Luminescent coordination polymers based on self-assembled cadmium dipyrrin complexes

Article abstract of DOI:10.1002/chem.201203133

A series of novel Cd^II complexes based on α,β- unsubstituted dipyrrin ligands (dpm) has been prepared and characterised both in solution and in the solid state. These compounds are of the [Cd(dpm) ₂] type, with the coordination sphere of the metal centre occupied by two dpm chelates. Interestingly, in contrast to what has been reported for the Zn^II analogues, in the presence of a pyridyl- or imidazolyl-appended dpm ligand, the coordination number of the Cd^II cation can be increased to six, leading to an octahedral coordination sphere. As a consequence, the formation of 1-, 2-, and 3D coordination polymers by self-assembly is observed. Photophysical investigations of the discrete complexes and self-assembled networks have demonstrated that both types of compounds are luminescent in the solid state. Let's go down the column! The first [Cd(dpm)₂] complexes based on α,β-unsubstituted dipyrrin ligands (dpm) have been prepared and characterised in both solution and the solid state. The coordination sphere of the metal centre, occupied by two dpm chelates, may be extended with additional pyridyl or imidazolyl groups, unlike what has been reported for the Zn^II analogues. This leads to self-assembly of these species into 1-, 2-, and 3D coordination polymers, which display luminescence in the crystalline state (see figure). Copyright

Full text of DOI:10.1002/chem.201203133

FULL PAPER
DOI: 10.1002/chem.201203133
Luminescent Coordination Polymers Based on Self-Assembled Cadmium
Dipyrrin Complexes
Antoine Bꢀziau, Stꢀphane A. Baudron,* Aurꢀlie Guenet, and Mir Wais Hosseini*[a]
Abstract: A series of novel CdII com-
plexes based on a,b-unsubstituted di-
pyrrin ligands (dpm) has been prepared
and characterised both in solution and
in the solid state. These compounds are
ported for the ZnII analogues, in the
presence of a pyridyl- or imidazolyl-ap-
pended dpm ligand, the coordination
number of the CdII cation can be in-
creased to six, leading to an octahedral
coordination sphere. As a consequence,
the formation of 1-, 2-, and 3D coordi-
nation polymers by self-assembly is ob-
served. Photophysical investigations of
the discrete complexes and self-assem-
bled networks have demonstrated that
both types of compounds are lumines-
cent in the solid state.
of the [CdACHTUNGTRENNUNG(dpm)2] type, with the coor-
Keywords: cadmium · coordination
polymers · dipyrrin · luminescence ·
self-assembly
dination sphere of the metal centre oc-
cupied by two dpm chelates. Interest-
ingly, in contrast to what has been re-
Introduction
lar AgI.[10,11] As regards homometallic analogues, the metal-
latectons are based on metal complexes bearing self-comple-
Over the past two decades, the field of coordination net-
works, also called coordination polymers (CPs) or metal–or-
ganic frameworks (MOFs), has been the subject of intense
research activity fuelled by their applications in gas storage,
sensing, separation, catalysis, and magnetism, among
others.[1] MOFs are also appealing as novel luminescent ma-
terials.[2] Indeed, in these species, resulting from the self-as-
sembly of metal centres and organic tectons,[3] the emission
properties can be generated by either the inorganic or or-
ganic components, as well as by metal–ligand charge-trans-
fer processes or by the presence of guest molecules in the
frameworks. The majority of the reported luminescent CPs
are based on ZnII, CdII, AgI, or lanthanide ions assembled
with polycarboxylate- or pyridyl-based tectons.[2] Interesting-
ly, to the best of our knowledge, no luminescent infinite
crystalline architectures based on dipyrrins (dpms)[4] have
hitherto been described. This is surprising, considering that
several discrete luminescent dpm complexes have been re-
ported, most of which are ZnII-based species,[5–8] along with
bispyrrolic-based homo- and heterometallic CPs.[9–12] Het-
mentary hydrogen-bonding groups[12] or [Cu
ACTHNGUTRE(NNUG acac-R)ACHTUNGTRENNUNG(dpm-
R’)] species (acac-R=functionalised acetylacetonate deriva-
tive) with functionalised monodipyrrin ligands capable of
self-assembly to form extended architectures by coordina-
tion.[11] Although one example of a luminescent nanoscale
architecture derived from the combination of ZnII cations
with divergent bisdpms has been reported,[5d] no self-assem-
bled Zn-based networks with monodpm have hitherto been
described. This may be related to the fact that, unlike what
is observed for Zn porphyrins, the metal cation in [Zn-
AHCTUNGRTEG(NNUN dpm)2]-type complexes has not been reported with a coor-
dination number greater than four (Figure 1).[6] For example,
Zn complexes of dpms 1–4 (Scheme 1) were found to crys-
tallise as discrete complexes with or without a peripheral co-
ordinating group (Figure 1b).[6,13] Furthermore, upon addi-
tion of excess pyridine or 1-methylimidazole to [Zn(1)2], no
binding of these ligands to the ZnII centre could be detected
by NMR spectroscopy in CDCl3 (Figure 1a).[6] In contrast,
the chemistry of dpm-based CdII complexes is almost unex-
plored, and some of the few reported examples of such spe-
cies incorporating a-substituted dpms show a coordination
number higher than four for the cadmium cation.[14] This
ACHTUNGTRENNUNGeroACHTUNGTRENNUNGmetallic dpm-based networks result from the association
of metallatectons bearing coordinating groups at the periph-
ery of the dpm moieties with other metal centres, in particu-
suggests that, unlike for [Zn
centre in [Cd(dpm)2] species may be capable of penta- or
(dpm)2] compounds, the CdII
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
hexacoordination in the presence of additional coordinating
groups (Figure 1). It is worth noting that the latter can be in-
troduced either independently, leading to discrete species
(Figure 1a) or at the periphery of the dpm moiety, thus pro-
moting self-assembly into infinite architectures (Figure 1b).
In addition, in light of the reported photophysical properties
of the Zn compounds,[5,6] luminescence can be anticipated
for the Cd analogues.
[a] A. Bꢀziau, Dr. S. A. Baudron, Dr. A. Guenet, Prof. M. W. Hosseini
Laboratoire de Chimie de Coordination Organique
UMR UdS-CNRS 7140, Institut Le Bel, Universitꢀ de Strasbourg
4 rue Blaise Pascal, CS 90032, 67081 Strasbourg cedex (France)
Fax : (+33)3-68-85-13-25
E-mail: sbaudron@unistra.fr
hosseini@unistra.fr
We report herein the synthesis and characterisation in so-
ACHUTNGRENlNUG uACTHUNGRTENtUNG ion and in the solid state of a,b-unsubstituted dipyrrin
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203133.
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Results and Discussion
Design:
Dipyrrins
1–4
(Scheme 1) were chosen as li-
gands for the synthesis of [Cd-
AHCTUNRTGEG(NNNU dpm)2] complexes. Derivative
1 consists of a dpm chelate and
a mesityl peripheral group. Al-
though this latter moiety is not
a coordinating unit, it has been
shown that the presence of
methyl groups in the ortho posi-
tions hinders rotation of the pe-
ripheral group with respect to
the chelate, which disfavours
non-radiative deactivation path-
ways, thus enhancing the emis-
sive properties of such com-
plexes.[8] Ligands 2–4 are based
on a dpm core appended with
peripheral coordinating groups,
namely cyanophenyl, pyridyl,
and phenylimidazolyl groups.
The coordinating ability of the
cyano group is expected to be
weaker than those of the other
two peripheral units. Further-
more, in ligand 4, the imidazol-
ꢀ
Figure 1. Schematic representation of the effects of the presence of additional coordinating units either a) as
an external ligand or b) at the periphery of the dpm as reported previously[6] for [Zn
(dpm)2] complexes and as
expected for [Cd(dpm)2] derivatives.
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
CdII complexes, with a particular emphasis on the use of
these compounds as metallatectons for the preparation of
luminescent coordination polymers.
yl group can rotate about a C N bond, offering more orien-
tational possibilities compared to 2 or 3. As a consequence,
one might anticipate that complexes 5 and 6 will be less
Scheme 1. Representations and compound numbers of the dipyrrin ligands and their Cd complexes.
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Luminescent MOFs Based on Cadmium Complexes
FULL PAPER
prone to self-assembly into CPs than 7 and 8 bearing stron-
ger binding moieties at their periphery.
Synthesis and characterisation in solution: Dipyrrins 1–4
were prepared as described previously[8b,15] and reacted with
CdACHTUNGTRENNUNG(OAc)2 in the presence of NEt3 to afford complexes 5–8
in yields of 48–88%. Although complexes 5 and 6 proved to
be soluble in common organic solvents, compounds 7 and 8
were found to be only sparingly soluble in MeOH, DMF,
and DMSO, suggesting the formation of oligomeric species
by self-assembly through coordination of the peripheral pyr-
idyl or imidazolyl groups.
Crystallisation of 6 by Et2O vapour diffusion into a solu-
tion of the complex in pyridine afforded large single crystals
of the pyridyl adduct [(Py)2(6)], 9. Interestingly, both the cis
and trans isomers of 9 could be isolated (see below).
NMR studies, elemental analysis, and structural investiga-
tions (see below) unambiguously demonstrated the forma-
Figure 2. Evolution of the absorption spectrum of complex 5 in a 4.9ꢂ
10ꢀ5 m solution in toluene at room temperature over 24 h.
tion of the [Cd
(dpm)2] complexes. For example, in the milli-
(Figure S5 in the Supporting Information). These observa-
tions clearly indicate either dissociation of the [CdACHTUNGTRENNUNG(dpm)2]
1
molar range, distinct H NMR spectra were obtained for the
free dipyrrins 1 and 2 compared to those of the correspond-
ing Cd complexes 5 and 6 in CDCl3 (Figures S1 and S3 in
the Supporting Information). Furthermore, DOSY NMR ex-
periments performed in [D8]toluene on the free ligands 1
and 2 and the CdII complexes 5 and 6 clearly demonstrated
the presence of a single species in solution in all four cases.
The observed spectra were clearly different for the free li-
gands and the corresponding complexes (Figures S2 and S4
in the Supporting Information). It is nevertheless worth
noting that Lindsey et al., on the basis of UV/Vis spectro-
scopic data, concluded that the reaction of 5-phenyldipyrrin
complexes or their transformation into other species in tol-
uene. Considering the non-coordinating and apolar nature
of this solvent, the observed phenomenon is surprising.
However, a possible explanation may be the presence of
traces of water.
Crystal structure: Crystals of 5 were obtained by slow evap-
oration of the solvent from a solution of the complex in
¯
Et2O. It crystallises in the triclinic space group P1 with one
molecule in a general position and a disordered Et2O sol-
vate molecule at an inversion centre. The cadmium cation is
in a distorted tetrahedral coordination environment with an
angle of 75.48 between the planes of the two dpm chelates
(Figure 3a), similar to the reported structure of the zinc ana-
logue.[6] As observed for other complexes bearing peripheral
mesityl groups, the latter are almost perpendicular to the
with CdACHTUNGTRENNUNG(OAc)2 in the presence of NEt3 in MeOH does not
afford the expected CdII complex.[5a] This statement was sub-
stantiated by the similarity of the UV/Vis spectra of the re-
action mixture and the free dpm ligand. In the micromolar
range, as usually used for UV/Vis studies, we found that the
bispyrrolic system (78.6 and 87.48).[8] The Cd N bond
ꢀ
prepared [Cd
N
in toluene. Indeed, the spectra of freshly prepared solutions
of the complexes, obtained by dissolving single crystals, ini-
tially featured two strong ab-
sorption bands at 463 and
483 nm (Figure 2 and Figure S5
in the Supporting Information)
corresponding to p–p* transi-
tions, as observed for other di-
pyrrin metal complexes.[5–12]
However, as shown in Figure 2
for complex 5, over the course
of 24 h, these two bands vanish-
ed and were replaced by a band
at around 430 nm correspond-
ing to the absorption of the free
dpm ligand 1. The conversion
of the complex into the free
ligand gives rise to spectral
lengths (Table 1) are similar to those reported for dipyrrin
and tripyrrin complexes of CdII.[14,16]
changes with isosbestic points.
Figure 3. Crystal structures of complexes a) 5, b) 6, c) trans-9, and d) D-cis-9. Hydrogen atoms and solvent mol-
The same holds for complex 6 ecules have been omitted for clarity. For bond lengths, see Table 1.
Chem. Eur. J. 2013, 19, 3215 – 3223
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S. A. Baudron, M. W. Hosseini et al.
Table 1. Selected average bond lengths [ꢃ] for complexes 5–9.
The structural investigation of these compounds illustrat-
ed that the CdII centre can form complexes with coordina-
tion numbers from four to six in the presence of coordinat-
ing groups capable of serving as auxiliary ligands, in addition
to the dpm chelates. It is striking that the coordination ar-
rangements in 5 and 6 differ in the orientation of the che-
ꢀ
ꢀ
ꢀ
Cd Ndpm
Cd Npy/Cd Nimid
5
6
2.180
2.226
2.307
2.273
2.275
2.250
2.258
2.305
–
–
trans-9
L-cis-9
D-cis-9
7·MeOH
7
2.448
2.551
2.553
2.447
2.579
2.438
ꢀ
lates while still retaining similar Cd N bond lengths. This
suggests a rather adaptable coordination sphere of the metal
centre in these species. Furthermore, no self-assembly of
complex 6 into an extended architecture was observed, de-
spite the presence of the peripheral nitrile groups. This fea-
8
Crystals of 6 were obtained upon vapour diffusion of n-
ture has previously been observed for [CuACTHNGUTERNNUG
(acac)(2)].[11a]
pentane into a solution of the complex in CHCl3. It crystal-
ACHTUNGTRENNUNGlises in the monoclinic space group C2/c with a complex on
Nevertheless, upon reaction of complex 6 with pyridine,
both cis and trans isomers of 9 could be isolated.
a two-fold axis. The Cd cation is tetracoordinated in a pseudo-
tetrahedral environment with an angle of 42.88 between the
two chelates (Figure 3b). Interestingly, this arrangement is
more similar to the reported structure of [Cu(2)2] than that
Upon recrystallisation of the as-synthesised complex 7
from hot MeOH, crystals of the methanol solvate
(7·MeOH) were obtained. It crystallises in the orthorhombic
Fdd2 space group with one complex and one solvent mole-
cule in general positions. The Cd cation is coordinated by
the two dpm chelates and one peripheral pyridyl group of a
neighbouring complex (Figure 4). This leads to the forma-
of 5.[11a] As observed for heteroleptic [Cu
ACTHNUTRGNEUNG(acac)(2)], the ni-
trile group is not coordinated to the metal centre.
Upon slow diffusion of Et2O vapour into a solution of 6
in pyridine, crystals of 9 were obtained, in which the Cd
centre is in an octahedral coordination environment com-
posed of two dipyrrin chelates and two monodentate pyri-
dine ligands. Both the cis and trans isomers of this com-
pound could be isolated. Complex trans-9 crystallises in the
ꢀ
ꢀ
tion of a 1D chain along the c axis. The Cd Ndpm and Cd
Npy distances are similar to those observed in trans-9. The
second pyridyl group forms a hydrogen bond with the meth-
ꢀ
anol
solvate
molecule
(OHN=149.68;
O H···N=
2.773(12) ꢃ).
¯
triclinic P1 space group with
one molecule at an inversion
centre (Figure 3c). The two bis-
pyrrolic ligands coordinate the
Cd cation in a square-planar ar-
ꢀ
rangement, with Cd Ndpm dis-
tances longer than those ob-
served in 5 and 6 (Table 1). As
observed for square-planar di-
pyrrin complexes, the pyrrolic
rings are not coplanar within
the chelate as a result of repul-
sion between the a-CH hydro-
gen atoms of the dpm li-
gands.[8d,12d,e] Two pyridine li-
gands occupy the axial positions
around the metal cation. Unlike
the trans analogue, the cis
isomer is chiral. In the analysed
crystals, only one enantiomer
(either D or L, see Table 3) was
found to be present and the
Figure 4. One-dimensional coordination polymer in the structure of 7·MeOH. For clarity, only the OH hydro-
gen atoms are presented. For bond lengths, see Table 1 and the text.
whole batch was a conglomerate. Indeed, the cis isomer
crystallises in the chiral monoclinic space group P212121 with
one enantiomer of the complex in a general position (Fig-
Interestingly, upon recrystallisation of 7 from hot DMF,
crystals of the non-solvated compound were obtained
(Figure 5). It crystallises in the monoclinic C2/c space group
with one complex on a two-fold axis. The CdII centre is in a
slightly distorted octahedral environment made up of two
dpm chelates and two pyridyl groups, in a cis configuration,
belonging to neighbouring complexes. This leads to the for-
mation of a 2D sheet. Interestingly, each 2D layer is homo-
chiral containing either the L- or D-enantiomer (Figure 5).
ꢀ
ꢀ
ure 3d). The Cd Ndpm and Cd Npy bond lengths were found
to be slightly shorter in the cis isomer than in the trans
isomer (Table 1). It is, however, interesting to note that the
ꢀ
Cd Npy bond lengths are longer than those reported for
structures of Cd porphyrin complexes with an axially coordi-
nated pyridine ligand.[17]
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Luminescent MOFs Based on Cadmium Complexes
FULL PAPER
observed in 7 resulting from the
unusual positioning of the pyr-
idyl groups.
Photophysical properties: The
dissociative behaviour observed
for complexes 5 and 6 ham-
pered thorough investigation of
the emissive properties of these
species in solution, since such
studies are normally performed
under dilute conditions (at con-
centrations below 10ꢀ6 m) and
require rather long preparation
times for degassing of the solu-
tions. Preliminary investigations
were performed by examining
solutions immediately after
Figure 5. Homochiral 2D arrangement formed by the L-enantiomers of 7. Hydrogen atoms have been omitted
for clarity. For bond lengths, see Table 1.
These sheets stack in an alternating DLDL fashion, thus
leading to an internal racemate (Figure S6 in the Supporting
their preparation. Upon excitation at 480 nm, both com-
plexes 5 and 6 showed an emission band at 515 nm, distinct
from that of the free ligand 1 (500 nm, F=0.0026; Figure S7
in the Supporting Information). This may have been due to
the presence of a small amount of an emissive complex in
the micromolar range.
ꢀ
Information). The Cd N bond lengths are similar to those
observed in cis-9 (Table 1). It is worth noting, however, that
the pyridyl groups are tilted away from their expected posi-
tions for an octahedral environment.
Crystallisation of the as-synthesised complex 8 from hot
DMSO afforded large crystals of the compound. It crystal-
In the solid state, the absorption spectra of the coordina-
tion polymers 7, 7·MeOH, and 8 feature similar bands
ACHTUNGTRENNUNGlises in the monoclinic Cc space
group with one complex in a
general position. Several disor-
dered DMSO molecules are
present in the crystal. Owing to
the high degree of disorder, the
SQUEEZE command was ap-
plied.[18] As in the structure of
7, the Cd cation is in an octahe-
dral environment with two dpm
chelates and two imidazolyl
groups of neighbouring mole-
cules in
a cis arrangement
(Figure 6). This leads to a 3D
ꢀ
coordination polymer. The Cd
Ndpm bond lengths are analo-
gous to those in 5–7 and 9,
ꢀ
whereas the Cd Nimid bond
lengths are slightly shorter than
ꢀ
the Cd Npy distances in 7 and 9
and shorter than that in the re-
ported structure of a Cd por-
phyrin with an axially coordi-
nated benzimidazole group.[19]
The presence of
a
phenyl
spacer between the dpm chelate
and the peripheral imidazolyl
group, as well as the possibility
of rotation of the latter unit
ꢀ
about a C N bond, seems to al-
leviate some of the deformation Cd cation. Hydrogen atoms have been omitted for clarity. For bond lengths, see Table 1.
Figure 6. a,b) Two views of the 3D coordination polymer in 8 and c) the coordination environment around the
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S. A. Baudron, M. W. Hosseini et al.
Table 2. Photophysical data for compounds 1, 2 and 5–8.
the mesityl analogue 5, structural investigation has revealed
that the metal centre is in a tetrahedral coordination sphere
composed solely of two dpm ligands. However, upon recrys-
tallisation of complex 6 from pyridine, an octahedral envi-
ronment is observed. Both the cis and trans isomers of the
bispyridyl adduct [(Py)2(6)] (complex 9) have been isolated
and characterised by X-ray diffraction analysis. Upon the in-
troduction of additional coordinating units at the periphery
of the dpm itself, as in the pyridyl- and imidazolyl-appended
derivatives 7 and 8, respectively, the formation of coordina-
tion polymers by self-assembly is observed. Interestingly, al-
labs [nm]
lem [nm]
in toluene at RT
1
438
500
no emission
–
–
2
433
5
6
463, 483
463, 483
in the solid state
7·MeOH
7
8
403, 491, 556
427, 494, 530
427, 494, 536
563, 628
563, 602
577, 616
though the coordination features of [Cd
ACHTUNGRTEN(NGNU dpm)2] complexes
(Table 2, Figure S8 in the Supporting Information). Upon
excitation at 430 nm, these compounds display two emission
bands (Table 2, Figure 7). Interestingly, complex 5 shows a
similar emission spectrum in the crystalline state (lem =577,
630 nm; Figure 7). These results suggest that the lumines-
differ from those of [Zn(dpm)2] species, these compounds
ACHTUNGTRENNUNG
are also luminescent in the crystalline state, regardless of
the coordination number of the CdII cation. To the best of
our knowledge, these compounds represent the first lumi-
nescent monodpm-based CPs. Future investigations will
focus on the use of other dpm ligands and external coordi-
nating groups such as chelates, and other metal centres.
Experimental Section
General: Dipyrrins 1–4 were prepared as described previously.[8b,11f,15] All
solvents were dried according to standard procedures. Other reagents
were obtained from commercial sources and used as received. 1H and
13C NMR spectra were acquired at 258C on Bruker AV 300 (300 MHz),
AV 400 (400 MHz), and AV 500 (500 MHz) spectrometers, utilising the
deuterated solvent as a lock and residual solvent as an internal reference.
NMR chemical shifts are given in ppm and referenced internally to the
residual solvent resonance. J values are given in Hz. Mass spectrometry
was performed at the Service Commun dꢄAnalyses, Universitꢀ de Stras-
bourg (France). UV/Vis spectra in solution and in the solid state were re-
corded on a Perkin–Elmer Lambda 650S spectrophotometer.
Synthesis of 5: A solution of CdACHTNUTRGNENG(U OAc)2 (127 mg, 0.48 mmol) in MeOH
(20 mL) was added to a solution of dipyrrin 1 (250 mg, 0.95 mmol) in
CHCl3 (20 mL) and the mixture was heated at reflux for 48 h. After
evaporation of the solvents under vacuum, the residue was re-dissolved
in CH2Cl2 (150 mL) and the solution was washed with water (3ꢂ50 mL).
The organic phase was concentrated to afford compound 5 as a dark-red
solid (223 mg, 0.35 mmol, 74%). Single crystals were obtained by slow
evaporation of the solvent from a solution in Et2O. 1H NMR (400 MHz,
CDCl3, 208C): d=2.13 (s, 12H), 2.37 (s, 6H), 6.36 (dd, J=1.0, 4.2 Hz,
4H), 6.55 (d, J=3.4 Hz, 4H), 6.93 (s, 4H), 7.55–7.57 ppm (m, 4H);
13C NMR (125 MHz, CDCl3, 208C): d=20.0, 21.3, 117.3, 127.8, 128.6,
134.5, 136.7, 137.4, 141.0, 142.8, 145.1 ppm; elemental analysis calcd (%)
for C78H78Cd2N8O: C 67.90, H 5.85, N 8.34; found: C 66.95, H 5.61, N
8.31.
Figure 7. Solid-state emission spectra (lexc =430 nm) of compounds 5, 7,
7·MeOH, and 8.
cence is ligand-centred and that the coordination number of
the CdII cation has no effect on the emission given that 7
and 7·MeOH show similar luminescence properties. Prelimi-
nary investigations have indicated that the quantum yield of
the luminescence in the solid state is below 1%. However,
to the best of our knowledge, these self-assembled CdII com-
plexes represent the first examples of luminescent mono-
Synthesis of 6: A solution of dipyrrin 2 (400 mg, 1.63 mmol) in CHCl3
(40 mL) was mixed with a solution of CdACHTNUTRGNEUNG(OAc)2 (216 mg, 0.82 mmol) in
ACHTUNGTRENNUNGdpm-based crystalline coordination polymers.
MeOH (40 mL) containing NEt3 (1 mL). The reaction mixture was stir-
red for 48 h at 708C and then the precipitate was separated by centrifu-
gation, washed with methanol and dried under vacuum to afford complex
Conclusion
1
6 as an orange powder (409.5 mg, 0.68 mmol, 83%). H NMR (300 MHz,
CDCl3, 208C): d=6.47 (dd, J=1.5, 4.2 Hz, 4H), 6.55 (dd, J=0.7, 4.2 Hz,
4H), 7.62–7.65 (m, 8H), 7.75–7.78 ppm (m, 4H); 13C NMR (125 MHz,
CDCl3, 208C): d=112.6, 117.9, 118.6, 131.2, 131.3, 133.9, 141.1, 144.1,
146.2, 151.9 ppm; elemental analysis calcd (%) for C32H20CdN6: C 63.96,
H 3.35, N 13.98; found: C 63.69, H 3.43, N 13.93.
The first cadmium complexes of the type [CdACTHNURGTNEUNG(dpm)2] incor-
porating a,b-unsubstituted dipyrrins have been designed,
prepared, and characterised both in solution and in the solid
state. Unlike in their Zn analogues, the CdII cation bound
by two dpm chelates adopts a coordination number higher
than four in the presence of additional coordinating groups.
Indeed, for the cyanophenyl-appended complex 6 and for
Synthesis of 7: A solution of dipyrrin 3 (294 mg, 1.32 mmol) in CHCl3
(100 mL) was mixed with a solution of CdACTHNUTRGNENUG(OAc)2 (117 mg, 0.66 mmol) in
MeOH (30 mL) containing NEt3 (1 mL). A red precipitate appeared
after 10 min. The reaction mixture was stirred for 24 h at room tempera-
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Luminescent MOFs Based on Cadmium Complexes
FULL PAPER
Table 3. Crystallographic data for compounds 5–9.
(5)2·Et2O
6
7·MeOH
C29H24CdN6O C28H20CdN6
584.94 552.92
orthorhombic monoclinic
7
8
trans-9
L-cis-9
D-cis-9
formula
C76H78Cd2N8O C32H20CdN6
C36H26CdN8
683.05
monoclinic
Cc
C42H30CdN8
758.91
C42H30CdN8
759.17
orthorhombic
P212121
C42H30CdN8
759.17
orthorhombic
P212121
Mr [gmolꢀ1
]
1343.66
triclinic
600.97
monoclinic
C2/c
crystal system
space group
a [ꢃ]
b [ꢃ]
c [ꢃ]
triclinic
¯
¯
P1
Fdd2
C2/c
P1
8.93390(10)
11.8931(2)
16.7197(4)
103.5330(10)
94.8060(10)
106.5020(10)
1634.38(5)
1
20.3370(5)
13.3180(3)
10.7752(3)
19.7582(9)
55.481(3)
9.2647(4)
17.8073(4)
9.0579(2)
16.4457(4)
24.6972(5)
9.6072(2)
18.2223(4)
8.6261(2)
10.1861(4)
11.4066(2)
106.0510(10)
110.1300(10)
98.2980(10)
871.91(4)
1
11.8565(2)
16.4163(3)
17.9239(3)
11.8642(2)
16.4322(3)
17.9354(3)
a [8]
b [8]
120.0620(10)
118.0580(10)
107.7100(10)
g [8]
V [ꢃ3]
Z
2525.86(11)
4
10155.9(8)
16
2340.88(9)
4
4118.72(15)
4
3488.71(10)
4
3496.59(10)
4
T [K]
173(2)
0.702
42635
173(2)
0.899
21207
173(2)
0.895
36158
173(2)
0.962
9818
173(2)
0.560
67813
173(2)
0.670
41785
173(2)
0.669
23013
173(2)
0.668
27872
m [mmꢀ1
]
refls. coll.
ind. refls. (Rint
)
8671 (0.0399)
0.0324
3683 (0.0213) 7214 (0.0894)
2676 (0.0211) 11739 (0.0318) 4613 (0.0283) 10173 (0.0238) 8392 (0.0292)
R1 (I>2s(I))[a]
0.0248
0.0715
0.0274
0.0734
1.077
0.0599
0.1159
0.0885
0.0516
1.069
4
0.0213
0.0505
0.0235
0.0638
1.034
0.0269
0.0703
0.0284
0.0516
1.053
0.0199
0.0515
0.0202
0.0749
1.044
0.0276
0.0602
0.0375
0.0645
1.035
0.0257
0.0592
0.0351
0.0710
1.048
wR2 (I>2s(I))[a] 0.0829
R1 (all data)[a]
wR2 (all data)[a]
GoF
0.0401
0.0920
1.107
2
[a] R1 =ꢀj jFo jꢀjFc j j/ꢀjFo j ; wR2 =[ꢀw
(Fo ꢀFc2)2/ꢀwFo ]1/2
.
ture and the orange solid was separated by centrifugation, washed with
MeOH and Et2O, and dried under vacuum to afford (177 mg,
SQUEEZE command was applied owing to the presence of highly disor-
dered DMSO solvate molecules.[18] The anomalous dispersion coefficients
for 48Cd at the MoKa wavelength are 1.005 and 1.202 for Df’ and Df’’, re-
spectively. CCDC-899363 ((5)2·Et2O)), CCDC-899364 (6), CCDC-899365
(7·MeOH), CCDC-899366 (7), CCDC-899367 (8), CCDC-899368 (8),
CCDC-899369 (trans-9), CCDC-899370 (L-cis-9), and CCDC-899371 (D-
cis-9) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif..
7
0.53 mmol, 88%). Crystals of 7 were obtained by concentration of a satu-
rated solution in DMF at 1008C, whereas crystals of 7·MeOH were ob-
tained by evaporation of the solvent from a solution in MeOH. 1H NMR
(500 MHz, [D6]DMSO, 208C): d=6.32 (d, J=3.9 Hz, 4H), 6.35 (d, J=
3.9 Hz, 4H), 7.40 (dd, J=1.6, 4.3 Hz, 4H), 7.51 (brs, 4H), 8.66 ppm (dd,
J=1.6, 4.3 Hz, 4H); 13C NMR (125 MHz, [D6]DMSO, 208C): d=116.8,
124.9, 131.7, 140.2, 144.1, 147.9, 148.5, 150.6 ppm; elemental analysis
calcd (%) for C28H20CdN6: C 60.82, H 3.65, N 15.20; found: C 60.44, H
3.80, N 14.98.
Steady-state photophysical measurements: Quartz cells and spectropho-
tometric grade solvents were employed. Degassing was carried out by
several freeze–pump–thaw cycles. UV/Vis spectra were recorded on a
BioTek Instruments Uvikon XL double-beam UV/Vis spectrophotometer
and were baseline-corrected. Steady-state luminescence emission spectra
were recorded on a HORIBA Jobin–Yvon FL-3-22 Fluorolog spectro-
fluorimeter equipped with a 450 W xenon arc lamp. All emission and ex-
citation spectra were corrected for source intensity (lamp and grating)
and emission spectral response (detector and grating) by standard correc-
tion curves. Appropriate cut-off filters were employed to avoid second-
order scattering lines from the excitation source. Solid-state measure-
ments were performed on a Perkin–Elmer LS 55 spectrometer.
Synthesis of 8: A solution of dipyrrin 4 (91.2 mg, 0.32 mmol) in DMF
(3 mL) was mixed with a solution of CdACHTUNRGTNEUNG(OAc)2 (42.2 mg, 0.16 mmol) in
MeOH (3 mL) and then NEt3 (1 mL) was added. The reaction mixture
was stirred at room temperature. The precipitate obtained was separated
by centrifugation, washed with MeOH and dried under vacuum to afford
8 as a dichroic green–orange solid (52.4 mg, 0.08 mmol, 48%). Single
crystals were obtained by slow evaporation of the solvent from a saturat-
ed solution of the complex in [D6]DMSO at 808C. 1H NMR (500 MHz,
[D6]DMSO, 208C): d=6.35 (dd, J=0.9, 4.0 Hz, 4H), 6.42 (d, J=3.3 Hz,
4H), 7.16 (s, 2H), 7.49–7.52 (m, 8H), 7.74 (d, J=8.4 Hz, 4H), 7.85–7.86
(m, 2H), 8.36–8.38 ppm (m, 2H); 13C NMR (125 MHz, [D6]DMSO,
208C): d=116.4, 116.8, 117.9, 118.8, 130.0, 131.5, 136.6, 136.5, 138.8,
141.2, 150.1 ppm.
Quantum yield determination: Based on the method of Crosby and
Demas,[21] luminescence quantum yields were measured from optically
dilute solutions (absorbance value lower than 0.1 at the excitation wave-
length and above) by using fluorescein[22] in 0.1m NaOH (F=0.92) as a
standard.
Synthesis of 9: Vapour diffusion of Et2O into a solution of complex 6
(50 mg, 0.083 mmol) in pyridine (3 mL) afforded crystals of 9 (35 mg,
0.046 mmol, 55%). 1H NMR (500 MHz, CDCl3, 208C): d=6.44 (d, J=
4.1 Hz, 4H), 6.53 (d, J=4.1 Hz, 4H), 7.28–7.31 (m, 4H), 7.57 (s, 4H),
7.63–7.65 (m, 4H), 7.71 (tt, J=1.9, 7.6 Hz, 2H), 7.74–7.76 (m, 4H), 8.47–
8.49 ppm (m, 4H); 13C NMR (125 MHz, CDCl3, 208C): d=112.3, 117.6,
118.7, 124.1, 131.3, 131.4, 133.5, 136.7, 141.5, 145.2, 146.1, 150.0,
151.6 ppm; elemental analysis calcd (%) for C43H30CdN8: C 66.45, H
3.98, N 14.76; found: C 66.82, H 4.18, N 14.57.
Acknowledgements
Support from the Universitꢀ de Strasbourg, the C.N.R.S., the Institut
Universitaire de France, and the Ministꢅre de lꢄEnseignement Supꢀrieur
et de la Recherche (Ph. D. fellowship to A.B.) is gratefully acknowl-
edged. The assistance of Martine Heinrich, Dr. Bruno Vincent, and Dr.
Matteo Mauro (Universitꢀ de Strasbourg) in the photophysical and
NMR investigations is gratefully acknowledged. We thank Elliot Christ
for preliminary investigations.
X-ray diffraction: Data (Table 3) were collected on a Bruker SMART
CCD diffractometer by using MoKa radiation. The structures were solved
by using SHELXS-97 and refined by full-matrix least-squares fitting on
F2 using SHELXL-97 with anisotropic thermal parameters for all non-hy-
drogen atoms.[20] Hydrogen atoms were introduced at calculated positions
and not refined (riding model). In the structure of (5)2·Et2O, the diethyl
ether solvate molecule is disordered. In the case of the structure of 8, the
Chem. Eur. J. 2013, 19, 3215 – 3223
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3221

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Chem. Eur. J. 2013, 19, 3215 – 3223

Luminescent MOFs Based on Cadmium Complexes
FULL PAPER
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Received: September 4, 2012
Revised: November 19, 2012
Published online: January 16, 2013
Chem. Eur. J. 2013, 19, 3215 – 3223
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3223