
on alumina using chloroform as the eluent. Phosphoryl chloride
(2.1 mmol) was then added dropwise to a suspension of the
pyrazolopyrimidine intermediate (1.0 mmol) in dimethylformamide
(2 ml) at 273 K. When the addition was complete, the reaction
mixture was stirred vigorously for 0.5 h at ambient temperature. The
resulting solid product, (I), was collected by filtration, dried and
recrystallized from dimethylformamide to give yellow crystals
suitable for single-crystal X-ray diffraction (yield 65%, m.p. 555–
557 K). MS (m/z, %): 410/408 (35/100, M+), 407 (53), 361 (51),
350 (70), 102 (31), 75 (42), 40 (82).
The intramolecular hydrogen bond mentioned earlier forms
an S(6) motif (Bernstein et al., 1995) and it is, in fact, the
longer and weaker component of an asymmetric three-centre
N—Hꢀ ꢀ ꢀ(O)2 system (Table 2), in which the shorter compo-
1
2
1
2
nent links the molecules at (x, y, z) and (12 ꢂ x, + y, ꢂ z),
1
which are related by the 21 screw axis along (14, y, ). Propa-
4
gation of this hydrogen bond forms a C(6) chain running
parallel to the [010] direction (Fig. 2). This [010] chain is
reinforced by a C—Hꢀ ꢀ ꢀO hydrogen bond which forms a C(9)
Crystal data
3
˚
C20H13ClN4O4
Mr = 408.79
V = 3486.7 (17) A
Z = 8
Monoclinic, C2=c
Mo Kꢁ radiation
ꢂ = 0.26 mmꢂ1
T = 120 (2) K
0.46 ꢃ 0.36 ꢃ 0.24 mm
˚
a = 23.943 (5) A
˚
b = 13.445 (2) A
˚
c = 12.336 (5) A
ꢀ = 118.594 (10)ꢁ
Data collection
Bruker–Nonius KappaCCD area-
detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.891, Tmax = 0.941
40202 measured reflections
4002 independent reflections
2520 reflections with I > 2ꢃ(I)
Rint = 0.066
Figure 2
A stereoview of part of the crystal structure of compound (I), showing the
formation of a hydrogen-bonded chain of rings. For the sake of clarity, H
atoms bonded to ring C atoms have been omitted.
ꢄ
o342 Trilleras et al. C20H13ClN4O4
Acta Cryst. (2008). C64, o341–o343
Trilleras, Jorge
