Synthesis and characterization of mono and polymeric cyclopalladated compounds: Crystal and molecular structure of [{Pd(dmba)(ONO2)}2(μ-pz)] · H2O (pz = pyrazine)

Article abstract of DOI:10.1016/j.poly.2008.10.048

In the treatment of cyclometallated dimer [Pd(dmba)(μ-Cl)]₂ (dmba = N,N-dimethylbenzylamine) with AgNO₃ and acetonitrile the result was the monomeric cationic precursor [Pd(dmba)(NCMe)₂](NO₃) (NCMe = acetonitril

Full text of DOI:10.1016/j.poly.2008.10.048

Polyhedron 28 (2009) 286–290
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Polyhedron
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Synthesis and characterization of mono and polymeric cyclopalladated compounds:
Crystal and molecular structure of [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O (pz = pyrazine)
Sandra R. Ananias a,b,c, Janaina G. Ferreira b,c, Antonio E. Mauro c, Adelino V.G. Netto c, Stanlei I. Klein c,
Regina H.A. Santos b,
*
a Departamento de Química, Faculdade de Ciências – UNESP, C.P. 1.401, CEP 17033-360, Bauru, SP, Brazil
b Departamento de Química e Física Molecular, Instituto de Química de São Carlos – USP, C.P. 780, CEP 13560-970, SP, Brazil
c Departamento de Química Geral e Inorgânca, Instituto de Química – UNESP, C.P. 355, CEP 14801-970, Araraquara, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2008
Accepted 22 October 2008
Available online 16 December 2008
In the treatment of cyclometallated dimer [Pd(dmba)(l-Cl)]2 (dmba = N,N-dimethylbenzylamine) with
AgNO3 and acetonitrile the result was the monomeric cationic precursor [Pd(dmba)(NCMe)2](NO3)
(NCMe = acetonitrile) (1). Compound 1 reacted with m-nitroaniline (m-NAN) and pirazine (pz), originat-
ing [Pd(dmba)(ONO2)(m-NAN)] (2) and [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O (3), respectively. These com-
pounds were characterized by elemental analysis, IR and NMR spectroscopy. The IR spectra of (2–3)
display typical bands of monodentade O-bonded nitrate groups, whereas the NMR data of 3 are consis-
tent with the presence of bridging pyrazine ligands. The structure of compound 3 was determined by X-
ray diffraction analysis. This packing consists of a supramolecular chain formed by hydrogen bonding
Keywords:
Cyclometallated
Palladium
Nitro compounds
between the water molecule and nitrato ligands of two consecutive [Pd2(dmba)2(ONO2)2(l-pz)] units.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
of 1 toward the used nitrogen ligands is discussed below, and the
solid state structure of the pyrazine dimer 3 is presented.
Over the past years the chemistry of cyclopalladated compounds,
mainly of those derived from N-donor ligands, has been investigated
by numerous research groups [1], due to important applications of
these compounds in various fields, such as organic and organome-
tallic synthesis [2], new materials (e.g. metallomesogens) [3], catal-
ysis [4] and medical science (e.g. antitumor drugs) [5].
2. Experimental
2.1. General comments
The syntheses were performed at room temperature. Commer-
cial reagents and solvents were employed without further purifica-
tion. The precursor [Pd(dmba)(NCMe)2](NO3) (1) was prepared
according to procedures described in the literature [6].
The relatively low cost and ready availability [6] of [Pd(dmba)-
(NCMe)2](NO3) (1), with two of its cis coordination sites occupied
by quite easily removable ligands, prompted us to try this com-
pound in reactions of the self-assembly type. The general idea
had been set forth by Fujita by using traditional transition metal
complexes and bidentated nitrogen ligands [7]; moreover, Huck al-
ready succeeded in producing dendrimers from cyclopalladated
compounds [8], and Spek, van Koten and their group advanced
the features of 90° square planar platinum and palladium (II) met-
allated complexes as corner acceptors units [9]. Therefore, com-
pound 1 seemed suitable for the preparation of tetramers and
higher nuclearity compounds, if one could bridge two distinct ter-
minal diamines to the [Pd(dmba)]2+ fragments. However, only one
terminal amine was allowed to be coordinated to the metal atom
in 1, originating monomers from monoamines and dimer com-
pounds from the addition of diamines to its solutions. The behavior
2.2. Synthesis of [Pd(dmba)(ONO2)(m-NAN)] (2)
0.0720 g (0.0520 mmol) of m-nitroaniline (m-NAN), dissolved in
10 cm3 of dichloromethane was added to 15 cm3 of solution 1
(0.100 g, 0.260 mmol), in the same solvent. The mixture was stirred
for 30 min, and the resulting yellow precipitate was isolated by
filtration. The product was thoroughly washed with ether and pen-
tane and dried in vacuo. The yield was about 90% after recrystalliza-
tion from dichloromethane and pentane. PdN4O5C15H18 (2)
requires: C, 40.87; H, 4.08; N, 12.71. Found: C, 40.3; H, 3,93; N, 12.4%.
2.3. Synthesis of [{Pd(dmba)(ONO2)}2(l-pz)] (3)
A solution of 0.389 mmol (0.031 g) of pirazine (pz) in 5 cm3 of
dichloromethane was added to a solution of 0.15 g (0.389 mmol)
* Corresponding author. Tel./fax: +55 16 3373 9975.
E-mail address: reginas@iqsc.usp.br (R.H.A. Santos).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.10.048

S.R. Ananias et al. / Polyhedron 28 (2009) 286–290
287
of [Pd(dmba)(MeCN)2](NO3) (1) in 10 cm3 of dichloromethane. The
Table 1
Crystal data and details of the structure determination for [{Pd(dmba)(ONO2)}2(l-
pz)] ꢀ H2O (3).
mixture was stirred for 1 h. The yellow solid which precipitated was
filtered, washed with acetone and pentane and dried in vacuo, and
re-crystallized. The yield was about 80%. Calc. for Pd2N6O6C22H28: C,
38.5; H, 4.08; N, 12.26. Found: C, 39.0; H, 2.95; N, 13.5%.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C22H28N6O6Pd2 ꢀ H2O
703.36
monoclinic
C2/c
13.402(2)
12.933(2)
14.864(3)
95.56(1)
2564.2(8)
4
2.4. Physical measurements
b (Å)
c (Å)
Infrared spectra were recorded as KBr pellets on a Nicolet Im-
pact 400 spectrophotometer (range 4000–400 cmꢁ1). 1H and 13C
NMR spectra were obtained as DMSO-d6 solutions and referred
to the high field SiMe4 signal, on a Varian INOVA 500 spectrometer.
Molar conductivities were measured in nitromethane solutions
(c ꢂ 1 ꢃ 10ꢁ3 mol Lꢁ1) with a Digimed-DM-31 conductimeter. Ele-
mental analyses were performed by the Central Analítica at IQSC/
University of São Paulo.
b (°)
V (Å3)
Z [dimer/cell]
Dcalc (Mg/m3)
F(000)
1.822
1408
1.456
l(Mo K
a
) (mmꢁ1
)
Crystal size (mm)
Temperature (K)
0.25 ꢃ 0.25 ꢃ 0.40
243
Radiation Mo K
hmin.–max. (°)
Dataset
Total unique data, Rint
Observed data (I > 2.0(I))
Nref, Npar
a
(Å)
0.71073
2.5, 30.0
ꢁ18 ꢄ h ꢄ 18, 0 ꢄ k ꢄ 18, ꢁ20 ꢄ l ꢄ 0
3860, 3727, 0.023
3204
2.5. X-ray structure determination for compound 3
A single crystal of the compound [{Pd(dmba)(ONO2)}2(
l-pz)]
3727, 170
(3) was mounted on a Enraf-Nonius CAD4 diffractometer at room
R, wR, S
0.0470, 0.1440, 1.07
w = 1/[s2(F2o) + (0.0867P)2 + 9.5183P]
where P = (F2o + 2Fc2)/3
Maximum and average shift/error
Minimum and maximum residual
density (e/Å3)
temperature using graphite monochromated Mo K
a
radiation
(k = 0.71073 Å). The data collection was taken in the
x
–2h scan
0.00, 0.00
ꢁ1.46, 2.10
mode. The unit cell parameters were determined using 25 auto-
matically centered reflections. Table 1 shows the data collection
and refinement conditions. The intensity data were reduced to F0
and corrected by absorption factors using the PSISCAN method [10].
The structures were solved by the WINGX system [11], using SIR92
[12] and SHELX97 [13]. The hydrogen atoms belonging to compound
3 were located in their ideal positions. The water H atoms were
placed at calculated positions using the HYDROGEN [14]. All non-
hydrogen atoms were refined anisotropically. The geometric anal-
ysis was performed by the PLATON system [15].
ever, in the NMR spectrum there is only one singlet NMR resonance
for the two nitriles’ CH3CN at ca. 119, and another singlet reso-
nance CH3CN carbon at 3 ppm. The other 13C resonances of that
spectrum are indicated in Fig. 1.
Upon N-coordination with the palladium metal in cyclopalla-
dated complexes such as 1, is formed a puckered five-membered
ring with a low barrier of inversion. Therefore, fast exchanges from
axial to equatorial position are possible, and the benzylic (–N–
CH2–) protons, as well the protons of the [–NMe2] group of dmba
usually appear as singlets in the proton NMR spectrum, and this
analysis is valid for complex 1, where those groups resonate at
3.91 and 2.78 ppm. However, this fast inversion on the NMR time
scale does not explain the equivalence of the 13C NMR signals of
the coordinated acetonitriles. The 500 MHz 1H spectrum of 1
showed two separated signals for the two distinct acetonitrile
groups at 2.78 and 2.36 ppm. The downfield shifted signal at
2.78 ppm was assigned to the methyl group of the acetonitrile in
cis position to the metallated aromatic ring since, it is located in
the deshielding area generated by the metallated aromatic ring.
This signal appeared in the spectrum overlapped by the six-proton
singlet of the [–NMe2] fragment of dmba. A closer examination on
other acetonitrile substituted cyclopalladates point to a similar dif-
ficulty in a proper assignment of their NMR spectra [21].
3. Results and discussion
3.1. Characteristics of [Pd(dmba)(NCMe)2](NO3) (1) and
[Pd(dmba)(ONO2)}(m-NAN)] (2)
[Pd(dmba)(NCMe)2](NO3), (1), can be easily prepared from
dichloromethane solutions of [Pd(dmba)Cl2] upon the addition of
silver nitrate dissolved in a mixture of dichloromethane and aceto-
nitrile [6]. This precursor is very interesting on its own, due to its
exquisite physical properties, which seems to be somewhat dic-
tated by the physical conditions to which it is submitted. For in-
stance, the ionic formulation for 1 seems to be evident from its
formulae, and from its solid state IR spectrum, which shows low
intensity bands at 2308 and 2249 cmꢁ1, attributed mainly to A1g
CN stretches and CCN combination bands of coordinated nitriles
[16,17], and quite intense bands for the presence of ionic nitrates
[18,19] at 1387 (m
ONO, vs) and 852 cmꢁ1 (d ONO, s). Nevertheless,
ready solubility of this compound in solvents such as chloroform is
not characteristic of a purely ionic compound. Indeed, molar con-
ductance measurements of 1 made in nitromethane indicated a va-
lue of 27.55 l
S cmꢁ1, which collocates that species among those
considered non-electrolytes [20].
In this context, it is also interesting to research the 1H and 13C
NMR spectra of 1. In spite of the ubiquitous square planar coordi-
nation geometry of the [Pd(dmba)(NCMe)2] core, the 125 MHz 13
C
NMR of 1 in CDCl3 at room temperature seemed to be exceedingly
simple, for it did not show the magnetic inequivalence of the 13C
nuclei of the acetonitriles. This magnetic inequivalence was ex-
pected on the grounds that the acetonitriles must be accommo-
dated, one in the trans position to the dmba’s nitrogen, and the
other, trans to the metallated carbon anchor of that ligand. How-
Fig. 1. Additional 13C resonances for the metal containing core of 1: Me2N = 51;
H2C = 73; 1 = 147; 2 = 143; 3,6 = 123; 4 = 134; 5 = 123 ppm.

288
S.R. Ananias et al. / Polyhedron 28 (2009) 286–290
In the first attempt to test the capacity of the precursor com-
showed the metallated carbon from dmba at 148.1 ppm. The pro-
ton NMR spectrum confirms the presence of the pyrazine by sig-
nals at 8.84 and 8.74 ppm. Although the signal for symmetrically
coordinated pyrazine occurs above 8.6 ppm [23], the presence of
two signals for 3 indicated some kind of molecular arrangement
as they were the pz protons magnetically non-equivalent. The sig-
nals for the diastereotopic protons of the –CH2– and [–NMe2]
groups of metallated dmba appear in the 1H NMR spectrum of 3
as slightly broadened resonances at the normal positions of 4.01
and 2.84 ppm, respectively.
pound 1 to react with heterocyclic nitrogen donors, it was chosen
the m-nitroaniline ligand only as monosubstituted compound; de-
spite the 1:2 stoichiometry of the addition. The IR spectrum of the
product suggested the coordination of the m-nitroaniline ligand by
the disappearance of the bands assigned to
mCN of the precursor.
However, new bands for a different type of nitrate ligand were also
readily assigned in that spectrum, at 1417 and 1305 (mONO), and at
806 cmꢁ1 (dNO), evidencing the presence of a monodentade O-
bound nitrate group [18,19].
The 1H NMR spectrum of 2 showed four multiplets, two at 7.37
and 7.23 ppm assigned to the m-nitroaniline, and two at 7.05 and
6.9 ppm, relative to the H-3 to H-5 dmba protons. The upfield shift
of dmba’s H-6 proton at 5.79 ppm should be the result of the
shielding effect of the nearby aromatic ring of the m-NAM ligand,
a conclusion which allows to allocate the nitrogen ends of m-
NAM and dmba, trans to each other in the complex [22]. Thus,
the nitrato ligand, which acts as pseudo-halogen in the structure
of compound 2, is in trans position to the metallated carbon,
according to the antisymbiotic effect [x]. The (–N–CH2–) protons
of the dmba ligand resonate at 4.03 ppm, and the [N–(CH3)2] frag-
ment was indicated by the proton resonance at 2.63 ppm. In the
13C NMR spectrum of 2 there are three important signals: the met-
allated, the benzylic and the [–NMe2] carbons, resonating at 148.7,
71.4 and 50.5 ppm, respectively, indicating the presence of dmba
in the complex. These evidences and the microanalysis data
pointed to the monomeric structure [Pd(dmba)(ONO2)(m-NAN)]
for compound 2.
3.3. X-ray structure of [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O (3)
Suitable crystals of [{Pd(dmba)(ONO2)}2(
l-pz)] ꢀ H2O (3) were
grown by slow evaporation of a water–acetone solution. The X-
ray structure showed that the asymmetric unit consists of a
Pd(dmba)(ONO2) unit linked to half of the pyrazine ring, forming
a dimer made by two fold crystallographic axis (Fig. 1). In the
asymmetric unit it is also found half water molecule, with the oxy-
gen atom lying in other twofold axis Fig. 2.
The X-ray diffraction study permitted the correct interpretation
of the analytical and NMR data, by showing the molecule as a dinu-
clear compound, with one pz bridging the two metals. The square
planar coordination of each palladium atom is composed by the
metallated carbon and the nitrogen atom from the dmba, the nitro-
gen from pz, and the coordinated oxygen of the NO3 group. This
feature could be inferred, but it was not explicit from previous
spectroscopic studies. This coordination may reflect the powerful
trans-influence of the C–Pd bond, which would labilize a bond be-
3.2. Characteristics of cyclopalladated complex
tween the metal and any incoming r-donor, neutral L ligand,
[{Pd(dmba)(ONO2)}2(
l
-pz)] (3)
inducing the coordination to conform to a C–Pd–L cis environment
in the final compound. In the solid structure, the palladium atom
occupies a position slightly below the mean squares plane defined
by C1, N1, O1 and N2 (0.537(1) Å).
The ability of precursor 1 to act as a corner acceptor unit for
self-assembled species was tested with the potential bridging li-
gand pz.
The reactions of 1 with pyrazine were the simplest, in the way
that only one type of compound could be detected by the occur-
rence of only one precipitate, after the mixture of reactants was
stirred at room temperature. This compound was determined as
Selected interatomic bond lengths and angles are given in
Tables 2 and 3. In molecule of 3, the various bonds and angles
involving the metals and directly coordinated atoms agree with
previous reports found in the literature for this class of metallated
compounds [24–29], but a few particular characteristics of 3 must
be discussed. For instance, the short Pd–C1 bond length of 1.971(4)
Å is shorter than a Pd(II)–C sp3 bond of 2.14 Å [21]. This value may
reflect a typical Pd(II)–C sp2 bond, but there seem to be a consensus
that the Pd–C bonds in metallated benzenoid rings must involve
some multiple bond character, which would cause a further short-
ening of this peculiar Pd–C bond [30a]. Also, the trans Pd–O bond
l-pz dinuclear, O-bound NO3 palladium complex of the type
[{Pd(dmba)(ONO2)}2(l-pz)], (3). For instance, the IR spectrum
showed the expected bands at 1621 and 1031 cmꢁ1 attributed to
the CN stretch and CH deformation of pz, respectively; and the
characteristic trio of absorptions for the –ONO2 coordinated nitrate
at 1424, 1296 and 810 cmꢁ1 [18,19]. The 13C NMR spectrum of 3
Fig. 2. ORTEP drawing with labeling scheme for [Pd2(dmba)2(
l-pz)(NO3)2]. Displacement ellipsoids are drawn at the 50% probability level.

S.R. Ananias et al. / Polyhedron 28 (2009) 286–290
289
Table 2
The solid state shows the presence of hydrogen bonds (Table 4).
Molecules of 3 self-assemble into a supramolecular chain through
intermolecular hydrogen bonds between crystallization water
molecules and nitrato ligands of 3, as can be observed in Fig. 3.
As a result of the oxygen atom (from the water molecule) being
positioned on the crystallographic twofold axis the polymeric
chain is generate by symmetry.
Bond distances (Å) for [{Pd(dmba)(ONO2)}2((–pz)] ꢀ H2O (3).
Pd
Pd
O1
N1
N
N
C7
C9
C2
C6
C3
2.208(4)
2.063(3)
1.237(5)
1.211(6)
1.497(5)
1.478(6)
1.395(6)
1.417(5)
1.392(7)
1.342(5)
1.334(5)
0.930
Pd
Pd
O2
C1
N2
N
1.971(4)
2.049(3)
1.249(7)
O1
O3
N1
N1
C1
C1
C2
N2
N2
O1W
N1
C6
C3
C4
C5
C8
C7
C4
C5
1.494(5)
1.493(6)
1.381(9)
1.385(8)
1.380(6)
1.383(7)
1.383(8)
In addition to this hydrogen bond, there are two C–Hꢀ ꢀ ꢀO
(3.195(9) and 3.460(6) Å) and two C–Hꢀ ꢀ ꢀ
p (3.804(5) and
C6
3.492(5) Å) interactions contributing to the stabilization of the
crystal packing, which results in a complex three-dimensional
framework.
C10
C11
H1W
C10
C11
C10*
C11*
As mentioned above, the other noteworthy feature of 3 which
was disclosed by the X-ray analysis was the severe tilt of the pz
plane of 57.6(2)° relative to the square planes defined by the met-
als and their four immediate bonded atoms. In this geometrical
arrangement around a d8 transition metal, the crystal field theory
*
Symmetry code: 1 ꢁ x, y, 1/2 ꢁ z.
Table 3
Selected angles (°) for [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O (3).
predicts that the metal’s empty dx2
orbital shall be antibonding,
ꢁy2
with the other four d orbitals lying close in energy, with the dz2
orbital assuming the role of the HOMO of the ML4 molecule. In this
O1
O1
O1
N1
N1
N2
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
N2
N2
C10
Pd
Pd
Pd
Pd
Pd
Pd
O1
N1
N1
N1
N2
N2
C1
C1
C10
C11
N2
N1
N2
C1
N2
C1
C1
N
C8
C9
95.8(1)
87.6(1)
169.1(2)
176.4(1)
82.0(1)
O1
O2
O1
H1OW
C1
C2
C3
C4
C1
C2
C1
C5
C7
C8
C7
N1
N
N
N
O1W
C2
C3
C4
C5
C6
C1
C6
C6
N1
N1
N1
C7
O3
O3
O2
H1OW**
C3
C4
C5
C6
C5
C6
C7
C7
C9
C9
C8
C6
122.3(5)
119.3(5)
118.4(5)
104.77
way, following the
modes through which d–
r
coordination, there will be essentially two
interactions may develop. The two
p
119.4(5)
121.7(5)
119.3(5)
120.2(5)
120.9(4)
118.4(4)
115.3(3)
123.7(4)
109.0(4)
108.6(4)
108.8(4)
108.5(3)
modes involve the metal and ligand B1g and B2g orbitals. The inter-
action of the empty B1g dx2ꢁy2 with the pz HOMO B1g should lower
the energy of that otherwise essentially antibonding orbital, and
94.9(1)
119.2(4)
110.0(3)
113.8(3)
106.5(2)
125.1(2)
118.4(2)
128.3(3)
113.3(3)
121.6(2)
121.8(2)
116.6(3)
this d
p interaction may thus help in further stabilization of the
C7
whole molecular assembly. On the other hand, the full dxy orbital,
of B2g symmetry, may interact with the LUMO of pz, which is also
B2g, allowing for the development of an effective mechanism for
C10
C11
C2
d?p* back donation. The interesting thing is that the d
p and
C6
C10*
C11*
C11
d?p
* overlaps can only develop if the plane of pz is severely tilted
in relation to the xy plane defined by the ML4 core, a tilting that, in
the present case, is 57.6(2)°. These d interactions may be found
in the half-filled dx2 of Cu(II) atoms and the B1g HOMO of pz
p
*
Symmetry code: 1 ꢁ x, y, 1/2 ꢁ z.
Symmetry code: ꢁx, y, 1/2 ꢁ z.
ꢁy2
**
which had been held responsible for magnetic processes in copper
dimers and supramolecules [31]. A number of other metal pyrazine
compounds which have been analyzed by X-ray crystallography
also showed variations in the orientation of the plane of the com-
plexes and the plane of coordinated pz, although the stabilizing ef-
fect of such canting has not always been emphasized [32].
Table 4
Hydrogen Bonds (Å, °) for [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O (3).
D–Hꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
Symetry code
O1W–H1Wꢀ ꢀ ꢀO3
C3–H3ꢀ ꢀ ꢀO2
0.930
0.940
0.980
0.941
0.979
2.13
2.50
2.52
2.85
3.00
3.043(8)
3.195(9)
3.460(6)
3.804(5)
3.492(5)
167.0
131.1
161.8
114
x, ꢁy, ꢁ1/2 + z
1 ꢁ x, ꢁy, ꢁz
4. Conclusions
C7–H72ꢀ ꢀ ꢀO3
C11–H11ꢀ ꢀ ꢀCg3
C7–H71ꢀ ꢀ ꢀCg3
x, ꢁy, ꢁ1/2 + z
1 ꢁ x, ꢁy, ꢁz
The nitrate group from the ionic [Pd(dmba)(MeCN)2](NO3), (1),
164
1/2 ꢁ x, ꢁ1/2 ꢁ y, ꢁz
seem to render this compound to be susceptible to a double substi-
Cg3: benzene ring.
tution to yield [Pd(dmba)L2]+ complexes only with very strong
r
donating L such as bipy, in which the interactions enables the
detection of polycations from strongly conducting nitromethane
(2.208(4) Å) is in good agreement with a square planar Pd(II) com-
plex structure [29].
solutions [33]. With poorer
r donors such as m-NAM or pz only
The most striking features of the crystal structure of 3 is the tilt
(57.6(2)°) of the plane of pz relative to the square plane of the two
palladium atoms (C1, N1, O1 and N2). The pyrazine ring is highly
symmetric because it is formed by symmetry operation.
complexes of the type [Pd(dmba)(ONO2)L] are formed. The biligand
nature of pz ensures the formation of the dinuclear compound
[Pd(dmba)(ONO2)]2(l-pz). This complex showed the square planes
defined by the metals ML4 cores severely tilted in relation to the
Fig. 3. Supramolecular chain formed by hydrogen bonding in the crystal structure of [{Pd(dmba)(ONO2)}2(
l-pz)] ꢀ H2O.

290
S.R. Ananias et al. / Polyhedron 28 (2009) 286–290
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plane of pz, suggesting the operation of strong d
p
and d?p*
interactions between the metals and the pyrazine ring.
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The authors wish to acknowledge CNPq, FAPESP and CAPES for
the financial support.
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CCDC 692054 contains the supplementary crystallographic data
for [{Pd(dmba)(ONO2)}2(
l
-pz)] ꢀ H2O. These data can be obtained
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free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
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