Molecular and crystal structures of 5,7-dichloro-4-nitro-2,1,3-benzoxadiazole and products of its reactions with secondary amines

Article abstract of DOI:10.1023/A:1015017931597

The molecular and crystal structures of 5,7-dichloro-4-nitro-2,1,3-benzoxadiazole and products of its reactions with hexamethyleneimine and dimethylamine were established by X-ray diffraction analysis. The molecular structures and the systems of hydrogen

Full text of DOI:10.1023/A:1015017931597

Russian Chemical Bulletin, International Edition, Vol. 51, No. 1, pp. 105—110, January, 2002
105
Molecular and crystal structures
of 5,7ꢀdichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole
and products of its reactions with secondary amines
b
b
b
F. S. Levinson,a S. I. Efimov,a B. I. Buzykin,b A. T. Gubaidullin, D. B. Krivolapov, and I. A. Litvinov

aKazan State Technological University,
68 ul. K. Marksa, 420015 Kazan, Russian Federation.
Fax: +7 (843 2) 76 1673
bA. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 76 7354. Eꢀmail: buz@iopc.knc.ru
The molecular and crystal structures of 5,7ꢀdichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole and
products of its reactions with hexamethyleneimine and dimethylamine were established by
Xꢀray diffraction analysis. The molecular structures and the systems of hydrogen bonds in the
crystals of these compounds are discussed.
Key words: 5,7ꢀdichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole, 7ꢀchloroꢀ5ꢀdimethylaminoꢀ4ꢀnitroꢀ
2,1,3ꢀbenzoxadiazole, 7ꢀchloroꢀ5ꢀhexamethyleneiminoꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole.
5,7ꢀDichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole (1a) is a
poorly studied electrophile. The only data on the relative
mobilities of the chlorine atoms were obtained when usꢀ
ing compound 1a in the synthesis of a 5ꢀazidoꢀ7ꢀchloroꢀ
4ꢀnitro derivative.1 We found that both chlorine atoms in
1a can be replaced in its reactions with amines. Dependꢀ
ing on the reaction conditions, compounds containing
either identical or different fragments of aromatic or aliꢀ
phatic amines at positions 5 and 7 can be synthesized. It is
reasonable that the replacement of the chlorine atom at
position 5 by an arylamino or alkylamino group leads to a
decrease in mobility of the intact chlorine atom. The
introduction of alkylamino or dialkylamino groups posꢀ
sessing strong donor properties has the most pronounced
effect on the mobility of the Cl atom and, what is very
important, this effect is different in different cases. For
example, the reaction of 5ꢀdimethylaminoꢀsubstituted
compound 1b with piperazine hexahydrate (DMF, ∼20 °C,
two equivalents of the nucleophile) was completed in
75 min, whereas the reactions of related 5ꢀХꢀsubstituted
derivatives (where Х is diethylamino, piperidino, morꢀ
pholino, or hexamethyleneimino groups) performed unꢀ
der the same conditions were completed in ∼360 min. The
duration of the reaction was determined by TLC from the
disappearance of the starting compound in the reaction
mixture.
nitroꢀ2,1,3ꢀbenzoxadiazole (1b) and 7ꢀchloroꢀ5ꢀhexameꢀ
thyleneiminoꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole (1c), which
are products of the reactions of 1a with dimethylamine
and hexamethyleneimine, respectively.
Results and Discussion
The structures of compounds 1a—c were established
by Xꢀray diffraction analysis, which allowed us to reveal
the order in which the chlorine atoms in substrate 1a are
replaced. It is a matter of common knowledge that the
nitro group in aromatic and heterocyclic systems located
in the ortho or para position with respect to the halogen
atom activates the latter. The most pronounced effect is
generally accounted for by the virtually planar arrangeꢀ
ment of the nitrophenyl fragment.
To our knowledge, the structures of about two tens of
2,1,3ꢀbenzoxadiazole derivatives were established by Xꢀray
diffraction analysis among which only 7ꢀchloroꢀ4ꢀnitroꢀ
2,1,3ꢀbenzoxadiazole (1d)2 is similar to the compounds
under study in the type of replacement. Under the
conditions described, the reaction of electrophile 1d,
The present study was aimed at revealing the reasons
for the aboveꢀmentioned changes based on the threeꢀ
dimensional molecular structures of compound 1a and
the newly synthesized 7ꢀchloroꢀ5ꢀdimethylaminoꢀ4ꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 101—106, January, 2002.
1066ꢀ5285/02/5101ꢀ105 $27.00 © 2002 Plenum Publishing Corporation

106
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Levinson et al.
whose nitro group is virtually coplanar with the benzene
fragment, with piperazine hexahydrate was completed
in 20 min.
zene ring comprise the nineꢀmembered fragment (the
maximum deviations of the atoms from the mean plane of
this fragment are 0.017(3), 0.073(3), and 0.070(3) Å, reꢀ
Let us consider the molecular structures of compounds
1a—c and compare them with the data for compound 1d.
There is one molecule per asymmetric unit in the crystal
structures of 1a—c. The molecular structures of 1a—c in
the crystals are shown in Fig. 1. The bond length, bond
angles, and torsion angles in compounds 1a—c are typical
of 2,1,3ꢀbenzoxadiazoles2—6 (Tables 1—3). In compounds
1a—c, the oxadiazole ring together with the fused benꢀ
Table 1. Selected bond lengths (d) in compounds 1a—c
Bond
d/Å
1a
1b
1c
Cl(1)—C(7)
O(41)—N(4)
O(42)—N(4)
O(2)—N(1)
O(2)—N(3)
N(1)—C(8)
N(3)—C(9)
N(4)—C(4)
N(5)—C(5)
N(5)—C(10)
N(5)—C(11)(С(15))
C(8)—C(7)
C(8)—C(9)
C(6)—C(7)
C(6)—C(5)
C(5)—C(4)
C(4)—C(9)
C(6)—H(6)
1.705(4)
1.211(4)
1.224(3)
1.369(4)
1.383(4)
1.310(4)
1.316(4)
1.464(4)
—
1.718(3)
1.247(3)
1.241(3)
1.374(4)
1.404(3)
1.307(3)
1.315(4)
1.412(4)
1.338(3)
1.455(4)
1.471(4)
1.422(4)
1.418(4)
1.348(3)
1.462(4)
1.400(4)
1.426(3)
0.96(3)
1.719(3)
1.242(3)
1.229(3)
1.378(4)
1.402(3)
1.295(4)
1.318(4)
1.429(4)
1.388(3)
1.481(4)
1.467(4)
1.439(4)
1.429(4)
1.335(4)
1.474(4)
1.410(4)
1.422(4)
0.97(3)
a
Cl(1)
C(7)
N(1)
O(2)
C(8)
C(9)
C(6)
C(5)
—
—
C(4)
N(3)
1.422(4)
1.422(5)
1.337(5)
1.429(5)
1.363(4)
1.404(5)
0.94(3)
Cl(5)
O(42)
N(4)
O(41)
Cl(1)
b
Table 2. Selected bond angles (ω) in compounds 1a—c
C(7)
N(1)
Angle
ω/deg
C(6)
C(4)
C(8)
C(5)
C(11)
1a
1b
1c
C(2)
C(9)
N(1)—O(2)—N(3)
O(41)—N(4)—O(42)
O(41)—N(4)—C(4)
O(42)—N(4)—C(4)
O(2)—N(1)—C(8)
O(2)—N(3)—C(9)
N(1)—C(8)—C(7)
N(1)—C(8)—C(9)
C(7)—C(6)—C(5)
Cl(1)—C(7)—C(8)
Cl(1)—C(7)—C(6)
C(8)—C(7)—C(6)
C(7)—C(8)—C(9)
C(6)—C(5)—C(4)
C(5)—C(4)—C(9)
C(7)—C(6)—H(6)
C(5)—C(6)—H(6)
N(3)—C(9)—C(8)
N(3)—C(9)—C(4)
C(8)—C(9)—C(4)
N(4)—C(4)—C(5)
N(4)—C(4)—C(9)
C(5)—N(5)—C(5)
C(5)—N(5)—C(10)
112.9(2)
124.1(3)
120.0(2)
115.9(3)
104.4(3)
103.9(3)
130.0(3)
109.5(3)
122.2(2)
119.1(3)
123.0(3)
117.9(2)
120.5(3)
120.9(3)
118.6(3)
121.0(2)
116.0(2)
109.3(3)
130.8(3)
119.9(3)
122.8(3)
118.7(2)
—
112.2(2)
121.8(2)
119.5(2)
118.6(2)
104.0(2)
104.2(2)
128.1(3)
110.9(3)
121.9(3)
119.3(2)
121.0(2)
118.8(2)
121.0(2)
118.7(2)
118.7(2)
118.0(1)
120.0(1)
108.7(2)
131.8(3)
119.5(3)
123.2(2)
117.9(3)
120.8(2)
121.0(2)
118.2(2)
112.3(2)
122.6(3)
119.0(2)
118.3(2)
104.1(2)
104.1(2)
129.5(3)
111.1(2)
122.6(2)
117.9(2)
122.4(2)
119.7(3)
119.4(2)
117.5(2)
119.5(2)
119.0(2)
118.0(2)
108.3(2)
131.3(3)
120.4(2)
123.1(2)
116.4(2)
121.6(2)
123.5(2)
114.6(2)
N(5)
N(3)
O(41)
N(4)
C(10)
O(42)
Cl(1)
c
C(7)
C(14)
N(1)
C(2)
C(6)
C(5)
C(13)
C(12)
C(15)
C(8)
C(9)
N(5)
C(11)
C(4)
N(4)
O(42)
N(3)
C(10)
O(41)
Fig. 1. Molecular structures of 5,7ꢀdichloroꢀ4ꢀnitroꢀ2,1,3ꢀ
benzoxadiazole (1a) (a), 7ꢀchloroꢀ5ꢀdimethylaminoꢀ4ꢀnitroꢀ
2,1,3ꢀbenzoxadiazole (1b) (b), and 7ꢀchloroꢀ5ꢀhexamethyleneꢀ
iminoꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole (1c) (c) in the crystals.
—
—
C(5)—N(5)—C(11)(C(15))

5,7ꢀDichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
107
Table 3. Selected torsion angles (ϕ) in compounds 1a—c
fact, the sums of the bond angles at the N(5) atom in
compounds 1b and 1c are close to 360° and the degree of
the pyramidality of N(5) is equal to zero, which is indicaꢀ
tive of essential interactions between the lone electron
pairs and the πꢀsystem of the benzoxadiazole fragment.
From a comparison of the structures of compound
Angle
ϕ/deg
1a
1b
1c
N(1)—O(2)—N(3)—C(9)
C(5)—C(4)—N(4)—O(41)
–0.7(3)
41.4(5) –24.6(4)
1.1(4)
0.8(4)
23.4(5)
1b and N,Nꢀdimethylꢀ2,4ꢀdinitroaniline (ϕNO = 32°,
2
C(5)—C(4)—N(4)—O(42) –140.7(3)
C(9)—C(4)—N(4)—O(41) –139.0(3)
C(9)—C(4)—N(4)—O(42)
159.5(3) –160.2(3)
149.2(3) –145.2(3)
ϕNMe = 14.4°),7 it can be concluded that the fused
oxadi2azole ring produces insignificant steric hindrances
to the nitro group. This is also evidenced by the angle
38.9(4) –26.7(4)
31.2(5)
N(4)—C(4)—C(5)—C(6)
C(9)—C(4)—C(5)—C(6)
N(4)—C(4)—C(5)— N(5)
N(4)—C(4)—C(9)—N(3)
177.9(3)
–1.7(5) –14.5(4)
—
2.4(5)
159.3(3) –157.1(3)
ϕNO = 1.7° in molecule 1d.2 Interestingly, the presence
11.1(4)
28.9(5)
2
–26.0(5)
of the dimethylamino or hexamethyleneimino fragment
(in compounds 1b and 1c, respectively) adjacent to the
nitro group leads to elongation of the C(4)—C(5) bond,
which approaches the length of the single bond, whereas
the C(6)—C(7) bond remains virtually unchanged. This is
also typical of 4ꢀRꢀ5,7ꢀdinitroꢀ2,1,3ꢀbenzoxadiazoles
bearing a substituent at position 4 adjacent to the nitro
group.4,5 Compound 1d has the longest C(6)—C(5) bond
in the benzoxadiazole system. It should be noted that this
bond length remains unchanged (to within the experiꢀ
mental error) after introduction of the chlorine atom at
position 5 (cf. the corresponding bond in 1a), whereas the
presence of the donor substituents leads to its elongation
by 0.03—0.04 Å (1b and 1c).
The molecules of the compounds under study are not
involved in hydrogen bonding of the classical type. In
molecule 1a, there are also no interactions of the C—H...O
or C—H...Cl type. Apparently, the crystal packing of molꢀ
ecules 1a is to a large extent determined by πꢀπ electron
interactions between the benzoxadiazole systems. As a
result, the molecules are packed in tilted stacks along the
crystallographic axis 0y. In these stacks, the adjacent molꢀ
ecules are arranged in a headꢀtoꢀtail fashion. The occurꢀ
rence of the stacking effect is evidenced by the following
parameters: the distances between the planes of the initial
molecule 1a and two adjacent molecules generated from
the initial molecule by the symmetry operations (–x,
1 – y, –z) and (–x, 2 – y, –z) are 3.463 and 2.934 Å,
respectively. The dihedral angle between the planes of the
molecules is equal to zero.
The intermolecular D—H...A contacts (D and A are
the donor and acceptor, respectively) were analyzed
based on the standard criteria for hydrogen bonding
(d(D...A) < R(D) + R(A) + 0.50 Å, d(H...A) < R(H) +
R(A) – 0.12 Å, the D—H...A angle is larger than 100.0°,
where R are the van der Waals radii of the atoms) with the
use of the PLATON program,9 which revealed the presꢀ
ence of hydrogen bonds in the crystal structures of comꢀ
pounds 1b and 1c (Table 4). In these crystal structures,
intraꢀ and intermolecular C—H...O hydrogen bonds are
observed, which formally satisfy the aboveꢀmentioned criꢀ
teria. In the crystals of both compounds, the molecules
are linked in dimers, but their mutual arrangements are
substantially different.
15.1(5) –15.9(5)
N(4)—C(4)—C(9)—C(8) –178.4(3) –163.6(3)
162.4(3)
20.8(5)
C(4)—C(5)—N(5)—C(10)
C(4)—C(5)—N(5)—C(11)
C(4)—C(5)—N(5)—C(15)
C(6)—C(5)—N(5)—C(10)
C(6)—C(5)—N(5)—C(11)
C(6)—C(5)—N(5)—C(15)
N(1)—C(8)—C(9)—N(3)
Cl(1)—C(7)—C(8)—C(9)
—
—
—
—
—
–21.8(5)
165.5(3) –160.3(3)
165.5(3) –160.3(3)
152.9(3) –153.1(3)
–19.8(5)
–19.8(5)
–0.4(4)
25.8(4)
25.8(4)
0.3(3)
—
0.4(4)
177.9(3)
179.1(3) –178.9(2)
spectively); the fiveꢀ and sixꢀmembered rings are approxiꢀ
mately coplanar (the dihedral angles between the rings
are 1.1(2)°, 0.9(2)°, and 3.0(1)°, respectively). Compared
to compound 1d, compound 1a contains the additional
chlorine atom in the ortho position with respect to the
nitro group giving rise to steric hindrances due to which
the nitro group is rotated about the C(4)—N(4) bond by
40.2(2)°. The atoms of the substituents directly bound to
the benzene fragment are located in the plane of this
ring. The maximum deviations of the Cl(1), Cl(5), and
N(4) atoms from this plane are 0.059(1), 0.032(1), and
0.050(3) Å, respectively.
In compounds 1b and 1c (see Fig. 1, b and c), the
chlorine atom at position 5 is replaced by the residues of
secondary amines, with a consequent increase in steric
hindrances. In these compounds, the rotation of the nitro
group about the C(4)—N(4) bond is somewhat smaller
(32.5(3)° and –31.0(4)°, respectively), but the N(4) and
N(5) atoms deviate substantially from the plane of the
ring in opposite directions (by –0.455(3) and 0.348(3) Å,
respectively, in 1b; and by –0.431(3) and 0.379(3) Å,
respectively, in 1c). The direction of rotation of the nitro
group about the C(4)—N(4) bond in molecule 1b differs
from that in compounds 1a and 1c, whereas the direction
of rotation of the dialkylamino groups in molecule 1b
is identical with than in 1c. The Cl(1) atom in 1b
deviates from the plane of the benzene fragment by
–0.046(3) Å, whereas the Cl(1) atom in 1c is located in
the plane of this ring. The dihedral angles between the
plane of the benzene ring and the planes of the diꢀ
methylamino [N(5)C(10)C(11)] and hexamethyleneimino
[C(5)N(10)C(15)] fragments are 27.8(3)°. In spite of this

108
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Levinson et al.
Table 4. Parameters of hydrogen bonds in compounds 1b and 1c
Comꢀ
pound
Bond typea
Triad DH...A
H...A
D...A
D—H—A angle
/deg
Å
1b
1c
InterHBb
IntraHB
InterHBc
InterHBd
IntraHB
InterHBc
C(6)—H(6)...O(41)
2.34(3)
2.16(3)
2.56(3)
2.36(3)
2.09(3)
2.56(2)
3.237(4)
2.714(4)
3.555(4)
3.260(3)
2.776(5)
3.577(4)
156(2)
110.6(2)
173(2)
155(2)
119.9(2)
160(2)
C(10)—H(101…)...O(42)
C(11)—H(111)...O(42)
C(6)—H(6…)...O(41)
C(10)—H(101)...O(41)
C(12)—H(121)...O(2)
a IntraHB and InterHB are intraꢀ and intermolecular hydrogen bonds, respectively. The molecules
are related by the following symmetry operations:
b 1/2 – x, 1/2 + y, –z;
c –x, 1 – y, –z;
d –1/2 – x, 1/2 + y, 1/2 – z.
In the crystal of compound 1b, the molecules are linked
and the O(41´) atom of the nitro group of the symmetriꢀ
cally related molecule (1/2 – x, 1/2 + y, 1/2 – z). As a
result, the crystal packing can be described as the parallel
arrangement of the infinite planar layers along the crysꢀ
tallographic axis 0z (Fig. 2).
A somewhat different situation is observed in the case
of compound 1c. In the crystal of the latter, the molecules
are linked in centrosymmetrical dimers through pairs of
interactions between the O(2) atoms and the methylene
in dimers via two hydrogen bonds between the correꢀ
sponding O(42) atoms of the nitro groups and the H(111)
atoms of the methyl groups of two molecules related by a
center of symmetry. It should be noted that the O(42)
atom is involved also in an intramolecular contact with
the methyl H(101) atom. These dimers are linked in infiꢀ
nite planar layers through intermolecular contacts beꢀ
tween the H(6) proton of the benzene ring of molecule 1b
Fig. 2. Formation of infinite planar layers of the hydrogenꢀbonded molecules in the crystal of 1b. The intermolecular hydrogen bonds
are indicated by dashed lines. The projection along the crystallographic axis 0z.

5,7ꢀDichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
109
structures. Apparently, these differences were to be looked
for in the characteristic features of solvation of the molꢀ
Table 5. Crystallographic characteristics of compounds 1a—c
and details of Xꢀray diffraction studies
Parameter
1a
1b
1c
Crystal system
Monoꢀ
clinic
Monoꢀ
clinic
Monoꢀ
clinic
Space group
a/Å
b/Å
c/Å
P21/n
P21/а
8.669(3)
13.951(3)
9.203(2)
117.87
983.9(5)
4
P21/n
8.782(2)
7.1474(8)
13.778(3)
105.47(2)
834.1(3)
4
6.683(3)
13.255(5)
14.691(5)
94.07(3)
1297.7(9)
4
Fig. 3. Fragment of the stacks formed by molecular dimers in the
crystal of 1c. Only protons involved in hydrogen bonding (dashed
lines) are shown. The projection along the crystallographic
axis 0y.
β/deg
V/Å3
Z
M
234.00
1.86
7.58
242.62
1.64
3.82
296.71
1.52
3.04
dcalc/g cm–3
Absorption
coefficient/cm–1
Radiation µ/Å
θ Scanning range/deg
Scanning technique
Scan angle
H(121) atoms, which is favored by the inclined arrangeꢀ
ment of the sevenꢀmembered ring (adopting a twistꢀchair
conformation) with respect to the plane of the benzene
ring (the dihedral angle is 57.7(2)°) (Fig. 3). The O(41)
atom of the nitro group is involved both in interꢀ and
intramolecular contacts. In 1c, the intramolecular hydroꢀ
gen bond is formed by the methylene H(101) atom and
the O(41) atom. In the crystal of 1c, the O(41) atom of
the nitro group and the H(6) atom of the phenyl ring of
each molecule are involved in hydrogen bonding with the
corresponding atoms of the adjacent symmetrically reꢀ
lated molecules (each molecule is involved in two interꢀ
molecular interactions as the donor and acceptor) to link
dimers in an infinite threeꢀdimensional framework of the
hydrogenꢀbonded molecules. In addition to the hydrogen
bonds, strong πꢀπ interactions between the benzoxadiazole
electron systems make a substantial contribution to the
molecular packing in the crystal resulting in the formaꢀ
tion of the molecular stacks along the crystallographic
axis 0x. Both molecules in the hydrogenꢀbonded dimers
are involved in such interactions either with each other or
with the adjacent molecules in the stacks. The distance
between the planes of the molecules in the dimer is 3.291 Å
and the dihedral angle is 0°. The distance between one
molecule of the dimer and the adjacent molecule in the
stack (the symmetry operation –1 – x, 1 – y, –z) is
3.207 Å and the dihedral angle is 0.93°. The supramoꢀ
lecular structure in the crystal of 1c can be described as a
system of hydrogenꢀbonded molecular stacks.
λ = MoꢀKα, 0.71073 Å
2.12 ≤ θ ≤ 26.3
ω/2θ
0.68 + 0.4 tgθ
Standard
reflections
Two control reflections for orientation and
three control reflections for intensity
after every 200 reflections
Ranges for measured –10 ≤ h ≤ 0 –10 ≤ h ≤ 9
indices
–8 ≤ h ≤ 0
0 ≤ k ≤ 0
–18 ≤ l ≤ 18
2998
–8 ≤ k ≤ 0 –17 ≤ k ≤ 0
–16 ≤ l ≤ 17 0 ≤ l ≤ 18
Number of measured
reflections
Number of observed
reflections
with I > 3σ(I )
Conditions for the
determination
and refinement of
hydrogen atoms
Final R and
1947
2221
1040
985
2045
Revealed from the difference electron
density map, refined isotropically
R = 0.0384 R = 0.03609 R = 0.05310
Rw = 0.0467
Rw factors
Rw = 0.03894
Rw = 0.06641
Figure of merit
∆/σ
Ratio of the number
of reflections to the
number of refinable
parameters
1.411
0
8.16
1.169
0
5.85
2.329
0.02
6.66
max
Note. Empirical absorption corrections were applied; the intenꢀ
sities of standard reflections showed no decrease in the course of
data collection and, hence, no corrections were applied; calcuꢀ
lations were carried out on an Alpha Station 200 using the
MolEN program8 and the SIR program (direct methods for the
structure solution).9 The structures were refined by the fullꢀ
Hence, the presence of a substituent at position 5
(independently of its nature) leads to changes only in the
adjacent positions. The other geometric parameters of the
molecules (see Tables 1—3) remain unchanged. Conseꢀ
quently, molecules 1a—c as a whole adopt virtually idenꢀ
tical conformations. Hence, the observed difference in
the reactivity of compounds 1b and 1c cannot be exꢀ
plained from the viewpoint of their threeꢀdimensional
matrix leastꢀsquares method; the
function was
minimized; extinction was ignored; the weighting scheme
4F02/[σ(I )2 + (0.04F02)]2 was used.

110
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Levinson et al.
Xꢀray diffraction analysis. The Xꢀray diffraction data for
compounds 1a—c were collected on an automated fourꢀcircle
EnrafꢀNonius CADꢀ4 diffractometer. The crystallographic charꢀ
acteristics of compounds 1a—c and details of the Xꢀray diffracꢀ
tion studies are given in Table 5.
The crystals of compounds 1a (C6HCl2N3O3), 1b
(C12H13ClN4O3), and 1c (C8H7ClN4O3) were grown from
PriOH, a 2 : 1 DMF—PriOH mixture, and a 1 : 1 PriOH—acetone
mixture, respectively.
ecules by the solvent as indicated also by the differences
in the intermolecular contacts and molecular packing in
the crystals of these compounds. Depending on the naꢀ
ture of the substituent at position 5, the supramolecular
structures of the compounds under study are characterꢀ
ized by the formation of molecular stacks exclusively
through πꢀπ interactions (in the crystal of 1a), the formaꢀ
tion of infinite planar layers of the molecules linked only
via C—H...O interactions (in the crystal of compound
1b), or the presence both of πꢀπ and C—H...O interacꢀ
tions giving rise to a threeꢀdimensional framework of parꢀ
allel molecular stacks (in the crystal of compound 1c).
References
1. A. J. Boulton, A. C. J. Gray, and A. R. Katritzky, J. Chem.
Soc. B, 1967, 9, 909.
2. H. Suzuki, T. Kurihara, T. Kaino, and F. Ebisawa, Acta
Crystallogr., Sect. C, Cryst. Struct. Commun., 1988, 44, 484.
3. M. Mathew and G. J. Palenik, Acta Crystallogr., Sect. B, Struct.
Sci., 1971, 27, 1388.
4. H.ꢀJ. Niclas, B. Gohrmann, M. Ramm, and B. Schulz,
J. Prakt. Chem., 1990, 332, 1005.
Experimental
5,7ꢀDichloroꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole (1a) was syntheꢀ
sized according to a known procedure,1 m.p. 89 °C (cf. lit. data:
87—88 °C).
5. M. Ramm, J. Kind, and H.ꢀJ. Niclas, Acta Crystallogr., Sect. C,
Cryst. Struct. Commun., 1993, 49, 1779.
Compounds 1b and 1c were synthesized as described below.
A solution of the corresponding amine (0.01 mol) in PriOH
(3 mL) was added dropwise to a suspension of compound 1a
(1.17 g, 0.005 mol) in PriOH (10 mL) at 10—15 °C. The course
of the reaction was monitored by chromatography on Silufol
UVꢀ254 plates. After completion of the reaction, the precipitate
that formed was filtered off, washed with water, dried, and crysꢀ
tallized from the appropriate solvent.
7ꢀChloroꢀ5ꢀdimethylaminoꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiazole (1b).
The yield was 93%, m.p. 175 °C, Rf 0.23 (toluene—AcOEt, 2 : 1).
7ꢀChloroꢀ5ꢀhexamethyleneiminoꢀ4ꢀnitroꢀ2,1,3ꢀbenzoxadiꢀ
azole (1c). The yield was 95%, m.p. 140—141 °C, Rf 0.51 (toluꢀ
ene—AcOEt, 2 : 1).
6. A. Altomare, G. Cascarano, C. Giacovazzo, and D. Viterbo,
Acta Crystallogr., Sect. A, Fund. Crystallogr., 1991, 47, 744.
7. J. N. Law, M. S. V. DaidgeꢀHarrisson, and J. Colo, Acta
Crystallogr., Sect. C, Cryst. Struct. Commun., 1996, 52, 964.
8. L. H. Straver and A. J. Schierbeek, MolEN, Structure Deterꢀ
mination System, Program Description, Nonius B. V., Delft,
1994, 1, 180.
9. A. L. Spek, Acta Crystallogr., Sect. A, Fund. Crystallogr.,
1990, 46, 34.
Received December 26, 2000;
in revised form June 4, 2001