An asymmetric TTF derivative bearing a phenyl β-diketone group as an efficient ligand towards functional materials

Article abstract of DOI:10.1039/c1nj20167k

A novel asymmetric tetrathiafulvalene (TTF) derivative bearing a conjugated phenyl β-diketone moiety 1-(4-tetrathiafulvalyphenyl)-4,4,4- trifluorobutane-1,3-dione (TTF-ph-tfacH) has been synthesized using feasible methods and fully characterized. The chel

Full text of DOI:10.1039/c1nj20167k

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PAPER
An asymmetric TTF derivative bearing a phenyl b-diketone group as an
efficient ligand towards functional materialsw
Yu Wang,a Bo Li,a Guolong Huang,a Jing-Ping Zhang*a and Yan Zhangb
Received (in Montpellier, France) 26th February 2011, Accepted 2nd April 2011
DOI: 10.1039/c1nj20167k
A novel asymmetric tetrathiafulvalene (TTF) derivative bearing a conjugated phenyl b-diketone
moiety 1-(4-tetrathiafulvalyphenyl)-4,4,4-trifluorobutane-1,3-dione (TTF-ph-tfacH) has been
synthesized using feasible methods and fully characterized. The chelating ability of its enolate
anion (TTF-ph-tfac) has been investigated with [MIICl2ꢀxH2O] (M = Zn and Co) leading to
complexes [Zn(TTF-ph-tfac)2(CH3OH)2] (2a) and [Co(TTF-ph-tfac)2(CH3OH)2] (2b), where the
metal center is coordinated with two TTF-ph-tfac ligands and two methanol molecules.
This redox active ligand shows promising features for the elaboration of hybrid
organic–inorganic building blocks. The magnetic analysis for 2b reveals very weak
antiferromagnetic interactions between spin centers, which would be a precursor for
magnetic conductors. The herein reported mono-substituted TTF derivative interconnected
via the phenyl group, which is of extended conjugation, enhanced planarity, and asymmetric
geometry, shows a great promise to multifunctional (conducting, non-linear optical, and
magnetic) materials.
substituted TTF family. Moreover, the deliberate introduction of
Introduction
the phenyl group enhances the coplanarity and extends the
For more than three decades, tetrathiafulvalene (TTF) and its
conjugation of the whole molecule, which facilitates the p–d
derivatives have been attracting continuous attention as
interaction between the conducting core and the magnetic center
precursors of molecular conductors.1,2 The research interest
beneficial to multifunctional materials. From another point of
is further kindled when the conducting building blocks (TTFs
view, the mono-substituted TTF aiming at grafting the non-linear
with p electrons) collaborate with the magnetic building blocks
(transition metal ions with d electrons) towards the multi-
optical (NLO) property into the multifunctional materials with
conductivity and magnetism should be a rational design but its
functional molecule-based material that is one of the most
multi-functionalized materials are difficult to obtain, which is
challenging issues in solid-state chemistry.3–6 Consequently,
restricted by the molecular organization.
various electroactive TTF based ligands have been synthesized
Recently, we have employed an efficient synthetic strategy to
targeting at, via their coordination to a transition metal, novel
covalently append binding sites onto TTF donors, targeting
at dual-property electronic and magnetic materials.15 In
hybrid organic–inorganic building blocks.7,8 Among lots of
coordination groups, the acetylacetonate ion formed in a basic
continuation of our researches on TTF based coordination
medium from the acetylacetone always presents powerful
complexes, we prepared a novel TTF derivative bearing a
chelating capability and forms complexes with various
transition metals and main group elements.9 For this reason,
conjugated phenyl b-diketone functional group (Scheme 1)
and its coordination counterparts with metal(II) centers
(M = ZnII, CoII) and systemically investigated the electro-
two types of acetylacetone substituted TTF derivatives either
connected through a sulfur atom2,7,8,10–14 to the donor core or
chemical variation of this redox-active ligand in the absence
directly linked13,14 to the TTF moiety have been reported
and presence of different metal centers. The detailed electro-
thus far. Accordingly, the herein reported novel acetylacetone
chemical analysis indicates that upon coordination, the
substituted TTF derivative interlinked by the phenyl group
observed shifts always move toward more cathodic potentials
should be categorized as a new type to enlarge the acetylacetone
and only E1/2(1) values are affected significantly, whereas
E
1/2(2) values remain almost unchanged. The downshift of
a Faculty of Chemistry, Northeast Normal University,
the potentials can be explained by the formation of the
negative enolate ion, which coordinates to the M(II) ions.
As far as our knowledge goes, no affiliation concerning
such TTF derivative and its complexes has been reported
so far.
Changchun 130024, China. E-mail: zhangjingping66@yahoo.cn
b Department of Physics, Peking University, Beijing 100871, China
w Electronic supplementary information (ESI) available: CCDC
reference number 735297 (2a). For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1nj20167k
c
1472 New J. Chem., 2011, 35, 1472–1476
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toluene gave dark blue crystals; yield: 0.4 g (48%). Mp
189–193 1C, 1H NMR (DMSO, 500 MHz): 6.784 (s, 2H),
7.020 (s, 1H), 7.651 (d, 3H, J = 8.4 Hz), 8.156 (d, 2H, J =
8.4 Hz). 13C NMR (DMSO, 125 MHz): 93.0, 105.7, 112.9,
120.0, 120.1, 120.3, 126.2, 128.7, 131.8, 133.1, 136.5, 174.5,
184.0. MS (m/z): C16H9F3O2S4 calcd: 417.9. Found: 417.9
[M]+. Anal. calcd for C14H10OS4: C, 45.92; H, 2.17; S,
30.65%. Found: C, 45.90; H, 2.17; S, 30.63%.
[M(TTF-ph-tfac)2(CH3OH)2] (M = ZnII (2a) and CoII (2b)).
Above a solution of ligand 2 (64 mg, 0.1 mmol) and triethyl-
amine (10 mmol) in CH2Cl2 (2 mL) was gently layered
a CH3OH solvent (1 mL), and furthermore above the
Scheme 1 Synthesis routes of 1, 2, 2a and 2b: (i) n-butyllithium, THF,
ꢁ78 1C; (ii) ClSnBu3, ꢁ78 1C, then room temperature; (iii) 4-bromo-
phenylethanone, Pd(PPh3)4, toluene, reflux; (iv) NaH, THF, 0.5 h,
0 1C; (v) ethyl trifluoroacetate, 6 h; (vi) the MIICl2ꢀxH2O (M = Zn (2a)
and Co (2b)) methanol solution layered on the ligand CH2Cl2 solution.
CH3OH solvent was gently layered
a
solution of
MIICl2ꢀxH2O (M = Zn and Co) (30 mg) in CH3OH (3 mL).
When this three-phase solution was kept at RT for about
1 week, orange-colored crystals, M(TTF-ph-tfac)2(CH3OH)2,
appeared at the interface between the upper two phases.
[Zn(TTF-ph-tfac)2(CH3OH)2], 2a yield: 61%, mp: 143–144 1C.
Maldi MS: calcd for C32H16F6O4S8Zn [M–CH3OH]+, 897.8;
found, 897.8. Anal. calcd for C32H16F6O4S8Zn: C, 42.69; H,
1.79; S, 28.49%. Found: C, 42.65; H, 1.81; S, 28.49%.
[Co(TTF-ph-tfac)2(CH3OH)2], 2b yield: 71%, mp: 135–136 1C.
Maldi MS: calcd for C32H16CoF6O4S8 [M-CH3OH]+,
892.8; found, 892.8. Anal. calcd for C32H16CoF6O4S8: C,
43.00; H, 1.80; S, 28.70%. Found: C, 43.01; H, 1.80; S,
28.72%.
Experimental
Materials
All chemicals used for the syntheses were of reagent grade
quality. THF and methanol were distilled from sodium/
benzophenone and MeOH/Mg(OMe)2, respectively. TTF
was synthesized according to the previous literature.16
Syntheses
1-(4-(Tetrathiafulvaleneyl)phenyl)ethanone (1). To a stirred
solution of TTF (2.04 g) in anhydr. THF (50 mL) at ꢁ78 1C
under an atmosphere of Ar was syringed n-butyl lithium
(6.9 mL, 2.93 M) over a period of 5 min. Then, after stirring
was continued for a further 30 min at ꢁ78 1C, tributyltin
chloride (2.9 mL) was added dropwise over 10 min at ꢁ78 1C.
The mixture was then slowly allowed to warm to the room
temperature over 3 h. The solvent was evaporated under
vacuum. The mixture was treated by Pd(PPh3)4 (0.113 g)
and 4-bromophenylethanone in the dry toluene solution
(60 mL), and the temperature was raised to 130 1C for 12 h.
After removal of the solvents, column chromatography of the
crude product on silica gel with hexane/CH2Cl2 (1 : 1, v/v)
afforded compound 1 as a red solid. Compound 1 was a deep
red solid; yield: 2.2 g (68%). Mp 159–160 1C, 1H NMR
(DMSO, 500 MHz): 2.592 (s, 3H), 6.785 (s, 2H), 7.526
(s, 1H), 7.614 (d, 2H, J = 8.4 Hz), 7.987 (d, 2H, J = 8.4 Hz).
13C NMR (DMSO, 125 MHz): 27.3, 119.8, 120.3, 120.7, 126.6,
127.3, 128.6, 129.9, 133.9, 136.2, 136.6, 197.6. MS (m/z):
C14H10OS4 calcd: 322.0. Found: 322.0 [M]+. Anal. calcd for
C14H10OS4: C, 52.14; H, 3.13; S, 39.77%. Found: C, 52.17; H,
3.10; S, 39.76%.
Physical measurements
1H and 13C NMR spectra were recorded on an Inova-500
instrument. Chemical shifts are quoted in parts per million
(ppm) and referenced to tetramethylsilane. X-Ray powder
diffraction data were collected with a Philips X0Pert MPD
system with Cu-Ka radiation. The simulated powder XRD
patterns of 2a were obtained from the single-crystal X-ray data
using the Mercury program.17 Elemental analyses were carried
out using a Perkin-Elmer elemental analyzer 2400CHN. The
mass spectrum was acquired in the positive ion mode on an
Autoflex III MALDI-TOF/TOF mass spectrometer. The
electrochemical properties were measured by an LK98B
electrochemistry system. The magnetic susceptibility measurement
on complex 2b was obtained on a polycrystalline sample with a
Quantum Design SQUID magnetometer MPMS-XL. The dc
measurements were collected from 2.0 to 300 K under
1000 Oe. Experimental data were also corrected for the sample
holder and for the diamagnetic contribution calculated from
Pascal constants.18
1-(4-Tetrathiafulvalyphenyl)-4,4,4-trifluorobutane-1,3-dione
(2). Compound 1 (0.644 g) was dissolved in 30 mL of dry THF
under an argon atmosphere and 60% NaH (0.1 g) was added
in three batches maintaining the temperature between ꢁ5 and
0 1C. After stirring at this temperature for 0.5 h, ethyl
trifluoroacetate (0.7 mL) was injected and the reaction mixture
was allowed to stir at ambient temperature for 4–5 h. The
mixture was poured into ice water, acidified with 2N HCl and
extracted with ethyl acetate. The combined organic layer was
washed with water, dried, and evaporated leaving a residue
which was washed with pet-ether. Recrystallization from
Results and discussion
Synthesis and structures
There are some kinds of similar reactions to result in the TTF
derivatives with aryl groups.19,20 To prevent the observed
decomposition of this tributylstannyl-TTF, we only evaporated
the solvent under vacuum without further purification
like other literature. Compound 1 was synthesized in a satis-
factory yield (68%). Compound 2 was synthesized by Claisen
condensation21 using compound 1 and ethyl trifluoroacetate
c
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Table 1 Crystallographic data and structural refinement parameters
for complex 2a
Complex
2a
Empirical formula
FW/g molꢁ1
T/K
C34H24F6O6S8Zn1
964.38
298(2)
Crystal system
Space group
Monoclinic
P21/n
a/A
b/A
c/A
a/1
5.2175(5)
10.5765(10)
34.092(3)
90
Fig. 2 The plot of the H-bonding interactions of 2a.
b/1
90.726(2)
90
1881.1(3)
2
1.703
g /1
V/A3
Z
r(calcd)/g cmꢁ3
GOF
1.048
0.0559, 0.1275
R1 [I 4 2s(I)], wR2
under slightly modified conditions involving sodium hydride
in dry THF at the temperature of ꢁ5 1C.
Fig. 3 The plot of the main Sꢀ ꢀ ꢀH interactions to construct the three-
dimensional structure of 2a.
The X-ray data were collected at 298(2) K from a single
crystal. Complex 2a crystallizes in the monoclinic P21/n space
group (Table 1). The crystal structure analysis reveals that 2a
is a mononuclear complex and the Zn atom lies on an
inversion centre. The ligands connect the ZnII centre in trans
conformations through their O atoms of two TTF-ph-tfac
anions in the equatorial plane. The octahedral coordination
geometry around the metal is completed by two axial CH3OH
ligands, as shown in Fig. 1. Selected bond lengths and angles
are listed in Table 2. The axial Zn–O(3) distance of 2.160(3) A
is slightly longer than the equatorial Zn–O distances that
range from 2.020(3) to 2.086(3) A, as a result of the negative
charge and the chelating coordination mode of the trifluoro-
acetone part. The bond angles around the equatorial plane are
in the range of 89.31–90.71. The central CQC bond length of
the TTF cores (1.338(7) A) is in the average range for neutral
donor cores.
As shown in Fig. 2, TTF-ph-tfac ligands in 2a interact with
methanol molecules through H-bonds O(3)–H(18)ꢀ ꢀ ꢀO(1)#2
(1.910(3) A, symmetry code: ꢁx + 2, ꢁy, ꢁz) to form columns
along the a-axis. Then, the TTF cores of the columns are
stacked via the Sꢀ ꢀ ꢀH interactions to obtain the 3 dimensional
(3D) structure. The distances of Sꢀ ꢀ ꢀH are 2.99–3.00 A
(Fig. 3).
The analysis by Maldi mass spectrometry of 2a and 2b
confirmed that the metal(II) center is chelated by two
TTF-ph-tfac units. Unfortunately, the growth of 2b single
crystals suitable for the structure determination failed,
although great efforts have been made. To verify whether 2b
is structurally similar to 2a, powder XRD patterns were
recorded for 2a and 2b, which are compared with the ones
obtained from the single crystal X-ray data of 2a by simulation.
Unit cell parameters from powder XRD data of 2b are
obtained using the XRD analysis software MDI jade 7
(Materials Data Inc., Liverpool, CA), giving a = 5.20(1) A,
b = 10.51(1) A, c = 34.10(3) A, b = 90.59(7)1, and Z = 2.
The close similarity of XRD results (Fig. 4) let us to conclude
that 2a and 2b are isomorphous complexes.22
Fig. 1 ORTEP drawing of 2a at the 50% probability level (#1
represents the symmetry transformation used to generate equivalent
atoms: 1 ꢁ x, ꢁy, ꢁz).
Table 2 Selected bond lengths [A] and angles [1] for complex 2aa
Zn–O(1)
Zn–O(2)
Zn–O(3)
O(1)–Zn–O(2)
O(1)–Zn–O(3)
O(1)–Zn–O(1)#1
2.086(3)
2.020(3)
2.160(3)
89.3(1)
91.4(1)
180
O(1)–Zn–O(2)#1
O(1)–Zn–O(3)#1
O(2)–Zn–O(3)
90.7(1)
88.6 (1)
90.5(1)
180
89.5(1)
180
O(2)–Zn–O(2)#1
O(2)–Zn–O(3)#1
O(3)–Zn–O(3)#1
a
#1 represents the symmetry transformation used to generate
equivalent atoms by (1 ꢁ x, ꢁy, ꢁz).
Fig. 4 Experimental powder XRD data of 2a and 2b vs. XRD
patterns simulated from the single-crystal X-ray data of 2a.
c
1474 New J. Chem., 2011, 35, 1472–1476
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Table 3 Cyclic voltammetric dataa
Compd.
Epc(1)
Epa(1)
E1/2(1)
Epc(2)
Epa(2)
E1/2(2)
1
2
2a
2b
0.52
0.51
0.51
0.50
0.60
0.60
0.58
0.57
0.57
0.56
0.54
0.54
0.76
0.76
0.76
0.75
0.84
0.85
0.82
0.82
0.80
0.80
0.79
0.79
a
E in V vs. Ag/AgCl, 0.1 M Bu4NPF6, Pt working electrode.
Fig. 6 Plots of wMT vs. T and wMꢁ1 vs. T for 2b. The solid line shows
the best fits to the model (see the text).
temperature may be ascribed to the presence of spin–orbit
coupling and the intermolecular antiferromagnetic interaction.
The high-temperature data (above 100 K) can be fitted to the
Curie–Weiss law with C = 2.30 cm3 K molꢁ1 and y = ꢁ0.29 K.
This indicates a nearly perfect paramagnetic system with very
weak antiferromagnetic interactions between the spin centres.
As complexes 2a and 2b are isostructural, the nearest Coꢀ ꢀ ꢀCo
separation should be ca. 5.218(3) A for 2b and TTF-ph-tfac
ligands in 2b interact with methanol molecules through
H-bonds O–Hꢀ ꢀ ꢀO (ca. 1.910(3) A) to form columns along
the a-axis (the same like those in 2a). The hydrogen bonds
should be the magnetic interaction pathway responsible for the
weak antiferromagnetic interaction.
Fig. 5 Cyclic voltammogram curves of 2, 2a, and 2b.
Electrochemical properties
The electrochemical properties of compounds 1, 2, 2a, and 2b
were investigated by cyclic voltammetry and carried out at the
room temperature under argon in THF with 0.1 M tetrabutyl-
ammonium perchlorate as the supporting electrolyte, Ag/AgCl
as the reference electrode, and platinum as working and
counter electrodes. The corresponding results are listed in
Table 3. As shown in Fig. 5, two reversible single-electron
oxidation waves are observed, corresponding to E1/2(1) and
Conclusions
In this article, we described the synthesis and full character-
ization of a new TTF-ph-tfacH and its new coordination
complexes 2a and 2b. The structural analysis from PXRD
experiments shows that 2b has the identical crystal structure as
that of 2a. In complex 2b, the TTF is neutral and therefore the
magnetic properties reveal a paramagnetic behavior corres-
ponding to isolated S = 3/2 spins of the CoII centers with a
weak antiferromagnetic coupling. Upon coordination, the
observed shifts are found to move toward more cathodic
potentials and only E1/2(1) values are affected, whereas
E
1/2(2) of the TTF derivatives system. Upon coordination, the
observed shifts always move toward more cathodic potentials
and only E1/2(1) values are affected significantly, whereas
E
1/2(2) values remain almost unchanged. The downshift of
the potentials can be explained by the formation of the
negative enolate ion, which coordinates to the M(II) ions.
E
1/2(2) values remain almost unchanged. The downshift of
Magnetic investigations
the potentials can be explained by the formation of the
negative enolate ion, which coordinates to the M(II) ions.
Further researches on this novel attractive system will focus
on the change of axial ligands by bridging ligands, to obtain
quite sophisticated architectures and new functionalities and
properties. Moreover, chemical and electrochemical oxidation
of this complex to prepare radical–cation salts is currently
under investigation in our group.
Fig. 6 shows the magnetic behaviour of [Co(TTF-ph-tfac)2-
(CH3OH)2] (2b) under an applied field of 1000 Oe in the form
of 1/wM vs. T and wMT vs. T. The wMT value of 2b at 300 K is
2.3 cm3 K molꢁ1, which is higher than the spin-only value
(1.875 cm3 K molꢁ1) expected for a magnetically isolated high-
spin CoII ion with g = 2.0 owing to the significant orbital
contribution characteristic for the HS CoII ion (for HS CoII,
the wMT value normally ranges from 2.3 to 3.4 cm3 molꢁ1 K).23
As the sample is cooled from room temperature, the
wMT value only slightly decreases from 2.3 cm3 molꢁ1 K to
2.2 cm3 molꢁ1 K at 100 K and then decreases rapidly at low
temperatures, reaching a value of 1.6 cm3 molꢁ1 K at 2 K.
For this complex, the decrease of the wMT product at low
Acknowledgements
Financial support from the NSFC (50873020; 20773022),
JLSDP (20082212), and NENU-STB07007 is gratefully
acknowledged.
c
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13 N. Bellec, J. Massue, T. Roisnel and D. Lorcy, Inorg. Chem.
Commun., 2007, 10, 1172.
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