Crystal and molecular structure of three biologically active nitroindazoles

Article abstract of DOI:10.1016/j.molstruc.2010.10.023

3-Bromo-1-methyl-7-nitro-1H-indazole (1), 3-bromo-2-methyl-7-nitro-2H- indazole (2) and 3,7-dinitro-1(2)H-indazole (3) have been synthesized and characterized by X-ray diffraction, ¹³C and ¹⁵N NMR spectroscopy in solution and in solid-state. The dihedral angles obtained in the crystal structures are in good agreement with the molecular parameters calculated using DFT B3LYP calculations employing the 6-311++G(d,p) basis set. Compounds 1 and 2 present intermolecular halogen bonds between the bromine and the oxygen atoms of the nitro group and in compound 3 inter- and intramolecular hydrogen bonding exists.

Full text of DOI:10.1016/j.molstruc.2010.10.023

Journal of Molecular Structure 985 (2011) 75–81
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Crystal and molecular structure of three biologically active nitroindazoles
a
a
a
Pilar Cabildo a, Rosa M. Claramunt a, , Concepción López , M. Ángeles García , Marta Pérez-Torralba ,
⇑
Elena Pinilla b, M. Rosario Torres b, Ibon Alkorta c, José Elguero c
a Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain
b Departamento de Química Inorgánica I, CAI de Difracción de Rayos-X, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
c Instituto de Química Médica, CSIC, Centro de Química Orgánica Manuel Lora-Tamayo, Juan de la Cierva 3, E-28006 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
3-Bromo-1-methyl-7-nitro-1H-indazole (1), 3-bromo-2-methyl-7-nitro-2H-indazole (2) and 3,7-dinitro-
1(2)H-indazole (3) have been synthesized and characterized by X-ray diffraction, 13C and 15N NMR spec-
troscopy in solution and in solid-state. The dihedral angles obtained in the crystal structures are in good
agreement with the molecular parameters calculated using DFT B3LYP calculations employing the 6-
311++G(d,p) basis set. Compounds 1 and 2 present intermolecular halogen bonds between the bromine
and the oxygen atoms of the nitro group and in compound 3 inter- and intramolecular hydrogen bonding
exists.
Received 7 September 2010
Received in revised form 13 October 2010
Accepted 13 October 2010
Available online 20 October 2010
Keywords:
NOS
Indazoles
Ó 2010 Elsevier B.V. All rights reserved.
Halogen bond
Hydrogen bonding
NMR
DFT calculations
1. Introduction
that can be easily separated [11–13]. Bromination of 6 and 7
affords 1 and 2 [11,12]. The same compounds are obtained by
C-nitroindazoles unsubstituted on the N atom, particularly 7-ni-
tro derivatives, are one the most potent families of nitric oxide syn-
thase (NOS) inhibitors. These enzymes catalyze the oxidation of
methylation of 5 resulting in a 70/30 ratio of 1/2 [12]. With slightly
different conditions, only 1 was obtained [14,15]. 3,7-Dinitro-
1(2)H-indazole (3) was first reported by Habraken and Cohen-
Fernandes in 1971 in a two-step procedure through the rather
unstable 2-nitro derivative 8 [16]. Compound 3 has been prepared
two more times by Wrzeciono, but always with the same proce-
dure [17,18].
L-arginine to L-citrulline and nitric oxide (NO), a molecule that
plays an important role in the regulation of blood pressure, neuro-
transmission, and the immune response [1]. We have been actively
working on these and other indazoles in two directions: first, in
their structural aspects related to N–Hꢀ ꢀ ꢀN hydrogen bonds and
prototropic tautomerism [2–6]; second, in their biological proper-
ties [7–9].
2. Results and discussion
We will describe in this paper the structure and spectroscopic
properties of three 7-nitroindazole derivatives (Scheme 1): 3-bro-
mo-1-methyl-7-nitro-1H-indazole (1), 3-bromo-2-methyl-7-nitro-
2H-indazole (2) and 3,7-dinitro-1(2)H-indazole (3) (1H-tautomer
3a and 2H-tautomer 3b).
The three compounds are known but their synthesis has been
reported in several papers not citing comprehensively the litera-
ture. The starting material is commercial 7-nitro-1H-indazole (4)
(Scheme 2). Bromination in acetic acid to afford 5 was reported
by Auwers and Demuth in 1927 [10]. Treatment of 4 with methyl
sulfate in basic conditions yields both N-methyl isomers 6 and 7
2.1. X-ray structures
An X-ray study of compounds 1, 2 and 3 has been carried out.
Figs. 1–3 show the molecular structure for the three compounds.
In all cases, the indazole rings are almost planar including the nitro
groups in the best least-square plane for 2 and 3 (maximum dihe-
dral angle about 7°), while for 1 the dihedral angle is about 30°.
For 1 and 2 intermolecular halogen bonding [19,20] between
the bromine and the oxygen atoms of the nitro group led to chains
parallels to axes c and a, respectively (Figs. 4 and 5). In the case of 1
the interaction involves only one O atom while in the case of 2 the
halogen bond is bifurcated (three-centered) and both O atoms of
the nitro group contact with the Br atom. Both situations, the first
one more common, have been described in the literature [21–23].
⇑
Corresponding author. Tel.: +34 913987322; fax: +34 913988372.
E-mail address: rclaramunt@ccia.uned.es (R.M. Claramunt).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.10.023

76
P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
4
3a
7a
3
Br
N
NO2
N
NO2
Br
N CH3
5
6
2
N
N H
N
N
N
N
N
CH3
H
NO2
NO2
NO2
NO2
7
1
1
2
3a
3b
Scheme 1. The three nitroindazoles and the numbering scheme.
Br
N CH3
Br
N
Br
N
NO2
N
XCH3
+
+
N
N
N
N
H
CH3
H
NO2
Br2
NO2
Br2
NO2
Br2
NO2
2
7
5
1
6
3
H+,
Δ
HNO3
XCH3
N CH3
N
N
N NO2
N
N
N
N
CH3
H
NO2
NO2
NO2
NO2
8
4
Scheme 2. Synthesis of compounds 1, 2 and 3.
In compound 3 bifurcated inter and intramolecular hydrogen
bonds form zig-zag chains parallels to axis a (Fig. 6). The existence
of bifurcated (three-centered) hydrogen bonds had also been re-
ported [24], with some examples involving the nitro group [25–
27].
nuclei have been straightforward and are in agreement with liter-
ature data reported for other indazoles [28–30].
The experimental CPMAS NMR spectra reported in Fig. 7 de-
serve special attention in what concerns their high resolution lead-
ing to the observation of all carbon and nitrogen atoms.
Bond lengths and angles including the hydrogen bonds and
electrostatic interactions are collected en Table 1.
2.3. Theoretical calculations
2.2. Solution and solid-state NMR
2.3.1. Geometries [B3LYP/6-311++G(d,p)]
According to the calculations, the dihedral angle of the 7-nitro
group is 30° for 1 and 0° for 2, which is expected due to the prox-
imity of the methyl group in 1. In compound 3 both nitro groups
The NMR results are reported in Table 2 (solution) and 3 (solid-
state). The assignments of all the signals to the corresponding
Fig. 1. ORTEP plot (30% probability for the ellipsoids) of 1 showing the labeling of
Fig. 2. ORTEP plot (30% probability for the ellipsoids) of 2 showing the labeling of
the asymmetric unit.
the asymmetric unit.

P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
77
Fig. 3. ORTEP plot (30% probability for the ellipsoids) of 3 showing the labeling of
the asymmetric unit. Dotted lines are used to express the intramolecular hydrogen
bond.
are in the plane of the ring (dihedral angles = 0°). These observa-
tions coincide with those reported in the crystallographic section.
Fig. 5. View along the b axis showing the Br–O interactions in compound 2.
cases, the difference exp.–calc. is between ꢁ15 and ꢁ20 ppm, as
we have already reported (ꢁ20 ppm [34]).
2.3.2. Energies [B3LYP/6-311++G(d,p)]
It is well known that in indazoles 1H-tautomers (benzenoid) are
more stable than 2H-tautomers (quinonoid) [31]. This is also the
case for compound 3 where 1H (3a) is 42.5 kJ molꢁ1 more stable
than 2H (3b). The same applies to the isomerism of N-substituted
derivatives and so the 1-methyl isomer 1 is 19.2 kJ molꢁ1 more sta-
ble than the 2-methyl isomer 2.
As we have calculated both tautomers of 3, in Fig. 8 are reported
the signals most sensitive to tautomerism. Only the chemical shifts
of 3a are consistent with the experimental data reported in Tables
2 and 3, those of 3b being rather different. This is the result ex-
pected both from energy considerations and from the X-ray struc-
ture for the solid-state, where only one tautomer is found (Fig. 3).
The solution data indicate that a low amount, if any, of tautomer
3b is present. A linear combination of the calculated values for
3a (94%) and 3b (6%) afford values very close to the experimental
ones.
2.3.3. NMR [GIAO/B3LYP/6-311++G(d,p)]
The absolute shieldings (r, ppm) provided by the GIAO calcula-
tions can be transformed to chemical shifts (d, ppm) by means of
three empirical equations statistically obtained from large collec-
tions of data:
d
13C = 175.7–0.963 ꢂ
r
13C [32],
r
d
15N = ꢁ152.0–
0.946 ꢂ
r
15N [32] and d1H = 31.0–0.970 ꢂ
1H [33]. We have com-
3. Conclusions
pared the chemical shifts thus obtained with the experimental data
for compounds 1 and 2 and the agreement has proved to be excel-
lent (both solution and solid-state) save for the 13C chemical shifts
of carbon C-3, the one bearing a bromine substituent. In these
Single-crystal X-ray diffraction analyses indicate that the inves-
tigated compounds 1, 2 and 3 crystallize in the orthorhombic Pbca,
monoclinic P2(1)/c and orthorhombic P2(1)2(1)2(1) space groups,
Fig. 4. View along the b axis showing the Br–O interactions in compound 1.

78
P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
Table 2
13C and 15N chemical shifts (d in ppm) and coupling constants (J in Hz).
Nuclei
1
2
3
3
DMSO-d6
300 K
DMSO-d6
300 K
CD3CN
300 K
THF-d8
207 K
C3
121.1 (d)
3J = 4.0
111.0 (m)
151.5 (m)
150.8
119.7
129.9
C3a
C4
127.3 (d)
124.9 (d)
2J = 9.2
128.3 (dd)
1J = 166.5
3J = 8.1
120.2 (d)
2J = 9.5
130.3 (dd)
1J = 171.7
3J = 8.6
2J = 9.4
127.2 (dd)
1J = 167.0
3J = 8.5
C5
C6
121.2 (d)
1J = 168.8
126.0 (ddd)
1J = 167.2
120.8 (d)
1J = 167.4
125.9 (ddd)
1J = 167.4
126.4 (d)
1J = 168.7
126.8 (ddd)
1J = 168.5
125.8
126.0
2J = 2.9, 3J = 7.7 2J = 2.9, 3J = 9.5 2J = 2.3, 3J = 8.6
C7
135.0 (d)
136.4 (d)
134.9 (m)
134.8
135.1
–
3J = 9.2
3J = 7.7
C7a
Me
131.9 (dd)
3J = 3J = 6.9
40.9 (q)
1J = 142.5
ꢁ198.9
139.3 (dd)
3J = 3J = 6.9
39.5 (q)
1J = 142.0
ꢁ87.1
135.4 (dd)
3J = 3J = 6.7
–
N1
N2
NO2
ꢁ199.7a
ꢁ64.2a
ꢁ200.0a
ꢁ63.3a
ꢁ53.6
ꢁ155.2
ꢁ11.3a
ꢁ11.3a
ꢁ21.5a (NO2-3) ꢁ24.6a (NO2-3)
ꢁ14.3a (NO2-7) ꢁ17.1a (NO2-7)
a
To obtain these 15N NMR chemical shifts the use of a 5-mm inverse detection
QNP probe equipped with a z-gradient coil, at 333 K for 1 and 2 and 300 K for 3, was
necessary; d: doublet; m: multiplet; q: quartet.
Fig. 6. View along the b axis showing the zig-zag chain and the H-bonds in
compound 3.
4.1.1. 3-Bromo-1-methyl-7-nitro-1H-indazole (1) and 3-bromo-2-
methyl-7-nitro-2H-indazole (2)
In a round-bottomed flask equipped with reflux condenser, 3-
bromo-7-nitro-1H-indazole (5) (0.63 g, 2.6 mmol) was dissolved
in dry methanol (25 mL). Then, sodium methoxyde (0.18 g,
3.3 mmol) and 0.55 g of methyl iodide (0.24 mL, 3.9 mmol) were
added. The mixture was heated to reflux for 2 days and then the
solvent was removed under reduced pressure. Water (30 mL)
was added and the residue was extracted with chloroform
(3 ꢃ 45 mL). The organic layers were combined, dried (Na2SO4),
and concentrated to afford a crude solid formed mainly by the
two isomers. After silica gel chromatography with (hexane/ethyl
acetate 30:1), 1 was obtained first (0.24, 37%) and increasing to
1:1 to afford 2 (0.29, 44%); m.p. (1): 161.1 °C (160–162 °C) [12];
m.p. (2): 200.5 °C (194–196 °C) [12].
Table 1
Halogen bond interactions (Å and °) for 1 and 2 and hydrogen bonds (Å and °) for 3.
Compound
Interactions
Symmetry operations
d(Br–O)
1
2
2
Brꢀ ꢀ ꢀO1
Brꢀ ꢀ ꢀO1
Brꢀ ꢀ ꢀO2
x, ꢁy + 1/2, z ꢁ 1/2
x ꢁ 1, y, z
3.089(1)
2.357(1)
2.194(1)
x ꢁ 1, y, z
D–Hꢀ ꢀ ꢀA
d(D–H) d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA) \(DHA)
3
3
N1–H1ꢀ ꢀ ꢀO2
1.04
2.15
2.21
2.708(3) 111.7
3.019(3) 133.8
N1–H1–N20 x ꢁ 1/2, ꢁy + 1/2, ꢁz + 1 1.04
(1) 1H NMR (DMSO-d6) d 8.28 (dd, 3J = 7.9, 4J = 0.7, 1H, H6), 8.03
(dd, 3J = 7.9, 4J = 0.7, 1H, H4), 7.43 (dd, 3J = 3J = 7.9, 1H, H5), 4.13 (s,
3H, CH3); (2) 1H NMR (DMSO-d6) d 8.35 (dd, 3J = 7.9, 4J = 0.8, 1H,
H6), 8.02 (dd, 3J = 7.9, 4J = 0.8, 1H, H4), 7.31 (dd, 3J = 3J = 7.9, 1H,
H5), 4.24 (s, 3H, CH3).
respectively. There is an excellent agreement between experimen-
tal (both solution and solid-state) and theoretically calculated 13C
and 15N NMR chemical shifts, save for the C-3 chemical shifts in
compounds 1 and 2. DFT calculations predict that the 1-methyl iso-
mer 1 is more stable than the 2-methyl one 2 in 19.2 kJ molꢁ1, and
from the two tautomers 1H- and 2H- in compound 3, the first form
is stabilized over the latter in about 42.5 kJ molꢁ1
.
4.1.2. 3,7-Dinitro-1H(2H)-indazole (3)
This compound was prepared according to Ref. [16] and ob-
tained as a yellow solid. M.p. 221.8 °C; m.p. 220 °C [16]. 1H NMR
(CD3CN) d 12.83 (br s, 1H, NH), 7.65 (t, 3J = 8.0, 1H, H5), 8.48 (d,
3J = 7.9, 1H, H6), 8.62 (d, 3J = 8.1, 1H, H4).
4. Experimental section
4.1. Chemistry
Melting points for compounds 1–3 were determined by DSC on
a Seiko DSC 220C connected to a Model SSC5200H Disk Station.
Thermograms (sample size 0.003–0.0010 g) were recorded at the
scanning rate of 2.0 °C minꢁ1. Thin-layer chromatography (TLC)
was performed with Merck silica gel (60 F254). Compounds were
detected with a 254-nm UV lamp. Silica gel (60–320 mesh) was
employed for routine column chromatography separations with
the indicated eluent.
4.2. NMR spectroscopy
Solution spectra were recorded at 300 K on a Bruker DRX 400
(9.4 T, 400.13 MHz for 1H, 100.62 MHz for 13C and 40.56 MHz for
15N) spectrometer with a 5-mm inverse detection H–X probe
equipped with a z-gradient coil for 1H, 13C and 15N, save specified.
Chemical shifts (d in ppm) are given from internal solvents, DMSO-
d6 (2.49) and CD3CN (1.93) for 1H and DMSO-d6 (39.5) and CD3CN
(118.7) for 13C. And external reference CH315NO2 (0.00) for 15N
NMR was used. 2D (1H–1H) gs-COSY and inverse proton detected
3- Bromo-7-nitro-1H-indazole (5) was prepared according to
the published procedure [12].

P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
79
Compound 1
N1
Me
C3a, C6
C4
C7a, C7
140
C3, C5
NO2
0
N2
120
100
80
60
40
40
-40
-80
-120
-160
N2
-200
-240
(ppm)
(ppm)
Compound 2
N1
C3a, C4, C6
C3, C5
Me
NO2
C7a, C7
140
120
100
(ppm)
80
60
40
40
0
-40
-80
(ppm)
-120
-160
-200
N1
-240
Compound 3
C6, C5
C4, C7
N2
NO2-7
0
C3a
C7a
NO2-3
-40
C3
40
-80
-120
-160
-200
-240
140
120
100
80
60
40
(ppm)
(ppm)
Fig. 7. The 13C and 15N CPMAS NMR spectra of compounds 1–3.
151.5
150.8
149.5
141.4
NO2
–64.2
NO2
–71.3
NO2
–171.7
N
N
N
N H
–71.6
N
N
–197.0
–199.7
N
H
H
NO2
NO2
NO2
NO2
135.1
134.6
142.0
3 (CD3CN)
3 (CPMAS)
3a
3b
150.9
NO2
–64.8
–199.0
N
N
H
NO2
134.6
3a (94%)–3b (6%)
Fig. 8. The tautomerism of 3,7-dinitro-1(2)H-indazole (3). Experimental results in solution and in the solid-state vs. calculated values in the gas phase.
heteronuclear shift correlation spectra, (1H–13C) gs-HMQC,
(1H–13C) gs-HMBC, (1H–15N) gs-HMQC, and (1H–15N) gs-HMBC,
were acquired and processed using standard Bruker NMR software
and in non-phase-sensitive mode [35]. Gradient selection was
achieved through a 5% sine truncated shaped pulse gradient of
1 ms. Variable temperature experiments were recorded on the
same spectrometer. A Bruker BVT3000 temperature unit was used
to control the temperature of the cooling gas stream and an ex-
changer to achieve low temperatures.
Solid state 13C (100.73 MHz) and 15N (40.60 MHz) CPMAS NMR
spectra have been obtained on a Bruker WB 400 spectrometer at
300 K using a 4 mm DVT probehead and a 4-mm diameter cylindri-
cal zirconia rotor with Kel-F end-caps. The non-quaternary sup-
pression (NQS) technique to observe only the quaternary carbon

80
P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
Table 3
13C and 15N chemical shifts (d in ppm) in solid-state (CPMAS, 300 K).
Comp.
C3
C3a
C4
C5
C6
C7
C7a
Me
N1
N2
NO2
1
2
3
118.7
121.5
149.5
126.0
127.5
117.5
128.6
127.5
132.3
118.7
121.5
126.3
124.6
127.5
126.3
132.2
136.5
132.3
131.8
138.0
134.6
42.4
40.5
–
ꢁ197.8
ꢁ87.1
ꢁ50.6
ꢁ153.5
ꢁ71.3
ꢁ7.0
ꢁ8.4
ꢁ197.0
ꢁ12.0 (NO2-7)
ꢁ20.5 (NO2-3)
Table 4
Crystal data and structure refinement for compounds 1, 2 and 3.
Crystal Data
1
2
3
Identification code
Empirical formula
Formula weight
Wavelength (Å)
Crystal system
Space group
CCDC – 780744
C8H6BrN3O2
256.07
0.71073
Orthorhombic
Pbca
CCDC – 780745
C8H6BrN3O2
256.07
0.71073
Monoclinic
P2(1)/c
CCDC – 780746
C7H4N4O4
208.14
0.71073
Orthorhombic
P2(1)2(1)2(1)
Unit cell dimensions
a (Å)
b (Å)
12.705(2)
6.994(1)
20.436(3)
–
1808.0(5)
8
9.882(2)
7.111(2)
13.357(3)
ꢁ106.255(4)
901.0(3)
4
4.9853(7)
12.265(2)
13.265(2)
–
811.1(2)
4
c (Å)
b (°)
Volume (Å3)
Z
Density (calculated) (Mg/m3)
Absorption coefficient
F(0 0 0)
1.881
1.888
1.713
4.522 (mmꢁ1
424
)
4.537 (mmꢁ1
504
)
0.144 (mmꢁ1
424
)
Theta range (°) for data collection
Index ranges
2.23–25.0
ꢁ156h613
ꢁ86k68
ꢁ246l624
12,237
2.29–25.0
ꢁ116h611
ꢁ86k68
ꢁ146l615
6300
2.26–25.00
ꢁ56h65
ꢁ146k612
ꢁ146l615
6204
Reflections collected
Independent reflec. [R(int)]
Data/restraints/parameters
Goodness-of-fit on F2
1594 [0.0532]
1594/0/128
1.012
0.0776 (1185)
0.2180
1580 [0.0448]
1580/0/127
1.006
0.0304 (1070)
0.0921
1422 [0.0654]
1422/0/137
0.833
0.0328(885)
0.0703
Ra[I > 2sigma(I)] (obs. reflec.)
b
RwF (all data)
P
P
a
||Fo|ꢁ|Fc||/ |Fo|.
P
P
2
{
[w(Fo2 ꢁ Fc2)2]/ [w(Fo2Þ ]}1/2
.
b
atoms was employed [35]. 13C spectra were originally referenced
to a glycine sample and then the chemical shifts were recalculated
to the Me4Si (for the carbonyl atom d (glycine) = 176.1 ppm) and
15N spectra to 15NH4Cl and then converted to nitromethane scale
using the relationship: d 15N(nitromethane) = d 15N(ammonium
chloride) – 338.1 ppm.
fixed isotropic contributions at their calculated positions deter-
mined by molecular geometry except for the H1 bonded to N1
for 3, which was located from the Fourier map and included. All
hydrogen refined riding on the corresponding bonded atom. All
the calculations were carried out with SHELX-97 [36].
4.4. Computational details
4.3. X-ray data collection and structure refinement for compounds 1, 2
and 3
Theoretical calculations were carried out within the Gaussian 03
facilities [37]. The geometries were fully optimized at the B3LYP/6-
311++G(d,p) level [38,39], and frequency calculations verified its
minimum nature. On these geometries GIAO calculations [40] were
carried out.
Suitable crystals for X-ray diffraction experiments were ob-
tained by crystallization from acetone–water for 1, from ethyl ace-
tate–hexane for 2 and from tetrahydrofurane for 3. Data collection
for all compounds was carried out at room temperature on a Bru-
ker Smart CCD diffractometer using graphite-monochromated
Supplementary material
Mo K
a radiation (k = 0.71073 Å) operating at 50 kV and 30 mA. In
Crystallographic data for molecules 1, 2 and 3 have been
deposited at the Cambridge Crystallographic Data Center with
the deposition numbers CCDC – 780744, CCDC – 780745 and CCDC
– 780746. Copies of the data can be obtained free of charge via
external link http://ccdc.cam.ac.uk/retrieving.html.
all cases, the data were collected over a hemisphere of the recipro-
cal space by combination of three exposure sets. Each frame expo-
sure time was 20 s, covering 0.3° in
x. The cell parameters were
determined and refined by least-squares fit of all reflections col-
lected. The first 100 frames were recollected at the end of the data
collection to monitor crystal decay, and no appreciable decay was
observed. An empirical absorption correction was applied for 1 and
2 compounds. A summary of the fundamental crystal and refine-
ment data is given in Table 4. The structures of all the compounds
were solved by direct methods and refined by full-matrix least-
squares on F2 (SHELXL-97). All non-hydrogen atoms were refined
anisotropically. In all cases the hydrogen atoms were included with
Acknowledgements
This work has been financed by the Spanish MICINN (CTQ2007-
62113, CTQ2009-13129-C02-02 and CTQ2010-16122) and Comun-
idad Autónoma de Madrid (Project MADRISOLAR2, ref S2009/PPQ-
1533).

P. Cabildo et al. / Journal of Molecular Structure 985 (2011) 75–81
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