Supramolecular polymers self-assembled from trans-bis(pyridine) dichloropalladium(II) and platinum(II) complexes

Article abstract of DOI:10.1002/chem.201304315

Two structurally similar trans-bis(pyridine) dichloropalladium(II)- and platinum(II)-type complexes were synthesized and characterized. They both self-assemble in n-hexane to form viscous fluids at lower concentrations, but form metallogels at sufficient

Full text of DOI:10.1002/chem.201304315

DOI: 10.1002/chem.201304315
Full Paper
&
Metallogels
Supramolecular Polymers Self-Assembled from trans-Bis(pyridine)
Dichloropalladium(II) and Platinum(II) Complexes
Mingming Chen,[a] Chengsha Wei,[b] Jiaojiao Tao,[a] Xibo Wu,[a] Ningdong Huang,[a]
Guobin Zhang,*[a] and Liangbin Li*[a, b]
Abstract: Two structurally similar trans-bis(pyridine) di-
chloropalladium(II)- and platinum(II)-type complexes were
synthesized and characterized. They both self-assemble in n-
hexane to form viscous fluids at lower concentrations, but
form metallogels at sufficient concentrations. The viscous
solutions were studied by capillary viscosity measurements
and UV/Vis absorption spectra monitored during the disas-
sembly process indicated that a metallophilic interaction
was involved in the supramolecular polymerization process.
For the two supramolecular assemblies, uncommon continu-
ous porous networks were observed by using SEM and TEM
revealed that they were built from nanofibers that fused and
crosslinked with the increase of concentration. The xerogels
of the palladium and platinum complexes were carefully
studied by using synchrotron radiation WAXD and EXAFS.
The WAXD data show close stacking distances driven by p–
p and metal–metal interactions and an evident dimer struc-
ture for the platinum complex was found. The coordination
bond lengths were extracted from fitting of the EXAFS data.
Moreover, close PtII–PtII (PdII–PdII) and PtÀCl (PdÀCl) interac-
tions proposed from DFT calculations in the reported oligo-
(phenylene ethynylene) (OPE)-based palladium(II) pyridyl
supramolecular polymers were also confirmed by using
EXAFS. The PtII–PtII interaction is more feasible for supra-
molecular interaction than the PdII–PdII interaction in our
simple case.
Introduction
ometry of these complexes greatly favors supramolecular inter-
actions. For instance, a series of metallogelators based on rod-
like platinum–acetylide complexes, which displayed intriguing
photophysical properties, have been reported.[4] In addition,
the d8 complexes are known to show metallophilic interac-
tions. The d–d interactions are very sensitive to external stimuli
and are often accompanied by luminescence. Thus they are
very promising materials for sensors and displays. Additionally,
d–d interactions can play an important part in the assembly
process. A representative class is terpyridine platinum(II) com-
plexes as they often aggregate through PtII–PtII combined with
p–p interactions.[5] A very recently work has also shown that
PdII–PdII interaction can be the driving force for cooperative
supramolecular polymerization.[6] Close metal–metal interac-
tions are often found in the solid state but may be weakened
in solution, especially in polar solvents, yet together with other
noncovalent interactions, such as p–p stacking, very tough as-
semblies can often been obtained.
Supramolecular systems polymerized through noncovalent sec-
ondary interactions have attracted tremendous interest recent-
ly.[1] In particular, supramolecular polymers self-assembled from
metal complexes are of great use in material science. By
tuning the metal–ligand interactions, the rich electronic, mag-
netic, and photonic properties of metal species can be intro-
duced to supramolecular polymers while maintaining the fasci-
nating self-healing and stimuli-response advantages. Thus they
have applications in emissive, photovoltaic, sensing, respon-
sive, healing, and even drug-delivery materials.[2]
Of the various metallosupramolecular systems, the research
of d8 platinum(II), palladium(II), gold(III) complexes has been
a hot topic[3] because they show rich photophysical properties
and biological applications. In addition, the square-planar ge-
[a] M. Chen, J. Tao, X. Wu, Dr. N. Huang, Prof. Dr. G. Zhang, Prof. Dr. L. Li
National Synchrotron Radiation Lab and
College of Nuclear Science and Technology
University of Science and Technology of China
No. 96, JinZhai Road, Hefei, Anhui 230026 (China)
Fax: (+86)551-5141078
Herein, we report the self-assembly behavior of two structur-
ally similar trans-bis(pyridine) dichloropalladium(II)- and plati-
num(II)-type complexes. Pyridyl ligand L has a pyridine head
group and a 3,4,5-tris(dodecyloxy)benzene tail linked with an
amide bond in the 3-position. The two complexes abbreviated
as [Pt(L)2Cl2] and [Pd(L)2Cl2] both self-assemble in n-hexane to
form viscous fluids and metallogels. Though AgI-based metallo-
gels with a similar ligand have already been studied,[7] the PtII
and PdII complexes herein have well-defined structures and are
charge-neutral. Their self-assembly behaviors are much like the
recently reported oligo(phenylene ethynylene) (OPE)-based
E-mail: gbzhang@ustc.edu.cn
lbli@ustc.edu.cn
[b] C. Wei, Prof. Dr. L. Li
CAS Key Laboratory of Soft Matter Chemistry
Department of Polymer Science and Engineering
University of Science and Technology of China
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304315.
Chem. Eur. J. 2014, 20, 2812 – 2818
2812
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
palladium(II) pyridyl supramolecular polymers.[6] The self-as-
sembly of terpyridine PtII- and PdII-type complexes has often
been reported but to the best of our knowledge trans-bis-
(pyridine) dichloropalladium(II)-type molecules seem to be
new. These mononuclear neutral complexes are easy to pre-
pare but have strong supramolecular interactions. Therefore,
we started with a simple ligand and further extended the new
concept to the corresponding platinum(II) complexes.
tions between the molecules. Metallogels form at sufficiently
high concentrations (Figure 2b and c) and [Pt(L)2Cl2] has
a higher gelation ability than [Pd(L)2Cl2]. The critical gelation
concentration is about 8 mm for [Pt(L)2Cl2] but 20 mm for
[Pd(L)2Cl2]. Ligand L is highly soluble in n-hexane and does not
show any aggregation character. Thus, aggregation takes place
after coordination.
The viscous solutions formed by the two complexes have
been examined by using capillary viscosity measurements in
the concentration range of 0.05 to 1 mm, with the ligand for
comparison. The measured specific viscosities of [Pt(L)2Cl2] sol-
utions were always higher than the corresponding [Pd(L)2Cl2]
solutions (Figure 3a). The two log–log plots both show a good
Results and Discussion
Complexes [Pt(L)2Cl2] and [Pd(L)2Cl2] (Figure 1) were prepared
by heating ligand L at reflux with PtCl2 and PdCl2, respectively,
in toluene. All the structures have been successfully character-
1
ized by using H NMR spectroscopy and ESI-MS (see the Sup-
Figure 1. Synthetic route for ligand L and the two complexes.
porting Information). EXAFS spectra further confirmed the
structures and will be analyzed in detail below. The two com-
plexes are only slightly soluble in n-hexane at room tempera-
ture but highly soluble at 608C. Upon cooling, either viscous
liquids or metallogels form. Microfibers can be pulled from the
viscous solutions (Figure 2a), which indicates strong interac-
~
&
Figure 3. a) Specific viscosity (218C) of ligand L ( ), [Pt(L)2Cl2] ( ), and
*
[Pd(L)2Cl2] ( ) in n-hexane and b) the corresponding log–log plots for
~
*
[Pt(L)2Cl2] ( ; slope=1.75), and [Pd(L)2Cl2] ( ; slope=1.69).
linear relationship (Figure 3b). The slopes for [Pt(L)2Cl2] and
[Pd(L)2Cl2] are 1.75 and 1.69, respectively. As the slope for non-
interacting species in solution should be close to 1,[8] self-as-
sembly certainly occurs in n-hexane. Moreover, supramolecular
aggregation abilities could be judged by the slope values[8]
and the association constant of [Pt(L)2Cl2] is thought to be
slightly higher than that of [Pd(L)2Cl2]. As discussed later, the
supramolecular polymerization process follows a cooperative
mechanism. The association constant here should belong to
the elongation period. This slight advantage cannot be the
Figure 2. a) A single microfiber pulled between two capillary tubes (inner di-
ameter 0.5 mm) from a viscous solution of [Pd(L)2Cl2] (18 mm). b,c) Gel
images of [Pd(L)2Cl2] (20 mm) and [Pt(L)2Cl2] (8 mm), respectively.
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2813
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Figure 4. a) UV/Vis spectra of ligand L (c), [Pt(L)2Cl2] (g), and [Pd(L)2Cl2] (a) in chloroform (5ꢁ10À5 m). b) UV/Vis spectra change due to the disaggrega-
tion process upon gradually adding chloroform to solutions of [Pt(L)2Cl2] in n-hexane. c) The absorbance decrease at l=312.6 nm in (b) deviates from a sig-
moidal fitting (isodesmic model). d) UV/Vis spectra change due to the disaggregation process upon adding 10% chloroform to solutions of [Pd(L)2Cl2] in n-
hexane.
sole cause of the large viscosity difference. [Pt(L)2Cl2] already
takes a lead over [Pd(L)2Cl2] in the nucleation period.
tively, motivated by the recent work of the Meijer group,[10] we
have checked the disassembly process by adding a good sol-
vent, chloroform, to the aggregated solutions in n-hexane. On
addition of chloroform to [Pt(L)2Cl2], the peak at l=312 nm
gradually disappeared and the peak at l=288 nm shifted to
l=294 nm (Figure 4b). A blueshift of the aggregated state re-
veals a H-type stack of pyridine moieties. The absorbance de-
crease at l=312.6 nm gives a typically nonsigmoidal shape,
which means the aggregating process follows a cooperative
mechanism (Figure 4c). For [Pd(L)2Cl2], a blueshift of about
8 nm upon addition of 10% percent chloroform was observed
(Figure 4d). The increase in solvent polarity generally causes
a redshift of the p–p* band, so the blueshift must be generat-
ed by disaggregation. Referring to the similar Pd complex,[6]
a redshift upon aggregation indicates interaction of the axial
dz2 orbitals of the central palladium(II) atoms. Thus although
no new band appears, metallophilic interactions do exist.
The self-assembly mechanisms of [Pt(L)2Cl2] and [Pd(L)2Cl2]
have been inspected by using UV/Vis absorption spectra. The
two complexes both showed one broad band in the region
from l=260 to 340 nm with some redshift compared to the
free ligand in chloroform (Figure 4a). We ascribe this band to
p–p* transition of the pyridine group. No obvious MLCT bands
appeared because they are often two orders lower in absorb-
ance.[9] In the aggregated state in n-hexane (0.6 mm),
[Pd(L)2Cl2] only showed a redshift of the p–p* band center
from l=288 to 294 nm. However, in [Pt(L)2Cl2] two peaks cen-
tered at l=288 and 312 nm emerged. UV/Vis absorption spec-
tra at elevated temperatures suggested that the shoulder band
gradually disappeared, which further confirmed that the new
peak at l=312 nm is due to aggregation (Figure S1 in the
Supporting Information). For the two complexes, spectra at
concentrations of 0.05 and 1 mm were almost identical. Be-
cause the 1 mm solutions are quite viscous, aggregation surely
takes place. We conclude the two complexes can already self-
assemble at a concentration of 0.05 mm in n-hexane. This con-
clusion has also been confirmed by the viscosity measure-
ments. Because more dilute solutions are not suitable for UV/
Vis studies, concentration-dependent work is unable. Alterna-
Electron microscopy observations gave an insight into the
microstructures of the aggregates. For [Pt(L)2Cl2], nanofibers
were observed in dilute solutions by using TEM. As shown in
Figure 5a, fibers with diameters around 10 nm formed pre-
dominantly at concentrations of 0.25 mm, then fused into
much thicker fibers as the concentration was increased to
1 mm (Figure 5b). The fibers observed by TEM were not bun-
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2814
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Figure 6. WAXD spectra of xerogels of [Pt(L)2Cl2] (c) and [Pd(L)2Cl2] (a),
normalized intensity was used.
a very broad diffraction centered at d=0.44 nm and another
sharper peak centered at d=0.40 nm were observed. For
[Pt(L)2Cl2], a relatively broad diffraction centered at d=0.39 nm
was also found. The d values of the two sharper peaks were
0.41 and 0.37 nm. Columnar stacking of molecules with periph-
eral long aliphatic chains often leads to broad diffractions
caused by packing of the alkyl groups, and the stacking of cen-
tral cores gives rise to sharp diffractions.[13] Therefore, the cen-
tral core of [Pt(L)2Cl2] stacks with two different distances and
the peripheral long aliphatic chains give only one broad dif-
fraction peak because they are too bulky. Now it is clear that
the growth of nanofibers of [Pt(L)2Cl2] is through a dimer for-
mation and elongation process, and the shorter diffraction dis-
tance corresponds to the dimer space. The results match the
UV/Vis analysis well because the aggregation of [Pt(L)2Cl2] fol-
lows a cooperative (nucleation and growth) mechanism. For
platinum(II) complexes, dimer structures have been often re-
ported due to PtII–PtII interactions.[5a,14] The same case was
found for OPE-based palladium(II) pyridyl dichloride supra-
molecular polymers.[6] However, no evident dimer structure
was observed for [Pd(L)2Cl2]. In addition, the [Pd(L)2Cl2] xerogel
features less-ordered structures than the corresponding
[Pt(L)2Cl2] xerogel because the peaks are relatively broader. By
comparing the d values of the two xerogels, we can see that
[Pt(L)2Cl2] dimers are more tightly stacked. So it is evident that
a PtII–PtII interaction is more feasible for supramolecular assem-
bly than a PdII–PdII interaction, at least in this case. This is why
[Pt(L)2Cl2] supramolecular polymers in n-hexane have higher
viscosity and a lower gelation concentration. Because the OPE-
based palladium(II) pyridyl dichloride supramolecular polymers
clearly showed a PdII–PdII interaction (about 0.35 nm),[6] we can
also conclude that extended conjugated systems favor metal-
lophilic interactions.
Figure 5. TEM images of freeze-dried solutions of a) 0.25 mm (scale bar:
200 nm; inset scale bar: 50 nm, arrow indicates 5 nm) and b) 1 mm
[Pt(L)2Cl2] in n-hexane and SEM images of freeze-dried solutions of 1 mm
[Pt(L)2Cl2] (c and d) and 4 mm [Pd(L)2Cl2] (e and f).
dles but easily connected with each other to form continuous
networks. The diameter of the thinnest fiber observed was
about 5 nm, which matches the length of the molecule well
(Figure 5a, insert). We concluded that the fibers were grown
from columnar stacking of the disc-like molecules. SEM analysis
also confirmed the structure of continuous fibrillar networks.
At a concentration of 1 mm, highly crosslinked and entangled
fibers formed a porous continuous network (Figure 5c and d),
and the diameters of the pores were mainly a few microme-
ters. Though similar structures in metallogels have also been
reported by Yam and co-workers,[11] continuous networks were
rarely observed. Very recently Yang and co-workers reported
a platinum-based gelator that forms uniform honeycomb mor-
phologies in nonpolar solvents; the pore-size distribution re-
ported herein is not as narrow as their example.[12] Interesting-
ly, for all three cases the gelators are all metal complexes with
amide linkers and the reason for this is still not clear. The
highly porous metal complexes might have some applications
in catalysis. Similar continuous fibrillar morphologies were ob-
tained in the case of [Pd(L)2Cl2]. For a more concentrated
sample (Figure 5e and f), fibers fused more extensively, but
pores could still be observed with diameters of less than 1 mm.
All the above results indicated that the two complexes self-as-
semble through columnar stacking into nanofibers in n-hexane
and then further crosslink and entangle to form continuous
networks and immobilize the solvents.
The two xerogels were analyzed in EXAFS experiments. The
Fourier transforms (FTs) of k3c(k) EXAFS data is dominated by
two intense N and Cl scattering peaks. To get precise coordina-
tion bond lengths, the first coordination spheres of MÀN and
MÀCl shells were fitted. The fitted FTs are shown in Figure 7
and the results are listed in Table 1. The fitted bond lengths
are very close to similar ones reported for single-crystal struc-
To further discover how the nanofibers are generated, the
xerogels were analyzed by using synchrotron radiation WAXD.
As expected, for both samples a few diffraction peaks related
to p–p stacking were observed (Figure 6). For [Pd(L)2Cl2],
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2815
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
The effective distances of paths 2, 4, and 5 are all around 4.3 ꢂ,
thus we were able to avoid them by fitting R below 3.5 ꢂ in
the FTs.
With the theoretical calculation in mind, we have checked
the whole FT of [Pt(L)2Cl2]. The peak centered at 2.52 ꢂ could
be ascribed to the PtÀC shell (path 1), but the other two peaks
in the range of 2.8 to 3.5 ꢂ were not expected. From the coop-
erative growing model of [Pt(L)2Cl2], short PtII–PtII interactions
are responsible for these peaks. Based on the WAXD data, we
can use a dimer model to fit the FTs from 1 t 3.5 ꢂ. A PtÀPt
shell surely exists but other shells are also expected. When two
platinum atoms closely contact, one chloride atom of the
second molecule can also reach a close contact with the first
platinum atom. According to the recently reported OPE-based
palladium(II) pyridyl gelator, a short PdÀCl separation also
exists in the dimer, which is comparative to the PdÀPd separa-
tion.[6] Therefore, a PtÀCl shell should also be considered. With
this dimer model, the spectra in the R range of 1 to 3.5 ꢂ were
fitted (Figure 8). The results are shown in Table 2. EXAFS data
Figure 7. k3c(R) of the EXAFS data in R space for a) [Pd(L)2Cl2] and
*
b) [Pt(L)2Cl2] xerogels and fitting of the first coordination spheres ( , R
range=1–2.5 ꢂ for [Pd(L)2Cl2] and 1–2.3 ꢂ for [Pt(L)2Cl2]).
Table 1. Structural parameters extracted from the first coordination
sphere EXAFS curve fitting.
3
*
Figure 8. Fitting of k c(R) of the EXAFS data for [Pt(L)2Cl2] in R space ( , R
range=1–3.5 ꢂ).
Bond
N[a]
R [ꢂ][b]
s2 [ꢂ2][c]
[Pt(L)2Cl2]
[Pd(L)2Cl2]
PtÀN
PtÀCl
PdÀN
PdÀCl
2
2
2
2
2.01(1)
2.30(1)
2.01(2)
2.31
0.0022(9)
0.0027(5)
0.0024(1)
0.0029(1)
Table 2. Structural parameters extracted from EXAFS curve fitting in the
range of 1–3.5 ꢂ.
[a] The coordination number, was set as a constant. [b] Interatomic dis-
tance R. [c] Debye–Waller factor s2.
Bond
N
R [ꢂ]
s2 [ꢂ2]
[Pt(L)2Cl2]
PtÀN
2
2
4
1
1
1.99(1)
2.32(1)
2.96
3.43(9)
3.38(5)
0.0028(3)[b]
PtÀCl
tures,[9,15] which also indicates that the two complexes are typi-
cally trans-palladium(II) and -platinum(II) bis(pyridine) dichlor-
ide complexes. To further analyze the EXAFS spectra, the theo-
retical scattering paths of a similar trans-dichloroplatinum(II)
bis(pyridine) single-crystal structure was calculated (Figure S4
in the Supporting Information). In the R region up to 4 ꢂ, there
are other two PtÀC single scattering pathways (Figure S4,
paths 1 and 2, in the Supporting Information). Strong multiple
scatterings from Pt-N-C and Pt-C-C (Figure S4, paths 4 and 5, in
the Supporting Information) are expected and the effective
distances are similar to PtÀC single scattering path 2. Fortu-
nately, the Pt-N-C multiple scattering (path 3) with a shorter ef-
fective distance is almost negligible. This is reasonable because
the Pt-N-C angle in path 3 is much smaller than the other two.
PtÀC
0.006(2)
0.007(2)
0.01
Pt1ÀPt2[a]
Pt1ÀCl2[a]
[a] 1 and 2 correspond to atoms of the first or second molecules in
a dimer model. [b] Identical values were used for neighboring shells to
simplify the curve fitting.
indicate that a dimer forms through close contact of PtÀPt and
PtÀCl of about 3.4 ꢂ. However, more accurate lengths for these
supramolecular interactions are difficult to determine. The in-
creased disorder at high R strongly weakens the scattering
peaks, which is easily shown from the fitted Debye–Waller fac-
tors. Moreover, overlap of other shells and also multiple scat-
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2816
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
trometer. Mass spectrum data were obtained by using a Thermo
LTQ instrument operated in electrospray ionization (ESI) mode, and
both positive and negative spectra were measured. Transmission
electron microscopy (TEM) observations were carried out by using
a JEM-2100F electron microscope operated at 200 kV. Scanning
electron microscopy (SEM) investigations were conducted by using
a Philips XL-30-ESEM TMP electron microscope. Viscosity measure-
ments were carried out at 218C in n-hexane by using a Ubbelohde
viscometer.
tering add to the difficulty. Thus though the diffraction peak
from the WAXD data does not correspond to the direct Pt–Pt
contact, the EXAFS Pt–Pt separation seems a little shorter. In
any case, close PtÀPt and PtÀCl interactions have been con-
firmed. For [Pd(L)2Cl2] the overlap is more complex and we
were not able to fit the EXAFS spectrum. By simply comparing
the two FTs, we can deduce that the supramolecular interac-
tions in [Pd(L)2Cl2] are of longer separations and more disorder.
EXAFS studies of metal–metal interactions have been rarely re-
ported and sometimes ambiguous results have been ob-
tained.[16] For supramolecular systems, single crystals are often
impossible to get and EXAFS remains a powerful tool for analy-
sis. Efforts should be made to enhance the scatterings of rela-
tively longer separations and distinguish them from other
shells. The characterization of metallosupramolecular interac-
tions with EXAFS is still ongoing.
Wide-angle X-ray diffraction (WAXD) measurements were carried
out at the beamline (BL16B1) of the Shanghai Synchrotron Radia-
tion Facility (SSRF). The X-ray wavelength was 0.124 nm and
a Mar165 CCD detector (2048ꢁ2048 pixels with pixel size 80 mm)
was employed to collect two-dimensional WAXD patterns. The
sample-to-detector distance was calibrated by using CeO2 powder.
Fit2D software from the European Synchrotron Radiation Facility
was used to analyze the WAXD patterns in terms of the scattering
vector q=4psinq/l with 2q as the scattering angle and l as the X-
ray wavelength.
Pd K-edge and Pt L3-edge EXAFS spectra were measured at the
BL14W1 beamline of the Shanghai Synchrotron Radiation Facility
(SSRF). A Si(311) double crystal monochromator was used. Data
were collected in transmission mode by using ion chambers with
mixed nitrogen and argon gas. The standard processing of EXAFS
spectra (background removal, Fourier transformation, and nonlin-
ear fitting) was performed by using the ATHENA and ARTEMIS pro-
grams of IFFEFIT.[19] Fourier transformation was performed over
a range of 3.4–13.5 ꢂÀ1 (Pd K-edge data) or 2.8–15.6 ꢂÀ1 (Pt L3-
edge data) with Hanning window functions. The theoretical phase
and amplitude functions for single and multiple scattering within
a similar molecular model were calculated by using ab initio meth-
ods in the FEFF6 program code.[20] The fitting procedure was per-
Conclusion
We have synthesized two trans-bis(pyridine) dichloropalladi-
um(II)- and platinum(II)-type complexes and studied their self-
assembly behavior. Supramolecular polymers were formed in
n-hexane as demonstrated by viscosity measurements. TEM
and SEM studies further showed nanofibers that fuse into
porous interconnected networks. Generally, the aggregation
mechanism of the two complexes is similar. The Van der Waals
and hydrogen bonding together with p–p stacking may all
assist the self-assembly process. Given the big difference be-
tween the viscosity and gelation ability of the two complexes,
metal–metal interactions must play a crucial role, which has
been confirmed by UV/Vis, WAXD, and EXAFS experiments. A
series of similar organic molecules without coordinated metal
ions has already been explored and do not show such strong
interactions as compared to the systems described herein.[17]
After incorporation of square-planar-coordinated metal ions,
supramolecular interactions are greatly favored. In our case,
the PtII–PtII interaction showed an advantage over the PdII–PdII
interaction. However, with the assistance of extended conju-
gated systems, strong aggregates could also be obtained for
such palladium complexes. Our results have proved that trans-
bis(pyridine) dichloropalladium(II)- and platinum(II)-type com-
plexes are very promising candidates for the construction of
supramolecular assemblies.
2
formed in R space. The inelastic reduction factor S0 was extracted
from standard Pd and Pt foils. For each coordination, the coordina-
tion number N was fixed as constant and the interatomic distance
R, the Debye–Waller factor s2, and the edge-energy shift ~E0 were
fitted.
Synthesis of L
3,4,5-Tris(dodecyloxy)benzoic acid (1.35 g, 2 mmol) was dissolved
in chloroform (50 mL) and cooled with ice. Oxalyl chloride (1.27 g,
10 mmol) was added dropwise and then a drop of DMF was
added. The solution was stirred for 4 h and the solvent was dis-
tilled under vacuum. The dried 3,4,5-tris(dodecyloxy)benzoyl chlo-
ride was dissolved in THF (50 mL) and cooled with ice. A solution
of 3-amino pyridine (0.28 g, 3 mmol) and pyridine (2 mL) in THF
(15 mL) was added dropwise. The resulting mixture was stirred
overnight and the poured into water (250 mL). The precipitate was
collected and recrystallized from THF/H2O to give L as a white
1
solid (0.98 g, 65%). H NMR (CDCl3 400 MHz): d=8.96 (s, 1H; PyH),
Experimental Section
8.47 (s, 1H; PyH), 8.35 (d, 1H; PyH), 7.44 (q, 1H; PyH), 7.16 (s, 2H;
ArH), 4.05 (m, 6H; OCH2), 1.80 (m, 6H; CH2), 1.47 (m, 6H; CH2), 1.26
(m, 48H; CH2), 0.88 ppm (t, 9H; CH3); ESI-MS: m/z calcd for
C48H83N2O4: 752.18; found: 751.71 [M+H]+.
Experimental methods
Tetrahydrofuran (THF), chloroform, toluene and pyridine were dis-
tilled under reduced pressure over calcium hydride and then
stored over 4 ꢂ molecular sieves. 3,4,5-Tris(dodecyloxy)benzoic acid
was prepared according to a reported method.[18] All other re-
agents and solvents are commercially available and were used as
received.
Synthesis of [Pd(L)2Cl2]
Palladium dichloride (177 mg, 1 mmol) and L (1.50 g, 2 mmol) in
toluene (50 mL) were heated at reflux for 4 h, then the solvents
were removed by vacuum. The residue was purified by using
column chromatography on silica gel (eluent CHCl3/petroleum
UV/Vis absorption spectra were recorded by using a Shimadzu UV-
2401 spectrophotometer. Quartz cells with 1 cm or 0.1 cm path
lengths were used to fit the various concentrations. H NMR spec-
1
1
ether (2:1)) to afford a yellow powder (0.8 g, 48%). H NMR (CDCl3
tra were obtained at 400 MHz by using a Bruker AV400 NMR spec-
400 MHz): d=9.47 (s, 2H; CONH), 8.69 (d, 2H; PyH), 8.57 (s, 2H;
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2817
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[4] a) T. Cardolaccia, Y. Li, K. S. Schanze, J. Am. Chem. Soc. 2008, 130, 2535–
2545; b) J. Zhang, X. D. Xu, L. J. Chen, Q. Luo, N. W. Wu, D. X. Wang,
X. L. Zhao, H. B. Yang, Organometallics 2011, 30, 4032–4038; c) L. J.
Chen, J. Zhang, J. He, X. D. Xu, N. W. Wu, D. X. Wang, Z. Abliz, H. B.
Yang, Organometallics 2011, 30, 5590–5594; d) Y. J. Tian, E. W. Meijer, F.
Wang, Chem. Commun. 2013, 49, 9197–9199.
[5] a) V. W. W. Yam, K. M. C. Wong, N. Zhu, J. Am. Chem. Soc. 2002, 124,
6506–6507; b) F. Camerel, R. Ziessel, B. Donnio, C. Bourgogne, D. Guil-
lon, M. Schmutz, C. Iacovita, J.-P. Bucher, Angew. Chem. 2007, 119,
2713–2716; Angew. Chem. Int. Ed. 2007, 46, 2659–2662; c) W. Lu, Y.
Chen, V. A. L. Roy, S. S.-Y. Chui, C.-M. Che, Angew. Chem. 2009, 121,
7757–7761; Angew. Chem. Int. Ed. 2009, 48, 7621–7625; d) C. Po, A. Y.-Y.
Tam, K. M.-C. Wong, V. W.-W. Yam, J. Am. Chem. Soc. 2011, 133, 12136–
12143.
PyH), 8.21 (d, 2H; PyH), 7.15 (s, 4H; ArH), 6.98 (q, 2H; PyH), 4.08
(m, 12H; OCH2), 1.80 (m, 12H; CH2), 1.48 (m, 12H; CH2), 1.26 (m,
96H; CH2), 0.88 ppm (t, 18H; CH3); ESI-MS (positive-ion mode): m/z
calcd for C98H168Cl2N5O8Pd: 1721.74; found: 1722.17 [M+CH3CN+
H]+; ESI-MS (negative-ion mode): m/z calcd for C96H164Cl3N4O8Pd:
1715.13; found: 1714.80 [M+Cl]À.
Synthesis of [Pt(L)2Cl2]
Platinum dichloride (266 mg, 1 mmol) and L (1.50 g, 2 mmol) in tol-
uene (50 mL) were heated at reflux for 4 h, then the solution was
cooled and filtered. The solvents of the filtrate were removed by
vacuum and the residue was washed with ethyl acetate and puri-
fied by using column chromatography on silica gel (eluent CHCl3/
petroleum ether (3:1)) to give a light green powder (0.62 g, 35%).
1H NMR (CDCl3 400 MHz): d=9.76 (s, 2H; CONH), 8.97 (s, 2H; PyH),
8.88 (d, 2H; PyH), 8.27 (d, 2H; PyH), 7.24 (s, 4H; ArH), 7.08 (q, 2H;
PyH), 4.08 (m, 12H; OCH2), 1.80 (m, 12H; CH2), 1.48 (m, 12H; CH2),
1.26 (m, 96H; CH2), 0.88 ppm (t, 18H; CH3); ESI-MS (positive-ion
mode): m/z calcd for C98H168Cl2N5O8Pt: 1810.40; found: 1810.46
[M+CH3CN+H]+; ESI-MS (negative-ion mode): m/z calcd for
C96H164Cl3N4O8Pt: 1803.79; found: 1803.30 [M+Cl]À; m/z calcd for
C96H163Cl2N4O8Pt: 1767.33; found: 1767.25 [MÀH]À.
[6] M. J. Mayoral, C. Rest, V. Stephanenko, J. Schellheimer, R. Q. Albuqerque,
G. Fernꢃndez, J. Am. Chem. Soc. 2013, 135, 2148–2151.
[7] Q. Liu, Y. Wang, W. Li, L. Wu, Langmuir 2007, 23, 8217–8223.
[8] a) F. Wang, C. Y. Han, C. L. He, Q. Z. Zhou, J. Q. Zhang, C. Wang, N. Li,
F. H. Huang, J. Am. Chem. Soc. 2008, 130, 11254–11255; b) J. B. Beck,
J. M. Ineman, S. J. Rowan, Macromolecules 2005, 38, 5060–5068.
[9] A. Krogul, J. Cedrowski, K. Wiktorska, W. P. Ozimi’nski, J. Skupi’nska, G.
Litwinienko, Dalton Trans. 2012, 41, 658–666.
[10] P. A. Korevaar, C. Schaefer, T. F. A. de Greef, E. W. Meijer, J. Am. Chem.
Soc. 2012, 134, 13482–13491.
[11] S.-T. Lam, G.-X. Wang, V. W.-W. Yam, Organometallics 2008, 27, 4545–
4548.
[12] X. D. Xu, J. Zhang, L. J. Chen, X. L. Zhao, D. X. Wang, H. B. Yang, Chem.
Eur. J. 2012, 18, 1659–1667.
[13] a) B. Mohr, G. Wegner, K. Ohta, J. Chem. Soc. Chem. Commun. 1995,
995–996; b) W. Lu, Y.-C. Law, J. Han, S. S.-Y. Chui, D.-L. Ma, N. Zhu, C.-M.
Che, Chem. Asian J. 2008, 3, 59–69.
[14] a) H. K. Yip, L. K. Cheng, K. K. Cheung, C. M. Che, J. Chem. Soc. Dalton
Trans. 1993, 2933–2938; b) J. A. Bailey, M. G. Hill, R. E. Marsh, V. M. Mis-
kowski, W. P. Schaefer, H. B. Gray, Inorg. Chem. 1995, 34, 4591–4599.
[15] A. N. Chernyshev, N. A. Bokach, Y. A. Izotova, M. Haukka, Acta. Cryst.
Sect. E 2009, 65, m60.
[16] a) N. Carr, J. G. Crossley, A. J. Dent, J. R. Gouge, G. N. Greaves, P. S. Jar-
rett, A. G. Orpen, J. Chem. Soc. Chem. Commun. 1990, 1369–1371; b) D.
Ellis, L. J. Farrugia, P. Wiegeleben, J. G. Crossley, A. G. Orpen, P. N. Waller,
Organometallics 1995, 14, 481–488; c) H. de La Riva, A. Pintado-Alba, M.
Nieuwenhuyzen, C. Hardacre, M. C. Lagunas, Chem. Commun. 2005,
4970–4972; d) E. J. Fernꢃndez, C. Hardacre, A. Laguna, M. C. Lagunas,
J. M. Lꢄpez-de-Luzuriaga, M. Monge, M. Montiel, M. E. Olmos, R. C.
Puelles, E. Sꢃnchez-Forcada, Chem. Eur. J. 2009, 15, 6222–6233.
[17] a) C. Xue, X. Weng, J.-J. Ge, Z. Shen, H. Shen, M. J. Graham, K.-U. Jeong,
H. Huang, D. Zhang, M. Guo, F. W. Harris, S. Z. D. Cheng, Chem. Mater.
2004, 16, 1014–1025; b) H. Shen, K.-U. Jeong, M. J. Graham, S. Leng,
J. X. Zheng, H. Huang, M. Guo, F. W. Harris, S. Z. D. Cheng, Soft Matter
2006, 2, 232–242.
Acknowledgements
This work is supported by the National Natural Science Foun-
dation of China (51325301, U1232129, 11275205, and
11204285), the 973 program of MOST (2010CB 934504), a spe-
cial financial grant from the China postdoctoral science foun-
dation (2012M521255), the Fundamental Research Funds for
the Central Universities (WK2310000025), and the experimental
fund of Shanghai Synchrotron Radiation Facility (SSRF).
Keywords: metallogels · metal–metal interactions · palladium ·
platinum · supramolecular polymers
[1] a) T. Aida, E. W. Meijer, S. I. Stupp, Science 2012, 335, 813–817; b) F.
Huang, O. A. Scherman, Chem. Soc. Rev. 2012, 41, 5879–5880; c) T. F. A.
de Greef, M. M. J. Smulders, M. Wolffs, A. P. H. J. Schenning, R. P. Sijbes-
ma, E. W. Meijer, Chem. Rev. 2009, 109, 5687–5754.
[2] a) M. O. M. Piepenbrock, G. O. Lloyd, N. Clarke, J. W. Steed, Chem. Rev.
2010, 110, 1960–2004; b) G. R. Whittell, M. D. Hager, U. S. Schubert, I.
Manners, Nat. Mater. 2011, 10, 176–188; c) M. Burnworth, T. Liming,
K. R. Justin, D. J. Andrew, F. L. Beyer, G. L. Fiore, S. J. Rowan, C. Weder,
Nature 2011, 472, 334–338; d) S.-i. Kawano, N. Fujita, S. Shinkai, J. Am.
Chem. Soc. 2004, 126, 8592–8593; e) J.-J. Zhang, W. Lu, R. W. Y. Sun, C.-
M. Che, Angew. Chem. 2012, 124, 4966–4970; Angew. Chem. Int. Ed.
2012, 51, 4882–4886; f) A. Kishimura, T. Yamashita, K. Yamaguchi, T.
Aida, Nat. Mater. 2005, 4, 546–549.
[18] E. Terazzi, S. Torelli, G. Bernardinelli, J.-P. Rivera, J.-M. BInech, C. Bour-
gogne, B. Donnio, D. Guillon, D. Imbert, J.-C. G. Bunzli, A. Pinto, D. Jean-
nerat, C. Piguet, J. Am. Chem. Soc. 2005, 127, 888–903.
[19] B. Ravel, M. Newville, J. Synchrotron Rad. 2005, 12, 537–541.
[20] M. Newville, J. Synchrotron Rad. 2001, 8, 322–324.
[3] a) I. Eryazici, C. N. Moorefield, G. R. Newkome, Chem. Rev. 2008, 108,
1834–1895; b) W.-W. Yam, K. M.-C. Wong, Chem. Commun. 2011, 47,
11579–11592.
Received: November 4, 2013
Published online on February 12, 2014
Chem. Eur. J. 2014, 20, 2812 – 2818
www.chemeurj.org
2818
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim