One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

Article abstract of DOI:10.1016/j.ica.2009.04.004

The rigid, π-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO₂C[PEP(hexyl)₂EP]CO₂H} has been used to synthesise the new crystalline coordination polymers {Zn(O₂C[PEP(hexyl

Full text of DOI:10.1016/j.ica.2009.04.004

Inorganica Chimica Acta 362 (2009) 3600–3606
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination
polymers: Synthesis, crystal structures, thermal and photoluminescent properties
a,b,
Andreas Schaate a,b, Miriam Schulte c, Michael Wiebcke a,b, Adelheid Godt c, , Peter Behrens
*
*
a Institute of Inorganic Chemistry, Leibniz University Hannover, Callinstr. 9, 30167 Hannover, Germany
b Centre for Solid-State Chemistry and New Materials, Leibniz University Hannover, Germany
c Department of Chemistry, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The rigid,
p-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene
Received 6 August 2008
Received in revised form 19 March 2009
Accepted 3 April 2009
{HO2C[PEP(hexyl)2EP]CO2H} has been used to synthesise the new crystalline coordination polymers
{Zn(O2C[PEP(hexyl)2EP]CO2)(DMF)2} (1) and {Zn(O2C[PEP(hexyl)2EP]CO2)(DEF)2} (2) in N,N-dimethyl-
formamide (DMF) and N,N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal
X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordina-
tion chains in which [Zn(formamide)2]2+ fragments are bridged by (O2C[PEP(hexyl)2EP]CO2)2À ligands.
The zigzag chains possess different intra-chain ZnÁ Á ÁZnÁ Á ÁZn angles due to the different volumes of the
coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions.
Upon heating 1 and 2 to 200 °C, removal of the coordinating formamide molecules occurs, yielding the
formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O2C[PEP(hexyl)2EP]CO2)}. According
to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still
possess partial ordering of intact, yet modified coordination chains in a structural arrangement which
appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit
blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with
respect to kmax of 1 and 2, respectively.
Available online 10 April 2009
Keywords:
Coordination polymer
Zinc
Oligo(phenyleneethynylene)dicarboxylic
acid
Crystal structure
Photoluminescence
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
arated excited states with electrons being localised on the Zn4O
clusters or delocalised in the conduction band can be generated
In the last decade micro- and mesoporous coordination poly-
mers or metal–organic frameworks (MOFs) have emerged as a
new class of materials with periodic host structures, which show
properties that cannot be obtained with purely inorganic porous
materials such as crystalline zeolites or ordered mesoporous oxi-
des and are therefore of great interest as new functional materials
[1]. Compared to zeolites MOFs allow a more rational design and
synthesis through the use of shape-persistent poly-dentate ligands
to bridge metal cations or clusters, as has been well demonstrated
for polycarboxylate ligands [2]. Interestingly, some recent papers
report on guest-dependent photoluminescence [3] as well as elec-
troluminescent [4] and photovoltaic properties [4,5] of porous
MOFs. In the case of the familiar MOF-5 it has been proposed that
photoluminescence originate from photoinduced electron-transfer
from the terephthalate bridges to the Zn4O clusters [6]. Further-
more, a recent study on MOF-5 revealed that different charge-sep-
and that the material behaves as a photoactive semiconductor with
valence and conduction band potentials that are very similar to
those of TiO2 [7]. These reports indicate that porous MOFs possess
potential as functional components in chemical sensors, dye-sensi-
tised (Grätzel-type) solar cells or light-emitting devices. Concern-
ing the further development of MOFs for such advanced
applications, poly-dentate ligands based on oligo(phenyleneethyn-
ylene) (OPE) are particularly promising bridges. OPEs are known to
exhibit photoluminescence and electroluminescence and are dis-
cussed as materials for transporting excitation energy and charge
over long distances [8]. Recently, carboxylate-terminated OPEs of
varying lengths have been used to anchor chromophors to TiO2-
nanoparticle films of dye-sensitised solar cells [9]. Monodisperse
OPEs are easily accessible via Pd-catalysed cross-coupling reac-
tions in varying lengths and architecture [10]. The end group func-
tionalities are attached at late steps during the multistep synthesis,
thereby opening a straightforward access to the variation of func-
tional end groups [10a,11]. Furthermore, the modular synthesis al-
lows for OPEs with additional functional groups in the solubilising
side chains of the backbone.
* Corresponding authors. Address: Institute of Inorganic Chemistry, Leibniz
University Hannover, Callinstr. 9, 30167 Hannover, Germany (P. Behrens). Tel.:
+49 511 762 3660; fax: +49 511 762 3006 (A. Godt), tel.: +49 521 106 2071; fax: +49
521 106 6417 (P. Behrens).
E-mail addresses: godt@uni-bielefeld.de (A. Godt), peter.behrens@acb.uni-han-
nover.de (P. Behrens).
With these facts and potential applications in mind we started
to explore OPEs with at least two carboxylate groups as bridging
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.04.004

A. Schaate et al. / Inorganica Chimica Acta 362 (2009) 3600–3606
3601
units for the construction of coordination polymers and porous
2.3. Synthesis of {Zn(O2C[PEP(hexyl)2EP]CO2)(DEF)2} (2)
MOFs. Known to us are only the Cd(II) and Pb(II) salts of OPE dicar-
boxylic acids, the crystal structures of which were not determined
[11]. The salts were primarily used for the preparation of organic/
inorganic composites with CdS and PbS nanoparticles embedded in
an OPE matrix. For our purposes, we first chose 1,4-bis-[2-(4-car-
boxyphenyl)ethynyl]-2,5-dihexylbenzene, the dicarboxylic acid
HO2C[PEP(hexyl)2EP]CO2H (Scheme 1), which is of nanosize length
(end-to-end distance 2.07 nm) and bears two hexyl side chains at
the central benzene ring to ensure solubility during the synthesis
of the diacid. We were able to obtain two crystalline Zn(II) coordi-
nation polymers, {Zn(O2C[PEP(hexyl)2EP]CO2)(DMF)2} (1) and
{Zn(O2C[PEP(hexyl)2EP]CO2)(DEF)2} (2). The new compounds were
characterised by single-crystal X-ray crystallography, powder X-
ray diffraction (XRD), simultaneous thermogravimetry (TG) and
difference thermal analysis (DTA) as well as FT-IR and photolumi-
nescence spectroscopy. Also, from both 1 and 2 the respective
formamide-free compounds 1-DMF and 2-DEF of composition
{Zn(O2C[PEP(hexyl)2EP]CO2)} were prepared by heat treatment
and characterised. Here, these experiments and their results are
reported.
Zn(NO3)2 Á 6H2O (0.020 g, 0.067 mmol) and HO2C[PEP(hexyl)2
EP]CO2H (0.036 g, 0.067 mmol) were dissolved in DEF (6.0 mL,
54 mmol) and distilled water (0.2 mL, 11 mmol) was added. The
resulting solution was kept in a sealed glass vessel at 40 °C for
65 h. Colourless crystals of 2 (0.039 g, 44% based on Zn) were ob-
tained by filtration, washing with DEF and subsequent drying. Anal.
Calc. for C46H58N2O6Zn: C, 69.03; H, 7.36; N, 3.50. Found: C, 68.78;
H, 7.36; N, 3.60%.
2.4. Single-crystal X-ray crystallography
The XRD measurements were performed on a Stoe IPDS single-
axis diffractometer with monochromatised Mo
Ka radiation
(k = 0.71073 Å). For this purpose, single crystals were coated with
a thin film of paraffin oil, glued to the tip of thin-walled glass cap-
illaries and freeze-fixed in the cold-gas stream of the diffractome-
ter (Oxford Cryostream device). All structure calculations were
done with WinGX software [12]. Absorption corrections based on
symmetry-equivalent reflections were applied to the intensity data
using the MULABS option in the PLATON software package [13].
The structures were solved by direct methods using the program
SHELXS-97 [14]. Subsequent Fourier syntheses and full-matrix
least-squares refinements including all data (F2) were performed
using the program SHELXL-97 [15]. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters. Hydrogen atoms
were placed geometrically and treated riding on the respective car-
bon atoms. The carbon atoms of the hexyl chains in 1 and 2 partly
exhibit large displacement parameters, possibly due to disorder in
these chains. For these carbon atoms hydrogen atoms were not
considered. In the case of 1, a split-atom model was introduced
for two hexyl carbon atoms (C17, C18) with occupancy factors of
0.5 for each position. Crystal data and further details of the struc-
ture analyses are listed in Table 1.
2. Experimental
2.1. General methods and materials
Powder XRD patterns were recorded at room temperature on a
Stoe STADI-P diffractometer in transmission geometry using
monochromatised Cu Ka1 radiation (k = 1.54060 Å). TG/DTA mea-
surements were performed simultaneously on a Netzsch STA 429
thermoanalyser. For this purpose, samples were filled into alumina
crucibles and heated under a flow of air at a rate of 5 °C/min up to
1000 °C. A Bruker TENSOR 27 instrument was used to collect FT-IR
spectra in the range from 4000 to 400 cmÀ1 from samples diluted
in pressed KBr pellets. Photoluminescence emission spectra were
recorded from powdered samples at room temperature on a Perkin
Elmer LS 50B spectrometer equipped with a Xe lamp.
3. Results and discussion
Commercial materials of reagent grade were used as received
for the preparations. The syntheses of HO2C[PEP(hexyl)2EP]CO2H
and its potassium salt have been reported [11].
3.1. Synthesis and thermal behaviour of 1 and 2
The new coordination polymers 1 and 2 were obtained as trans-
parent colourless crystals by reacting equimolar amounts of
2.2. Synthesis of {Zn(O2C[PEP(hexyl)2EP]CO2)(DMF)2} (1)
Zn(NO3)2 Á 6H2O (0.033 g, 0.110 mmol) and HO2C[PEP(hexyl)2-
EP]CO2H (0.059 g, 0.110 mmol) were dissolved in DMF (6.0 mL,
77 mmol) and distilled water (0.2 mL, 11 mmol) was added. The
resulting solution was charged into a Teflon-lined stainless-steel
autoclave (8 mL internal capacity) and kept in an oven at 105 °C
for 42 h. Colourless crystals of 1 (0.076 g, 93% based on Zn) were
obtained by filtration, washing with DMF and subsequent drying.
Anal. Calc. for C42H50N2O6Zn: C, 67.78; H, 6.77; N, 3.76. Found: C,
66.57; H, 6.85; N, 3.67%.
Table 1
Crystal data and details of the structure analysis for {Zn(O2C[PEP(hexyl)2EP]-
CO2)(DMF)2} (1) and {Zn(O2C[PEP(hexyl)2EP]CO2)(DEF)2} (2).
1
2
Empirical formula
Formula weight
Crystal system
Space group/Z
a (Å)
C42H28N2O6Zn
722.05
C46H48N2O6Zn
790.25
monoclinic
C2/c (No. 15)/4
40.738(6)
5.900(2)
16.407(2)
93.98(2)
3934.0(13)
213
monoclinic
C2/c (No. 15)/4
37.134(7)
7.192(3)
16.303(3)
93.99(2)
4344(2)
213
b (Å)
c (Å)
ß (°)
V (Å3)
T (K)
qcalc (Mg m3)
1.219
0.671
1.208
0.613
l(Mo K
a
) (mmÀ1
)
2Hmax (°)
51.10
50.62
Total data
25694
28197
Unique data/Rint
3653 / 0.083
249
0.046
3892 / 0.097
249
0.040
Refined parameters
R1 (I > 2rI
)
wR2 (all data)
0.118
0.979
+0.39/À0.34
0.061
0.849
+0.37/À0.20
Goodness-of-fit on F2
Largest difference peak/hole (e ÅÀ3
)
Scheme 1. Structure of HO2C[PEP(hexyl)2EP]CO2H.

3602
A. Schaate et al. / Inorganica Chimica Acta 362 (2009) 3600–3606
HO2C[PEP(hexyl)2EP]CO2H and Zn(NO3)2 Á 6H2O in DMF and DEF,
respectively, under mild conditions at temperatures up to 105 °C.
Elemental CHN microanalysis and comparison of the experimental
and simulated powder XRD patterns (see Fig. S1 in the Supplemen-
tary Material) indicate that the bulk products are pure-phase
materials, corresponding to the formulations obtained by single-
crystal X-ray crystallography. However, TG analysis (see below) re-
vealed that the compounds are not completely free from solvent. It
should be noted that 1 and 2 are not stable in air, in vacuum or un-
der an inert Ar atmosphere. The clear crystals slowly (on the time-
scale of hours) become opaque when not protected under DMF or
DEF. The decomposition process is more rapid for 2. So, the origin
of the instability of the materials seems to be the partial loss of
coordinating formamide molecules.
TG measurements reveal similar thermal behaviour of 1 and 2
(Fig. 1). The first endothermic mass losses of 2.0% (for 1) and
5.4% (2) at temperatures up to 100 °C are ascribed to non-coordi-
nated DMF or DEF crystal solvent. The following endothermic mass
losses result in a clear plateau at 200 °C (1) or 225 °C (2), respec-
tively, and correspond to the release of the DMF (1) and DEF (2)
molecules (exp./calc. mass loss after correction for the desolvation
step: 20.0/19.6% for 1; 24.0/25.3% for 2). The formamide-free mate-
rials, 1-DMF and 2-DEF, remain stable up to a temperature of ca.
310 °C. Above this temperature exothermic decomposition of the
organic moieties takes place at temperatures up to 510 and
570 °C, respectively (exp./calc. mass loss: 69.0/69.4% for 1; 66.4/
64.9% for 2). In both cases, the residue was identified as ZnO by
powder XRD.
Fig. 2. Molecular structures of 1 (a) and 2 (b). Atomic labelling is given for the
atoms in the asymmetric units. Hydrogen atoms are omitted. Displacement
ellipsoids correspond to the 50% probability level. For the twofold disordered
atoms (C17, C18) in 1, only one position (C17A, C18A) is shown, respectively. Colour
code: green, zinc; black, carbon; blue, nitrogen; red, oxygen.
ported when considering all bond lengths and angles in the coordi-
nation spheres of the Zn cations (see Table 2). Additionally, the two
coordinating carboxylate groups take in quite different relative ori-
entations in 1 and 2; their planes are tilted against each other by an
angle of 57.5(4)° and 21.4(5)°, respectively. The bridges
(O2C[PEP(hexyl)2EP]CO2)2À possess Ci symmetry. The lengths of
the central C10–C11 triple bonds and adjacent single bonds (see
Table 2) are in good agreement with reported values [16].
The resulting zigzag coordination chains propagate along [1 0 1]
and are arranged side-by-side into layers parallel (1 0 1) from
which the hexyl side chains of the (O2C[PEP(hexyl)2EP]CO2)2À
bridges and the formamide molecules extend in up and down
directions (Fig. 3), thereby filling the inter-layer spaces which
are generated by the stacking of such layers along [1 0 4] (Fig. 4).
3.2. Crystal structures and IR spectra of 1 and 2
Compounds 1 and 2 both crystallise in the space group C2/c and
are isostructural. The crystals consist of uncharged one-dimen-
sional coordination polymers in which [Zn(formamide)2]2+ frag-
ments are bridged by (O2C[PEP(hexyl)2EP]CO2)2À ligands.
The one crystallographically distinct Zn cation sits on a C2 axis
and is coordinated by two carbonyl oxygen atoms from two form-
amide molecules and two carboxylate groups from two bridging li-
gands (Fig. 2). In 2, the binding mode of the carboxylate groups is
monodentate (bond lengths: Zn–O1 = 1.919(2) and Zn–O3 = 2.899
(2) Å), resulting in a slightly distorted tetrahedral coordination
geometry at the Zn centre. A somewhat different situation is found
in 1 where the carboxylate groups coordinate in a semi-chelating
fashion (bond lengths: Zn–O1 = 2.033(3) and Zn–O3 = 2.436(3) Å),
and thus the environment around the Zn centre may be described
as a distorted octahedral [4 + 2] coordination. This view is sup-
Table 2
Selected bond lengths (Å) and angles (°) for {Zn(O2C[PEP(hexyl)2EP]CO2)(DMF)2} (1)
and {Zn(O2C[PEP(hexyl)2EP]CO2)(DEF)2} (2).
1
2
Zn–O1
Zn–O3
Zn–O21
O1–C2
2.033(3)
2.436(3)
2.004(2)
1.259(5)
1.237(5)
92.2(2)
1.919(2)
2.899(2)
1.965(2)
1.298(4)
1.226(3)
104.2(1)
50.20(8)
152.91(8)
114.44(9)
108.10(8)
156.51(9)
80.55(7)
85.65(8)
107.7(1)
123.9(9)
1.453(4)
1.183(4)
1.436(4)
O3–C2
O1–Zn–O1#1
O1–Zn–O3
O1–Zn–O3#1
O1–Zn–O21
O1–Zn–O21#1
O3–Zn–O3#1
O3–Zn–O21
O3–Zn–O21#1
O21–Zn–O21#1
O1–C2–O3
C7–C10
57.7(1)
130.8(1)
135.9(1)
96.4(1)
170.0(1)
85.0(1)
89.0(1)
106.6(1)
122.3(4)
1.437(5)
1.197(5)
1.440(5)
C10–C11
C11–C12
Fig. 1. TG curves for 1 (solid line) and 2 (dotted line) measured in dynamic air
atomsphere.
Symmetry code: #1 Àx, y, Àz + 1/2.

A. Schaate et al. / Inorganica Chimica Acta 362 (2009) 3600–3606
3603
Adjacent layers are related by inversion centres. When the struc-
tures are viewed along the b axis one-dimensional channels are
seen which are filled with the formamide molecules (Fig. 4).
Due to the different volumes of the formamide ligands the
interactions, the conformations with the O2C[PEP(hexyl)2EP]CO2)2À
moieties are different. These are flat entities in 1, whereas the cen-
tral benzene ring of 2 is tilted by an angle of 19.3(2)° with respect to
the neighbouring benzene rings (Fig. 4).
coordination chains of
1
and
2
have different intra-chain
In the IR spectra of 1 and 2 asymmetric and symmetric stretch-
ing vibrations of carboxylate groups are seen with mas (1 and 2) at
ZnÁ Á ÁZnÁ Á ÁZn angles (132.51° in 1, 115.44° in 2) and thus different
periodicities (44.963 Å in 1, 41.581 Å in 2). This is clearly reflected
by the length of the crystallographic a axes (compare the crystal
data in Table 1). An analysis of the interatomic distances indicates
that the inter-chain interactions are dominated by van der Waals
forces between the benzene rings and the alkyl groups (i.e., the hex-
yl and methyl or ethyl groups). The different inter-layer distances,
which are slightly larger in 1 than in 2, obviously force the hexyl
chains to adopt different bent conformations, in which the carbon
atoms partly exhibit large displacement parameters and, in the case
of 1, some positional disorder indicating considerable mobility of
the alkyl groups even at À60 °C (the temperature of the single-crys-
tal XRD measurements). Recently, bent conformations of hexyl side
chains have been also observed in the crystal structures of some
functionalized OPEs [17]. In 1 and 2, also effected by intermolecular
1539 cmÀ1 msy (1) at 1375 cmÀ1 and msy (2) at 1352 cmÀ1. The dif-
,
ferences between the wavenumbers of the stretching vibrations,
D
=
mas
À
m
sy, of 164 cmÀ1 (for 1) and 187 cmÀ1 (2) are significantly
larger than the difference of 144 cmÀ1 determined for {K2(O2C[PE-
P(hexyl)2EP]CO2)}. According to known correlations [18], this find-
ing indicates a monodentate coordination of the carboxylate
groups to the Zn centres which is in agreement with the crystal
structures. Furthermore, the lower
D value for 1 is in line with a
tendency towards a semi-chelating coordination mode as found
in the crystal structure of 1. The characteristic bands mas(CO) of
the formamide molecules appear at 1653 cmÀ1 (DMF) and
1643 cmÀ1 (DEF) in the IR spectra. The absence of the characteristic
band
mas(CO) of the free acid HO2C[PEP(hexyl)2EP]CO2H at
1719 cmÀ1 confirms complete deprotonation.
Fig. 3. Crystal structures of 1 (a) and 2 (b). Side-by-side arrangement of the zigzag coordination chains in a layer parallel (101) as viewed normal to the layer. Colour code:
green, zinc; black, carbon; blue, nitrogen; red, oxygen.

3604
A. Schaate et al. / Inorganica Chimica Acta 362 (2009) 3600–3606
Fig. 4. Crystal structures of 1 (a) and 2 (b) as viewed parallel to the b axis showing the stacking of layers along [1 0 4]. The black ellipses indicate cross-sections of the
channels along the b axis which are filled with coordinating DMF or DEF molecules. Colour code: green, zinc; black, carbon; blue, nitrogen; red, oxygen.
3.3. Powder X-ray diffraction patterns and IR spectra of 1-DMF and 2-
XRD pattern of 2-DEF at 5.7° 2H which is not related to any reflec-
DEF
tion in the pattern of 2 and most likely indicates the appearance of
an additional solid phase.
The formamide-free materials 1-DMF and 2-DEF were prepared
by heating samples of as-synthesised 1 and 2 in an oven to 200 °C
for 40 min. In Fig. 5, the XRD patterns are compared with those of
the parent compounds. It can be seen that crystallinity was lost in
both cases but that partial ordering still remains which is signifi-
cantly more pronounced for 1-DMF. Clearly, the non-covalent
interactions between the coordination chains are too weak to
maintain a periodic ordering after removal of the formamide mol-
ecules. The two peaks seen in both XRD patterns being centred at
ca. 4.3° and 8.5° 2H obviously correspond to the 200 and 400
reflections of 1 and 2, indicating that the coordination polymers re-
main intact in 1-DMF and 2-DEF and that their structural arrange-
ment is related to that in
1 and 2. From the 2H values
characteristic lengths of 41.30 and 40.00 Å (at 24 °C) were esti-
mated for 1-DMF and 2-DEF, respectively, which reveal that the
chains differ in their periodicity despite of the same chemical com-
position of the materials. By comparison of the characteristic
lengths with the lengths of the crystallographic a axes of 1
(40.76(2) Å, 24 °C) and 2 (38.83(2) Å, 24 °C) it is further inferred
that the chains in the formamide-free compounds possess larger
intra-chain ZnÁ Á ÁZnÁ Á ÁZn angles than in the corresponding parent
compounds. An additional peak of low intensity is seen in the
Fig. 5. Powder XRD patterns for 1 (a), 1-DMF (b), 2 (c) and 2-DEF (d); CuKa1
radiation.

A. Schaate et al. / Inorganica Chimica Acta 362 (2009) 3600–3606
3605
mers with interesting properties (e.g., photoluminescence). Most
likely due to the presence of the long hydrophobic hexyl substitu-
ents at the central benzene rings the dimensionality of the coordi-
nation compounds 1 and 2 is limited to chains. The construction of
porous coordination polymers with three-dimensional frameworks
likely requires the introduction of OPE polycarboxylates with
shorter alkyl substituents. Such work is currently underway in
our laboratories.
Acknowledgements
The authors thank Birgit Beisse and Falk Heinroth for perform-
ing TG/DTA measurements and the reviewers for valuable
comments.
Appendix A. Supplementary material
CCDC 677224 and 677225 contain the supplementary crystallo-
graphic data for compounds 1 and 2. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Fig. 6. Photoluminescence emission spectra for 1 (blue solid line), 1-DMF (blue
dotted line), 2 (red solid line), 2-DEF (red dotted line), (HO2C[PEP(hexyl)2EP]CO2H)
(black solid line) and [K(O2C[PEP(hexyl)2EP]CO2)K} (black dotted line) recorded
upon excitation at 310 nm.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2009.04.004.
In the IR spectra of 1-DMF and 2-DEF stretching vibrations of
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,
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