Supramolecular assemblies of cis-palladium complexes dominated by C{single bond}H?Cl interactions

Article abstract of DOI:10.1016/j.inoche.2006.02.012

Two cis-related palladium(II) complexes [PdCl₂(PPh₃)(tu)] (1) and [PdCl₂(tmen)] (2) {PPh₃ = triphenylphosphine, tu = thiourea, tmen = N,N,N′,N′-tetramethylethylenediamine} have been synthesized and characterized by elemental analysis, IR and NMR spectroscopies, and single crystal X-ray diffraction. In 1, N{single bond}H?Cl hydrogen bonds are responsible for the formation of a dimer which connects to an adjacent one through weak C{single bond}H?Cl interactions, yielding 1D tapes. The crystal packing of compound 2 consists of zigzag ribbons of [PdCl₂(tmen)] self-assembled by C{single bond}H?Cl hydrogen bonds which also holds the chains together, giving rise to a 2D layered structure.

Full text of DOI:10.1016/j.inoche.2006.02.012

Inorganic Chemistry Communications 9 (2006) 493–496
www.elsevier.com/locate/inoche
Supramolecular assemblies of cis-palladium complexes dominated
by CAHꢀ ꢀ ꢀCl interactions
a
a
a,
a
A.C. Moro , F.W. Watanabe , S.R. Ananias a,b, A.E. Mauro *, A.V.G. Netto ,
b
b
b
A.P.R. Lima , J.G. Ferreira , R.H.A. Santos
a
Instituto de Quı´mica de Araraquara, UNESP, C.P. 355, 14801-970, Araraquara-S.P., Brazil
b
Instituto de Quı´mica de Sa˜o Carlos, USP, C.P. 780, 13560-970, Sa˜o Carlos-S.P., Brazil
Received 20 December 2005; accepted 4 February 2006
Available online 22 March 2006
Abstract
Two cis-related palladium(II) complexes [PdCl2(PPh3)(tu)] (1) and [PdCl2(tmen)] (2) {PPh3 = triphenylphosphine, tu = thiourea,
tmen = N,N,N0,N0-tetramethylethylenediamine} have been synthesized and characterized by elemental analysis, IR and NMR spectros-
copies, and single crystal X-ray diffraction. In 1, NAHꢀ ꢀ ꢀCl hydrogen bonds are responsible for the formation of a dimer which connects
to an adjacent one through weak CAHꢀ ꢀ ꢀCl interactions, yielding 1D tapes. The crystal packing of compound 2 consists of zigzag rib-
bons of [PdCl2(tmen)] self-assembled by CAHꢀ ꢀ ꢀCl hydrogen bonds which also holds the chains together, giving rise to a 2D layered
structure.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Supramolecular chemistry; CAHꢀ ꢀ ꢀCl hydrogen bonds; Palladium(II); Self-assembly
The design of new solid state architectures with pecu-
liar properties involving the self-assembly of molecular
building blocks into sophisticated supramolecules via
non-covalent intermolecular interactions has become one
of the most exciting topics in current chemistry [1].
Among the intermolecular forces, hydrogen bonds have
been considered as the most powerful organizing element
in molecular assembly due its highly selective and direc-
tional character. Besides the conventional strong hydro-
gen bonds of the OAHꢀ ꢀ ꢀO, NAHꢀ ꢀ ꢀO, and NAHꢀ ꢀ ꢀN
type, weak forces such as CAHꢀ ꢀ ꢀX (X = O, N, Cl) also
play an important role in determining crystal structure
stability [2].
[3]. Particularly, special attention has been devoted to the
CAHꢀ ꢀ ꢀCl interactions since the HB acceptor capability
of terminal metal-bound chlorine (MACl) is stronger than
their CACl analogues [4]. Therefore, the CAHꢀ ꢀ ꢀClAM
hydrogen bonding can be used to assembly transition-
metal based building blocks into well-defined structures.
In previous investigations, we have successfully obtained
transition-metal based supramolecular species based on
the self-assembly of [PdX2 (3,5-dimethylpyrazole)2] build-
ing blocks via intermolecular hydrogen bonds of the
NAHꢀ ꢀ ꢀXAPd type (X = NCS, N3) [5].
Extending our interest in the coordination and supra-
molecular chemistry of palladium complexes containing
halides and pseudohalides as co-ligands [6], we wish to
report the synthesis and crystal structures of two cis-related
palladium(II) complexes [PdCl2(PPh3)(tu)] (1) and
[PdCl2(tmen)] (2) {PPh3 = triphenylphosphine, tu = thio-
urea, tmen = N,N,N0,N0-tetramethylethylenediamine} in
which the CAHꢀ ꢀ ꢀClAPd interactions play an important
role in the crystal packing of the two new structures. Both
In recent years, some authors have obtained detailed
information regarding the properties of halogens as hydro-
gen bond acceptor as well the reproducibility of such weak
interactions in constructing supramolecular architectures
*
Corresponding author. Tel.: +5501633016625; fax: +5501633227932.
E-mail address: mauro@iq.unesp.br (A.E. Mauro).
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.02.012

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A.C. Moro et al. / Inorganic Chemistry Communications 9 (2006) 493–496
˚
compounds have been synthesized [7] and characterized by
X-ray crystallographic methods [8].
to the sulfur in [PdCl2(PPh3)(tu)] is 2.3186(2) A, which is
˚
shorter by 0.0615 A than the PdACl one trans to phospho-
In the IR spectrum of 1, recorded as KBr pellet, the
mNH and dNH2 vibrational modes of thiourea ligand were
found as a broad band extending from 3339 to 3182 cmꢁ1
and a strong absorption at 1625 cmꢁ1, respectively. Some
characteristic IR absorptions of coordinated PPh3 were
observed at 3056 cmꢁ1 (mCH) and 1480, 1431, 1312 cmꢁ1
(mring). NMR spectra of 1, recorded in dmso-d6 solution,
also indicated the coordination of thiourea and
rus, clearly showing the trans influence of the thiourea and
triphenylphosphine ligands. Methanol solvate molecules
are linked with N1 atoms from thiourea ligands via hydro-
˚
gen bonding interaction (N1ꢀ ꢀ ꢀO1a 2.846(8) A, H2ꢀ ꢀ ꢀO1a
˚
2.060 A, N1AH2ꢀ ꢀ ꢀO1a 154.00°).
The ORTEP perspective of the molecular structure of
complex 2 with the atom numbering scheme is given in
Fig. 2. The molecular structure of 2 revealed that the geom-
etry around the Pd(II) is essentially square planar in which
the metal atom is coordinated to two chloride anions and a
neutral N,N,N0,N0-tetramethylethylenediamine chelate.
In the past few years, much attention have been devoted
to the hydrogen bonding involving metal–halides (MAX)
since they can be successfully employed to assembly molec-
ular building blocks into highly ordered transition metal-
based supramolecular architectures owing their directional
character. Metal-bound chlorides (MACl) are able to
engage in hydrogen bonds with strong (i.e. NAH, OAH)
and weak donors groups (i.e. CAH). According to Bram-
mer et al. [3], CAHꢀ ꢀ ꢀClAM hydrogen bonds behave sim-
ilarly to the stronger DAHꢀ ꢀ ꢀClAM (D = N, O) despite
the fact that CAHꢀ ꢀ ꢀClAM interactions possess less direc-
tional preference.
1
triphenylphosphine: H NMR (ppm): d 8.13 (s, –NH2), d
7.80 (s, –NH2), d 7.63–7.46 (m, ArAH), d 2.48 (s, –CH3);
13C{1H} (ppm): d 206.9 (C@S), d 134.2–128.4 (CAr).
31P{1H} NMR (ppm): d 194.6. The presence of a CH3OH
1
solvate was detected by the low-field H NMR signal at d
9.75 (s, –OH). Regarding to the IR spectrum of 2, the
coordination of the tmen ligand was detected by the disap-
pearance of the band at 2329 cmꢁ1, attributed to mCN of
[PdCl2(CH3CN)2] precursor and the presence of multiple
bands centered at 3020–2850 cmꢁ1 (mCH3 and mCH2 vibra-
tional modes) as well the absorptions found at 1468 (mCN)
and 808 cmꢁ1 (dCH).
The ORTEP representation of the molecular structure
of the asymmetric units for compound 1 Æ CH3OH with
the atom labeling schemes is presented in Fig. 1.
In compound 1 Æ CH3OH, the palladium coordination
geometry is approximately square planar formed by one
sulfur (from tu), one phosphorus (from PPh3) and two
cis-related chloro atoms. The PdACl bond distance trans
In the crystal packing of 1, cis-coordinated chloride
groups participate in hydrogen bonding of the
NAHꢀ ꢀ ꢀClAPd and CAHꢀ ꢀ ꢀClAPd type. Two molecules
of 1 are joined via NAHꢀ ꢀ ꢀClAPd hydrogen bonds
˚
˚
(N2ꢀ ꢀ ꢀCl1 3.382(6) A, H2ꢀ ꢀ ꢀCl1 2.670 A, N2AH2ꢀ ꢀ ꢀCl1
140.00°), involving one of the two ClAPd moieties and
one NH2 group from the thiourea ligand, giving rise to
the formation of a R22(12)dimer. The same ClAPd moiety
also takes part in weak interaction CAHꢀ ꢀ ꢀClAPd
˚
˚
(C10ꢀ ꢀ ꢀCl1 3.590(7) A, H10ꢀ ꢀ ꢀCl1 2.810 A, C10AH10ꢀ ꢀ ꢀCl1
Fig. 1. ORTEP representation of the asymmetric unit with labeling
Fig. 2. ORTEP representation of the asymmetric unit with labeling
˚
˚
scheme for 1 Æ CH3OH. Key geometrical parameters: PdACl1 2.3186(2) A,
scheme for 2. Key geometrical parameters: PdACl1 2.303(3) A, PdACl2
˚
˚
˚
˚
˚
˚
PdACl2 2.3801(1) A, PdAP 2.2440(1) A, PdAS 2.3191(1) A, and
Cl1APdACl2 88.94(6)°, Cl1APdAS 177.44(5)°, Cl1APdAP 93.24(5)°,
SAPdAP 84.30(5)°, Cl2APdAS 93.56(5)°, Cl2APdAP 175.12(6)°.
2.300(3) A, PdAN1 2.080(7) A, PdAN2 2.063(7) A, and Cl1APdACl2
90.97(11)°, N1APdAN2 84.90(3)°, Cl1APdAN1 91.50(2)°, Cl1APdAN2
176.20(2)°, Cl2APdAN1 177.50(2)°, Cl2APdAN2 92.70(2)°.

A.C. Moro et al. / Inorganic Chemistry Communications 9 (2006) 493–496
495
Fig. 3. Packing view of the supramolecular ribbon formed by NAHꢀ ꢀ ꢀClAPd and CAHꢀ ꢀ ꢀClAPd interactions in 1.
143.00°) with a phenyl ring of a neighboring dimer. The
into a 2D layered structure through intermolecular
˚
˚
CAHꢀ ꢀ ꢀClAPd distance of 2.810 A for 1 agrees well with
CAHꢀ ꢀ ꢀCl hydrogen bonds (C6ꢀ ꢀ ꢀCl2 3.747(8) A,
˚
the values found for the [PdCl2(3-Xpy)2] complexes
H62ꢀ ꢀ ꢀCl1 2.800 A, C6AH62ꢀ ꢀ ꢀCl1 167.00°). Analysis of
˚
(X = F, Cl, Br, I; py = pyridine) (2.783–2.864 A) [9].
the crystal structure of 2 also reveals the presence of intra-
molecular C5AH51ꢀ ꢀ ꢀCl1 and C3AH31ꢀ ꢀ ꢀCl2 interactions,
The cooperative effect of NAHꢀ ꢀ ꢀClAPd and
CAHꢀ ꢀ ꢀClAPd intermolecular forces results in extended
supramolecular chains (Fig. 3).
˚
whose Cꢀ ꢀ ꢀCl separations are 3.320(9) and 3.239(11) A
˚
with Hꢀ ꢀ ꢀCl distances of 2.760 and 2.690 A, respectively.
The crystal packing of 2 is determined by non-conven-
tional CAHꢀ ꢀ ꢀClAPd hydrogen bonds since other stronger
interactions are absent (Fig. 4). Molecules of 2 self-assem-
ble into one-dimensional infinite zig-zag ribbons through
CAHꢀ ꢀ ꢀClAPd hydrogen bonding involving one chloride
acceptor from ClAPd moiety and one hydrogen atom from
–CH3 group of the N,N,N0,N0-tetramethylethylenediamine
ligand of an adjacent [PdCl2(tmen)] molecule (C2ꢀ ꢀ ꢀCl1
The C5AH51ꢀ ꢀ ꢀCl1 and C3AH31ꢀ ꢀ ꢀCl2 bond angles are
118.0° and 117.0(0)°, respectively. The CAHꢀ ꢀ ꢀCl intermo-
˚
lecular H-bonds of 2.712 and 2.784 A are also responsible
for the formation of supramolecular sheets of [CoCl2
(tmen)] [10].
In conclusion, the present study showed that the
CAHꢀ ꢀ ꢀClAPd interactions play an important role in the
self-assembly of cis-palladium complexes as building
blocks. However, systematic investigations on such non-
conventional hydrogen bonds in coordination compounds
are necessary in order to explore their potential use as orga-
nizing elements in the rational construction of functional
˚
˚
3.611(9) A, H22ꢀ ꢀ ꢀCl1 2.820 A, C2AH22ꢀ ꢀ ꢀCl1 140.00°).
Methylene groups (–CH2–) from N,N,N0,N0-tetramethyle-
thylenediamine ligand do not participate in CAHꢀ ꢀ ꢀCl
interactions. Neighbouring 1D chains of 2 are assembled
Fig. 4. Packing view of 2D supramolecular sheet formed by CAHꢀ ꢀ ꢀClAPd hydrogen bonds in 2.

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A.C. Moro et al. / Inorganic Chemistry Communications 9 (2006) 493–496
´
[6] A.C. Moro, A.E. Mauro, S.R. Ananias, Eclet. Quım. 29 (2004) 57;
A.V.G. Netto, R.C.G. Frem, A.E. Mauro, Polyhedron 24 (2005)
1086;
transition metal-based supramolecules. Further investiga-
tion on the hydrogen-bonded metallosupramolecular spe-
cies is still in progress in our laboratory.
A.V.G. Netto, R.C.G. Frem, A.E. Mauro, Mol. Cryst. Liq. Cryst.
374 (2002) 255.
Acknowledgements
[7] Compound 1 Æ CH3OH was prepared by adding a mixture containing
thiourea (30 mg; 0.39 mmol) and triphenylphosphine (100 mg;
0.39 mmol) dissolved in 10 ml of CHCl3/CH3OH (1:1) to an orange
suspension of [PdCl2(CH3CN)2] (1) (100 mg; 0.39 mmol) in 10 ml of
CHCl3. Slow evaporation of the yellow solution afforded orange
crystals of good quality for X-ray diffraction studies. Yield 45 %.
m.p. = 148 °C. Anal. Calc. for C20H23N2SOPCl2Pd: C, 43.80; H, 4.24;
N, 5.12. Found: C, 43.70%; H, 4.04%; N, 5.38%. Compound 2: To a
solution of [PdCl2(CH3CN)2] (1) (1.00 g; 3.85 mmol) in 10 ml of
acetone, was added 0.58 mL of N,N,N0,N0-tetramethylethylenedi-
amine (tmen). The precipitation initialized immediately. After 30 min
of stirring at room temperature, the suspension was filtered off and
the yellow solid was washed with acetone and dried in vacuo Yield
85%. The filtrate was left to evaporate, yielding suitable single crystals
for X-ray diffraction determination. m.p. = 218 °C. Anal. Calc. for
C6H16N2Cl2Pd: C, 24.6; H, 5.51; N, 9.50. Found: C, 24.7%; H, 5.67%;
N, 9.70 %.
The authors acknowledge CNPq, FAPESP and CAPES
for financial support.
Appendix A. Supplementary material
Additional materials, consisting of atomic coordinates
and equivalent isotropic displacement parameters for non-
hydrogen atoms, H-atom coordinates and isotropic dis-
placement parameters, interatomic bond lengths and bond
angles have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC No. CCDC 262005 (complex
1), and CCDC 262004 (complex 2). Copies of this informa-
tion may be obtained free of charge from de Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223 336 033; email:deposit@ccdc.cam.ac.uk). Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2006.02.012.
[8] Data were collected on
a Enraf-Nonius CAD4 diffractometer.
Crystallographic data for 1 Æ CH3OH: Mw = 547.76, triclinic, space
˚
˚
˚
ꢀ
group P1, a = 9.8900(1) A, b = 10.5556(1) A, c = 12.9519(1) A, Z = 2,
3
˚
a = 99.370(1)°, b = 111.223(1)°, c = 108.266(1)°, V = 1137.1(2) A ,
Dc = 1.600 mg mꢁ3, l = 1.227 mmꢁ1, F(000) = 552, crystal dimension
0.10 Æ 0.15 Æ 0.15 mm, of 829 reflections collected, 799 were indepen-
dent [Rint = 0.009] and used in all calculations. The R values are
R1 = 0.0182 and wR2 = 0.0542 [I > 2r(I)]; max/min residual electron
References
3
˚
density: 0.47, ꢁ0.53 e/A . Crystallographic data for 2: Mw = 293.53,
˚
˚
monoclinic, space group Cc, a = 16.0805(1) A, b = 6.023(1) A,
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3
˚
˚
Ka = 0.71073 A, T = 293 K, crystal dimension 0.10 Æ 0.10 Æ 0.15 mm,
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3
˚
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