Three-dimensional triazenido layers attained through classical and non-classical hydrogen interactions and its coordination to palladium under prolific occurrence of bifurcated hydrogen bonding

Article abstract of DOI:10.1016/j.poly.2011.10.009

The new ligand 1,3-bis(3-methoxy-4-methylbenzoate) triazene (1, bmmbt), and the already known ligand 1,3-bis(4-acetylphenyl)triazene (bapht), yield the two new palladium(II) complexes [(bmmbt)Pd(PPh₃)₂Cl] ·DMSO (2) and [(bapht)Pd(PPh

Full text of DOI:10.1016/j.poly.2011.10.009

Polyhedron 31 (2012) 558–564
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Polyhedron
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Three-dimensional triazenido layers attained through classical and
non-classical hydrogen interactions and its coordination to palladium under
prolific occurrence of bifurcated hydrogen bonding
⇑
⇑
Davi Fernando Back, Manfredo Hörner , Fernanda Broch, Gelson Manzoni de Oliveira
Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria-RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
The new ligand 1,3-bis(3-methoxy-4-methylbenzoate) triazene (1, bmmbt), and the already known
ligand 1,3-bis(4-acetylphenyl)triazene (bapht), yield the two new palladium(II) complexes
[(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2) and [(bapht)Pd(PPh3)2Cl] (3) (Ph = phenyl; DMSO = dimethylsulfoxide).
Compound 1 shows the existence of more than one interaction promoting the coupling between the tria-
zene chains. Other remarkable types of interactions in 1 are bifurcated hydrogen contacts and non-
Received 24 June 2011
Accepted 7 October 2011
Available online 17 October 2011
Keywords:
Triazenes
Bifurcated hydrogen interactions
Trifurcated hydrogen interactions
classical CHꢀꢀꢀ
p bonding. Complexes 2 and 3 present a planar geometry, supported also through bifur-
cated intramolecular ClꢀꢀꢀH–C interactions, as well as the occurrence of trifurcated ClꢀꢀꢀH–C intermolecular
interactions.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
tronics [7]. Recently, Gothelf and Ferapontovo [8] have reported
the use of triazenes also for immobilization and characterization
The chemistry of the triazenes (R–N@N–NH–R) started formally
in 1859 with the synthesis of 1,3-bis(phenyl)triazene by Griess [1].
Nevertheless, only during the decade of 60 this type of molecules
has received attention with biological and technological purposes.
At that time Shealy and co-workers reported the synthesis of
5-(3,3-dimethyl-1-triazenes) imidazole-4-carboxamide, clinically
known as Dacarbazine [2–4]. DacarbazineÒ is currently prescribed
as a chemotherapeutic for the treatment of metastatic malignant
melanoma, brain tumors, leukemia and Hodgkin’s disease [5].
Taking advantage of the recognized ability of triazenes regard-
ing the alkylation of DNA, Rachid et al. [6] have attained a single
molecule presenting multiple antiproliferative action, based upon
a synergistic mechanism which gives greater efficiency to the syn-
thesized compound. The remarkable species was able to interact
with the receptor of epidermal cellular growth factor, being also
able to connect simultaneously to DNA, inhibiting or impairing
their functions. This molecule inhibited both the growth and pro-
liferation of tumors after decomposition at physiological pH.
Fig. 1 represents the possible hydrolytic pathway for the tria-
zene-containing molecule.
of oligonucleotides.
Acting as ligands, the triazene units [–N–N@N–] exhibit high
versatility regarding coordination modes, as a result of its geome-
try and the presence of electron donor sites. The ligands can act as
monodentate, bidentate, chelate or bridge-forming, showing a
remarkable ability to suit the stereochemical requirements to per-
form a wide variety of transition metal complexes [9–12], as
shown in Fig. 2.
There are only few reports in the literature about the existence
of palladium complexes containing triazene fragments. In one of
these, Bombieri et al. [13] describe a possible mechanism involving
reactions between triazene ligands and Pd(II), showing the exis-
tence of a pentacoordinated intermediate complex in which the
triazene ligand achieves a four-membered ring chelate with the
metal, according to Fig. 3 [13]. This mechanism involves a fluxional
arrangement in solution, i.e., the Pd–N g
1 bond migrates in relation
to the nitrogen atoms of the diazoaminic chain.
It has been already reported that triazenes show a noteworthy
trend to achieve intermolecular, secondary metal–ligand and
ligand–ligand interactions due to hydrogen bonding. Such charac-
teristics make these species also proficient to assemble unique
supramolecular aggregates. Recently some examples of these
classes of compounds were discussed, with 1D [14–17] and 2D
[18–20] polymeric, supramolecular assemblies. This work deals
mainly with the synthesis and the structural characterization of
the new symmetrical triazene ligand 1,3-bis(3-methoxy-4-meth-
ylbenzoate) triazene (1, bmmbt), the already known ligand 1,
Besides this confirmed biological applicability, triazenes seem
also to act as facilitators of arenes coupling to silicon surfaces, with
major applications in the semiconductors chemistry and nano elec-
⇑
Corresponding authors. Tel.: +55 55 3220 8757; fax: +55 55 3220 8031.
E-mail addresses: horner@smail.ufsm.br (M. Hörner), manzonideo@smail.
ufsm.br (G. Manzoni de Oliveira).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.009

D.F. Back et al. / Polyhedron 31 (2012) 558–564
559
H
H
H
N
N
N
Cl
+
N
N
N
Cl
-
R
R
N
H2N
N
N
Hydrolysis
N
N
N
N
+
Cl
Cl
Interacts with the epidermal
growth factor receptor (EGFR)
R= Methyl, p-methoxyphenyl, p-chlorophenyl
On DNA
Fig. 1. Possible mechanism of hydrolysis for the triazene-containing molecule.
25.73. Found: C, 57.60; H, 5.23; N, 11.45; O, 26.71%. IR (KBr) free
ligand [cmꢁ1]: 3365 [
s, medium (N–H)], 1701 [ s, strong (C@O)],
1614 [ , strong (C–Caryl)], 1464 [das, medium (CH3)], 1435 [ds, med-
ium (CH3)], 1284 [ s, medium (N–N@N), 1404 [ , medium (N@N)],
m
m
m
m
m
1245 [das, medium (C–O–C)], 1031 [ds, medium (C–O–C)].
2.2. Preparation of the complex [(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2)
0.037 g (0.1 mmol) of 1 was dissolved in methanol by heating
the mixture at 65 °C for 30 min. To this solution, 0.070 g
(0.1 mmol) of [(PPh3)2PdCl2] {bis(triphenylphosphine)palla-
dium(II) dichloride} and 0.15 ml of triethylamine were added. After
1 h stirring the color turned intensely dark. After drying, the prod-
uct was redissolved in DMSO at 50° C. From this solution, tabular
orange crystals, suitable for X-ray diffraction, were formed after
3 days. Yield: 35% (based on [(PPh3)2PdCl2]).
Properties: air stable, tabular, orange crystals. Melting point:
231–233 °C (decomposition). Anal. Calc. for C56H54N3O7P2SClPd
(1116.87): C, 62.24; H, 4.06; N, 4.6; O, 9.2. Found: C, 62.1; H,
6.03; N, 4.51; O, 9.12%. IR (KBr) complex (cmꢁ1): The N–H band
Fig. 2. Main coordination modes of triazenes: (a) neutral monodentate terminal;
(b) anionic monodentate terminal; (c) chelating bidentate; (d) bridge-forming; (e)
bridge-type syn–syn – g1 g1
: :l2; (f) central nitrogen coordination.
is absent. 1716 [
(CH3)], 1434 [ds, m (CH3)], 1288 [
(N@N)], 1230 [das, m (C–O–C)], 1029 [ds, m (C–O–C)], 1125, 692
s, s, m (P–Caryl)].
ms, s (C@O)], 1594 [
m, s (C–Caryl)], 1481 [das, m
m
s, m (N–N@N), 1404 [
m
, medium
[m
Fig. 3. Mechanism for fluxional monocatenaded triazenes.
2.3. Preparation of the ligand 1,3-bis(4-acetylphenyl)triazene
This ligand was prepared according to the modified procedure
described by Polanc and co-workers [21]. 4-Amino acetophenone
(0.271 g, 2 mmol) was added to a solution of Na3Co(NO2)6 (sodium
hexanitrocobaltate (III), 0.670 g, 1.87 mmol), in 10 mL of water.
The mixture was stirred at room temperature for 4 h, the solid
material was isolated by filtration and washed with cold water
(3 ꢂ 10 mL). Yield: 97%. Properties: Melting point: 181–184 °C.
Anal. Calc.: C, 68.34; H, 5:33; N, 14.94; O, 11.38. Found: C, 68.4;
H, 5.39; N, 15.4; O, 11.6%. IR (KBr) free ligand (cmꢁ1): 3197
3-bis(4-acetylphenyl)triazene (bapht), and the two new palla-
dium(II) complexes [(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2) and
[(bapht)Pd(PPh3)2Cl] (3) (Ph = phenyl; DMSO = dimethylsulfoxide).
With basis on the results here discussed, our aim is also to show
the possibilities of obtaining novel and significant hydrogen inter-
actions in the solid state.
2. Experimental
[m
s, m (N–H)], 1672 [
m
s, s (C@O)], 1599 [
m, s (C–Caryl)], 1440 [ds, m
(CH3)], 1398 [ , m (N@N)], 1270 [
m
ms, m (N–N@N)].
2.1. Preparation of the ligand 1,3-bis(3-methoxy-4-methylbenzoate)
triazene (1)
2.4. Preparation of the complex [(bapht)Pd(PPh3)2Cl] (3)
Ethyl 4-aminobenzoate (0.5 g, 2.76 mmol) was dissolved in a
mixture of 15 mL of CH3COOH and 5 mL of distilled water and
the system was cooled to 0 °C. Under constant stirring, sodium ni-
trite1 (0.10 g, 2.76 mmol) was also added. After 30 min stirring the
medium was neutralized to pH around 6, with a solution of sodium
acetate. The yellow precipitate was filtered under vacuum and
washed several times with cold water. The product was dried in vac-
uum. Yield: 53%.
1,3-Bis(4-acetylphenyl)triazene (0.034 g, 0.12 mmol) was dis-
solved in methanol by heating the mixture at 65 °C for 10 min.
Thereafter [(PPh3)2PdCl2] (0.070 g, 0.1 mmol) and 0.05 ml of trieth-
ylamine were added. After 1 h stirring the solution color turned
intensely orange. After drying in vacuum, the product was redis-
solved in pyridine at 50 °C, giving tabular orange crystals, suitable
for X-ray diffractometry analysis. Yield: 68% (based on
[(PPh3)2PdCl2]).
Properties: dark yellow powder. Melting point: 182 °C. Anal.
Calc. for C18H19N3O (373.36): C, 57.90; H, 5.09; N, 11.26; O,
Properties: air stable, tabular, orange crystals. Melting point:
228 °C (decomposition at 232 °C). Anal. Calc. for C52H44ClN3O2P2Pd
(946.69): C, 65.9; H, 4.65; N, 4.44; O, 3.38. Found: C, 66.06; H, 4.5;
1
The procedure carried out with isoamyl nitrite gives a yield of 43%.

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D.F. Back et al. / Polyhedron 31 (2012) 558–564
Table 1
Crystal data and structure refinement for 1, 2 and 3.
1
2
3
Empirical formula
Formula weight
T (K)
C
18H19N3O
C56H54N3O7P2SClPd
1116.87
293(2)
C52H44ClN3O2P2Pd
946.69
293(2)
373.36
293(2)
Radiation, k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
Mo K
monoclinic
P21/c
a
, 0.7107
Mo K
a
, 0.7107
Mo Ka, 0.7107
monoclinic
P21/c
triclinic
ꢀ
P1
12.6400(10)
14.7190(10)
9.81900(10)
90
9.2123(10)
13.8922(15)
21.114(2)
13.2634(3)
24.2208(6)
14.2368(3)
90
b (Å)
c (Å)
a
(°)
79.955(7)
b (°)
97.5680(10)
90
1810.89(3)
4
1.369
0.104
88.328(6)
86.048(6)
2654.0(5)
2
1.398
0.554
1152
106.5450(10)
90
4384.21(17)
4
1.434
0.603
c
(°)
V (Å3)
Z
Calculated density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F (000)
)
784
1944
Crystal size (mm)
h (°)
Index ranges
0.312 ꢂ 0.11 ꢂ 0.074
1.63–23.57
ꢁ15 ꢃ h ꢃ 15,
ꢁ18 ꢃ k ꢃ 18,
ꢁ12 ꢃ l ꢃ 12
15635
0.160 ꢂ 0.103 ꢂ 0.087
1.49–26.84
ꢁ11 ꢃ h ꢃ 11,
ꢁ17 ꢃ k ꢃ 16,
ꢁ26 ꢃ l ꢃ 26
22782
0.799 ꢂ 0.372 ꢂ 0.290
1.81–28.33
ꢁ17 ꢃ h ꢃ 17,
ꢁ32 ꢃ k ꢃ 32,
ꢁ19 ꢃ l ꢃ 14
76303
Reflections collected
Reflections unique
Completeness to theta maximum (%)
Absorption correction
3861 [Rint = 0.0378]
99.8
10532 [Rint = 0.0630]
98.2
10887 [Rint = 0.0322]
99.6
GAUSSIAN
GAUSSIAN
GAUSSIAN
Maximum and minimum transmission
Refinement method
0.9987 and 0.9383
full-matrix
least-squares on F2
3861/0/245
1.02
0.99895 and 0.9136
full-matrix
least-squares on F2
10532/0/649
0.970
0.9987and 0.9209
full-matrix
least-squares on F2
10887/9/550
1.053
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0463,
wR2 = 0.1189
R1 = 0.0864,
wR2 = 0.1499
0.263 and ꢁ0.174
R1 = 0.0531,
wR2 = 0.1108
R1 = 0.0979,
wR2 = 0.1329
1.379 and ꢁ1.085
R1 = 0.0296,
wR2 = 0.0725
R1 = 0.0377,
wR2 = 0.0785
1.424 and ꢁ0.716
R indices (all data)
Largest difference peak and hole (e Åꢁ3
)
Fig. 4. Molecular structure of the ligand 1,3-bis(3-methoxy-4-methylbenzoate) triazene (1). The thermal ellipsoids are represented in a percentage of 30%.
Table 2
2.5. X-ray structural determination
Bond lengths (Å) and angles (°) of selected triazene compounds described in the
literature.
Data were collected with a Bruker APEX II CCD area-detector
diffractometer and graphite-monochromatized Mo K radiation.
0
Bond angles (°)
Bond lengths (AÅ)
a
The structures were solved by direct methods using SHELXS-97
[22]. Subsequent Fourier-difference map analyses yielded the posi-
tions of the non-hydrogen atoms. Refinements were carried out
with the SHELXL-97 package [22]. All refinements were made by
full-matrix least-squares on F2 with anisotropic displacement
parameters for all non-hydrogen atoms. Hydrogen atoms were in-
cluded in the refinement in calculated positions. Crystal data and
more details of the data collections and refinements are contained
in Table 1.
N1–N2
N2@N3
Caryl –N1–N2
N1–N2–N3
N2–N3–Caryl
[23]
[24]
[25]
1.316(5)
1.335(4)
1.332(7)
1.285(3)
1.271(3)
1.267(7)
117.70(2)
119.03(3)
120.20(5)
112.78(2)
112.93(2)
111.60(5)
113.79(2)
111.87(3)
112.90(5)
N, 4.40; O, 3.8%. IR (KBr) complex (cmꢁ1): The N–H band is absent.
1733 [ s, s (C@O)], 1673 [ , s (C–Caryl)], 1480 [das, m (CH3)], 1435
[ds, m (CH3)], 1265 [ s, m (N–N@N)], 1390 [das, m (N@N)], 1146,
693 [ s, s, m (P–Caryl)].
m
m
m
m

D.F. Back et al. / Polyhedron 31 (2012) 558–564
561
Fig. 5. Representation of the OꢀꢀꢀH secondary interactions for the free triazene ligand 1 along the crystallographic bc plane.
Fig. 6. Representation of the hydrogen interactions (dashed lines) between the layers of crystallization in 1.
Fig. 7. Molecular structure of [(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2). The thermal ellipsoids are represented in a percentage of 30%. The dashed lines show a bifurcated ClꢀꢀꢀH
interaction. For clarity, the DMSO molecule does not appear.

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D.F. Back et al. / Polyhedron 31 (2012) 558–564
Fig. 8. Representation of [(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2) showing the intra- and intermolecular trifurcated acceptor ClꢀꢀꢀH–C interactions of the palladium complex (2). For
clarity the hydrogen atoms are not shown.
1.416(3) Å; N12–N13–C21 = 112.89(17)°} are shorter than those
expected for a single N–Caryl bond (1.452 Å for secondary amines,
NHR2). Thus, all the bonds previously cited indicate partial double
3. Results and discussion
3.1. Crystal structure
bond character, implying a delocalization of
p electrons in the tria-
zenido chains. Table 2 shows some values of bond lengths and an-
gles for selected reported triazene compounds.
The molecular structure of a single triazene ligand 1 is repre-
sented in Fig. 4. The bond distance N12–N11 (1.335(2) Å) of 1 is
smaller than the characteristic value for a N–N single bond
(1.44 Å), while the distance N13–N12 (1.264(2) Å) is larger than
the typical N@N double bond distance (1.24 Å). The distances
and angles involving the bonds N11–C11 and N13–C21
{N11–C11 = 1.384(3) Å; N12–N11–C11 = 120.83(16)°}/{C21–N13 =
Fig. 5 depicts the reachable (secondary) interactions between
the molecules of the free ligand 1 nearby the crystallographic bc
plane. There is a predominance of bifurcated hydrogen interactions
[26–29] between (N11)H11ꢀꢀꢀO2 and (C16)H16#ꢀꢀꢀO2 with
distances of 2.093(2) and 2.485(2) Å respectively, and classical
Fig. 9. Representation of complex 2 along the crystallographic bc plane, showing the secondary, bifurcated and non-classical (CꢀꢀꢀH) hydrogen interactions.

D.F. Back et al. / Polyhedron 31 (2012) 558–564
563
interactions between the atoms (C5)O7ꢀꢀꢀH3A#3 in the order of
2.392(2) Å. Moreover, is also evident the formation of rings by
the reciprocal coupling of the methoxy groups O4ꢀꢀꢀH4A#2(C4#2)
and (C4)H4AꢀꢀꢀO4#2 with a distance of 2.626(2) Å (symmetry trans-
formations used to generate equivalent atoms: (#) 1 ꢁ x, 0.5 + y,
0.5 ꢁ z; (#2) 2 ꢁ x, 1 ꢁ y, 2 ꢁ z; (#3) ꢁ1 + x, 0.5 ꢁ y, ꢁ1.5 + z).
Besides the existence of the mentioned interactions, according
to Fig. 6 it seems to be evident that there is more than one type
of secondary contact promoting the coupling between the triazen-
ido layers. An interesting pairing is achieved by the reciprocal
interaction between the groups (C3#)H3B#ꢀꢀꢀO1 and (C3)H3BꢀꢀꢀO1#,
with a distance of 2.701(2) Å. Another remarkable type of interac-
tion in the synthesized molecule is the hydrogen non-classical
CHꢀꢀꢀ
p contact. For these weak interactions is assigned a distance
of 2.822(2) Å between the atoms (C6)H6CꢀꢀꢀC24#2(aryl) (symmetry
transformations used to generate equivalent atoms: (#) 1 ꢁ x,
1 ꢁ y, ꢁz; (#2) x, 0.5 ꢁ y, 0.5 + z).
The CHꢀꢀꢀ
p interaction has attracted considerable interest due to
its importance for several parameters, such as the control of the
crystalline packing [30], the structural organization of biological
molecules [31] and some processes of molecular recognition [32].
Despite the importance of the CHꢀꢀꢀ
p interactions, the physical nat-
ure of this process is yet not clear, since the precise evaluation of
the energy involved in the interaction is difficult to quantify. In
view of this, the CHꢀꢀꢀ
bond. Nevertheless, in contrast with the conventional hydrogen
bonds, the directionality of the CHꢀꢀꢀ interaction is also very poor.
In this regard, statistical analysis of crystal structures also show
that CHꢀꢀꢀ interactions prefer to point toward the aromatic ring,
being, however, not perpendicular to the plane of the ring.
According to quantum mechanical calculations, the energy associ-
ated with this interaction is approximately 1.5–2.5 kcal molꢁ1
[33–35].
In the structure of complex [(bmmbt)Pd(PPh3)2Cl]ꢀDMSO (2),
displayed in Fig. 7, the triazene ligand coordinates to Pd(II) in a
monodentade way. The formal negative charge of the triazenido
chain, as well as the charge of the Clꢁ ligand, are counter balanced
by the central cation Pd2+, so that the neutrality of the complex is
achieved. The coordination polyhedron of the metal atom is consis-
tent with the examples in the literature, since the interaction
N13ꢀꢀꢀPd is not strong enough to produce a distorted square geom-
etry. Undoubtedly, the bifurcated intramolecular ClꢀꢀꢀH–C interac-
p interaction has been treated as a hydrogen
p
Fig. 10. Molecular structure of [(bapht)Pd(PPh3)2Cl] (3). The thermal ellipsoids are
represented in a percentage of 50%.
p
tions H012 and H036 must be emphasized, since they also
support the complex structure and the geometry of the metal
atom. The distances of the bifurcated interaction are 2.814(3)
and 2.795(6) Å respectively, and the H012ꢀꢀꢀClꢀꢀꢀH036 angle is
64.53(3)°.
The representation of complex 2 along the ab plane, depicted in
Fig. 8, allows the visualization of a further bifurcated intermolecular
ClꢀꢀꢀH–C interaction, between the atoms (C16#)H16#ꢀꢀꢀCl
(2.786(7)) and (C26#)H26#ꢀꢀꢀCl (2.671(8) Å). The H16#ꢀꢀꢀClꢀꢀꢀH26#
angle has 70.08(3)°, and these intermolecular bonds support the
growth of the polymeric supramolecular assembly of complex 2
(see Fig. 8, symmetry transformations used to generate equivalent
atoms: (#) ꢁ1x, y, z). If we consider only these three secondary
p
Fig. 11. Centrosymmetric dimer and trifurcated hydrogen interactions formed by the association of two neighboring molecules of [(bapht)Pd(PPh3)2Cl] (3). The thermal
ellipsoids are represented in a percentage of 50%.

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D.F. Back et al. / Polyhedron 31 (2012) 558–564
ClꢀꢀꢀH–C interactions appearing in Fig. 8, we are talking about trifur-
cated acceptor ClꢀꢀꢀH–C bonds.
enabling us to select the best data for the search of new, specific
interactions.
Fig. 9 shows two neighboring molecules of complex 2 along the
bc plane. As is clear to see in this position, there are two bifurcated
intramolecular ClꢀꢀꢀH–C interactions and a intermolecular, centro-
symmetric pair of non-classical hydrogen bonds, between the
atoms H08/C05# and H08#/C05, with a distance of 2.806 Å (sym-
metry code (#): 1 ꢁ x, ꢁy, 2 ꢁ z). Each of these units can be viewed
as a dimer related by an inversion center, and its linkage through
further H08xꢀꢀꢀC05y ‘‘double’’ interactions produces a 1-D supramo-
lecular arrangement (see Fig. 9).
Fig. 10 displays the molecular structure of the second title com-
plex, [(bapht)Pd(PPh3)2Cl] (3), which is structurally similar to the
previous described complex 2. The coordination model is the same,
with the triazenido ligand coordinating in a monodentate way the
divalent cation Pd(II). Also in 3 the neutrality of the complex is
achieved through the coordination of a chloride ligand to the metal
ion. A bifurcated intramolecular interaction between the hydrogen
atoms of the near located aromatic rings and the chloride ligand
are also present (H036 and H018), however, in this case, the
ClꢀꢀꢀH–C distances are slightly shorter than in 2 (2.730(2) and
2.679(1) Å respectively), although the HꢀꢀꢀClꢀꢀꢀH angle appears sig-
nificantly altered (154.42(1)°).
Fig. 11 shows the interesting association of two molecules of 3,
in a similar manner to that already seen for 2 (see Fig. 9). The link-
age of the neighboring molecules of 3 occurs, however, under for-
mation of a third secondary, intermolecular HꢀꢀꢀCl interaction, i.e.,
attaining a trifurcated hydrogen bonding. A good explanation for
the increase of the bond angle between the atoms of hydrogen
and chloride in the bifurcated HꢀꢀꢀCl interaction in 3 is this type
of intermolecular trifurcated donation, involving three receivers
[36–39]. This interaction is also responsible for the achievement
of a centrosymmetric dimer (Fig. 11), but, unlike complex 2, the di-
mers of complex 3 do not interact with each other, preventing the
formation of supramolecular assemblies in the crystal lattice. The
distances between the atoms involved in the trifurcated interac-
tions in the dimers of complex 3 are 2.679(1), 2.730(2) and
2.875(1) Å for H018ꢀꢀꢀCl, H036ꢀꢀꢀCl and H035#ꢀꢀꢀCl, respectively.
The bond angles are 68.15(2)° (H035#ꢀꢀꢀClꢀꢀꢀH018) and 120.3(1)°
(H035#ꢀꢀꢀClꢀꢀꢀH036) (symmetry transformations used to generate
equivalent atoms: (#) 2 ꢁ x, 1 ꢁ y, 1 ꢁ z).
Acknowledgment
Fapergs – Fundação de Amparo à Pesquisa do Estado do Rio
Grande do Sul. Edital No 003/2009.
Appendix A. Supplementary data
CCDC 818520, 818521 and 818522 contains the supplementary
crystallographic data for 1, 2 and 3. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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