Novel coordination polymers based on the tetrathioterephthalate dianion as the bridging ligand

Article abstract of DOI:10.1021/ic701414v

The first examples of coordination polymers based on the tetrathioterephthalate dianion as the bridging ligand are reported. Two novel compounds, [M(S₂CC₆H₄CS₂)(DMF) ₂](DMF) (M = Zn, Mn; DMF = dimethy

Full text of DOI:10.1021/ic701414v

Inorg. Chem. 2007, 46, 8487−8489
Novel Coordination Polymers Based on the Tetrathioterephthalate
Dianion as the Bridging Ligand
Eleftheria Neofotistou,† Christos D. Malliakas,‡ and Pantelis N. Trikalitis*,†
Department of Chemistry, UniVersity of Crete, Voutes 71003, Heraklion Crete, Greece, and
Department of Chemistry, Northwestern UniVersity, EVanston, Illinois 60208-3113
Received July 16, 2007
The first examples of coordination polymers based on the
tetrathioterephthalate dianion as the bridging ligand are reported.
polymers is the result of the low electroactivity of the organic
bridging units and their weak electronic coupling with metal
centers.4a The donor atoms are usually hard, such as O or
N, resulting in strong electronic barriers between the metal
centers and the rest of the organic molecule. Therefore, the
proper selection or design of the organic ligand is a key
element, and in accordance with the above considerations,
examples based on aromatic multifunctional ligands with
chalcogenide donor atoms, such as S, have been reported.5
Our approach involves the use of chalcogenide-substituted
aromatic polycarboxylate-based ligands, such as the tetrathio-
terephthalate dianion (tttp2-). The parent terephthalate di-
anion (1,4-benzenedicarboxylate, BDC) is a robust bridging
ligand that has been used extensively for the construction
of important porous metal-organic frameworks (MOFs).6
In terms of electronic properties, the substitution of O by S
decreases the lowest unoccupied molecular orbital (LUMO)
energy of the ligand because C-S π bonds are weaker than
C-O π bonds and also increases the highest occupied
molecular orbital (HOMO) energy because S is less elec-
tronegative than O.7 The decrease in the HOMO-LUMO
gap may lead to enhanced electronic communication between
the ligand and metal centers. Therefore, the synthesis and
characterization of new coordination polymers based on the
tttp2- dianion is highly attractive because it may open the
pathway to a novel class of optoelectronically active,
multifunctional metal-organic materials.
Two novel compounds, [M(S2CC6H4CS2)(DMF)2](DMF) (M
Mn; DMF dimethylformamide), have been synthesized, and their
structural and optical properties were investigated.
) Zn,
)
Coordination polymers are an important class of functional
solids in which strong coordinative chemical bonds between
metal centers and organic bridging ligands exist at least in
one dimension.1,2 Although they have a long history, cur-
rently there is enormous research activity in the design and
synthesis of porous coordination polymers for potential
application primarily in the field of gas storage and cataly-
sis.1,3 In addition to these efforts, there is a steadily increasing
interest for the development of metal-organic solids with
interesting optoelectronic properties and, in particular, with
semiconductive or conductive behavior.4 For example, the
development of three-dimensional (3D) metal-organic net-
works that combine accessible porosity with useful electronic
properties similar to those found in pure inorganic chalco-
genide-based materials is highly desirable. The lack of these
properties in the overwhelming majority of coordination
* To whom correspondence should be addressed. E-mail: ptrikal@
chemistry.uoc.gr.
† University of Crete.
‡ Northwestern University.
(1) Robin, A. Y.; Fromm, K. M. Coord. Chem. ReV. 2006, 250, 2127.
(2) Janiak, C. Dalton Trans. 2003, 2781-2804.
Herein, we report for the first time that tttp2- anions are
readily combine with Zn2+ in dimethylformamide (DMF) to
form an insoluble, dark-red crystalline solid with a chemical
formula [Zn(S2CC6H4CS2)(DMF)2](DMF) (1). X-ray single-
crystal analysis8 revealed that 1 consists of one-dimensional
(3) (a) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.;
O’Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127-1129. (b) Chae,
H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y.; Eddaoudi, M.; Matzger,
A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004, 427, 523-527. (c)
Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R. D.; Uribe-
Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Proc. Natl.
Acad. Sci. U.S.A. 2006, 103, 10186-10191. (d) Ferey, G.; Mellot-
Draznieks, C.; Serre, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217-
225. (e) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed.
2004, 43, 2334-2375. (f) Ferey, G.; Mellot-Draznieks, C.; Serre, C.;
Millange, F.; Dutour, J.; Surble, S.; Margiolaki, I. Science 2005, 309,
2040-2042. (g) Liu, Y. L.; Kravtsov, V. C.; Larsen, R.; Eddaoudi,
M. Chem. Commun. 2006, 1488-1490. (h) Yaghi, O. M.; O’Keeffe,
M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003,
423, 705-714.
(1D) zigzag [1 Zn(S2CC6H4CS2)(DMF)2] chains and free
∞
DMF molecules, as shown in Figure 1a. The Zn atom in 1
has a highly distorted octahedral coordination environment,
with four S atoms from two crystallographically nonequiva-
lent tttp ligands acting in an asymmetric bischelating mode
and two O atoms from the DMF ligands (Figure 1b). The
(4) (a) Xu, Z. Coord. Chem. ReV. 2006, 250, 2745-2757. (b) Li, K. H.;
Xu, H. H.; Xu, Z. T.; Zeller, M.; Hunter, A. D. Inorg. Chem. 2005,
44, 8855-8860. (c) Zhong, J. C.; Misaki, Y.; Munakata, M.; Kuroda-
Sowa, T.; Maekawa, M.; Suenaga, Y.; Konaka, H. Inorg. Chem. 2001,
40, 7096.
(5) Han, L.; Bu, X. H.; Zhang, Q. C.; Feng, P. Y. Inorg. Chem. 2006, 45,
5736-5738 and references cited therein.
(6) Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.;
Pastre, J. J. Mater. Chem. 2006, 16, 626-636.
(7) Chisholm, M. H.; Patmore, N. J. Dalton Trans. 2006, 3164-3169.
10.1021/ic701414v CCC: $37.00
Published on Web 09/15/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 21, 2007 8487

COMMUNICATION
our knowledge, 1 represents the first example of an extended,
metal-organic solid in which C-H‚‚‚S hydrogen bonds are
essential elements in the crystal structure.9a
The synthesis of porous MOFs based on the BDC ligand
relies on the formation of secondary building units (SBUs)
through slow deprotonation of the acidic form of the ligand.10
In contrast, when the anionic form of this ligand reacts
directly with divalent metal ions such as Zn2+, no SBUs are
formed and the products are nonporous 1D coordination
polymers with 1:1 metal-to-ligand stoichiometry, similar to
that of 1.11 Therefore, the instantaneous reaction between
the tttp2- dianion and the labile Zn2+ cations most likely
prohibits the formation of an extended open-framework
structure. It is important to note here that the tttp2- ligand is
expected to form various types of SBUs similar to the
molecular clusters that have been observed in the case of
the dithiobenzoate ligand.12 These clusters or SBUs are
different from those obtained with carboxylate ligands
because the S atom is larger than the O atom and, more
importantly, because S has the ability to form three-
coordinated sites. For these reasons, novel porous architec-
tures may be accessible based on the SBU strategy, using a
suitable precursor of the tttp ligand and appropriate synthetic
conditions. It is noteworthy that a similar approach is not
feasible in the case of aromatic thiolate ligands.5
Figure 1. (a) Representative view of 1 looking approximately down the
a axis. (b) Coordination environment of the Zn atoms in 1. Selected
crystallographic distances (Å) and angles (deg): Zn1-S1 2.430(2),
Zn1-S2 2.648(2), S1-Zn1-S2 70.30(7), Zn1-S3 2.507(2), Zn1-S4
2.498(2), S3-Zn1-S4 71.45(7), Zn1-O1 2.134(5), Zn1-O2 2.057(6). H
atoms are omitted for clarity.
Thermal gravimetric analysis (TGA) performed on a
polycrystalline sample of 1 showed that the DMF molecules
are completely removed in two distinct steps (Figure S3 in
the Supporting Information). The first weight loss of 28.7%
at 125 °C corresponds to the removal of two DMF molecules
per formula unit (28.5% calculated) and the second of 14.0%
at 180 °C to the removal of one DMF per formula unit
(14.2% calculated). Interestingly, no weight loss was ob-
served in the temperature range 180-300 °C, indicating the
formation of a stable phase formulated as Zn(S2CC6H4CS2).13
These results prompt us to investigate 1 further and especially
to explore the chemistry associated with the labile DMF
molecules. We found that when 1 is treated with CHCl3 at
room temperature, all DMF molecules are completely
removed and the final solid, designated as 2, contains no
solvent molecules. This is confirmed by TGA and IR spect-
Figure 2. (a) Interchain C(sp2)-H‚‚‚S hydrogen bonds in 1. (b) Addi-
tional C(sp3)-H‚‚‚S hydrogen bonds along the
b axis between
1 Zn(S2CC6H4CS2)(DMF)2] chains from adjacent layers, exclusively via
interdigitated DMF-1 molecules. Selected distances and angles: dC4-H2···S2
[
∞
) 2.864 Å, θC4-H2···S2 ) 137.7°, and æH2···S2-C1 ) 152.0° and dC10-H7···S2
2.897 Å, θC10-H7···S2 ) 159.0°, and æH7···S2-C1 ) 87.4° (see ref 9).
)
[1 Zn(S2CC6H4CS2)(DMF)2] chains are running parallel and
∞
side by side along the [102] crystallographic direction and
stack one on top of the other along the b axis. This
arrangement reveals the existence of an extended two-
dimensional (2D) network of C(sp2)-H‚‚‚S hydrogen bonds9
between adjacent chains and the formation of infinite
supramolecular zigzag layers (see Figures 1a and 2a). The
layers are packed efficiently via interdigitation of the
coordinated DMF molecules along the b axis and held
together by additional C(sp3)-H‚‚‚S hydrogen bonds (Figure
2b). The resulting 3D supramolecular network features small
cavities running along the a axis, in which noncoordinated
DMF molecules reside (see Figure 1a). These molecules form
relatively strong O‚‚‚H-C hydrogen bonds with the coor-
dinated DMF-1 molecules.
(8) Single-crystal X-ray diffraction data: triclinic, space group P1h, a )
7.0008(10) Å, b ) 9.7164(11) Å, c ) 16.693(2) Å, R ) 94.219(10)°,
â ) 99.415(11)°, γ ) 92.663(10)°, V ) 1115.2(3) Å3, Z ) 2, Fcalcd
)
1.527 g/cm3, T ) 100.0(3) K, 2θ ) 50.06°. Refinement of 253
parameters on 3204 independent reflections out of 14 818 measured
reflections (Rint ) 0.1433) led to R1 ) 0.0724 [I > 2σ(I)], wR2 )
0.1277 (all data), and S ) 1.19 with the largest difference peak and
hole of 0.60 and -0.54 e/Å3.
(9) We have identified C-H‚‚‚S hydrogen bonds using common criteria.
These are the sum of the van der Waals radii for H and S (H, 1.20 Å;
S, 1.80 Å) and the angles C-H‚‚‚S (θ) and H‚‚‚S-C (æ). See: (a)
Cosp, A.; Larrosa, I.; Anglada, J. M.; Bofill, J. M.; Romea, P.; Urpi,
F. Org. Lett. 2003, 5, 2809. (b) Novoa, J. J.; Rovira, M. C.; Rovira,
C.; Veciana, J.; Tarres, J. AdV. Mater. 1995, 7, 233. (c) Bondi, A. J.
Phys. Chem. 1964, 68, 441.
In the absence of any ionic interactions in 1, the packing
arrangement of the neutral 1 Zn(S2CC6H4CS2)(DMF)2]
(10) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402,
276-279.
[
∞
chains is clearly influenced by the C-H‚‚‚S interactions
between them. Moreover, the fact that 1 grows in the form
of single crystals demonstrates their significant role in both
directing and stabilizing the final structure. To the best of
(11) Guilera, G.; Steed, J. W. Chem. Commun. 1999, 1563-1564.
(12) Kano, N.; Kawashima, T. Chalcogenocarboxylic Acid Derivatives.
Topics in Current Chemistry; Springer: Berlin, 2005; Vol. 251, pp
141-180.
(13) No Bragg peaks were observed in the PXRD pattern of the solid
obtained after heating 1 at 180 °C under an Ar flow.
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COMMUNICATION
Figure 4. Solid-state UV-vis/near-IR diffuse-reflectance spectra of the
precursor salt of the ligand and the corresponding coordination polymers
recorded at room temperature.
Figure 3. PXRD pattern (Cu KR radiation) of (a) the as-made material 1,
(b) the corresponding solid 2 after DMF removal with CHCl3 treatment,
and (c) the solid obtained after reintroduction of DMF.
the n f π* transition of the -CSS- chromophore.17 In con-
trast, the coordination polymers show optical absorptions that
are clearly red-shifted and strongly depend on the nature of
the transition metal. In the case of [Mn(S2CC6H4CS2)(DMF)2]-
(DMF), the absorption occurs at 925 nm (1.34 eV), in
accordance with its almost black color, while the isostructural
Zn analogue (1), having dark-red color, absorbs at 660 nm
(1.88 eV) (see Figure 4). The energies of these electronic
transitions, which most likely originate from ligand-to-metal
charge-transfer processes, are among the lowest that have
been observed in the entire family of extended metal-organic
networks, featuring no metal-metal bond, metal-π interac-
tions, or π-π stacking.4 A possible semiconductive behavior
of these materials is currently under investigation.
In conclusion, the present work demonstrates that it is
possible to construct crystalline coordination polymers based
on the tetrathioterephthalate dianion as the bridging ligand.
We anticipate that the two novel 1D [M(S2CC6H4CS2)-
(DMF)2](DMF) (M ) Zn, Mn) compounds represent the first
members of a new family of optoelectronically active metal-
organic materials.
roscopy (Figure S3 in the Supporting Information). Most sur-
prising is the fact that 2 shows crystalline order, as evidenced
by the diffraction lines observed in its powder X-ray diffrac-
tion (PXRD) pattern, albeit broadened and dissimilar to 1
(see Figure 3b). Remarkably, upon reintroduction of DMF,
the solid exhibits the same PXRD pattern as 1, as shown in
Figure 3c. This facile and reversible removal of both coordi-
nated and noncoordinated DMF molecules is quit impressive,
especially if we take into account the fact that 1 is made of
1D chains held together only by C-H‚‚‚S hydrogen bonds,
which usually are considered to be very weak with no clear
role in the solid state.14 It is entirely possible that in 2 the
1 Zn(S2CC6H4CS2)] chains maintain their side-by-side
[
∞
C-H‚‚‚S hydrogen bonds (see Figure 2a) and the 2D
supramolecular network is therefore susceptible to reversible
removal of DMF molecules. In other words, 1 behaves like
a layered material with intercalation properties.15 Moreover,
because this solid-to-solid-to-solid transformation involves
only solvent molecules and occurs at room temperature, the
structure of 2 should be closed to that of 1. Therefore, it is
highly unlikely that 2 is a collapsed version of 1, but it most
probably maintains an open architecture that is accessible
by coordinating molecules.16 A strong indication for the
above arguments comes from the PXRD pattern of 2 (see
Figure 3b), which shows a relatively strong Bragg peak in
the low-angle region with a d spacing of 10.4 Å.
Acknowledgment. We are grateful to Prof. Mercouri G.
Kanatzidis for providing the use of single-crystal XRD and
solid-state diffuse-reflectance equipment. Financial support
from the GSRT in Greece (PENED-03ED581) and Interreg
IIIA (Gr-Cy, k2301.004) is gratefully acknowledged. We also
thank Dr. Alexandros Lappas and Othon Adamopoulos at
IESL-FORTH for the magnetic measurements.
The reaction between the tttp2- anions and Mn2+ under
the same experimental conditions as those used in the
synthesis of 1 leads to the formation of the isostructural
compound [Mn(S2CC6H4CS2)(DMF)2](DMF) as judged from
its PXRD pattern and elemental analysis (Figure S6 in the
Supporting Information). In addition, magnetic susceptibility
measurement confirms the presence of Mn2+ (Figure S7 in
the Supporting Information). However, in contrast to the Zn
analogue, this material does not show a reversible removal
of the DMF molecules.
The optical properties of the materials were investigated
by solid-state diffuse-reflectance UV-vis/near-IR spectros-
copy, and the results are shown in Figure 4. The free tttp2-
in the form of its dipiperidinium salt shows a well-defined
optical absorption at 590 nm (2.10 eV) that originates from
Supporting Information Available: Instrumentation, experi-
mental procedure, X-ray crystallographic file for 1 in CIF format,
and additional characterization data. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC701414V
(14) Bond, A. D.; Jones, W. J. Chem. Soc., Dalton Trans. 2001, 3045.
(15) When 2 is treated with something other than DMF coordinating
molecules, such as pyridine and small alkylamines, new crystalline
materials are formed. The corresponding PXRD patterns are provided
in the Supporting Information. However, the atomic structures of these
solids are currently unknown because the quality of the crystals does
not allow single-crystal X-ray analysis.
(16) A possible porosity in 2 was investigated by recording the nitrogen
adsorption isotherm at 77 K. The results show that there is no
permanent porosity, accessible at least by this probe molecule (see
Figure S4 in the Supporting Information).
(17) Furlani, C.; Luciani, M. L. Inorg. Chem. 1968, 7, 1586-1592.
Inorganic Chemistry, Vol. 46, No. 21, 2007 8489