Metal complexes based on tetrathiafulvalene-fused π-extended schiff base ligands - Syntheses, characterization, and properties

Article abstract of DOI:10.1002/ejic.201101022

π-Conjugated tetrathiafulvalene (TTF)-based donors with a monoamine moiety, 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3-benzodithiol-5-amine (L_a) and 2-(5,6-dihydro[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-1, 3-benzodithiol-5-amine (L_b), have been synthesized. Condensation of the TTF amines with different pyridinecarbaldehydes afforded new TTF-fused π-extended Schiff base ligands, L_a-imine-4-pyridyl (L ₁), L_a-imine-3-pyridyl (L₂), and L _b-imine-2-pyridyl (L₃). Four metal complexes based on these Schiff base pyridine ligands, M(hfac)₂(L)₂ (M = Cu^II, L = L₁, 4; M = Mn^II, L = L₁, 5; M = Cu^II, L = L₂, 6; hfac = hexafluoroacetylacetonate) and [Re(CO)₄(L₃)][Re₂(CO)₆Cl ₃] (7), have been synthesized and structurally characterized. The ligands in all of the complexes show a near planar structure, and the different coordination modes of the metal ions and relative orientation of the terminal N donors result in a different crystalline organization in the solid state. The absorption spectra and redox behavior of these new compounds have been studied. These paramagnetic complexes are promising building blocks for the construction of multifunctional materials due to their planar structures and inherent redox properties. Copyright

Full text of DOI:10.1002/ejic.201101022

FULL PAPER
DOI: 10.1002/ejic.201101022
Metal Complexes Based on Tetrathiafulvalene-Fused π-Extended Schiff Base
Ligands – Syntheses, Characterization, and Properties
Jie Qin,[a] Chen-Xi Qian,[a] Nan Zhou,[a] Rong-Mei Zhu,[a] Yi-Zhi Li,[a] Jing-Lin Zuo,*[a]
and Xiao-Zeng You[a]
Keywords: Redox chemistry / Materials science / Schiff bases / N ligands / Tetrathiafulvalene
π-Conjugated tetrathiafulvalene (TTF)-based donors with a
[Re(CO)4(L3)][Re2(CO)6Cl3] (7), have been synthesized and
monoamine moiety, 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylid-
structurally characterized. The ligands in all of the com-
ene]-1,3-benzodithiol-5-amine (La) and 2-(5,6-dihydro[1,3]di- plexes show a near planar structure, and the different coordi-
thiolo[4,5-b][1,4]dithiin-2-ylidene)-1,3-benzodithiol-5-amine
(Lb), have been synthesized. Condensation of the TTF
amines with different pyridinecarbaldehydes afforded new
nation modes of the metal ions and relative orientation of the
terminal N donors result in a different crystalline organiza-
tion in the solid state. The absorption spectra and redox be-
TTF-fused π-extended Schiff base ligands, La-imine-4-pyr- havior of these new compounds have been studied. These
idyl (L1), La-imine-3-pyridyl (L2), and Lb-imine-2-pyridyl (L3).
Four metal complexes based on these Schiff base pyridine
ligands, M(hfac)2(L)2 (M = CuII, L = L1, 4; M = MnII, L = L1,
5; M = CuII, L = L2, 6; hfac = hexafluoroacetylacetonate) and
paramagnetic complexes are promising building blocks for
the construction of multifunctional materials due to their
planar structures and inherent redox properties.
been attached to the TTF moiety, and their corresponding
electroactive complexes have been reported.[9–14] Among
them, pyridine and bipyridine groups have attracted the
most attention due to their well-known coordination ability
to different metal ions.[15–21]
Introduction
Tetrathiafulvalene (TTF) and its derivatives have re-
ceived much attention because of their strongly electron-
donating and attractive reversible redox properties. With
these advantages, they can be used as building blocks for
molecular conductors,[1–2] molecular switches,[3] and solar
energy systems.[4] However, the preparation of materials
that exhibit synergy between two or more properties (multi-
functional materials) is still a challenge. In consequence,
much effort has been devoted to associate the TTF core
with spin-carrier centers through π-conjugated linkages,
which may improve the electron mobility along the mole-
cule as well as enhance the stacking interaction by π-orbital
overlap.[5–8] This approach combines the electrochemically
active properties of TTF donors with the optical or mag-
netic properties of transitional metal ions to obtain interest-
ing multifunctional molecular materials. The appropriate
linkages or effective bridges are important to link the para-
magnetic centers and conduct electrons. A variety of mono-
or polydentate organic ligands for metal coordination have
In order to obtain new electroactive complexes with intri-
guing structures and interesting properties, we have studied
several new π-extended Schiff base pyridine ligands with
different coordinated orientations. The TTF-based donors
with monoamine moieties, 2-[4,5-bis(methylthio)-1,3-di-
thiol-2-ylidene]-1,3-benzodithiol-5-amine (La) and 2-(5,6-
dihydro[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-1,3-benzo-
dithiol-5-amine (Lb), were chosen for condensation reac-
tions with different pyridylaldehydes. Three TTF–Schiff
base ligands, in which the TTF fragment is covalently
linked to 4-pyridyl (L1), 3-pyridyl (L2), and 2-pyridyl (L3,
Scheme 1), have been synthesized. The coordination abili-
ties of monodentate ligands L1 and L2 have been demon-
strated. Their reactions with CuII or MnII in the presence of
hexafluoroacetylacetonate (hfac–) afforded three new metal
complexes, M(hfac)2(L)2 (M = CuII, L = L1, 4; M = MnII,
L = L1, 5; M = CuII, L = L2, 6). Unlike L1 and L2, L3 can
adopt a chelating coordination mode. Our previous reports
show that chelating ligands based on TTF derivatives are
good for the formation of ReI complexes.[22] The reaction
between L3 and Re(CO)5Cl afforded the new ReI complex
[Re(CO)4(L3)][Re2(CO)6Cl3] (7). This paper describes the
full characterization of all of the ligands and complexes,
and their spectroscopic and electrochemical properties.
[a] State Key Laboratory of Coordination Chemistry, School of
Chemistry and Chemical Engineering, Nanjing National
Laboratory of Microstructures, Nanjing University,
Nanjing 210093, P. R. China
Fax: +86-25-83314502
E-mail: zuojl@nju.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101022.
234
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Complexes with TTF-Fused π-Extended Schiff Bases
Scheme 1. Structures of La–L3.
served. For 4–6, a sharp absorption band of hfac is clearly
visible at around 1645 cm–1, and the coordinated CϵO
stretching bands in 7 are found in the 2100–1880 cm–1 re-
gion.
Results and Discussion
Synthesis and Characterization
The synthetic pathway is outlined in Scheme 2. The ni-
tro-substituted 1,3-dithiole-2-thione 1 is the key starting
material. Although it has been synthesized by a nucleophilic
reaction in moderate yield,[23–24] we describe here a facile
approach for the synthesis of 1 in high yield starting from
1,2-dibromo-4-nitrobenzene and potassium trithiocarbon-
ate. Compound 2 was synthesized by a literature method.[25]
The cross-coupling reactions of 2 with 3a and 3b in the
presence of triethyl phosphite afforded La and Lb, respec-
tively. The Schiff bases L1–L3 were prepared by the direct
condensation of La and Lb with the corresponding pyridine-
carbaldehyde in moderate yield. Three mononuclear com-
plexes 4–6 were obtained by the coordination of L1 or L2
1
In their H NMR spectra, La and Lb exhibit resonances
at about 3.65 ppm for the NH2 proton, and L1–L3 show
singlets at around 8.56 ppm, which are assigned to the
imine CH proton. Compared with L3, all of the H signals
in the aromatic rings of 7 are shifted by ca. 0.22–0.27 ppm
to lower field, which is in agreement with the decrease of
electron density around the pyridyl and phenyl units caused
by chelation to ReI.
Crystal Structures
The solid-state structures of La, Lb, L1, L2, and 4–7 were
with M(hfac)2 (M = Cu or Mn), whereas the reaction of determined by single-crystal X-ray diffraction. The crystal-
Re(CO)5Cl with 1 equiv. of L3 afforded 7. All of the new lographic and data collection parameters are given in
ligands and complexes show good solubility in common po- Tables 1 and 2; selected bond lengths and angles are listed
lar organic solvents such as CH2Cl2, CHCl3, and CH3CN.
in Tables 3, 4, 5, 6, and S1.
The compounds were characterized by IR, 1H NMR,
Orange crystals of La and Lb, suitable for X-ray structure
and UV/Vis spectroscopy and MS. In their IR spectra, La analysis, were obtained by slow evaporation of solutions of
and Lb display typical NH2 stretching bands at 3328 and a mixture of dichloromethane and hexane. Both com-
3362 cm–1, whereas in those of L1–L3, the NH2 stretching pounds crystallize in monoclinic systems (P21 and P21/c,
band disappeared and a new band at around 1620 cm–1, respectively). La has an approximately planar structure ex-
which results from the C=N stretching vibration, is ob- cept one of the methyl group stretches out of the plane (Fig-
Scheme 2. Synthetic routes to L1–L3.
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Table 1. Crystallographic data for La–L2.
La
Lb
L1
L2
Empirical formula
Mr
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C12H11NS6
361.58
monoclinic
P21
7.8668(13)
5.1367(8)
18.488(3)
90.00
C12H9NS6
359.56
monoclinic
P21/c
6.5417(10)
14.206(2)
16.4475(19)
90.00
C18H14N2S6
450.67
monoclinic
P21/c
5.8316(7)
10.6633(12)
31.467(4)
90.00
C18H14N2S6
450.67
monoclinic
P21/c
5.0109(8)
26.163(4)
15.370(2)
90.00
α [°]
β [°]
94.667(2)
90.00
744.6(2)
2
1.613
372
109.515(5)
90.00
1440.7(3)
4
1.658
736
90.593(2)
90.00
1956.6(4)
4
1.530
928
97.556(3)
90.00
1997.6(5)
4
1.499
928
γ [°]
V [Å3]
Z
ρc [gcm–3]
F(000)
T [K]
291(2)
0.902
291(2)
0.932
291(2)
0.705
291(2)
0.690
μ(Mo-Kα) [mm–1]
Index ranges
–10 Յ h Յ 10, –6 Յ k Յ 6,
–20 Յ l Յ 23
1.055
–7 Յ h Յ 7, –13 Յ k Յ 17,
–20 Յ l Յ 17
1.069
–7 Յ h Յ 7, –12 Յ k Յ 13 –5 Յ h Յ 6, –32 Յ k Յ 27
–38 Յ l Յ 21
1.059
–18 Յ l Յ 18
1.045
GOF (F2)
Flack parameters
0.02(15)
–
–
–
R1[a], wR2[b] [IϾ2σ(I)] 0.0460, 0.0902
0.0624, 0.1188
0.0451, 0.0891
0.0573, 0.1076
2
2 2
[a] R1 = Σ||C| – |Fc||/ΣFo|. [b] wR2 = [Σw(Fo – Fc ) /Σw(Fo2)]1/2
.
Table 2. Crystallographic data for 4–7.
4
5
6
7
Empirical formula
Mr
C46H30CuF12N4O4S12
1379.00
C46H30F12MnN4O4S12
1370.40
C46H30CuF12N4O4S12
1379.00
C28H12Cl3N2O10Re3S6
1393.71
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
monoclinic
P21/c
20.982(13)
8.271(5)
16.794(11)
90.00
99.442(12)
90.00
2875(3)
triclinic
P1
triclinic
P1
orthorhombic
Pbca
13.8540(11)
11.7330(10)
47.050(4)
90.00
90.00
90.00
7647.9(11)
8
2.421
¯
¯
9.2030(10)
9.8087(10)
34.192(4)
93.633(2)
93.477(2)
114.3620(10)
2793.2(5)
2
1.629
1382
296(2)
0.772
8.8546(14)
9.9736(15)
16.136(2)
78.023(3)
78.905(3)
89.499(3)
1367.3(4)
1
1.675
695
296(2)
0.946
γ [°]
V [Å3]
Z
2
ρc [gcm–3]
F(000)
T [K]
1.593
1390
291(2)
0.900
5168
296(2)
10.065
μ(Mo-Kα) [mm–1]
–25 Յ h Յ 24,
–10 Յ k Յ 7,
–20 Յ l Յ 20
1.042
–10 Յ h Յ 10,
–11 Յ k Յ 8,
–38 Յ l Յ 40
1.087
–10 Յ h Յ 8,
–12 Յ k Յ 7,
–17 Յ l Յ 19
1.175
–17 Յ h Յ 17,
–14 Յ k Յ 14,
–58 Յ l Յ 57
1.166
Index ranges
GOF (F2)
[b]
R1[a], wR2 [IϾ2σ(I)] 0.0514, 0.0903
0.0578, 0.1554
0.0834, 0.2199
0.0457, 0.1122
2
2 2
[a] R1 = Σ||C| – |Fc||/ΣFo|. [b] wR2 = [Σw(Fo – Fc ) /Σw(Fo2)]1/2
.
Table 4. Selected bond lengths [Å] and angles [°] for 5.
Mn(1)–N(3)
Mn (1)–O(1)
Mn (1)–O(3)
C(1)–C(2)
C(5)–C(6)
C(17)–C(18)
C(21)–C(22)
2.273(3)
2.151(3)
2.206(3)
1.332(7)
1.382(6)
1.350(6)
1.391(6)
Mn(1)–N(4)
Mn (1)–O(2)
Mn (1)–O(4)
C(3)–C(4)
C(11)–N(2)
C(19)–C(20)
C(27)–N(1)
O(1)–Mn (1)–O(4) 177.59(12)
O(2)–Mn (1)–O(4) 99.05(12)
N(3)–Mn(1)–O(3) 164.09(13)
N(4)–Mn(1)–O(2) 166.61(13)
C(28)–C(27)–N(1) 120.9(5)
2.245(4)
2.171(3)
2.152(3)
1.328(8)
1.134(7)
1.339(6)
1.246(6)
Table 3. Selected bond lengths [Å] and angles [°] for 4.
Cu(1)–N(2)
Cu(1)–O(2)
C(5)–C(6)
2.012(3)
2.161(2)
1.299(4)
1.450(4)
85.64(10)
Cu(1)–O(1)
C(3)–C(4)
C(7)–C(8)
C(13)–N(1)
N(2)–Cu(1)–O(1)
N(2)–Cu(1)–O(2)
2.098(3)
1.347(5)
1.378(5)
1.241(4)
90.41(11)
87.12(11)
C(10)–N(1)
O(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(1)#1 89.59(11)
O(1)–Mn (1)–O(2) 82.21(11)
N(2)–Cu(1)–O(2)#1 92.88(11)
N(2)–Cu(1)–N(2)#1 180.00(15) O(2)–Mn (1)–O(3) 82.20(12)
C(10)–N(1)–C(13)
124.0(3)
C(14)–C(13)–N(1)
125.2(3)
O(3)–Mn (1)–O(4) 80.97(11)
N(3)–Mn(1)–N(4) 97.13(13)
C(12)–C(11)–N(2) 124.0(6)
Symmetry transformations used to generate equivalent atoms:
#1: –x, –y + 2, –z + 1.
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Complexes with TTF-Fused π-Extended Schiff Bases
Table 5. Selected bond lengths [Å] and angles [°] for 6.
Figures 1 and 2 show the molecular structure of L1 and
L2, respectively. For L1, the TTF skeleton has a nonplanar
boat-like conformation, and the average deviation from the
least-squares plane is 0.1669 Å. The dihedral angle between
the two five-membered rings (containing S1, S2, S3, and
S4) is 20.81(1)°. For L2, the TTF backbone is nearly planar
with a dihedral angle of 2.61(1)° between the two five-mem-
bered rings (containing S1, S2, S3, and S4), and the average
deviation from a least-squares plane is only 0.0190 Å. The
pyridyl ring and phenyl group are not coplanar and the
dihedral angles between them are 12.83(1) and 35.49(1)° in
L1 and L2, respectively. Due to crystal packing effects, the
methyl substituents in the two ligands are arranged in a
distinctly out-of-plane conformation. In L1, the two methyl
groups point in opposite positions, whereas in L2, they are
on the same side.
The asymmetric unit of 4 contains one molecule. As
shown in Figure 3, the central Cu2+ ion lies on the inversion
center and adopts a pseudooctahedral coordination envi-
ronment, which is defined by four oxygen donors from two
hfac anions in the equatorial plane. The Cu1–O1 and Cu1–
O2 distances are 2.098(3) and 2.161(2) Å, respectively. The
trans pyridine nitrogen atoms of L1 occupy the axial posi-
tions with a short Cu1–N2 bond length of 2.012(3) Å. The
dihedral angle between the pyridyl plane and the acac plane
is 80.77(1)°. The Cu–O and Cu–N bond lengths are com-
parable to those found in the similar complex, trans-
Cu(hfac)2(TTF–Py)2.[26]
Cu(1)–N(2)
Cu(1)–O(2)
C(5)–C(6)
C(13)–C(14)
2.046(6)
2.282(5)
1.330(9)
1.471(10)
1.238(9)
94.03(19)
90.0(2)
Cu(1)–O(1)
C(3)–C(4)
C(7)–C(8)
C(12)–N(1)
2.004(5)
1.331(10)
1.393(9)
1.426(8)
C(13)–N(1)
O(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(1) #1
N(2)–Cu(1)–O(2) #1
C(12)–N(1)–C(13)
N(2)–Cu(1)–O(1)
N(2)–Cu(1)–O(2)
90.0(2)
91.3(2)
88.7(2)
122.1(7)
N(2)–Cu(1)–N(2)#1 180.000(1)
C(14)–C(13)–N(1) 121.4(7)
Symmetry transformations used to generate equivalent atoms:
#1: –x, –y + 1, –z.
Table 6. Selected bond lengths [Å] and angles [°] for 7.
Re(1)–N(1)
Re(1)–C(1)
Re(1)–C(3)
Re(2)–Cl(1)
Re(2)–Cl(3)
Re(3)–Cl(2)
Re(2)–C(26)
Re(2)–C(28)
Re(3)–C(24)
C(9)–C(10)
C(17)–C(18)
C(10)–N(2)
N(1)–Re(1)–N(2)
N(2)–Re(1)–C(1)
Cl(1)–Re(2)–Cl(3)
Cl(1)–Re(2)–C(28)
Cl(3)–Re(2)–C(27)
C(24)–Re(3)–C(25)
Cl(2)–Re(3)–C(24)
Re(2)–Cl(1)–Re(3)
Re(2)–Cl(3)–Re(3)
2.164(8)
1.933(8)
1.917(12)
2.524(2)
2.509(2)
2.501(2)
1.894(12)
1.888(10)
1.892(11)
1.453(14)
1.352(15)
1.283(12)
74.8(3)
174.2(4)
78.68(8)
170.9(3)
174.4(3)
89.6(5)
174.2(3)
83.93(8)
84.84(8)
Re(1)–N(2)
Re(1)–C(2)
Re(1)–C(4)
2.191(7)
2.006(10)
2.038(12)
2.510(3)
2.537(3)
2.508(2)
1.891(12)
1.881(13)
1.898(11)
1.393(13)
1.342(15)
1.444(12)
173.4(4)
178.1(5)
Re(2)–Cl(2)
Re(3)–Cl(1)
Re(3)–Cl(3)
Re(2)–C(27)
Re(3)–C(23)
Re(3)–C(25)
C(14)–C(15)
C(19)–C(20)
C(11)–N(2)
N(1)–Re(1)–C(3)
C(2)–Re(1)–C(4)
C(27)–Re(2)–C(28) 87.6(4)
Cl(2)–Re(2)–C(26) 174.9(4)
Cl(1)–Re(3)–Cl(2)
Cl(1)–Re(3)–C(25) 171.6(3)
Cl(3)–Re(3)–C(23) 174.9(3)
Re(2)–Cl(2)–Re(3) 84.96(8)
79.88(8)
The central C=C bond length of the TTF core is
1.299(4) Å, which is within the normal range for a neutral
molecule.[26–27] In 4, L1 is not planar, and the TTF back-
bone is more bent than in the free ligand, which is evi-
denced by the dihedral angle of 33.33(1)° between the two
five-membered rings (containing S3, S4, S5, and S6). The
ure S1). The average deviation from a least-squares plane dihedral angle between the coordinated pyridyl unit and
through the remaining atoms is 0.0591 Å, whereas for the phenyl group is 12.01(1)°, which indicates that they are not
TTF core alone, it amounts to 0.0441 Å. For Lb (Figure coplanar. The adjacent molecules are stacked in an overlap-
S2), the average deviation from a least-squares plane ping arrangement in a palisade fashion (Figure 4). The
through all the atoms is 0.1601 Å, and 0.0898 Å for the shortest intermolecular S···S distance is 3.844 Å (S1···S6).
TTF core alone, which reflects its almost coplanar confor-
mation.
The ORTEP diagram of 5 is depicted in Figure 5. The
MnII ion lies on a two-fold axis and adopts a distorted octa-
Figure 1. Molecular structure of L1 (50% probability displacement ellipsoids), front and side views are presented.
Eur. J. Inorg. Chem. 2012, 234–245
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237

J.-L. Zuo et al.
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Figure 2. Molecular structure of L2 (50% probability displacement ellipsoids), front and side views are presented.
Figure 3. ORTEP view of 4 with the atom numbering scheme (50% probability displacement ellipsoids, H atoms are omitted for clarity).
hedral coordination geometry. L1 has a cis coordination
mode with an N3–Mn1–N4 bond angle of 97.13(13)°,
which is different to that in 4. The Mn–N bond lengths
range from 2.245(4)–2.273(3) Å. The average central C=C
bond length of the TTF core is 1.341 Å, which is longer
than that in 4. In contrast to 4, L1 is almost planar in 5.
The average dihedral angle between the two five-membered
rings is 6.43(1)°, and the average dihedral angle between the
coordinated pyridyl ring and the phenyl group is 10.26(1)°.
In the solid state, the molecules are stacked in a head-
to-tail fashion. The shortest intermolecular S···S contact is
3.642 Å (S12···S12#2, symmetry code: #2 –x-1, –y – 2, –z),
which is slightly shorter than the sum of the van der Waals
radii (3.70 Å) and leads to the formation of dimers. The
dimers are aligned side by side along the c axis and further
connected through S6···S11 contacts (3.633 Å) to give a 1D
zigzag chain structure (Figure 6).
The use of 3-pyridine-type L2 is to control the supra-
molecular motifs as the relative orientations of the nitrogen
donors on the pyridyl rings might result in different build-
ing blocks. Crystallization of L2 with Cu(hfac)2 from the
Figure 4. Crystal packing of 4 viewed along the c axis (H atoms
and hfac– units are omitted for clarity).
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Complexes with TTF-Fused π-Extended Schiff Bases
Figure 5. ORTEP view of 5 with the atom numbering scheme (50% probability displacement ellipsoids, H atoms are omitted for clarity).
Figure 6. The 1D zigzag chain of 5 formed by short intermolecular S···S interactions (H atoms are omitted for clarity).
same solvent system as 4 afforded 6. As shown Figure 7,
Different from L1 and L2, L3 prefers a bidentate binding
the central Cu2+ ion in 6 lies on the inversion center and mode for the chelation of transition metal ions. The reac-
adopts a pseudooctahedral coordination environment, sur- tion of L3 with 1 equiv. of Re(CO)5Cl afforded 7 in high
rounded by four oxygen atoms from two hfac– ligands and yield. In previous reports, the common products of reac-
two nitrogen atoms from the pyridine moiety of L2. The tions between Re(CO)5Cl and NʝN ligands (such as 2-pyr-
central C=C bond length of the TTF core is 1.330(9) Å. L2 idinylimine and its derivatives) are ReI tricarbonyl com-
is almost planar in 6. In the TTF skeleton, the dihedral plexes.[28–31] As shown in Figure 9, the asymmetric unit in
angle between the two five-membered rings (containing S3, 7 consists of cationic [Re(CO)4(L3)]+ with [Re2Cl3(CO)6]–
S4, S5, and S6) is 2.70(1)°. In the solid state, unlike 4, the [tri-μ-halogenohexacarbonyldirhenate(I)] as the counterion.
molecules of 6 are face-to-face self-assembled to form a 1D
In the cation, L3 coordinates Re(1) by two nitrogen
chain-like structure along the c axis through short π–π atoms to form a strained five-membered metallacycle. As a
stacking interactions [the centroid···centroid distance be- result, the pyridyl ring forms a large dihedral angle of
tween benzene rings of adjacent molecules is 3.663(6) Å, 51.70(1)° with the phenyl ring. The average Re1–N bond
Figure 8].
length is 2.177 Å. The N1–Re1–N2 angle of 74.8(3)° is sig-
Eur. J. Inorg. Chem. 2012, 234–245
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Figure 7. ORTEP view of 6 with the atom numbering scheme (50% probability displacement ellipsoids, H atoms are omitted for clarity).
Figure 8. π–π stacking interactions in 6 viewed along the a axis (H atoms are omitted for clarity).
The anion consists of two rhenium atoms bridged by
three chlorine atoms, and three terminal carbonyl groups
complete the octahedral coordination for each rhenium
atom. The average Re–Cl distance is 2.515 Å, and the
average Re–C distance is 1.891 Å, which is shorter than that
in the cation. The Re–CϵO bond angles of 176.5(9)–
177.1(10)° are slightly distorted from linearity. The average
angle of Re2–Cl–Re3 is 84.58°. These values agree well with
those found in similar complexes.[34] The Re(2)–Re(3) dis-
tance of 3.384(1) Å is too long to postulate a direct metal–
metal interaction.
Shorter intermolecular S···S contacts are observed be-
tween the cations [S4···S5 3.672(5) Å], which form a 1D
chain motif along the a axis. The dinuclear rhenium(I)
anions are located between the cations (Figure 10).
Figure 9. ORTEP view of 7 with the atom numbering scheme (50%
probability displacement ellipsoids).
nificantly smaller than the ideal value of 90°, which is due
to the steric requirement of L3. The average Re–C (C1 and
C3) bond length for the terminal CO groups in the equato-
rial plane that includes the pyridine–imine ligand is
1.925 Å, which is shorter than the average value for the Re–
C (C2 and C4) bond (2.022 Å) in the axial position. All
other bond lengths and angles are in good agreement with
the related complexes [Re(bpy)(CO)4](PF6)[32] and
[Re(bpy)(CO)4](OSO2CF3)[33] (bpy = 2,2Ј-bipyridine or its
derivatives).
Figure 10. View of the crystal packing arrangement of 7. The
dashed lines represent S···S nonbonded contacts.
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Complexes with TTF-Fused π-Extended Schiff Bases
Spectroscopic Properties
Table 7. Electronic absorption data for La–L3 and 4–7.
Absorption, λabs [nm] (ε /m–1 cm–1)
The absorption spectra of all of the reported compounds
were measured in dichloromethane/acetonitrile (1:1) solu- La
229 (49293)
225 (32948)
231 (44649)
228 (54468)
226 (68213)
235 (44387)
233 (41869)
232 (41755)
230 (55542)
261 (25959)
315 (10876)
258 (28066)
259 (29895)
258 (34659)
305 (42416)
304 (39744)
304 (39744)
305 (24911)
328 (10903)
336 (8307)
325 (16110) 425 (3408)
325 (17239) 412 (3217)
332 (13777) 410 (2544)
422 (5412)
417 (5674)
410 (5506)
436 (4021)
Lb
tion at room temperature (Figure 11). The absorption data
are summarized in Table 7.
L1
L2
L3
4
5
6
7
an additional weak broad absorption band at lower energy
(400–500 nm), which corresponds to the intramolecular
charge-transfer transition from the highest occupied molec-
ular orbital in TTF to the lowest unoccupied molecular or-
bital in the electron-accepting pyridyl unit.[35] However, for
mononuclear 4–6, no obvious bands with metal-to-ligand
charge transfer (MLCT) character are observed, whereas 7
shows a weak MLCT [dπ(Re)Ǟπ*(L)] band at around 500–
600 nm.
The UV/Vis/NIR spectra of 4–7 were investigated upon
addition of the oxidant NOPF6 in dichloromethane/aceto-
nitrile (1:1) solution (Figure 12). In 4, a characteristic ab-
sorption band of TTF is exhibited at 305 nm. Upon the
addition of NOPF6, two characteristic absorption bands of
the TTF·+ species at around 450 and 950 nm are ob-
served.[36] After further oxidation with NOPF6, the charac-
teristic band of the dicationic TTF species at around
600 nm is no longer observed. The oxidation experiments
were also performed in different solvents, and the results are
Figure 11. Absorption spectra of La, Lb, L1–L3, and 4–7 in CH2Cl2/
CH3CN (1:1, v/v; c = 2.0ϫ 10–5 m).
All the ligands exhibit a strong absorption band at high similar, which suggests that the oxidized compounds can be
energy (λ Ͻ 400 nm), which is assigned to the intraligand obtained chemically. Similar phenomena were also ob-
πǞπ* transition. Compared with La and Lb, L1–L3 show served for 5–7.
Figure 12. UV/Vis/NIR absorption spectra of 4–7 upon the addition of NOPF6.
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J.-L. Zuo et al.
FULL PAPER
Electrochemical Properties
The electrochemical properties were studied by cyclic
voltammetry, and the data are collected in Table 8.
Table 8. Summary of redox potentials [V] for La–L3 and 4–7 (vs.
Ag/AgNO3).
1
2
ox
E1/2
E1/2
Ep
La
Lb
L1
L2
L3
4
0.32
034
0.60
0.63
0.72
0.71
0.71
0.72
0.72
0.74
0.79
–
–
–
–
–
0.43
0.42
0.41
0.42
0.42
0.41
0.47
Figure 14. Cyclic voltammograms of 4–7 (5ϫ 10–4 m) in CH2Cl2/
CH3CN (1:1, v/v) with nBu4NClO4 (0.1 m) at a sweep rate of
100 mV/s.
5
6
7
1.38
In 7, chelation to the ReI ion enhances the electron-with-
drawing ability of the 2-pyridine ring even further, which
causes a decrease of the electron density at the TTF core
and results in the large positive shifts of E1 and E2
As shown in Figure 13, La, Lb, and L1–L3 exhibit the
usual two-step reversible single-electron oxidations of TTF
ox
ox
derivatives, which are derived from the successive oxidation
(about 60 and 75 mV, respectively) compared to L3.[40] The
third irreversible oxidation peak at about 1.36 V is assigned
to the ReI-centered one-electron oxidation process.[22,41]
of the TTF unit to TTF+ and TTF2+, respectively. The E1
ox
and E2 values for La and Lb are around 0.33 and 0.61 V,
ox
respectively. Compared with the precursors, the electron-
withdrawing nature of the pyridine ring through the conju-
gated bridge makes the oxidation of the TTF core more
difficult for L1–L3.[4a,37] The two redox peaks are positively
shifted by 90 and 100 mV, respectively, which also confirms
the conjugation through the imine junction.[38]
Conclusions
A useful synthetic approach for π-extended TTF–Schiff
base ligands has been reported. Four coordination com-
plexes based on these redox active ligands have been pre-
pared and structurally characterized. The different coordi-
nation modes of the metal ions and relative orientation of
the terminal N donors result in the different crystalline or-
ganization of the complexes in the solid state. Electrochemi-
cal studies confirmed π-electron conjugated structures and
interesting redox active properties for all compounds. The
results demonstrate that these new imine-bridged TTF li-
gands that bear diverse substitution patterns are useful for
the synthesis and design of new metal complexes. Further
work to obtain oxidized complexes that combine magnetic
and conducting properties is in progress.
Experimental Section
General Procedures: IR spectra were recorded with a Vector22
Bruker spectrophotometer (400–4000 cm–1) as KBr pellets. UV/Vis
spectra were measured with a UV-3100 spectrophotometer. Ele-
mental analyses were performed with a Perkin–Elmer 240C an-
alyzer. NMR spectra were measured with a Bruker AM 500 spec-
trometer. Mass spectra were determined with an Autoflex II TM
instrument for MALDI-TOF-MS, GC-TOF instrument for EI-MS
and an LCQ Fleet instrument for ESI-MS. Absorption spectra
were measured with a Shimadzu UV-3100 spectrophotometer. Cy-
clic voltammograms were recorded with an Im6eX electrochemical
analytical instrument, with glassy carbon as the working electrode,
platinum as the counter electrode, Ag/AgNO3 as the reference elec-
trode, and 0.1 m nBu4NClO4 as the supporting electrolyte. All the
potentials were run at a scan rate of 100 mV/s. 4,5-Bis(methylthio)-
1,3-dithiol-2-thione (3a) and 4,5-ethylenedithio-1,3-dithiol-2-thione
(3b) were synthesized according to literature procedures.[41b]
Figure 13. Cyclic voltammograms of La, Lb, and L1–L3 (5ϫ 10–4 m)
in CH2Cl2/CH3CN (1:1, v/v) with nBu4NClO4 (0.1 m) at a sweep
rate of 100 mV/s.
In 4–6, the two observed redox potentials for the TTF
core remain almost unchanged (Figure 14). The small effect
of complexation on the oxidation potentials can be ascribed
to the large separation between the TTF core and the met-
allic fragment.[39]
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Complexes with TTF-Fused π-Extended Schiff Bases
5-Nitro-1,3-benzodithiole-2-thione (1): A mixture of potassium sulf-
ide (43%, 2.06 g, 8.03 mmol), carbon disulfide (1 mL), and N,N-
dimethylformamide (5 mL) was stirred for 2 h at room temperature.
To the red suspension of potassium trithiocarbonate was added
1,2-dibromo-4-nitro benzene (2.10 g, 7.40 mmol), and the mixture
was stirred for 32 h at 85 °C. The mixture was poured into water
(100 mL), and the precipitate was collected by filtration. The solid
was purified by chromatography on silica gel with dichlorometh-
ane/petroleum ether (v/v = 1:1) to obtain 1 as a pure yellow solid;
1623, 1598, 1551, 1457, 1411, 1242, 988, 886, 819, 772, 586, 502
1
cm–1. H NMR (500 MHz, CDCl3): δ = 8.86 (d, J = 5.0 Hz, 2 H),
8.54 (s, 1 H), 7.84 (d, J = 5.5 Hz, 2 H), 7.37 (s, 1 H), 7.35 (s, 1 H),
7.14 (d, J = 8.0 Hz, 1 H), 2.53 (s, 6 H) ppm. MS (MALDI-TOF):
m/z = 449.9 [M]+. C18H14N2S6 (450.71): calcd. C 47.97, H 3.13, N
6.21; found C 48.02, H 3.10, N 6.27.
La-Imine-3-pyridyl (L2): L2 was obtained from La and pyridine-3-
carbaldehyde according to a similar procedure to that described
above for L1.Red crystals suitable for X-ray diffraction were ob-
tained from evaporation of a solution of L2 in chloroform; yield
yield 1.53 g (93%). IR (KBr): ν = 1564, 1511, 1338, 1306, 1067,
˜
1
891, 767, 736 cm–1. H NMR (500 MHz, CDCl3): δ = 8.35 (d, J =
62%. IR (KBr): ν = 2919, 1615, 1454, 1417, 1324, 1203, 1125, 1024,
˜
1.5 Hz, 1 H), 8.24 (dd, J = 9.0, 2.0 Hz, 1 H), 7.62 (d, J = 9.0 Hz,
1 H) ppm. EI-MS: m/z (%) = 229.0 (100) [M]+, 185.0 (30) [M –
CS]+. C7H3NO2S3 (229.29): calcd. C 36.67, H 1.32, N 6.11; found
C 36.71, H 1.28, N 6.14.
891, 810, 772, 706, 467 cm–1. 1H NMR (500 MHz, CDCl3): δ =
9.01 (s, 1 H), 8.72 (d, J = 4.5 Hz, 1 H), 8.50 (s, 1 H), 8.30 (d, J =
8.0 Hz, 1 H), 7.45 (dd, J = 8.0, 5.0 Hz, 1 H), 7.27 (s, 1 H), 7.16 (d,
J = 1.0 Hz, 1 H), 7.03 (d, J = 8.0 Hz, 1 H), 2.44 (s, 6 H) ppm. MS
(MALDI-TOF): m/z = 450.1 [M]+. C18H14N2S6 (450.71): calcd. C
47.97, H 3.13, N 6.21; found C 48.02, H 3.10, N 6.27.
5-Amino-1,3-benzodithiole-2-thione (2): A solution of SnCl2·2H2O
(7.80 g, 34.57 mmol) in ethanol (10 mL) was added to a stirring
solution of 1 (2.00 g, 8.73 mmol) in HCl (90 mL, 12 m) and ethanol
(45 mL), and the mixture was heated to reflux for 13 h. The precipi-
tate was collected by filtration and washed with water. The crude
product was purified by silica gel chromatography with dichloro-
methane/petroleum ether (v/v = 2:1) as an eluent to obtain 2 as a
Lb-Imine-2-pyridyl (L3): L3 was obtained according to a similar pro-
cedure to that described above for L1 starting from Lb and pyr-
idine-2-carbaldehyde; yield 59%. IR (KBr): ν = 2911, 1626, 1584,
˜
1562, 1466, 1408, 1259, 1113, 996, 876, 805, 773, 740, 584, 893
1
cm–1. H NMR (500 MHz, CDCl3): δ = 8.76 (d, J = 3.5 Hz, 1 H),
light yellow solid; yield 0.69 g (40%). IR (KBr): ν = 3364, 1635,
˜
8.63 (s, 1 H), 8.21 (d, J = 8.0 Hz, 1 H), 7.87 (t, 1 H), 7.43 (q, 1 H),
7.31 (s, 2 H), 7.13 (d, J = 8.0 Hz, 1 H), 3.35 (s, 4 H) ppm. MS
(MALDI-TOF): m/z = 448.1 [M]+. C18H12N2S6 (448.69): calcd. C
48.18, H 2.69, N 6.24; found C 48.14, H 2.63, N 6.27.
1583, 1464, 1423, 1297, 1242, 1062, 833, 809, 568, 446 cm–1. 1H
NMR (500 MHz, CDCl3): δ = 7.22 (d, J = 8.5 Hz, 1 H), 6.77 (d,
J = 1.9 Hz, 1 H), 6.72 (dd, J = 8.5, 2.0 Hz, 1 H), 3.88 (s, 2 H) ppm.
EI-MS: m/z (%) = 199.0 (100) [M]+, 155.0 (42) [M – CS]+. C7H5NS3
(199.30): calcd. C 42.18, H 2.53, N 7.03; found C 42.38, H 2.61, N
7.08.
[Cu(hfac)2(L1)2] (4): A solution of L1 (9.0 mg, 0.02 mmol) in dichlo-
romethane (5 mL) was added to a hot solution of Cu(hfac)2·2H2O
(10.4 mg, 0.02 mmol) in hexane (6 mL). The dark red mixture was
stirred at room temperature for 15 min. Slow evaporation of the
resulting solution in the dark gave wine-colored platelets of 4,
which were suitable for single-crystal X-ray diffraction; yield 70%.
2-[4,5-Bis(methylthio)-1,3-dithiol-2-ylidene]-1,3-benzodithiol-5-amine
(La): Under an argon atmosphere, a solution of 2 (0.40 g,
2.01 mmol), 3a (0.48 g, 2.28 mmol), and P(OEt)3 (4.10 mL) in tolu-
ene (15 mL) was heated to 120 °C for 4 h. After the reaction, excess
solvent was removed under vacuum to afford a red oily residue,
which was subjected to silica gel column chromatography with
dichloromethane/petroleum ether (v/v = 1:1) as the eluent; yield
26%. Orange crystals suitable for X-ray diffraction were obtained
from evaporation of a solution of La in dichloromethane and hex-
IR (KBr): ν = 2924, 1642, 1615, 1555, 1525, 1482, 1427, 1322, 1258,
˜
1202, 1140, 1030, 870, 825, 790, 773, 688, 668, 587 cm–1.
[Mn(hfac)2(L1)2] (5): Dark red crystals 5 were obtained according
to a similar procedure to that described for 4 with Mn(hfac)2·2H2O
instead of Cu(hfac) ·2H O; yield 81%. IR (KBr): ν = 2906, 2359,
˜
2
2
1645, 1610, 1555, 1522, 1490, 1455, 1421, 1323, 1254, 1191, 1142,
ane. IR (KBr): ν = 3328, 2914, 1584, 1460, 1422, 1298, 1242, 1061,
˜
1012, 969, 884, 823, 789, 771, 687, 663, 583 cm–1.
1
897, 836, 811, 772, 568, 444 cm–1. H NMR (500 MHz, CDCl3): δ
= 6.99 (d, J = 7.5 Hz, 1 H), 6.61 (s, 1 H), 6.46 (d, J = 8.0 Hz, 1
H), 3.66 (s, 2 H), 2.43 (s, 6 H) ppm. MS (MALDI-TOF): m/z =
361.1 [M]+. C12H11NS6 (361.61): calcd. C 39.86, H 3.07, N 3.87;
found C 39.82, H 3.09, N 3.94.
[Cu(hfac)2(L2)2] (6): Dark red crystals 6 were obtained according
to a similar procedure to that described for 4 with L2 instead of
L ; yield 63%. IR (KBr): ν = 2920, 1645, 1616, 1557, 1531, 1463,
˜
1
1422, 1344, 1258, 1208, 1138, 1087, 868, 824, 800, 774, 744, 669,
582 cm–1.
2-(5,6-Dihydro[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-1,3-benzodi-
thiol-5-amine (Lb): Lb was obtained according to the procedure re-
ported above for La by using 3b instead of 3a. Orange crystals
suitable for X-ray diffraction were obtained from evaporation of a
solution of Lb in dichloromethane and hexane; yield 34%. IR
[Re(CO)4(L3)][Re2(CO)6Cl3] (7): Under a nitrogen atmosphere, a
mixture of Re(CO)5Cl (37 mg, 0.1 mmol) and L3 (49 mg, 0.1 mmol)
in toluene (8 mL) was heated to reflux for 2 h to give a black sus-
pension, which was cooled to room temperature, and the resulting
precipitate was collected by filtration. The crude solid was purified
by flash chromatography using dichloromethane as the eluent; yield
84%. Black crystals were obtained by diffusing diethyl ether into a
(KBr): ν = 3362, 2919, 1609, 1586, 1463, 1283, 1120, 884, 840, 802,
˜
771, 421 cm–1. 1H NMR (500 MHz, CDCl3): δ = 6.98 (d, J =
8.5 Hz, 1 H), 6.60 (s, 1 H), 6.46 (d, J = 8.5 Hz, 1 H), 3.64 (s, 2
H),3.27 (s, 4 H) ppm. MS (MALDI-TOF): m/z = 359.1 [M]+.
C12H9NS6 (359.60): calcd. C 40.08, H 2.52, N 3.89; found C 40.12,
H 2.47, N 3.93.
dichloromethane solution of 7. IR (KBr): ν = 2020, 1959, 1927,
˜
1886, 1474, 1453, 1355, 1302, 1236, 1114, 809, 770, 643, 530 cm–1.
1H NMR (500 MHz, DMSO): δ = 9.34 (s, 1 H), 9.06 (d, J = 5.5 Hz,
1 H), 8.35 (t, 2 H), 7.85 (m, 1 H), 7.74 (d, J = 8.5 Hz, 1 H), 7.72
(d, J = 2.0 Hz, 1 H), 7.44 (dd, J = 8.5, 6.5 Hz, 1 H), 3.40 (s, 4 H)
ppm. ESI-MS: m/z = 747.00 [Re(CO)4(L3)]+, 646.92 [Re2(CO)6-
Cl3]–, 341.33 [Re (CO)3Cl2]–.
La-Imine-4-pyridyl (L1): A mixture of La (0.12 g, 0.33 mmol), pyr-
idine-4-carbaldehyde (32 μL), and a catalytic amount of formic
acid in distilled ethanol (15 mL) was heated to reflux. After stirring
for 5 h, a red precipitate was collected by filtration, washed with
ethanol, and dried under vacuum. Red crystals suitable for X-ray
diffraction were obtained from evaporation of a solution of L1 in
Crystal Structure Determination: The data were collected with a
Bruker Smart Apex CCD diffractometer equipped with graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å) using a ω-2θ
dichloromethane and ethanol; yield 65%. IR (KBr): ν = 2916,
˜
Eur. J. Inorg. Chem. 2012, 234–245
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.
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Acknowledgments
This work was supported by the Major State Basic Research Devel-
opment Program (grant number 2011CB808704), the National Sci-
ence Fund for Distinguished Young Scholars of China (grant
number 20725104), and the National Natural Science Foundation
of China (NSFC) (grant numbers 21021062 and 51173075).
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Received: September 26, 2011
Published Online: December 7, 2011
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