Self-assembly of a bis-tridentate Py2S4 ligand and cadmium cation into 1- and 2-D coordination networks

Article abstract of DOI:10.1039/a900501c

Using a Py₂S₄ bis-tridentate ligand and Cd(II), 1- and 2-D coordination networks were obtained and characterised in the solid state; whereas a 1-D network was obtained using the cadmium(II) dichloride salt, a 2-D network was obtained

Full text of DOI:10.1039/a900501c

Self-assembly of a bis-tridentate Py2S4 ligand and cadmium cation into 1- and
2-D coordination networks†
Marielle Loï,a Ernest Graf,a Mir Wais Hosseini,*a André De Cianb and Jean Fischerb
a Laboratoire de Chimie de Coordination Organique and b Laboratoire de Cristallochimie et Chimie Structurale,
Université Louis Pasteur, F-67000 Strasbourg, UMR CNRS 7513, France. E-mail: hosseini@chimie.u-strasbg.fr
Received (in Basel, Switzerland) 18th January 1999, Accepted 16th February 1999
Using a Py2S4 bis-tridentate ligand and Cd(ii), 1- and 2-D
coordination networks were obtained and characterised in
the solid state; whereas a 1-D network was obtained using
the cadmium(ii) dichloride salt, a 2-D network was obtained
using a mixed chloride and tetrafluoroborate cadmium(ii)
salt; in the latter case, the inclusion of two CHCl3 molecules
within cavities formed by the organic and inorganic frag-
ments was observed.
The synthesis of 7 was achieved starting from chelidamic
acid 2, which was first transformed into 3.10 The latter was
reduced to 4.11 Pd(PPh3)4 catalysed coupling reaction of 4 with
1,4-phenyldiboronic acid12 in dry THF gave 5 in 65% yield.
Bromination of the latter using 33% HBr–AcOH afforded 6 in
61% yield. Finally, the treatment of 6 with NaSMe in dry THF
afforded 7 in 71% yield. The latter, in addition to spectroscopic
methods, was characterised by X-ray crystallography.
Upon slow diffusion at room temp. of a MeOH solution
containing CdCl2·xH2O into a CHCl3 solution of 7 (1 : 1 ratio of
Cd: 7), colourless crystals were deposited after 24 h. The X-ray
study‡ showed the following features (Fig. 1): the crystal I
(monoclinic) was composed of 7, Cd(ii), Cl2 anions, CHCl3 and
H2O molecules. 7, Cd(II) and Cl2 anions formed a neutral,
infinite 1-D coordination network (Fig. 2).
For some time now, intensive research on the design and
preparation of coordination networks or polymers has been
performed.1 Although, nearly all cases reported deal with bis- or
tris-monodentate systems,2 examples of coordination polymers
using bis-bidentate ligands have also been published.3,4 On the
other hand, only a few examples of characterised systems based
on bis-tridentate ligands are known.5,6
Depending on the definition of the assembling core, the 1-D
network (7Cd2Cl4)n thus obtained may be described in two
different ways. Considering the metallic core as a binuclear
Cd2Cl4 unit (Fig. 2), the network may be regarded as resulting
from the binding of two such units by the two PyS2 fragments
of 7 leading thus to the exo-tetranuclear Cd(ii) complex and the
repetition of the binding process leads to the 1-D coordination
network. The same system may be also described as resulting
from the bridging of consecutive exo-binuclear 7·Cd2 units by
two Cl2 anions, and the remaining other two Cl2 anions
behaving as ancillary ligands. For the ligand part, the pyridine
rings were tilted by 237.6 and 38.3° with respect to the phenyl
group. The CS and CN distances were roughly the same as those
observed for free 7. The coordination sphere around the Cd
cations was composed of one N atom (dNCd = 2.426 Å), two S
atoms (dSCd = 2.730, 2.747 Å) and three Cl2 anions. Among
the three Cl2 present, two of them were shared between two Cd
centres (dClCd = 2.591, 2.651 Å) whereas the third one was
acting as an ancillary ligand (dClCd = 2.511 Å). The coordina-
tion geometry around the metal centre was distorted octahedral
with S–Cd–S, Cl–Cd–Cl and N–Cd–Cl angles of 146.5, 172.0
and 175.2°, respectively. Within the Cd2…Cl4 unit, the Cd…Cd
distance was found to be 3.946 Å. The CHCl3 and H2O
molecules were localised between the 1-D chains.
The formation of coordination networks in the crystalline
phase takes place under self-assembly conditions which require,
on one hand, the reversible formation of the assembling core by
complexation processes and its translation and, on the other
hand, the conformity to the packing forces within the crystalline
phase. Thus, for simple coordination networks, the choice of the
two partners (metal, ligand) is the dominant feature. For porous
coordination networks, in addition to the two partners men-
tioned before, one should also take into account the guest
molecules initially occupying the pores. Owing to the fact that
tridentate centres form rather stable and non-labile complexes
with transition metals, the choice of the metal and the ligand is
not obvious and therefore, not many characterised examples are
available so far.
Here, we report the synthesis of a new bis-tridentate ligand
and its self-assembly into 1- and 2-D coordination polymers
using Cd(ii) cation.
The design of the linear bis-tridentate ligand 7 (Scheme 1) is
based on a combination of two pyridine moieties and four
thioether groups. The two tridentate ligands are interconnected
by a phenyl ring. Examples of other bis-tridentate ligands have
been reported.7
Dealing with the metal cation, it has been shown previously
that 1 forms a binuclear Cd(ii) complex in which the two metal
centres are bridged by two Cl2 anions.8 This type of doubly
bridged metal system has been reported for Co(ii)6b and for
Ni(ii) complexes.9
Interestingly, when instead of using CdCl2, a mixed Cl2 and
2
BF4 salt [CdCl(BF4)] was used, the same diffusion method
afforded after two days another type of colourless crystal. The
solid state analysis (Fig. 3)‡ showed that the crystal II was
composed of 7, Cd(ii) cations, Cl2 and BF42 anions, CHCl3 and
MeOH molecules. 7, Cd(ii) and Cl2 anions formed a cationic
infinite 2-D coordination network (Fig. 2). The latter may be
described as the result of mutual interconnection of the 1-D
coordination polymers described above through Cl2 anions
acting now as bridging ligands. In a sense, the poor coordination
ability of BF42 has created a Cl2 deficiency in the coordination
sphere of Cd(ii), made up for by an additional Cl2 bridging
interaction.
Z
Z
Y
N
N
X
N
X
Z
Z
1 X = CH2SEt, Y = H
2 X = CO2H, Y = OH
3 X = CO2Et, Y = Br
4 X = CH2OH, Y = Br
5 Z = OH
6 Z = Br
7 Z = SMe
Thus, the 2-D network may be regarded as the translation into
two different space directions of an assembling core which may
be defined [74Cd4Cl7]+ (Fig. 2). The charge neutrality being
Scheme 1
2
achieved by BF4 anions present in the lattice. Owing to the
aromatic nature of the ligand used, the 2-D network was
composed of cavities delimited in an alternating fashion by
† Dedicated to Professor John A. Osborn on the occasion of his 60th
birthday.
Chem. Commun., 1999, 603–604
603

Fig. 1 A section of the X-ray structure of the 1-D coordination network I formed between 7 and CdCl2. H atoms, anions and solvent molecules are not
presented for clarity.
2-D sheets, the CHCl3 molecules were included within the
Cl
Cl Cd
Cl
S
S
S
S
Cl
Cl
cyclophane type cavities composing the 2-D network.
In conclusion, using the N2S4 bis-tridentate ligand and Cd(ii),
1- and 2-D coordination networks were obtained and charac-
terised in the solid state. For the 2-D network the inclusion of
two CHCl3 molecules within cavities formed by the organic and
inorganic fragments was observed. Based on the same strategy,
the formation of magnetic networks using paramagnetic metal
cations is currently under investigation.
Cl
Cl
S
S
S
S
N
N
Cd
Cl
Cl
Cd
N
N
Cd
Cl
Cl
S
S
Cl
Cl
S
S
Cl Cd
N
N
Cd
Cl
Cl
Cd
N
N
Cd
Cl
S
N
S
Cl
Cl
Cl
S
N
S
Cl
S
S
N
S
S
Cl
Cl
Cl
Notes and references
Cl
Cl
S
S
N
S
S
Cl Cd
Cl
N
S
S
Cd
Cl
Cl
Cl
Cl
Cl
Cd
N
S
S
Cd
‡ Crystal data: I (colorless, 294 K), C12H14CdCl2NS2·CHCl3·2H2O, M =
575.09, monoclinic, a = 29.037(1), b = 8.4340(2), c = 22.5310(8) Å, b =
Cl
S
126.63(1), U = 4428(2) Å3, Z = 8, space group C2/c, Dc = 1.73 g cm23
,
S
S
Cl Cd
N
Cd
Nonius Kappa CCD, Mo-Ka, m = 1.785 mm21, 5315 data with I > 3s(I),
R = 0.056, Rw = 0.076.
Cl
Cd
N
Cd
Cl
Cl
S
II (colorless, 173 K), C24H28Cd2Cl3N2S4·BF4·2CHCl3·CH3OH, M =
1161.52, orthorhombic, a = 16.3181(4), b = 14.8660(3), c = 35.9037(8)
Å, U = 8709.7(6) Å3, Z = 8, space group Pbcn, Dc = 1.77 g cm23, Nonius
Kappa CCD, Mo-Ka, m = 1.764 mm21, 4036 data with I > 3s(I), R =
0.051, Rw = 0.061. CCDC 182/1173.
Fig. 2 Partial representation of the 1- and 2-D coordination polymers I and
II.
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Fig. 3 A section of the X-ray structure of the 2-D coordination network II
(see text). H atoms, anions and MeOH molecules are not presented for
clarity.
organic and inorganic fragments. For 7, the pyridine rings were
tilted by 230.7 and 32.2° with respect to the phenyl group. The
C–S and C–N distances were roughly the same as those
observed for the free 7 and for the above-mentioned 1-D
network. The coordination sphere around the Cd cations was
again composed of one N atom (average dNCd = 2.385 Å), two
S atoms (average dSCd = 2.697 Å) and three Cl2 anions.
Although all three Cl2, present in the coordination sphere of Cd
cation, adopted a bridging role between the metallic centres,
two of them were shared between two Cd centres (average dClCd
= 2.608 Å) within the 1-D network, whereas the third one
bridged two consecutive linear networks (dClCd = 2.559 Å) thus
leading to a two-dimensional polymer. The coordination
geometry around the metal centre was again distorted octahe-
dral with S–Cd–S, Cl–Cd–Cl and N–Cd–Cl angles of 147.6,
169.0 and 163.6°, respectively. With the Cd4Cl7 unit, the
Cd…Cd distances varied from 3.921 Å for the doubly bridged
cations to 4.625 Å for the singly bridged centres. Interestingly,
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2
whereas MeOH and BF4 anions were localised between the
Communication 9/00501C
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Chem. Commun., 1999, 603–604