Conformation and crystal packing sensitivity to substitution of thioxo- and oxo-tetrazane derivatives

Article abstract of DOI:10.1039/b902225b

The synthesis of a series of six thioxo-tetrazane derivatives is reported. The crystal structures of five of these new products and the corresponding oxo-compounds (except the 4,6-dimethylpyrimidyl derivative) including two new crystal structures are also

Full text of DOI:10.1039/b902225b

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Conformation and crystal packing sensitivity to substitution
of thioxo- and oxo-tetrazane derivativesw
´
Olivier Oms,* Lucie Norel, Lise-Marie Chamoreau, Helene Rousseliere
and Cyrille Train*
Received (in Montpellier, France) 3rd February 2009, Accepted 1st April 2009
First published as an Advance Article on the web 12th May 2009
DOI: 10.1039/b902225b
The synthesis of a series of six thioxo-tetrazane derivatives is reported. The crystal structures of
five of these new products and the corresponding oxo-compounds (except the 4,6-
dimethylpyrimidyl derivative) including two new crystal structures are also described and
compared. The structural data show the importance of the substituent for the intramolecular
arrangement while the heteroatom (S, O) does not play any role at this stage: the 2-pyridyl,
4,6-dimethylpyrimidyl and 8-quinolyl groups occupy a pseudo-equatorial position related to the
existence of an intramolecular hydrogen bond where the substituent acts as an acceptor.
2-Hydroxyphenyl moieties occupy a pseudo-axial position related to the existence of an
intramolecular hydrogen bond where the substituent acts as a donor. In the sole example where
an intramolecular hydrogen bond is not present (2-imidazolyl derivatives), the preference for the
pseudo-axial conformation is determined by the hyperconjugative effect. In contrast with the
intramolecular arrangement, the crystal packing strongly depends on the choice of the
heteroatom. It shows noticeable differences related to the variable involvement of CQS and
CQO functions as hydrogen-bond acceptors and the occurrence of p stacking between the
molecules. It thus appears that the sulfur atom of the thioxotetrazanes is always involved in
hydrogen bonding whereas this is not the case for the oxygen atom of the oxotetrazane
analogues. This result contrasts with the statistical treatment of the crystal structures of the
Cambridge Structural Database in the urea/thiourea series and could be related to the steric
hindrance imposed by the two methyl groups borne by the nitrogen atoms located in the
a positions of the CQX function (X = S, O).
By displacing the hydrogen-bond donors and modifying the
Introduction
electronic delocalisation involving the nitrogen atoms and the
heteroatom, the study of tetrazane containing derivatives
(Scheme 1) appear as a natural extension of the study of the
(thio)ureas. The versatility of their chemistry4–9 allows varying
the heteroatom as well as the substituent almost at will.
Nevertheless, up to date, this family of molecules has mainly
been used as a precursor of verdazyl radicals, promising
species in molecular magnetism,10–14 and little is known about
their organisation in the solid state.9,15
The synthesis of molecular materials fully exploits the whole
range of interactions from strong intramolecular to weaker
intermolecular ones.1 Among the latter, hydrogen bonds are
the most reliable for crystal engineering because of their
geometrical constraints and intensities. For every family
of compounds, the anticipation of the crystal packing
of forthcoming compounds relies on the description and
understanding of the crystal structures of as many members
of the family as possible.2 In this respect the urea and, to a
lesser extent, thiourea derivatives (Scheme 1) is a case study.
They have been widely studied because they are synthetically
versatile and able to develop rich hydrogen-bond patterns
that have been used to form superstructures with various
topologies or to design anion binding groups.3 The hydrogen
bonds exploit the accepting ability of the O or S heteroatom
and the donating ability of the nitrogen atoms.
We report herein the synthesis of six original compounds,
mainly thione derivatives. We present seven novel crystal
structures of tetrazane-based derivatives and compare the
conformation of the molecules and the crystal packing of nine
of such compounds by analysing the nature of the interactions
´
´
´
‘‘Materiaux Magnetiques Moleculaires et Absorption X’’ et ‘‘Centre
de Re´solution de Structures’’, Institut Parisien de Chimie Mole´culaire,
UMR CNRS 7201UPMC-Univ. Paris 06, case 42, 4 place Jussieu,
F-75252, Paris cedex 05
w CCDC reference numbers 714410 (1b), 714408 (1c), 714409(1e),
714411(1f), 714425 (1g), 714424 (2f) and 714423 (2g). For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b902225b
Scheme 1 (Thio)urea- (left) and (thio)oxotetrazane- (right) based
molecules (with crystallographic numbering scheme).
ꢀc
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(hydrogen bonds, p stacking) and the influence of the R
substituent and X heteroatom.
molecules of salicylaldehyde. High temperatures favor the
formation of the diimine. By working at room temperature
using a slight excess of 1a, we obtained 91% of 1g and 9% of
the by-product (estimated by 1H NMR). The higher solubility
of the diimine in chloroform allows the isolation of 1g in
relatively good yield (60%). Similarly, 2g is a minor product
when the reaction occurs in refluxing methanol (19%
Results
Synthesis
The synthesis of the 1,5-dimethyl-3-R-6-thioxo-1,2,4,5-
tetrazanes 1b–g (b: R = 2-imidazolyl, c: R = 2-pyridyl,
d: R = carboxylic acid, e: R = 4,6-dimethylpyrimidyl,
f: R = 8-quinolyl, g: R = 2-hydroxyphenyl) and the corres-
ponding oxo derivatives 2b–g follows the synthetic pathway
described by Neugebauer4 with minor modifications.
2,4-Dimethylthiocarbonohydrazide (1a) and 2,4-dimethyl
carbonohydrazide (2a) are prepared by the reaction of methyl-
hydrazine with thiophosgene or triphosgene, respectively. In a
second step, the condensation of 1a or 2a with selected
aldehydes leads to the desired products. While 2b–e and 2g
have been already reported,4,7,12,15 only 1b is mentioned in the
literature16 for the thioxo series and, in this case, no further
data were presented. The synthesis of six new sulfur-substituted
derivatives thus demonstrates the versatility of the synthetic
scheme proposed by Neugebauer while the obtained yields
demonstrate its efficiency (Scheme 2). We notice better results
for the oxo derivatives (yield range: 65–100%) than for the
thioxo ones (51–75%). Following the conditions described for
the preparation of the 4-pyridyl derivative,4 1c was obtained in
low yield (20%, room temperature). Working in refluxing
methanol leads to an improvement of the reaction yield
(44%). 1g and 2g are the only compounds that must be
synthesized at room temperature. In the first case, the crude
product of the reaction is a mixture of 1g with a diimine
formed by the reaction of one molecule of 1a and two
1
estimated by H NMR) whereas the reaction is more efficient
at room temperature with an excess of 2a (yield: 69%). In this
case, the purification consists of triturating the residue with
ethyl acetate to eliminate the diimine by-product.
Crystal structure analysis
The structures of 2b and 2c were previously described12,15
while no structural data were obtained for 1d, 2d and 2e. We
report here the crystal structures of seven compounds
(1b–g, 2f–g) whose crystallographic parameters are summarized
in Table 1.
In all these structures, the tetrazane rings present an
overall similar arrangement: N2 and N3 have essentially
planar geometries while N1 and N4 adopt pyramidal
ones (Scheme 1). Opposite to the sp2-hybridized C1 atom,
C2 presents
a tetrahedral environment related to its
sp3-hybridization. The bond lengths of the tetrazane rings
are given in Table 2. To go beyond these general features,
we will examine the specificities of the seven new structures
reported here.
1,5-Dimethyl-3-(20-imidazolyl)-6-thioxo-1,2,4,5-tetrazane 1b
The molecular structure of 1b is shown in Fig. 1. C2 is 0.652 A
away from the average plane constituted by the five other
atoms of the tetrazane ring. The imidazole group occupies a
pseudo-axial position and the dihedral angle between the
average planes of imidazole and tetrazane ring is 87.03(10)1.
The crystal packing is governed by hydrogen bonds (Fig. 2)
between: (i) the nitrogen atom and the NH group of the
imidazole substituent, (ii) the sulfur atom and the NH
group of the tetrazane moiety. In the former case, the
non-protonated nitrogen atom of imidazole acts as
a
hydrogen-bond acceptor and the NH group acts as a hydrogen-
bond donor leading to chains along the b-axis (N5ꢁ ꢁ ꢁN6,
2.993(2) A, N6ꢁ ꢁ ꢁH–N5 angle, 1761). In the latter, the CQS
function is involved in two bifurcated hydrogen bonds with
N1H (Sꢁ ꢁ ꢁN1, 3.487(2) A; Sꢁ ꢁ ꢁH–N1 angle, 1491) and N4H
(Sꢁ ꢁ ꢁN4, 3.437(2) A; Sꢁ ꢁ ꢁH–N4 angle, 1501) forming of zigzag
chains of aligned molecules along the c-axis. Two neighbouring
rows are running in opposite directions. Altogether, hydrogen
bonds lead to the formation of two-dimensional arrays of
molecules.
1,5-Dimethyl-3-(20-pyridyl)-6-thioxo-1,2,4,5-tetrazane 1c
The molecular structure of 1c is shown in Fig. 3. The distance
between C2 and the average plane constituted by the five other
atoms of the tetrazane ring is 0.582 A. The pyridine moiety
linked to the C2 atom occupies a pseudo-equatorial position
and the dihedral angle between the average planes of pyridine
and tetrazane ring is 77.85(13)1. The nitrogen atom of the
pyridine group is directed towards the axial hydrogen atom
Scheme 2 Synthesis of tetrazanes.
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Table 1 Crystallographic data for the tetrazane derivatives
1b
C7H12N6S
1c
C9H13N5S
1e
C10H16N6S
1f
C13H15N5S
1g
C10H14N4OS
2f
C13H15N5O
2g
C10H14N4O2
Formula
Mr
T/K
System
Space group
212.29
250(2)
Monoclinic
P21/c
223.30
200(2)
Monoclinic
P21/c
252.35
200(2)
Triclinic
273.36
200(2)
Monoclinic
P21/c
238.31
200(2)
Monoclinic
P21/c
257.30
200(2)
Monoclinic
P21/c
222.25
200(2)
Monoclinic
Cc
ꢀ
P1
a/A
b/A
c/A
a/1
9.8198(12)
9.615(2)
10.898(3)
90
92.127(17)
90
1028.2(4)
4
1.371
0.287
448
11.9056(17)
9.6629(7)
11.3482(19)
90
118.320(9)
90
1149.3(3)
4
1.291
0.258
472
7.6762(13)
8.5120(12)
10.3122(12)
104.177(10)
102.599(11)
93.444(13)
632.94(16)
2
1.324
0.245
268
2.10–32.00
12.1254(10)
14.916(2)
15.9171(19)
90
108.354(8)
90
2732.4(6)
8
1.329
0.231
1152
5.6910(5)
18.042(2)
11.6058(12)
90
101.178(11)
90
1169.0(2)
4
1.354
0.262
504
7.8076(7)
15.593(2)
10.9987(14)
90
107.222(10)
90
1279.0(3)
4
1.336
0.090
544
5.3123(8)
23.048(3)
9.1244(14)
90
103.276(13)
90
1087.3(3)
4
1.358
0.098
472
b/1
g/1
V/A3
Z
Dc/g cm3
mMo-Ka)/mmꢂ1
F(000)
y range/1
Refl. coll./indep./obs. 7533/2963/1669 16 000/3352/2162 17386/4321/2711 18467/7840/2881 14544/3396/2199 15171/3699/2154 5680/1584/1096
2.83–30.00
2.87–30.01
1.77–30.01
2.88–30.00
3.03– 30.00
3.54–29.99
R(int)
No. variables
Gof on F2
R1 (I 4 2s(I))
wR2 (all data)
0.0577
129
0.995
0.0543
0.1399
0.0477
136
1.086
0.0621
0.2046
0.0532
158
1.018
0.0483
0.1334
0.0807
343
0.911
0.0552
0.1632
0.0664
148
1.005
0.0451
0.1226
0.0573
175
1.030
0.0511
0.1404
0.0479
147
1.036
0.0459
0.1086
Table 2 Bond lengths (A) for the tetrazane core
C1–N2 C1–N3 N2–N1 N3–N4 N1–C2 N4–C2
1b
1c
1e
1.361(3) 1.356(3) 1.438(2) 1.443(2) 1.467(3) 1.468(2)
1.359(3) 1.354(3) 1.431(3) 1.439(3) 1.451(3) 1.441(3)
1.365(2) 1.368(2) 1.440(2) 1.439(2) 1.475(2) 1.478(2)
1f (1) 1.357(4) 1.351(4) 1.455(3) 1.444(3) 1.473(3) 1.470(3)
1f (2)a 1.356(4) 1.354(4) 1.445(3) 1.447(3) 1.469(3) 1.480(3)
1g
2f
2g
1.358(2) 1.353(2) 1.435(2) 1.439(2) 1.490(2) 1.456(2)
1.370(2) 1.371(2) 1.445(2) 1.435(2) 1.472(2) 1.465(2)
1.373(3) 1.368(3) 1.443(3) 1.448(3) 1.477(3) 1.465(4)
a
Values related to the second tetrazane ring of 1f: C14–N8, C14–N7,
N8–N9, N7–N6, N9–C15 and N6–C15, respectively.
Fig. 2 Intermolecular interactions in 1b (left) and 2b (right) (dashed
pink line: CQXꢁ ꢁ ꢁHN, dashed green line: Nꢁ ꢁ ꢁHN hydrogen bonds).
Hydrogen atoms of C–H groups are omitted for clarity.
1,5-Dimethyl-3-(40,60-dimethylpyrimidyl)-6-thioxo-1,2,4,5-
tetrazane 1e
The molecular structure and the crystal packing of 1e are
shown in Fig. 5. C2 is 0.620 A from the average plane of the
tetrazane ring. The pyrimidyl substituent occupies a pseudo-
equatorial position and the dihedral angle is 88.09(7)1. One
nitrogen atom of the pyrimidine substituent is involved in two
intramolecular hydrogen bonds with N1H (N5ꢁꢁꢁN1, 2.841(2) A,
N5ꢁ ꢁ ꢁH–N1 angle, 1041) and N4H (N5ꢁ ꢁ ꢁN4, 2.855(2) A,
N5ꢁ ꢁ ꢁH–N4 angle, 1091). The CQS group participates to
two bifurcated intermolecular hydrogen bonds with N1H
(Sꢁ ꢁ ꢁN1, 3.603(2) A; Sꢁ ꢁ ꢁH–N1 angle, 1451) and N4H
(Sꢁ ꢁ ꢁN4, 3.570(1) A; Sꢁ ꢁ ꢁH–N4 angle, 1461) of the tetrazane
ring. A distance of 3.416 A, associated with p–p interactions,
separates the average planes of the pyrimidine rings leading to
the formation of staggered dimers along the b axis. The
combination of these two types of intermolecular interactions
leads to the formation of mixed supramolecular chains.
Fig. 1 Structures of 1b (left) and 2b (right, adapted from ref. 12).
Thermal ellipsoids drawn at 30% probability level.
HN4 constituting an intramolecular hydrogen bond
(N5ꢁ ꢁ ꢁN4, 2.833(3) A, N5ꢁ ꢁ ꢁH–N4 angle, 1081) leading to
the formation of
a five-membered ring. Intermolecular
hydrogen bonding is also observed (Fig. 4). Two neighboring
molecules are connected to one another by two hydrogen
bonds involving the CQS function and one NH group
(Sꢁ ꢁ ꢁN1, 3.529(2) A; Sꢁ ꢁ ꢁH–N1 angle, 1611) leading to the
formation of dimers.
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1,5-Dimethyl-3-(80-quinolyl)-6-thioxo-1,2,4,5-tetrazane 1f
Two molecules are present in the asymmetric unit (Fig. 6). For
the S1-containing molecule, the quinolyl substituent occupies
a pseudo-equatorial position and is almost perpendicular to
the tetrazane ring (dihedral angle: 87.88(11)1). An intra-
molecular hydrogen bonding is observed (N5ꢁ ꢁ ꢁN4,
2.953(3) A, N5ꢁ ꢁ ꢁH–N4 angle, 1301; N5ꢁ ꢁ ꢁN1, 3.030(3) A,
N5ꢁ ꢁ ꢁH–N1 angle, 1181). For the S2-containing molecule,
the quinolyl substituent also occupies a pseudo-equatorial
position with a dihedral angle of 85.15(11)1 and it is involved
in intramolecular hydrogen bonding (N6ꢁ ꢁ ꢁN10, 2.923(3) A,
N10ꢁ ꢁ ꢁH–N6 angle, 1241; N9ꢁ ꢁ ꢁN10, 3.101(3) A, N10ꢁ ꢁ ꢁH–N9
angle, 1231) as well. In the overall structure (Fig. 7), only one
weak intermolecular hydrogen bond is observed involving the
CQS function and a NH group (S1ꢁ ꢁ ꢁN9, 3.628(2) A;
S1ꢁ ꢁ ꢁH–N9 angle, 1511). Concerning the quinoline moieties
along the b axis, the measured distances between the centroids
of the four cycles range from 3.955(2) to 5.101(2) A. Although
the minimum angle between close quinoline planes is relatively
high (6.93(8)1), these values can be associated with p–p inter-
actions leading to the formation of infinite stacks along the
b-axis.17 The hydrogen bonds between these stacks lead to
the formation of mixed supramolecular two dimensional
brick-wall features.
Fig. 3 Structures of 1c (top) and 2c (below) (dashed purple line:
intramolecular interactions). Thermal ellipsoids drawn at 30%
probability level.
Fig. 4 Intermolecular interactions in 1c (top) and 2c (below) (dashed
pink line: hydrogen bonds, dashed gold line: p stacking). Hydrogen
atoms of C–H groups are omitted for clarity.
Fig. 5 Structure (top, dashed purple line: intramolecular interactions,
thermal ellipsoids drawn at 30% probability level) and intermolecular
interactions (below, dashed pink line: CQSꢁ ꢁ ꢁHN hydrogen bonds,
dashed gold line: p stacking) of 1e.
Fig. 6 Structures of 1f (top) and 2f (below) (dashed purple line:
intramolecular interactions). Thermal ellipsoids drawn at 30%
probability level.
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occupies a pseudo-axial position and the dihedral angle
between the average planes of the two rings is 86.05(8)1. We
observe an intramolecular hydrogen bond involving the
hydroxyl group (O1ꢁ ꢁ ꢁN1, 2.722(2) A, N1ꢁ ꢁ ꢁH–O1 angle,
1501). In the crystal packing (Fig. 9), two bifurcated hydrogen
bonds involving the CQS function and two NH groups
(S1ꢁ ꢁ ꢁN1, 3.576(2) A, S1ꢁ ꢁ ꢁH–N1 angle, 1541; S1ꢁ ꢁ ꢁN4,
3.371(2) A, S1ꢁ ꢁ ꢁH–N4 angle, 1541) lead to the formation of
chains along the a-axis.
1,5-Dimethyl-3-(20-hydroxyphenyl)-6-oxo-1,2,4,5-tetrazane 2g
The molecular structure of 2g is shown in Fig. 8. C2 is
0.688 A far from the average plane of the tetrazane ring.
The 2-hydroxyphenyl substituent occupies a pseudo-axial
position and the OH group is involved in an intramolecular
hydrogen bond (O2ꢁ ꢁ ꢁN1, 2.716(3) A, N1ꢁ ꢁ ꢁH–O2 angle,
1471). The dihedral angle between the average planes of the
tetrazane ring and the 2-hydroxyphenyl moiety is 85.82(13)1.
The crystal packing (Fig. 9) reveals two bifurcated hydrogen
bonds involving the carbonyl group and two NH functions of
the neighboring molecule (O1ꢁ ꢁ ꢁN1, 3.024(3) A, O1ꢁ ꢁ ꢁH–N1
angle, 1451; O1ꢁ ꢁ ꢁN4, 3.052(3) A, O1ꢁ ꢁ ꢁH–N4 angle, 1511)
leading to the formation of chains along the a-axis.
Fig. 7 Intermolecular interactions in 1f (top) and 2f (below) (dashed
pink line: CQXꢁ ꢁ ꢁHN hydrogen bonds, dashed gold line: p stacking).
Hydrogen atoms of C–H groups are omitted for clarity.
1,5-Dimethyl-3-(80-quinolyl)-6-oxo-1,2,4,5-tetrazane 2f
In this compound (Fig. 6), the distance from the average plane of
the tetrazane ring to C2 is 0.617 A. The quinolyl substituent
occupies a pseudo-equatorial position leading to two intra-
molecular hydrogen bonds (N5ꢁꢁꢁN1, 2.956(2) A, N5ꢁꢁꢁH–N1
angle, 1291; N5ꢁꢁꢁN4, 3.087(2) A, N5ꢁꢁꢁH–N4 angle, 1241). The
dihedral angle formed with the tetrazane average plane is
84.55(6)1. p-Stacking between quinoline moieties is observed in
the overall structure (Fig. 7) characterized by an inter-planar
distance of 3.601 A leading to the formation of staggered dimers
along the b-axis. Moreover, one weak intermolecular hydrogen
bond involves the oxygen atom and a NH group of a neighboring
molecule (O1ꢁ ꢁ ꢁN4, 3.383(2) A, O1ꢁ ꢁ ꢁH–N4 angle, 1421)
forming hydrogen-bonded dimers. The combination of these
two types of intermolecular interactions leads to the formation
of mixed supramolecular chains running along the c-axis.
Discussion
The analysis of the crystal structures of thioxo- and
oxo-tetrazanes allows to delineate the influence of the R
substituent as well as of the heteroatom on both the
intra- and the inter-molecular organization of the tetrazane
molecules.
As far as intramolecular arrangement is concerned (data for
intramolecular hydrogen bonds are summarized in Table 3),
two situations have been encountered: the R substituent can be
either in pseudo-equatorial (pyridyl, pyrimidyl and quinolyl)
1,5-Dimethyl-3-(20-hydroxyphenyl)-6-thioxo-1,2,4,5-tetrazane 1g
The molecular structure of 1g is shown in Fig. 8. C2 is
0.658 A away from the average plane constituted by the five
other atoms of the tetrazane ring. The hydroxyphenyl group
Fig. 8 Structures of 1g (left) and 2g (right) (dashed purple line:
intramolecular interactions). Thermal ellipsoids drawn at 30%
probability level.
Fig. 9 Intermolecular interactions in 1g (top) and 2g (below) (dashed
pink line: CQXꢁ ꢁ ꢁHN hydrogen bonds). Hydrogen atoms of C–H
groups are omitted for clarity.
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Table 3 Intramolecular hydrogen bonds
DHꢁ ꢁ ꢁA distance (A)
Table 4 Parameters relating to CQSꢁ ꢁ ꢁH bonds
DHꢁ ꢁ ꢁA angle (1)
H-Bond
d(C–S)/A
d(Sꢁ ꢁ ꢁH)/A
a/1
1c
1e
N4Hꢁ ꢁ ꢁN5
N4Hꢁ ꢁ ꢁN5
N1Hꢁ ꢁ ꢁN5
N4Hꢁ ꢁ ꢁN5
N1Hꢁ ꢁ ꢁN5
N6Hꢁ ꢁ ꢁN10
N9Hꢁ ꢁ ꢁN10
N4Hꢁ ꢁ ꢁN5
N1Hꢁ ꢁ ꢁN5
O1Hꢁ ꢁ ꢁN1
O2Hꢁ ꢁ ꢁN1
2.44
2.43
2.47
2.32
2.53
2.34
2.53
2.42
2.26
1.86
2.07
108
109
104
130
118
124
123
124
129
150
147
1b
CQSꢁ ꢁ ꢁHN1
CQSꢁ ꢁ ꢁHN4
CQSꢁ ꢁ ꢁHN1
CQSꢁ ꢁ ꢁHN1
CQSꢁ ꢁ ꢁHN4
C1QS1ꢁ ꢁ ꢁHN9
CQSꢁ ꢁ ꢁHN1
CQSꢁ ꢁ ꢁHN4
1.724(2)
2.66
2.64
2.68
2.81
2.77
2.83
2.73
2.48
149
150
161
145
146
151
154
154
1c
1e
1.705(1)
1.712(2)
1f
1f
1g
1.717(3)
1.715(2)
2f
1g
2g
exhibit intermolecular hydrogen bonds involving the CQS
function and NH groups. Allen et al. accurately analyzed
hydrogen bonding at sulfur acceptors in various systems.24,25
In Table 4, we adopt the same parameters, d(CS), the CQS
bond length, d(Sꢁ ꢁ ꢁH), the Sꢁ ꢁ ꢁH distance and a, the Sꢁ ꢁ ꢁH–N
valence angle to describe these interactions in the 1b–g series.
For comparison, Table 5 gathers the parameters for the
oxo-derivatives related to hydrogen bond involving the
carbonyl function, when it exists.
or pseudo-axial (imidazolyl, hydroxyphenyl) positions. This is
actually independent of the heteroatom and fully determined
by the R substituent. By scrutinizing the intramolecular
interactions encountered when the compounds adopt a
pseudo-equatorial position, it appears that in all cases this
conformation is linked with the existence of an intramolecular
hydrogen bond between the substituent, whose heteroatom
acts as an acceptor and the N1–H and/or N4–H groups of the
tetrazane ring, acting as donors (Table 3). The importance
of intramolecular hydrogen bonding also holds for the
hydroxyphenyl substituted derivatives 1g and 2g. Nevertheless,
in these cases, the pseudo-axial conformation is favored
because it allows the formation of a hydrogen bond between
the substituent acting as a donor and the N1 atom of the
tetrazane ring acting as an acceptor. The imidazole substituted
derivatives 1b and 2b (Fig. 1) deserve additional inspection
since no intramolecular hydrogen bond is observed. A similar
arrangement is obtained with 4-pyridyl,15 imidazolium18 or
pyrazolyl9 substituted oxotetrazanes. In 1b and 2b, an intra-
molecular hydrogen bond, that is observed in other derivatives
when the substituent is in pseudo-equatorial position (1c, 1e,
1f, 2c, 2f), would be only very weak since the geometry of the
five-membered imidazole ring would lengthen the distances
between the hydrogen atoms of the tetrazane ring and the
nitrogen atom of the imidazole. The absence of intramolecular
hydrogen bonds may also be due to the intermolecular
hydrogen bonding. Such a situation has recently been
described in imidazole-substituted urea.19 In the present case,
this argument is reinforced by the fact that due to the sp3
hybridization of C2 (Scheme 1), we are not in a situation
where intramolecular hydrogen bonding is the most favorable
according to the systematic survey of Cambridge Structural
Database (CSD) performed by Bilton et al.20
The d(C–S) values are ranging from 1.705(1) to 1.724(2) A.
This falls into the 1.65–1.72 A range for seven compounds
including the N–N–C(S)–N–N motif found in the CSD though
such a low number do not allow any statistical treatment.
These values are relatively high compared to the 1.61 A bond
length proposed for a 100% double-bond character. The
lengthening of this bond is indeed associated with an increase
of the electronic delocalisation.24 Because of the lower electro-
negativity of S compared to O, it is well known that CQS
bond is less polar. It is thus more sensitive to electronic effects
and its length range is broader than that of the CQO bond.
Compared to the result of the systematic statistical data
analysis performed by Allen et al. (Fig. 3 in ref. 24), for both
the oxygen and the sulfur derivatives, we observe rather long
CQX bond lengths though the C–N distances are also in the
medium to long range. This result can be tentatively related to
the influence of the lone pairs of the N2 and N3 nitrogen
atoms on the electronic delocalisation.
The d(Sꢁ ꢁ ꢁH) range (2.48–2.83 A) in our compounds is also
in good agreement with the reported values. The longest ones
observed for 1e (2.81 and 2.77 A) and 1f (2.83 A) are still
shorter than the sum of van der Waals radii (2.90 A). The a
values are between 145 and 1611 which are in the 130–1801
range reported by Allen et al.24 In contrast to the oxo
derivatives, the electronic delocalisation revealed by the
increase of the CQS bond length is indeed the key element
for the sulfur to act as a hydrogen-bond acceptor. In the
1.70–1.72 A range, CQS is involved in hydrogen bonding in
more than 70% of the encountered cases.24
In the absence of an intramolecular hydrogen bond,
the preference for the pseudo-axial conformation can be
tentatively explained by an electronic effect through hyper-
conjugative interaction. Such a kind of interaction is proposed
as an important factor in the conformational equilibria of
3,5-disubstituted piperidones or cyclohexyl esters.21–23 In
contrast with the intramolecular interactions, the intermolecular
interactions are strongly dependent on the nature of the
heteroatom borne by the tetrazane ring. A detailed analysis
and comparison of the two families of derivatives are thus
worthwhile. It can be performed throughout the series except
for the pyrimidine-substituted derivatives because only the
structure of 1e has been solved. All the thioxo derivatives
Allen et al. also mentions that the Xꢁ ꢁ ꢁH–N valence angle
ranges are similar for X = S or O and, when the hydrogen
Table 5 Parameters relating to CQOꢁ ꢁ ꢁH bonds
H-Bond
d(CQO)/A
d(Oꢁ ꢁ ꢁH)/A
a/1
2b
2f
2g
CQOꢁ ꢁ ꢁHN5
CQOꢁ ꢁ ꢁHN4
CQOꢁ ꢁ ꢁHN1
CQOꢁ ꢁ ꢁHN4
1.243(3)
1.245(2)
1.252(3)
2.03
2.55
2.16
2.20
175
142
145
151
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bonds are present, our observations are in accord with this
statement.
difference is reduced upon increased electronic delocalisation,
CQO is a better hydrogen-bond acceptor than CQS in any
case. Interestingly, the Oꢁ ꢁ ꢁHN distance in carbohydrazide27
is slightly higher than the calculated value found for
N,N0-dimethylurea (1.9 A) while the Sꢁ ꢁ ꢁHN distance in
thiocarbohydrazide26 is slightly shorter than the value
calculated for N,N0-dimethylthiourea (2.6 A).25 This statement
confirms that the terminal nitrogen atoms of the
N–N–C(X)–N–N (X = O, S) motif modulates the hydrogen-
bond accepting capability of the X atom in favor of the sulfur
atom. Given the moderate energy of hydrogen bonds, they
are relatively sensitive to other geometrical and electronic
features. In the series of compounds presented here, through
increased stiffness, the ring closure of the tetrazane derivatives
might reinforce the delocalisation effect mentioned above.
Moreover, the steric hindrance brought about by the two
methyl groups bonded to N2 and N3 can noticeably reduce
the hydrogen-bond accepting ability of the neighboring CQX
(X = O, S) function. Due to a reduction of the CQX distance
that can reach 0.5 A when going from sulfur to oxygen, this
hindrance is more acute in the latter case. In borderline cases,
this phenomenon can preclude the formation of hydrogen
bonds for the oxygenated derivatives while it still can form
for the corresponding sulfurated compound as observed for
1c and 2c.
The crystal packing of thioxo and oxo compounds bearing
the imidazole moiety are noticeably different. In 1b,
homomeric associations are observed.19 This segregation of
imidazole–imidazole and tetrazane–tetrazane interactions
leads to the formation of a 2D hydrogen-bonded architecture
(Fig. 2). In 2b, the oxygen atom is hydrogen bonded to the NH
group of the imidazole substituent (Fig. 2). The Oꢁ ꢁ ꢁH–N
arrangement is nearly linear (1751) which expresses a strong
hydrogen bond as also demonstrated by the short d(Oꢁ ꢁ ꢁH)
value (2.03 A). This heteromeric association governs the
formation of helices along the c-axis which are interconnected
by hydrogen bonds in the ab plane. The comparison of the
crystal packing of the pyridine derivatives 1c and 2c (Fig. 4) is
more surprising. First, no p stacking is observed in 1c while the
combination of p stacking and hydrogen bonding between one
NH function of the tetrazane ring and the nitrogen atom of the
pyridine of a neighboring molecule in 2c lead to the formation
of mixed supramolecular chains which are similar to those
encountered in (6-methyl-2-pyridyl)oxotetrazane.15 Moreover,
whereas an intermolecular hydrogen bond involving the CQS
group is observed in 1c, there is no such interaction involving
the carbonyl function in the corresponding oxo derivative 2c.
Such a marked discrepancy is not observed in all the cases.
Indeed, both quinolyl substituted tetrazane structures
(1f and 2f) are characterized by weak intermolecular hydrogen
bonds. In both compounds, these interactions are combined
with p–p interactions to give rise to mixed supramolecular
extended structures. Nevertheless, in 1f, the dimensionality of
this supramolecular arrangement is two dimensional while
it is unidimensional in 2f. The hydroxyphenyl derivatives
(1g and 2g) present a very similar structural arrangement
constituted of hydrogen bonding along the a-axis. For two
neighboring rows, these chains run in opposite directions for
1g whereas they run in the same direction for 2g.
Conclusion
A series of 1,5-dimethyl-3-R-6-thioxo-1,2,4,5-tetrazanes in
which R is a potential coordinative entity have been prepared.
Generally, we noticed better yield for the synthesis of the
analogous oxo derivatives. The crystal structures of both
families of compounds have been described. The conformation
of the molecules is fully determined by the nature of the R
substituent and independent on X = O or S. It is actually
driven by the ability to form intramolecular hydrogen bonds
between R and the tetrazane moiety. In the sole example where
such interaction is not present, the conformation could be
determined by a hyperconjugative effect. The intermolecular
interactions (hydrogen bonds, p stacking) observed in these
two series of compounds depend both on the R substituent
and on the nature of the X heteroatom leading to the
formation of pure hydrogen-bonded as well as mixed
hydrogen-bonded/p-stacked supramolecular structures whose
dimensionality varies from 0 to 2. Actually for a given
substituent, the packing is always different for the sulfurated
and the oxygenated derivatives, the differences ranging from
subtle for the hydroxyphenyl derivatives to striking for
the pyridine derivatives. In the latter case, the presence of
hydrogen bonds involving the CQS group, whereas CQO is
not implied in intermolecular hydrogen bonding in the
oxygenated analogue, is surprising though not unexplainable
given the combination of electronic effects associated with the
tetrazane heterocycle and of the steric hindrance brought
about by its two methyl substituents.
Comparison of the hydrogen bonding in these derivatives
with the compounds found in the CSD that present the
N–N–C(S)–N–N motif can be made. There are seven such
derivatives and, for only three of them, the oxygenated
analogues have also been described. One pair of derivatives
(SIVNAM, SIVMUF) does not present any hydrogen bonding
at all because of the absence of hydrogen-donating groups. In
the second one (DPCBHZ, DPTCBZ), the hydrogen
atoms have not been resolved for the sulfur containing
derivative. The third pair is constituted of (thio)carbohydrazide
derivatives26,27 and allows comparison. Hydrogen-bonding
features are present in both compounds but, as observed in
the case of 1b and 2b, they are different. The shorter hydrogen
bonds are 2.153 A (CQOꢁ ꢁ ꢁHN; Oꢁ ꢁ ꢁHN angle is 154.41)
and 2.492 A (CQSꢁ ꢁ ꢁHN; Sꢁ ꢁ ꢁHN angle is 157.31) in the
oxygenated (CBOHAZ)27 and the sulfurated (THCHYD)26
derivatives, respectively. A scrutiny of the hydrogen-bonding
in these compounds within the general framework set by a
recent study that compares hydrogen bonding to CQO and
CQS acceptors25 is worthwhile. By combining a statistical
treatment of the parameters of hydrogen bonds implying
CQX (X = O, S) with intermolecular perturbation theory
(IMPT) calculations, the authors demonstrate that, though the
By exploiting the versatility of the tetrazane chemistry, it
will be possible to gather new crystal packing observations on
such systems and by using crystal analysis combined with
ab initio calculation to go towards reliable predicting rules.
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This would allow to use these molecules for crystal engineering
as has been done for a while in the urea/thiourea family.3
Moreover, the ability of such compounds to coordinate metal
ions, either as tetrazanes10–11,28–29 or as verdazyls,13,30–32 the
oxidized form of tetrazane, appears as a valuable way to
modulate and enrich the intermolecular interactions.
H
Pyr), 5.80 (d, 2H, J = 10.4 Hz, NH), 4.96 (t, 1H,
J = 10.4 Hz, C2H), 3.45 (s, 6H, CH3). 13C NMR (101 MHz,
CDCl3, ppm): 171.9 (CQS), 151.6, 148.4, 135.9, 123.0, 122.2,
67.4 (C2), 43.2. IR (cmꢂ1): nmax 3174 (NH, m), 2932 (CH, w),
1596 (m), 1475 (s), 1436 (s), 1326 (s), 1292 (s), 1085 (s), 935 (s),
773 (s), 483 (s). Elemental analysis. Found: C, 48.55; H, 6.03;
N, 31.28; S, 13.92%. C9H13N5S requires C, 48.43; H, 5.83; N,
31.39; S, 14.35%.
Experimental
1,5-Dimethyl-3-carboxy-6-thioxo-1,2,4,5-tetrazane 1d
General
As 1b. Recrystallization of the residue from a 5 : 1 ethyl
acetate–methanol mixture afforded a white crystalline powder
(M = 190 g molꢂ1, 75%).
(1H-Imidazole)-2-carbaldehyde, 2-pyridinecarbaldehyde, glyoxylic
acid, 8-quinolinecarbaldehyde and salicylaldehyde were used
as purchased. 4,6-Dimethyl-2-pyrimidinecarbaldehyde was
prepared following the route developed by Barr et al.7
2,4-Dimethylthiocarbonohydrazide 1a and 2,4-dimethyl-
carbonohydrazide 2a were prepared according to the
literature.4 The synthesis and characterization of compounds
2b–e and 2g have already been reported.4,7,12,15
1H NMR (400 MHz, d6-DMSO, ppm): 5.79 (br s, 2H, NH),
4.48 (s, 1H, CH), 3.39 (s, 6H, CH3). 13C NMR (101 MHz,
d6-DMSO, ppm): 173.3 (CQS), 168.1 (CQO), 66.8, 43.8.
IR (cmꢂ1): nmax 3508 (OH, m), 3163 (m), 3128 (NH, m),
2936 (CH, m), 2463 (m), 1717 (CO), 1508 (m), 1475 (m), 1426
(m), 1351 (m), 1246 (s), 1081 (s), 962 (s), 874 (s), 759 (m), 704
(m), 481 (s). Elemental analysis. Found: C, 28.82; H, 5.88; N,
26.81; S, 15.03%. C5H10N4SO2ꢁH2O requires C, 28.85; H,
5.77; N, 26.92; S, 15.38%.
1
The H and 13C{1H} NMR spectra were recorded using a
Bruker Avance 400 NMR spectrometer at 400 and 101 MHz,
respectively; chemical shifts d in ppm with respect to SiMe4,
J in Hz. Infrared spectra were recorded from KBr discs on a
Bio-Rad FTIR spectrometer FTS 165; n in cmꢂ1. Elemental
analyses were performed at Service Central d’Analyses du
CNRS in Vernaison (France).
1,5-Dimethyl-3-(40,60-dimethylpyrimidyl)-6-thioxo-1,2,4,5-
tetrazane 1e
As 1b. Recrystallization of the residue from ethyl acetate
afforded colorless crystals (M = 252 g molꢂ1, 71%).
Synthesis of compounds
1H NMR (400 MHz, CDCl3, ppm): 7.07 (s, 1H, Haro), 4.97
(s, 1H, C2H), 4.70 (br s, 2H, NH), 3.66 (s, 6H, NCH3), 2.52
(s, 6H, CH3) ppm. 13C NMR (101 MHz, CDCl3, ppm): 175.0
(CQS), 169.1, 162.8, 121.6, 71.3 (C2), 45.7 (NCH3), 24.9
(CH3). IR (cmꢂ1): nmax 3169 (m), 3150 (NH, m), 2923 (CH,
w), 1597 (s), 1542 (m), 1487 (s), 1437 (s), 1332 (s), 1287 (s),
1080 (s), 948 (s), 866 (s), 542 (m), 491 (m). Elemental analysis.
Found: C, 47.70; H, 6.69; N, 33.40; S, 12.51%. C10H16N6S
requires C, 47.62; H, 6.35; N, 33.33; S, 12.70%.
All the reactions occurred in refluxing methanol, except that
for the synthesis of the 6-(20-hydroxyphenyl) derivatives 1g
and 2g which were carried on at room temperature. The
synthesis of 1b is fully described as a representative example.
1,5-Dimethyl-3-(20-imidazolyl)-6-thioxo-1,2,4,5-tetrazane 1b
1a (1.653 g, 12.3 mmol) was dissolved in 140 mL of methanol.
The solution was heated to 60 1C before a suspension of
1H-imidazole-2-carbaldehyde (1.184 g, 12.3 mmol) in 240 mL
of methanol was added dropwise. 30 min after the end of
the addition, the reaction mixture was suspension-free. The
solution was then refluxed overnight. Finally, the solvent was
removed by evaporation under reduced pressure to give a light
yellow solid. Colorless crystals (1.508 g, 58%) suitable for
X-ray diffraction were obtained by recrystallization from a
2 : 1 ethyl acetate–methanol mixture.
1H NMR (400 MHz, d6-DMSO, ppm): 7.01 (br s, 2H, CHim),
5.78 (d, 2H, J = 10 Hz, NH), 4.96 (t, 1H, J = 10 Hz, C2H),
3.43 (s, 6H, CH3). 13C NMR (101 MHz, d6-DMSO, ppm):
174.3 (CQS), 143.3, 129.2, 118.6, 65.4 (C2), 45.3. IR (cmꢂ1):
1,5-Dimethyl-3-(80-quinolyl)-6-thioxo-1,2,4,5-tetrazane 1f
As 1b. Recrystallization of the residue from a 3 : 1 ethyl
acetate–methanol mixture afforded light-brown crystals
(M = 273 g molꢂ1, 51%).
1H NMR (400 MHz, CDCl3, ppm): 8.86 (dd, 1H, J = 4.3
and 1.8 Hz, Haro), 8.26 (dd, 1H, J = 8.3 and 1.8 Hz, Haro),
7.88 (dd, 1H, J = 8.3 and 1.4 Hz), 7.79 (dd, 1H, J = 7.0 and
1.4 Hz), 7.59 (dd, 1H, J = 8.3 and 7.1 Hz), 7.50 (dd, 1H,
J = 8.3 and 4.3 Hz), 6.51 (d, 2H, J = 11.5 Hz, NH), 5.17 (t, 1H,
J = 11.5 Hz, C2H), 3.71 (s, 6H, CH3). 13C NMR (101 MHz,
CDCl3, ppm): 174.3 (CQS), 151.1, 147.3, 138.5, 132.4, 130.5,
130.1, 128.0, 122.8, 74.8 (C2), 45.8. IR (cmꢂ1): nmax 3208 (m),
3172 (NH, m), 2918 (CH, m), 1596 (m), 1499 (s), 1464 (s), 1428
(s), 1373 (s), 1090 (s), 939 (s), 823 (s), 790 (s). Elemental
analysis. Found: C, 57.04; H, 5.65; N, 25.53; S, 11.42%.
C13H15N5S requires C, 57.14; H, 5.49; N, 25.64; S, 11.72%.
nmax 3167 (m), 3153 (NH, m), 2930 (CH, m), 1508 (m), 1420 (s),
1373 (s), 1088 (s), 1060 (s), 765 (s), 462 (s). Elemental analysis.
Found: C, 39.38; H, 5.84; N, 39.09; S, 14.64%. C7H12N6S
requires C, 39.62; H, 5.66; N, 39.62; S, 15.09%.
1,5-Dimethyl-3-(20-pyridyl)-6-thioxo-1,2,4,5-tetrazane 1c
As 1b. Colorless crystals (M = 223 g molꢂ1, 44%) were
obtained.
1,5-Dimethyl-3-(20-hydroxyphenyl)-6-thioxo-1,2,4,5-tetrazane 1g
1H NMR (400 MHz, d6-DMSO, ppm): 8.58 (d, 1H,
J = 4.8 Hz, HPyr), 7.87 (t, 1H, J = 7.7 Hz, HPyr), 7.56
(d, 1H, J = 7.7 Hz, HPyr), 7.42 (dd, 1H, J = 7.7 and 4.8 Hz,
The reaction of 1a (1.092 g, 8.1 mmol) with 0.7 mL of
salicylaldehyde (r = 1.16 g mL, 6.8 mmol) in 160 mL of
methanol occurred at room temperature overnight. A mixture
ꢀc
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of the target molecule (91%, estimated by 1H NMR) and
diimine (9%) was obtained. The crude solid was washed with a
few mL of chloroform and the product was isolated as a white
powder (0.971 g, 60%).
X-Ray crystallography
A single crystal of each compound was selected, mounted
onto a glass fiber, and transferred in a cold nitrogen gas
stream. Intensity data were collected with a Bruker-Nonius
Kappa-CCD with graphite-monochromated Mo-Ka radiation
(0,71073 A). Unit-cell parameters determination, data collection
strategy and integration were carried out with the Nonius
EVAL-14 suite of programs.33 Multi-scan absorption correction
was applied.34 The structure was solved by direct methods
using the SIR92 program35 and refined anisotropically by
full-matrix least-squares methods using the SHELXL-97
software package.36 Hydrogen atoms involved in hydrogen
bonding were located from Fourier difference map and
restrained to their position.
1H NMR (400 MHz, d6-DMSO, ppm): 9.82 (s, 1H, OH),
7.27 (dd, 1H, J = 7.5 and 1.5 Hz, Haro), 7.16 (m, 1H, Haro),
6.85 (m, 2H, Harom), 5.85 (d, 2H, J = 10.3 Hz, NH), 5.04
(t, 1H, J = 10.3 Hz, C2H), 3.43 (s, 6H, CH3). 13C NMR (101
MHz, d6-DMSO, ppm): 173.8 (CQS), 156.4, 131.2, 129.2,
123.2, 120.7, 117.1, 66.4 (C2), 45.2. IR (cmꢂ1): nmax 3140 (NH, m),
2979 (w), 2923 (CH, w), 1617 (m), 1588 (m), 1521 (s), 1474 (s),
1364 (s), 1288 (s), 1237 (s), 1095 (s), 1059 (s), 959 (s), 834 (s),
754 (s), 473 (s). Elemental analysis. Found: C, 50.32; H, 5.96;
N, 23.54; S, 13.66%. C10H14N4SO requires C, 50.42; H, 5.88;
N, 23.53; S, 13.45%.
Acknowledgements
1,5-Dimethyl-3-(80-quinolyl)-6-oxo-1,2,4,5-tetrazane 2f
This work was developed within the framework of the ANR
project ‘fdp magnets’ in particular through the post-doctoral
grant of Olivier Oms. It was also supported by the UPMC,
Univ Paris 06 and CNRS. Lucie Norel acknowledges the
2a (0.376 g, 3.2 mmol) was dissolved in 100 mL of methanol.
The solution was heated to 60 1C before a solution of
8-quinolinecarbaldehyde (0.475 g, 3.0 mmol) in 150 mL of
methanol was added dropwise. The solution was then refluxed
for 2 h. Finally, the solvent was removed by evaporation under
reduced pressure to give a pale yellow solid. Recrystallization
of the residue from a 5 : 1 ethyl acetate–methanol mixture
afforded pale orange crystals (0.772 g, 67%).
Ministere de l’Enseignement Superieur et de la Recherche
´
(MESR) for her PhD grant.
References
1H NMR (400 MHz, d6-DMSO, ppm): 8.91 (dd, 1H,
J = 4.2 and 1.8 Hz, Haro), 8.37 (dd, 1H, J = 8.7 and
1.8 Hz, Haro), 7.94 (dd, 1H, J = 8.1 and 1.5 Hz, Haro), 7.83
(dd, 1H, J = 6.9 and 1.5 Hz, Haro), 7.53–7.58 (m, 2H, Harom),
6.22 (d, 2H, J = 11.4 Hz, NH), 5.59 (t, 1H, J = 11.4 Hz,
C2–H), 3.00 (s, 6H, CH3). 13C NMR (101 MHz, d6-DMSO,
ppm): 156.1 (CQO), 151.8, 146.6, 138.5, 135.0, 130.3,
130.1, 129.6, 127.9, 123.3, 70.0 (C2), 39.2 (CH3).
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1594 (m), 1483 (m), 1434 (s), 1386 (s), 954 (s), 890 (s), 829 (s),
791 (s), 521 (s). Elemental analysis. Found: C, 60.59; H,
5.90; N, 27.17% C13H15N5O requires C, 60.70; H, 5.84;
N, 27.23%.
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1,5-Dimethyl-3-(20-hydroxyphenyl)-6-oxo-1,2,4,5-tetrazane 2g
The reaction of 2a (2.486 g, 21.2 mmol) with 1.8 mL of
salicylaldehyde (17.1 mmol) in 250 mL of methanol occurred
at room temperature overnight. The solvent was removed by
evaporation under reduced pressure. The crude solid was
washed with ethyl acetate (2 ꢃ 10 mL) and the product was
isolated as a white powder. Recrystallization from a 1 : 1
ethyl acetate–methanol mixture afforded colorless crystals
(2.600 g, 69%).
1H NMR (400 MHz, d6-DMSO, ppm): 9.85 (s, 1H, OH),
7–8 (m, 4H, Haro), 7.16 (m, 1H, Haro), 5.72 (d, 2H, J = 9.9 Hz,
NH), 5.02 (t, 1H, J = 9.9 Hz, N–CH), 2.96 (s, 6H, CH3).
13C NMR (101 MHz, d6-DMSO, ppm): 156.6 (CQO), 155.8,
130.9, 129.2, 123.3, 120.6, 117.2, 67.6 (C2), 39.0 (CH3). IR
(cmꢂ1): nmax 3232 (m), 2982 (CH, m), 2878 (w), 1599 (s), 1579
(s), 1480 (s), 1222 (s), 980 (s), 838 (m), 754 (s), 521 (s).
Elemental analysis. Found: C, 53.88; H, 6.16; N, 25.17%.
C10H14N4O2 requires C, 54.04; H, 6.35; N, 25.21%.
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1672 | New J. Chem., 2009, 33, 1663–1672