Quasi-planar organic synthon and S···X (X = S or H-C) contacts in flat copper coordination chains: Syntheses, structures and conductive behaviour

Article abstract of DOI:10.1002/ejic.201301401

A new organic building block, TEPB, has been synthesized that comprises three 2-ethylthio-substituted pyrimidine groups coupled to one central phenyl ring at the 1-, 3- and 5-positions. TEPB exhibits a quasi-planar conformation due to its intramolecular C-H···N hydrogen bonds. The assembly of TEPB with CuI and CuCl₂ produced two flat coordination chains 1 and 2, both exhibiting similar assembly hierarchies from chain through 2D layer to 3D architecture. It was found that extensive S·· ·S and C-H···S contacts exist in the 2D layers of 1 and 2, respectively. Between the 2D layers of 2, there are O- H···Cl hydrogen-bonding interactions between water molecules and coordinated Cl atoms that provide a proton-transfer network. Complex 2 exhibits a smaller optical band gap (1.11 eV) than 1 (1.93 eV), which has been attributed to d-electron transition in the copper(II) ion. The d.c. conductivities of 1 and 2 at room temperature were measured to be 2.84 × 10^-12 and 2.42 × 10^-10 S cm^-1, respectively. The a.c. conductivity of 2 obtained at room temperature by the complex impedance technique is about 5.90 × 10^-9 S cm ^-1, which can be attributed largely to proton conduction. Moreover, the a.c. conductivity of 2 decreases almost linearly with increasing temperature, presumably as a result of its temperature-sensitive O-H···Cl hydrogen-bonding network that allows for proton conduction. The assembly of quasi-planar organic synthon TEPB with CuI and CuCl₂ produced two flat coordination chain structures (1 and 2) that incorporate S···S and C-H···S contacts in their packing structures. Complex 1 is an insulator, whereas 2 shows conductive properties with an a.c. conductivity of 5.90 × 10^-9 S cm^-1 at room temperature.

Full text of DOI:10.1002/ejic.201301401

FULL PAPER
DOI:10.1002/ejic.201301401
Quasi-Planar Organic Synthon and S···X (X = S or H–C)
Contacts in Flat Copper Coordination Chains: Syntheses,
Structures and Conductive Behaviour
Hai-Bin Zhu,*[a] Ru-Yu Shan,[a] Yan-Fang Wu,[a] and
Yong-Bing Lou*[a]
Keywords: Conducting materials / Coordination polymers / Impedance / Sulfur / Copper
A new organic building block, TEPB, has been synthesized
that comprises three 2-ethylthio-substituted pyrimidine
groups coupled to one central phenyl ring at the 1-, 3- and
5-positions. TEPB exhibits a quasi-planar conformation due
to its intramolecular C–H···N hydrogen bonds. The assembly
of TEPB with CuI and CuCl2 produced two flat coordination
chains 1 and 2, both exhibiting similar assembly hierarchies
from chain through 2D layer to 3D architecture. It was found
that extensive S···S and C–H···S contacts exist in the 2D lay-
ers of 1 and 2, respectively. Between the 2D layers of 2, there
are O–H···Cl hydrogen-bonding interactions between water
molecules and coordinated Cl atoms that provide a proton-
transfer network. Complex 2 exhibits a smaller optical band
gap (1.11 eV) than 1 (1.93 eV), which has been attributed to
d-electron transition in the copper(II) ion. The d.c. conductiv-
ities of 1 and 2 at room temperature were measured to be
2.84ϫ10–12 and 2.42ϫ10–10 Scm–1, respectively. The a.c.
conductivity of 2 obtained at room temperature by the com-
plex impedance technique is about 5.90ϫ10–9 Scm–1, which
can be attributed largely to proton conduction. Moreover, the
a.c. conductivity of 2 decreases almost linearly with increas-
ing temperature, presumably as a result of its temperature-
sensitive O–H···Cl hydrogen-bonding network that allows for
proton conduction.
productive approach towards conductive CPs, as exem-
plified by the well-known MX[8–10] or MMX chains (M =
metal)[11–15] and “Shish-Kebab” molecular systems.[16]
Moreover, CPs based on metal thiolate bonds have received
long-standing interest because the π-donating character of
the sulfur p orbital would improve metal-to-ligand electron
exchange.[17–23] One practical strategy for gaining greater
electrical conduction or even superconduction is to fabri-
cate columnar organic molecular stacking with closely over-
lapping π orbitals in CPs, which constitute the principal
electron transport pathway. In this regard, outstanding ex-
amples are provided by CPs based on organic radical mo-
lecules such as DCNQI,[24,25] TCNQ,[26–28] TANC,[29] and
tetrathiafulvalene (TTF) derivatives.[30] For ion-conductive
CPs, ion transport is primarily governed by two important
factors, namely the ion carrier and their transport networks,
for which there is an excellent review recently published by
Kitagawa and co-workers.[31]
In sharp contrast with their numerous applications in,
for example, gas storage, separation and catalysis,[32–34] the
development of conductive properties in CPs is yet in its
infancy, and there still is great scope for imaginative design
in this interdisciplinary field. To the best of our knowledge,
small-molecule organic semi-conductors have led to great
improvements in organic field effect transistors (OFETs)
and organic semi-conductors (OSCs), largely due to the
good understanding of the relationship between device per-
formance and molecular structure.[35,36] For example, it is
Introduction
In recent years there has been an upsurge of interest in
the design of conductive coordination polymers (CPs)[1–4]
due to their great potential in solid-state electronic de-
vices.[5] Although conductive CPs can be categorized into
two general families according to their conduction mecha-
nism (electron or ion), the key to their success is in estab-
lishing an either electrical or ionic conduction pathway. For
electrically conductive CPs, there are several strategies that
have been systematically explored over the past decade. For
example, the incorporation of metal coordination bonds
has been attempted to promote electronic communication
across organic molecules by enhancing intermolecular in-
teractions beyond the van der Waals limit, which has been
well demonstrated by Xu and co-workers’ work on multiple
thioether-substituted polycyclic aromatic hydrocarbons
(PAHs) with BiX3 (X = Cl, Br).[6,7] In addition, elaboration
of a pπ–dπ conjugated spine through coordinative interac-
tions between metal centres (including mixed valence) and
organic bridging molecules or halogen atoms is another
[a] School of Chemistry and Chemical Engineering, Southeast
University, Jiulong Lake Campus,
211189 Nanjing, China
E-mail: zhuhaibin@seu.edu.cn
lou@seu.edu.cn
http://chem.seu.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301401.
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well recognized that intermolecular π–π stacking together intermolecular columnar stacking.[43–46] Finally, the two
with S···S or C–H···S contacts are responsible for the charge unequal pyrimidine N atoms may allow different modes of
transport in sulfur-containing organic conductors (e.g., coordination for structural diversity. In this paper we report
TTF and its derivatives) in which the delocalized π orbital on our initial results of the assembly of TEPB with CuI and
generally shows a planar or quasi-planar conforma- CuCl2, the CuI and CuII atoms being selected as metal
tion.[37–39] Moreover, it has also been discovered that S···S centres because of their redox-active nature which might
interactions can direct molecular stacking from a herring- enhance metal–ligand electronic communication (e.g.,
bone motif to a face-to-face π–π overlapping motif, which MLCT or LMCT).
is believed to facilitate charge transport.[40–42] Learning
from the design rules of organic conductors, we have de-
vised a new organic building block, namely 1,3,5-tris[2-(eth-
ylthio)pyrimidin-4-yl]benzene (TEPB; Scheme 1) in order
Results and Discussion
to construct CPs showing conductive properties. The design
of TEPB has taken into account the following issues. First,
Synthesis and Characterization of TEPB
the intramolecular C–H···N hydrogen bonds between the
The synthetic procedure for TEPB was developed on the
basis of our previous work on heterothione ligands.[47–49]
As outlined in Scheme 2, the title organic molecule, TEPB,
was prepared in three steps starting from 1,3,5-triacetyl-
benzene (P1). Aldol condensation of P1 with N,N-dimethyl-
formamide dimethyl acetal almost quantitatively produced
the intermediate P2. Under basic conditions, the reaction
of P2 with thiourea furnished P3 bearing three pyrimidinyl-
thiol groups, which was ethylated with EtI as the alkylating
agent in the presence of sodium methoxide to give TEPB.
The molecular structure of TEPB was characterized by
spectroscopic methods and confirmed by microanalysis
techniques. The 1H NMR spectrum of TEPB in CDCl3
shows a singlet of the central phenyl proton at δ = 8.93 ppm
(3 H), the pyrimidine units of TEPB give rise to two reso-
nances at δ = 8.65 (d, J = 5.1 Hz, 3 H) and 7.52 ppm (d, J
= 5.2 Hz, 3 H), and the ethyl groups of TEPB appear at δ
= 3.30 (-CH2-) and 1.51 ppm (CH3). The observation of
central phenyl ring and the outer pyrimidinyl ring are be-
lieved to lock the molecule into a quasi-planar conforma-
tion, maximizing π-orbital delocalization. Secondly, the
presence of the thioether S atom is expected to form S···S
or C–H···S contacts. Thirdly, it was hoped that the choice
of the modest-sized ethyl substituent would influence the
molecular packing but without blocking the metal coordi-
nation to the pyrimidine N atom due to steric hindrance
because introduction of a substituent at the periphery of the
organic conductor backbone has been reported to promote
1
only one set of H NMR signals for TEPB suggests that
the rotation of pyrimidine units with respect to the central
phenyl ring occurs faster in solution than the NMR times-
cale.
Scheme 1. Schematic representation of the TEPB molecule.
Scheme 2. Synthesis of TEPB.
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Note that the TEPB molecule is intrinsically chiral ac- only a microcrystalline powder. It is assumed that the water
cording to the definition of chirality, and should exhibit slows the rate of reaction between TEPB and CuI, which
planar chirality with the central phenyl ring as its chiral assists single-crystal growth. Dark-green plate-like crystals
plane. Nevertheless, it should remain racemic in solution of 2 were readily obtained from the binary diffusion system
as isomerization occurs easily by the so-called Kurland flip EtOH/CH2Cl2 in which an EtOH solution of CuCl2 was
mechanism.[50] Indeed, a solution of TEPB in ethyl acetate layered over a CH2Cl2 solution of TEPB. Compounds 1
shows no optical rotation. Interestingly, single-crystal X-ray and 2 are insoluble in common solvents, which precludes
diffraction analysis showed that the crystallized TEPB further solution characterization. The phase purity of 1 and
forms in the chiral space group P65 with a flack parameter 2 was confirmed by comparing their simulated and experi-
of 0.0(2), which indicates that crystallization of TEPB leads mental PXRD patterns (see Figure S3 in the Supporting In-
to spontaneous resolution of its racemate. As shown in Fig- formation).
ure 1, the TEPB molecule has three identical 2-ethylthiopy-
rimidin-4-yl functional groups coupled through C–C bonds
Crystal Structure of 1
to the central phenyl ring at its 1-, 3- and 5-positions, and
are arranged clockwise in terms of space orientation of
three S–C(ethyl) bonds around the central phenyl ring. As
we expected, there exist intramolecular C–H···N hydrogen
bonds (C22–H22A···N2, C20–H20A···N4 and C24–
H24A···N6) between the central phenyl ring and the three
pyrimidinyl rings leading to small dihedral angles (9.87,
14.51 and 1.68°). As a consequence, the TEPB mo-
lecule exhibits a quasi-planar conformation with four rings
almost in the same plane.
Assembly 1 crystallizes in the monoclinic crystal system
and C2/c space group. As shown in Figure 2, assembly 1
has a one-dimensional (1D) chain structure with alternate
linking of the Cu4I4 cluster and TEPB molecule pairs. Each
Cu4I4 cluster comprises four copper atoms, two μ-4 I atoms
and two μ-2 I atoms, all being related by a local symmetric
centre. Specifically, four copper atoms are organized into a
planar square with the two Cu–Cu lengths being 2.438 Å
and 3.204 Å. The two μ-4 I atoms are located above and
below the plane defined by Cu4 with Cu–I distances ranging
from 2.773 to 2.838 Å. In contrast, the two μ-2 I atoms are
coplanar with the Cu4 plane and situated near the short
sides of the Cu4 square with Cu–I bond lengths of 2.590
and 2.643 Å. In the coordination chain of 1, each Cu4I4
cluster serves as a four-connecting inorganic node because
each tetrahedral Cu atom has only one coordination site
available. However, the coordination directions of the four
Cu atoms are almost parallel due to their square-planar ar-
rangement, which limits the structural dimension of 1.
Alongside the coordination chain of 1, adjoining Cu4I4
clusters are spaced by a pair of TEPB molecules through
four Cu–N coordination bonds, with a mean Cu–N dis-
tance of 1.983 Å, and the N–Cu–Cu linkage is approxi-
mately linear. Also, the Cu4I4 clusters are orientated in such
a way that the Cu4 planes from two neighbouring Cu4I4
clusters are tilted towards each other with a dihedral angle
of 76.64°. A single TEPB molecule behaves as a bis(mono-
Figure 1. Molecular structure of TEPB with the numbering of the
selected atoms (the central phenyl plane is highlighted in pink and
the C–H···N hydrogen bonds are denoted with a green dotted line).
In its solid-state packing, the TEPB molecules are linked
through C–H···S interactions into a 2D sheet-like network
parallel to the ab plane (see Figure S1 in the Supporting
Information). All the 2D sheets are packed one above an-
other with equivalent interplanar spacings of 3.830 Å (see
Figure S2 in the Supporting Information). Each TEPB mo-
lecule in one sheet is stacked over another TEPB molecule
from the adjacent sheet in an offset manner such that aro-
matic π–π interactions can be observed between the central
phenyl ring and pyrimidinyl rings.
Synthesis and Characterization of 1 and 2
The assembly of TEPB with CuI in the ternary solvent
system CH3CN/H2O/CH2Cl2 by a layering method pro-
duced orange block crystals of 1. The presence of the water
buffer layer is important for the growth of single crystals
Figure 2. One-dimensional chain structure of 1 (I atom: purple ball;
because the binary solvent system CH3CN/CH2Cl2 gives Cu atom: yellow ball).
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dentate) bridging ligand with one 2-ethylthiopyrimidinyl S···S contacts (dS···S = 3.680 Å) to form a 2D sheet. The
(EP) unit free of coordination, which also accounts for the 2D sheets are overlain with an equal interplanar spacing of
low dimension of 1. The ethylthiol S atoms of TEPB are around 6.964 Å, with the chains in each layer displaced
not involved in metal coordination, the mean Cu–S distance with respect to those in adjacent layers (see Figure S5 in the
of about 3.122 Å being far beyond the sum of the covalent Supporting Information).
radii of copper(I) and S (2.39 Å). The two TEPB molecules
between two Cu4I4 clusters are stacked in a slipped face-to-
Crystal Structure of 2
face fashion and close aromatic π–π interactions are ob-
served, as manifested by short centroid-to-centroid dis-
tances ranging from 3.439 to 3.581 Å (Figure S4 in the Sup-
porting Information). In particular, the two chiral TEPB
molecules in one pair display the same absolute configura-
tion, but the neighbouring pairs are totally opposite in con-
figuration. Therefore the whole coordination chain is essen-
tially achiral.
The alignment of Cu4I4 clusters is almost linear in the
chains of 1, whereas the TEPB molecule pairs are in a zig-
zag arrangement. Similarly to the free TEPB molecule, the
coordinated TEPB molecules in 1 retain a nearly planar
conformation due to intramolecular C–H···N hydrogen
bonds, the corresponding dihedral angles varying from 7.06
to 14.85°. In summary, 1 might be viewed as a one-dimen-
sional zig-zag double-decked chain constructed from quasi-
planar TEPB molecules and Cu4I4 clusters. In the crystal
packing of 1 (Figure 3), chains interact side-by-side through
Assembly 2 crystallizes in the same crystal system and
space group as 1. As depicted in Figure 4, 2 also exhibits a
1D chain structure constructed from alternately linking sin-
gle molecules of TEPB and the CuCl2 inorganic compo-
nent. The copper(II) atom in 2 is four-coordinate rather
than a typical five- or six-coordinate structure and adopts
a distorted square-planar geometry that is completed by
two N atoms from two TEPB molecules and two chlorine
atoms. The Cu–N bond lengths are identical [Cu1–N1:
2.012(3) Å, Cu1–N3: 2.011(3) Å], and the Cu–Cl bond
lengths are almost equal [Cu1–Cl1: 2.220(1) Å, Cu1–Cl2:
2.230(1) Å]. The bond angles for N1–Cu1–N3 and Cl1–
Cu1–Cl2 are 161.5(1) and 160.08(6)°, respectively. Similarly
to 1, the TEPB molecule in 2 also acts as a bridging ligand
in a bis(monodentate) coordination mode leaving one EP
unit unbound. The distance between the sulfur atom in
each coordinating EP unit and the copper(II) atom (Cu1–
S1: 3.104 Å, Cu1–S2: 3.214 Å) is much longer than the sum
of the covalent radii of the CuII and S atoms (2.34 Å),
which suggests the absence of Cu–S interactions. Distinctive
from 1, one EP unit in the TEPB molecule in 2 flips from
one side to the other, thereby changing its molecular shape
from a three-bladed propeller to an “m” shape. Despite its
variation in shape, the TEPB molecule retains its chiral na-
ture. Alongside the chain of 2, molecules of TEPB with
opposite configurations are positioned sequentially in a
broad Z shape just like the alignment of the copper(II)
atoms. Notably, with the assistance of intramolecular C–
H···N hydrogen bonds, the TEPB molecules in 2 exhibit a
more rigid planar conformation with smaller dihedral
angles (2.78, 5.48 and 4.55°) than 1. Moreover, all CuII
atoms and TEPB molecules lie approximately in the same
plane, showing a one-dimensional flat zig-zag coordination
chain structure motif.
Figure 3. Chains of 1 interacting through S···S contacts (red dotted
line).
Figure 4. One-dimensional chain structure of 2.
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In the crystal packing of 2, the chains associate through tion edge),[51] the HOMO–LUMO gaps (Eg = band gaps)
C–H···S (dH···S = 2.748 Å) interactions to form a 2D sheet- of 1 and 2 were estimated from their absorption edges to
like network (Figure 5). However, the shortest S···S separa- be 1.93 and 1.11 eV, respectively. The HOMO–LUMO gap
tion is 4.627 Å between two neighbouring chains in the of 2 is comparable to the band gap of the Si semi-conductor
same layer. The layers are parallel to each other and further (1.11 eV at 300 K). In comparison with 1, a narrow
stacked with an interplanar spacing of 6.940 Å, with every HOMO–LUMO gap is observed in 2, which may be attrib-
chain in one layer also displaced with respect to that in the uted to 1) a low-energy d-electron transition in the cop-
neighbouring layer. Note that water molecules in one layer per(II) ion and 2) the more planar geometry of TEPB in 2
form O–H···Cl hydrogen bonds with the Cl atoms from ad- maximizing π-electron delocalization.
jacent layers, and thus parallel layers assemble to form a
3D hydrogen-bonded supramolecular architecture (see Fig-
ure S6 in the Supporting Information).
Conductive Properties
The conducting properties were studied by complex im-
pedance spectroscopy [Z* = ZЈ – jZЈЈ, in which j = (–1)1/2],
which gives the conductive properties of bulk materials as
a function of temperature and frequency. The impedance
measurements were conducted on pressed powder pellet
samples sandwiched by
a
square brass electrode
(10.2ϫ10.2 mm2); the thicknesses of the pellet samples of
1 and 2 were 0.32 and 0.30 mm, respectively. ZView soft-
ware was used to fit the experimental impedance data in
the frequency range of 100 Hz–10 MHz to obtain bulk con-
ductivity, which applies the least-squares fitting method to
the equivalent model.[52] In this case, the equivalent circuit
comprises three resistances (R1, R2 and R3), two capaci-
tances (C1 and C2) and one constant phase element
(CPE3), with the R1–C1, R2–C2 and R3–CPE3 parallel cir-
cuits representing the resistances and capacitances corre-
sponding to the bulk sample, grain boundary and electrode
interfaces, respectively.[53–55] The conductivities were calcu-
lated by using the equation σ = 1/R1ϫd/S, in which d is the
thickness of the pellet sample and S is the electrode area.
First, we examined the direct-current (d.c.) conductivities
of 1 and 2 at room temperature (see Figure S7 in the Sup-
porting Information). It was found that 1 behaves as an
insulator with a conductivity of 2.84ϫ10–12 Scm–1 whereas
2 exhibits a conductivity of 2.42ϫ10–10 Scm–1 at room tem-
perature. The higher d.c. conductivity of 2 compared with
1 agrees with its smaller band gap. According to the initial
d.c. conductivity data, we also scrutinized the temperature
dependence of the conductivity of 2 through the complex
impedance technique. Figure 7 (a) shows the plots of ZЈ
versus ZЈЈ (Nyquist diagram) over a wide range of fre-
quencies at different temperatures; the Nyquist plots pres-
ent semi-circular arcs, the diameters of which increase with
increasing temperature. Processed by using the ZView
software, the conductivity–temperature (σ–1/T) profile was
obtained, as shown in Figure 7 (b). Assembly 2 exhibits
Figure 5. Interchain interactions of 2 through C–H···S contacts
(shown by red dotted lines).
Spectroscopic Properties
Figure 6 depicts the absorption spectra of 1 and 2. As-
sembly 1 shows a broad absorption in the visible region, the
peaks at around 230 and 382 nm arising from a transition in
the ligand itself, and the shoulder peak at around 466 nm
has been attributed to metal-to-ligand charge transfer
(MLCT). In contrast, assembly 2 displays a strong absorp-
tion at around 611 nm as well as two ligand-based absorp-
tion peaks at 222 and 346 nm. The absorption maximum at
611 nm has been ascribed to the d-electron transition in the
copper(II) ion in 2, which might be enhanced by mixing of
the d orbitals of the copper(II) ion and the HOMOs of the
TEPB ligands. By using the equation Eg = 1240/λ(absorp-
a.c. (a.c.
=
alternating current) conductivity of
5.90ϫ10–9 Scm–1 at room temperature, which is one order
of magnitude higher than its d.c. conductivity. Moreover, it
was also observed that its a.c. conductivity decreases almost
linearly with increasing temperature.
Although 1 and 2 exhibit similar assembly hierarchies,
both being from 1D chain through 2D layer to 3D architec-
ture, the distinctive difference between them is that the 2D
layer stacking in 2 is largely a result of O–H···Cl hydrogen
Figure 6. UV/Vis absorption spectra of 1 and 2 in the solid state
[the absorption edge corresponds to the intersection point between
the baseline along the wavelength axis and a line (dotted line) ex-
trapolated from the linear portion of the threshold.].
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It has been found that strong S···S and C–H···S contacts
in 1 and 2, respectively link the chains to form 2D layers.
Moreover, the stacking of 2D layers in 2 is reinforced
through O–H···Cl hydrogen-bonding interactions involving
free water molecules and coordinated chlorine atoms. The
d.c. conductivity of 2 is almost 100 times greater than that
of 1, which might be ascribed to its smaller band gap.
Moreover, it was found that the a.c. conductivity of 2 arises
mainly from proton conductivity as a result of free water
molecules and the O–H···Cl hydrogen-bonding network.
Furthermore, the results of this study also indicate that the
electrical conductivities of 1 and 2 are still fairly low despite
the presence of a quasi-planar organic synthon and exten-
sive S···S (for 1) or C–H···S contacts (for 2), and are more
likely limited by the lack of effective π-orbital stacking be-
tween 2D layers in 1 and 2. This issue is currently being
investigated by our group.
Experimental Section
Materials and Measurements: All solvents and reagents of analyti-
cal grade were used as received without prior purification. 1,3,5-
Triacetylbenzene (P1) was synthesized according to a literature
method.[58] IR spectra were recorded with a Thermo Scientific
Nicolet 5700 FT-IR spectrophotometer with KBr pellets in the
400–4000 cm–1 region. 1H NMR spectra were recorded with a
Bruker AVANCE-500 spectrometer. Electrospray ionization (ESI)
mass spectra were recorded with a Finnigan MAT SSQ 710 mass
spectrometer in the scan range 100–1200amu. The solid-state UV/
Vis absorption spectra were recorded with a Shimadzu UV-2450
UV/Vis spectrophotometer. Electrochemical impedance spectra
(EIS) were recorded with a CHI660D (Chenghua, Shanghai) elec-
trochemistry workstation with an applied frequency range of
100 kHz to 1 Hz and an oscillation voltage of 100 mV.
Figure 7. a) Complex impedance ZЈ-ZЈЈ plot for 2; b) temperature-
dependence of the a.c. conductivity of 2 (inset: equivalent circuit
model for 2; red line represents the linear fit).
bonding between free water molecules and coordinating
chlorine atoms. It is known that the a.c. conductivity ob-
tained by the complex impedance technique includes both
electrical and ionic contributions.[56,57] On the basis of their
structures, the free water molecules in 2 may contribute to
the whole conductivity of 2 through a proton-conduction
mechanism. By comparing its d.c. and a.c. conductivities, it
is apparent that the a.c. conductivity of 2 is dominated by
proton conduction, which should rely on the free water mo-
lecules and the O–H···Cl hydrogen-bonding network. The
exact explanation for the decrease in the a.c. conductivity
of 2 with increasing temperature remains to be explored,
but one possible reason is that increasing temperature may
destroy the temperature-sensitive O–H···Cl hydrogen-bond-
ing network resulting in a drop in conductivity because
thermal gravimetric analysis (TGA) has shown that 2 loses
its water molecules in the temperature range of 40–100 °C
(see Figure S8 in the Supporting Information).
Synthesis of P2: A mixture of P1 (1.22 g, 6.0 mmol) and N,N-di-
methylformamide dimethyl acetal (2.86 g, 24.0 mmol) was stirred
whilst heating under a gentle reflux for 10 h. After cooling to room
temperature, the reaction solution was evaporated under vacuum
to dryness. The resulting solid was triturated with diethyl ether,
filtered and dried under vacuum to afford P2 as a yellow powder,
yield 1.8 g, 81.1%. IR (KBr): ν = 2915 (w), 2804 (w), 1634 (vs),
˜
1593 (vs), 1543 (vs), 1414 (s), 1358 (m), 1277 (s), 1227 (m), 1196
(m), 1118 (s), 1085 (m), 977 (w), 946 (w), 850 (w), 777 (w), 693
1
(m) cm–1. H NMR (CDCl3, 25 °C): δ = 8.53 (s, 3 H), 7.82 (d, J =
12.3 Hz, 3 H), 5.86 (d, J = 12.3 Hz, 3 H), 3.16 (s, 9 H), 2.95 (s, 9
H) ppm. C21H27N3O3 (369.46): calcd. C 68.27, H 7.37, N 11.37;
found C, 68.39, H 7.56, N 11.56.
Synthesis of P3: Sodium metal (0.78 g, 34.0 mmol) was added por-
tionwise to stirred anhydrous EtOH (50 mL) at room temperature.
Upon disappearance of the sodium metal, P2 (1.11 g, 3.0 mmol)
and thiourea (0.72 g, 9.5 mmol) were added in sequence to the solu-
tion, which was then heated at reflux for 12 h. After complete reac-
tion, the reaction solution was poured into water (100 mL) and
neutralized with 5% diluted HCl solution to pH 6–7. The precipi-
tated orange yellow solid (P3) was collected by suction filtration
and dried under vacuum at 40 °C overnight, yield 1.1 g, 89.4%. IR
Conclusions
In this work we have synthesized a new organic building
block, TEPB, which contains three 2-ethylthio-substituted
pyrimidine groups and shows a quasi-planar conformation
even when coordinated to metal ions due to intramolecular
C–H···N hydrogen bonds. The assembly of TEPB with CuI
and CuCl2 led to two flat coordination chains, 1 and 2,
respectively, both of which exhibit analogous assembly hier-
(KBr): ν = 3074 (w), 2988 (w), 2921 (w), 1595 (s), 1562 (m), 1483
˜
(w), 1439 (w), 1377 (w), 1247 (m), 1205 (w), 1163 (m), 976 (w), 794
1
(w), 724 (w) cm–1. H NMR ([D6]DMSO, 25 °C): δ = 13.05 (br., 3
archies from 1D chain through 2D layer to 3D architecture. H, SH), 8.99 (s, 3 H), 8.20 (d, J = 6.5 Hz, 3 H), 7.69 (d, J = 6.6 Hz,
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3 H) ppm. C18H12N6S3 (408.51): calcd. C 52.92, H 2.96, N 20.57;
found C 52.89, H 2.76, N 20.86.
Table 1. Crystallographic data for TEPB, 1 and 2.
TEPB
1
2
Synthesis of TEPB: Sodium metal (1.04 g, 45.0 mmol) was dis-
solved in anhydrous EtOH (30 mL) at room temperature to give a
clear colourless solution. P3 (1.02 g, 2.5 mmol) was then added and
the mixture stirred for 30 min to form a cloudy solution. Upon
addition of EtI (14.0 g, 90.0 mmol), the resulting solution was
stirred at room temperature for a further 24 h. The reaction was
quenched by the addition of water (100 mL). The resultant precipi-
tate was filtered and washed thoroughly with water. Upon decol-
ourization with active carbon in CHCl3, the final product TEPB
was afforded as a pale-yellow solid. Single crystals of TEPB suit-
able for X-ray diffraction were obtained by slow diffusion of
MeOH into its solution of CH2Cl2, yield 0.6 g, 49.2%. IR (KBr):
Formula
Mr
Crystal system hexagonal
Space group
a [Å]
b [Å]
c [Å]
α [°]
C
492.00
24H24N6S3
C26H27Cu2I2N7S3 C24H26Cl2CuN6OS3
914.66
monoclinic
645.17
monoclinic
C2/c (No. 15)
27.172(4)
14.924(2)
14.398(2)
90
P65 (No.170) C2/c (No. 15)
13.6450(8)
13.6450(8)
22.236(3)
90
90
120
3585.4(3)
6
1.369
31.272(1)
14.5238(4)
14.0363(4)
90
β [°]
106.613(4)
90
105.306(2)
90
γ [°]
V [Å3]
Z
6109.0(3)
8
5632(1)
8
Dcalc [gcm–3
F(000)
]
1.989
1.522
ν = 3079 (w), 2971 (w), 2928 (w), 2868 (w), 1544 (s), 1448 (m),
˜
1548
3552
2648
1400 (m), 1343 (m), 1264 (w), 1200 (m), 1183 (m), 899 (w), 824
(m), 772 (w), 733 (m), 681 (w), 630 (m) cm–1. 1H NMR (CDCl3,
25 °C): δ = 8.93 (s, 3 H), 8.66 (d, J = 5.1 Hz, 3 H), 7.52 (d, J =
5.2 Hz, 3 H), 3.30 (t, 6 H), 1.51 (t, 9 H) ppm. MS (ESI): m/z (%)
= 493 (100) [M + H]+. C24H24N6S3 (492.67): calcd. C 58.51, H
4.91, N 17.06; found C 58.62, H 4.96, N 17.26.
Reflections
collected
Unique
reflections
R(int)
R1, wR2
[IϾ2σ(I)]
R1, wR2
(all data)
GOF
25515
17812
22912
4065
5380
2793
0.041
0.025
0.041
0.0645,
0.1455
0.0813,
0.1577
1.03
0.0312,
0.0737
0.0377,
0.0766
1.00
0.0440,
0.1322
0.0662,
0.1454
1.01
Preparation of 1: A CH3CN solution (3.0 mL) containing CuI
(0.06 mmol) was carefully layered above
a CH2Cl2 solution
(3.0 mL) of TEPB (0.02 mmol), with H2O (5.0 mL) as a buffer layer
being placed between them. Crystals of {[(C24H24N6S3)Cu2I2]·
CH3CN}n (1) were formed over a period of 1 month. A single crys-
tal suitable for X-ray diffraction analysis was selected from the bulk
crystals.
Supporting Information (see footnote on the first page of this arti-
cle): Packing structure graphics for TEPB and two coordination
compounds, PXRD characterization of 1and 2, I-V plots of 1 and
2, TGA data of 2.
1: Yield: 43.6% (based on TEPB). IR (KBr): ν = 3510 (w), 3074
˜
(w), 2962 (w), 2924 (w), 2363 (w), 1561 (s), 1449 (w), 1392 (m),
1338 (m), 1269 (w), 1203 (m), 1178 (m), 1119 (w), 821 (m), 732 (w),
635 (w) cm–1. C26H27Cu2I2N7S3 (914.63): calcd. C 34.14, H 2.98,
N 10.72; found C 34.25, H 2.80, N 10.78.
Acknowledgments
Preparation of 2: An EtOH solution (5.0 mL) containing
CuCl2·2H2O (0.08 mmol) was carefully layered above a CH2Cl2
solution (5.0 mL) of TEPB (0.02 mmol). Crystals of
{[(C24H24N6S3)CuCl2]·H2O}n (2) were formed over a period of
1 week. A single crystal suitable for X-ray diffraction analysis was
selected from the bulk crystals.
We acknowledge financial support from the National Natural
Science Foundation of China (NSFC) (grant number 21171036)
and the Teaching and Research Program for the Excellent Young
Teachers of Southeast University.
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2: Yield: 53.5% (based on TEPB). IR (KBr): ν = 3593 (w), 3507
˜
(w), 3074 (w), 2930 (w), 2359 (w), 1567 (s), 1454 (m), 1420 (m),
1343 (m), 1365 (m), 1330 (m), 1260 (w), 1206 (m), 1181 (w), 828
(m), 799 (w), 771 (w), 732 (w), 691 (w), 649 (w), 638 (w) cm–1.
C24H26Cl2CuN6OS3 (645.14): calcd. C 44.68, H 4.06, N 13.03;
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Received: November 1, 2013
Published Online: February 3, 2014
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