A homochiral Cu(II) coordination polymer built from helical motif based on two V-shaped ligands

Article abstract of DOI:10.1016/j.inoche.2014.04.020

By using a V-shaped N-containing ligand and a V-shaped carboxylate ligand, we have successfully synthesized a 3D novel copper homochiral coordination polymer, namely [Cu(OPY)(1,3-bdc)]_n (complex 1), [1,3-H ₂bdc = isophthalic acid, OPY = 4,4′-(oxybis(4,1-phenylene)) dipyridine]. The compound has been solvothermally synthesized and characterized by IR, elemental analysis, single crystal X-ray diffraction, XRD, UV-vis, and TG analysis. The complex 1 crystallizes in the chiral space group P6₅ and possesses an unprecedented uninodal 3D 7⁵· 8 topology. However, the complex was synthesized by achiral materials. The complex 1 displays a moderate SHG response and its SHG efficiency is about 0.3 times that of urea. In addition, the compound shows high thermal stability.

Full text of DOI:10.1016/j.inoche.2014.04.020

A homochiral Cu(II) coordination polymer built from helical motif based on
two V - shaped ligands
Zhi-Liang Zhang, Xiao-Qiang Yao, Ni An, Heng-Chang Ma, Zi-Qiang
Lei, Jia-Cheng Liu
PII:
DOI:
Reference:
S1387-7003(14)00182-8
doi: 10.1016/j.inoche.2014.04.020
INOCHE 5559
To appear in:
Inorganic Chemistry Communications
Received date:
Revised date:
Accepted date:
6 February 2014
4 April 2014
10 April 2014
Please cite this article as: Zhi-Liang Zhang, Xiao-Qiang Yao, Ni An, Heng-Chang Ma, Zi-
Qiang Lei, Jia-Cheng Liu, A homochiral Cu(II) coordination polymer built from helical
motif based on two V - shaped ligands, Inorganic Chemistry Communications (2014), doi:
10.1016/j.inoche.2014.04.020
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ACCEPTED MANUSCRIPT
A homochiral Cu(II) coordination polymer built from helical motif
based on two V−shaped ligands
Zhi-Liang Zhang, Xiao-Qiang Yao*, Ni An, Heng-Chang Ma, Zi-Qiang Lei,
Jia-Cheng Liu*
Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of
Education, Key Laboratory of Polymer Materials of Gansu Province, Key Laboratory
of Bio electrochemistry & Environmental Analysis of Gansu Province, College of
Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou
730070, P. R. China
ABSTRACT
By using a V−shaped N-containing ligand and a V−shaped carboxylate ligand, we
have successfully synthesized a 3D novel copper homochiral coordination polymer,
namely [Cu(OPY)(1,3-bdc)]n (complex 1), [1,3-H2bdc = isophthalic acid, OPY =
4,4′-(oxybis(4,1-phenylene))dipyridine]. The compound has been solvothermally
synthesized and characterized by IR, elemental analysis, single crystal X-ray
diffraction, XRD, UV−Vis, and TG analysis. The complex 1 crystallizes in the chiral
space group P65 and possesses an unprecedented uninodal 3D 75∙8 topology. However,
the complex was synthesized by achiral materials. The complex 1 displays a moderate
SHG response and its SHG efficiency is about 0.3 times that of urea. In addition, the
compound shows high thermal stability.
Keywords
V−Shaped Ligand; Cu(II) coordination polymer; Homochiral; Topology; SHG
Chirality is an essential characteristic of nature and plays a significant role in
biological systems, pharmacy and advanced material chemistry [1−3]. Recently,
rational design and synthesis of homochiral coordination polymers (CPs) have been
paid much attention owing to their potential applications in asymmetric catalysis,
* Corresponding author. E-mail addresses:yxq@nwnu.edu.cn (X. Q. Yao), jcliu8@nwnu.edu.cn (J.
C. Liu).
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enantioselective separation, and second-harmonic generation (SHG) [4–6]. Most of
the homochiral CPs were synthesized by chiral precursors (i.e. chiral organic ligands
or chiral additives) [7−9], which are usually expensive. However, chiral CPs could
also be synthesized by achiral precursors under spontaneous resolution process, their
chirality commonly derive from the spatial organization (e.g. helix) of achiral
components [10–13]. V-shaped ligands are frequently used to construct chiral CPs
because they make it easier to form chiral helical chains in the structure [14–16].
Moreover, we noticed that some chiral coordination polymers were synthesized by
using V−shaped N-containing and muti−carboxylate ligands simultaneously without
any chiral precursors. For example, LaDuca R. L. reported a chiral 3D coordination
polymer {[Cd(pht)(dpa)(H2O)]∙4H2O}n based V−shaped pht and dpa ligands (pht =
phthalate; dpa = 4,4′-dipyridylamine) which built from the interlocking of [Cd(dpa)]n
double helices with [Cd(pht)]n single helices [17]. Recently, Qin and co-works
reported a homochiral cobalt coordination polymer {[Co(L)(OBA)]∙H2O}n, which
also constructed from two V−shaped ligands (L = 1,1′-oxybis[3,5-dipyridine-benzene]
and H2OBA = 4,4′-oxybis(benzoate)), and the homochirality of the bulk samples are
verified by solid-state CD spectrum [18]. Inspired by the aforementioned examples,
two V−shaped ligands (Scheme 1): OPY and 1,3-H2bdc ligands were chose to
construct chiral CPs. The OPY ligand is a semi-rigid N-containing ligand and the
1,3-H2bdc ligand is a multidentate carboxylate ligand.
Scheme 1. The V-shaped OPY and 1,3-H2bdc ligands.
Herein, we report the syntheses, structural characterization, topological analysis
and the properties of the homochiral coordination polymer [Cu(OPY)(1,3-bdc)]n
which represents one of a few examples of chiral complexes constructed by two
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achiral V−shaped ligands. Blue crystals of [Cu(OPY)(1,3-bdc)]n (complex 1) have
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been obtained by solvothermal synthesis (95 C) for three days [19]. The single
crystal X-ray diffraction reveals that the complex 1 crystallizes in the hexagonal chiral
space group P65 [20]. As depicted in Fig. 1. The asymmetric unit of 1 contains one
Cu(II) ion, one OPY ligand and one 1,3-bdc2– dianion. Each Cu(II) center is
four-coordinated in square-planar geometry and connects to two nitrogen atoms from
OPY ligand (Cu–N = 1.972(6)Ǻ), and two oxygen atoms from 1,3-bdc2– dianion
(Cu–O = 1.967(4)Ǻ).
Fig. 1. Coordination environment of the Cu(II) atom in 1 with the thermal ellipsoids
drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. (The
symmetry codes: A = –x + y, 1 – x, –2/3 + z; B = 1 – y, 1 + x – y, 2/3 + z; C = y, 1 – x
+ y, 1/3 + z; D = 1 + x – y, x, –1/3 + z)
Each Cu(II) ion is connected by two OPY ligands and two 1,3-H2bdc ligands to
form a 3D non-interpenetrated chiral coordination polymer [Cu(OPY)(1,3-bdc)]n (Fig.
2a). The chirality induced by two achiral V−shaped ligands is the prominent
characteristic of complex 1. From the topological point of view, the Cu(II) ions can be
regarded as 4–connected nodes. As determined by TOPOS software [21], the Schläfli
symbol for this uninodal network is 75∙8, representing a rather simple yet unreported
topology (Fig. 2b). Viewed along the c axis, the structural features of complex 1 can
be easily found out in the topological graph. Obviously, the structure of 1 can be
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considered as the combination of many parallel helical chains (Fig. 3a). Further
analysis shows that all helical chains in 1 are exclusively left-handed, which
are probably the real reason for the chirality of 1. It is noted that each left-handed
helix chain is bordered around with six other equivalent ones via OPY ligands to form
a 3D homochiral coordination polymer (Fig. 3b). The basic chiral motif of complex 1
is showed in Fig. 4b, the adjacent helical chains are connected by the OPY ligands
and each left-handed helical chain [Cu(1,3-bdc)]n is constructed by Cu(II) ions and
1,3-bdc2– ligands. The single left-handed helix chain is generated around the
crystallographic 65 axis with a long pitch of 27.99 Å (Fig. 4a).
Fig. 2. (a) View of the 3D non-interpenetrated framework of 1 along the c axis. (b)
Uninodal 75∙8 network with exclusively left-handed helical chains.
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Fig. 3. (a) The left-handed helical chains are parallel to each other. (b) The
left-handed helical chains are joined by OPY ligands to form a 3D homochiral
coordination polymer. (The red pillars: OPY ligand).
As is well-known, the basic requirement for SHG property is that the CPs must be
chiral. In each crystal of complex 1, all 65 helices are exclusively left-handed. As such,
complex 1 crystallizes in hexagonal chiral space group P65 which belongs to a polar
point C6 associated with SHG response. Therefore, its nonlinear optical property was
studied. Preliminary experimental result shows that bulk material of complex 1
displays a modest SHG response that is about 0.3 times that of urea.
Fig. 4. (a) View of a left-handed helix chain [Cu(1,3-bdc)]n. (b) The chiral motif of
complex 1. (The green pillars: 1,3–bdc2– ligand, The red pillars: OPY ligand).
The solid-state UV−Vis spectra of OPY, 1,3-H2bdc and complex 1 (Fig. 5) were
carried out at room temperature. The OPY ligand displays a moderate intensity of
absorption peak bands at 306 nm, arising from the π-π* transition of the aromatic rings,
as well as the coligand 1,3-H2bdc. The crystal of 1 also displays a strong absorption
band at 276 nm–1, deriving from the π-π* transition of the aromatic rings. The band is
not changed compared to that of complex 1 based on OPY and 1,3-H2bdc ligands,
revealing that coordination of the Cu(II) ions didn’t alter the intrinsic electronic
properties of the ligands. For complex 1, the weak broad shoulder band from 550 to
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800 nm–1 can be assigned to the d−d spin−forbidden transition of the d9 (Cu2+) ion.
The phase purity of 1 was confirmed by powder X-ray diffraction (PXRD) at room
temperature. As shown in Fig. S2, the peak positions of the simulated and
experimental PXRD patterns are consistent with each other, indicating the phase
purity of the complex. The thermogravimetric analysis (TGA) of complex 1 was
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performed in the temperature rang (35–800 C) under a flow of nitrogen with a
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heating rate of 10 C·min–1 (Fig. S3). Complex 1 is stable before the temperature at
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o
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260 C. The weight loss in the range of from 260 C to 272 C is attributed to the
gradual release of 1,3-H2bdc (obsd 27.5%, calcd 27.3% ). The removal of OPY occurs
o
in the range of 272–580 C (obsd 58.4%, calcd 58.7%). The residue weight, 14.1%
(calcd 14.0%), corresponds to CuO.
Fig. 5. UV-Vis absorption spectrum of complex 1.
In conclusion, a homochiral 3D coordination polymer has been synthesized by
achiral V−Shaped N-containing and muti-carboxylate ligands. The chirality of
complex 1 derives from the left-handed helix [Cu(1,3-bdc)]n paralleled to each other.
All helices are interconnected by OPY ligands and thus extended to a 3D framework.
Topology analysis for this chiral framework reveals a simple yet unreported 75∙8
topology.
Acknowledgments
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This work was supported by grants from the Natural Science Foundation of China
(Nos. 21361023 and 21202133), Fundamental Research Funds for the Gansu
Universities, and the Program for Promoting Research Capacity of Young Faculty of
Northwest Normal University (grant No. NWNU–LKQN–11–13). We also thank Key
Laboratory of Eco-Environment-Related Polymer Materials (Northwest Normal
University) for financial support.
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[19]A mixture of Cu(NO3)2·3H2O (20 mg, 0.08 mmol), OPY (51.8 mg, 0.16 mmol),
1,3-H2bdc (13.29 mg, 0.08 mmol), H2O (6 ml) and DMF (2 ml, DMF =
N,N′-dimethylformamide) was stirred for 10 min at room temperature, sealed in a
o
Teflon–lined stainless steel vessel and heated to 140 C for 3 days under
o
autogenous pressure, and then cooled to room temperature at the rate of 0.5 C
min–1. Blue block crystals [Cu(OPY)(1,3-bdc)]n were obtained and washed with
deionized water and absolute ethanol. Yield: 50% (25.9 mg) based on OPY. Anal.
Calc. for C30H20CuN2O5: C, 65.27%; H, 3.65%; N, 5.07%. Found: C, 65.20%; H,
3.62%; N, 5.12%. The IR spectrum of the crystal is shown in the Fig. S1
(supporting information). Selected IR for crystal (KBr, cm–1): 3419 (b, m), 3035
(w), 1593 (s), 1545 (w), 1485 (s), 1402 (m), 1284 (w), 1227(s), 1774 (w), 809
(vs).
[20]Crystal data for complex 1, [Cu(OPY)(1,3-bdc)]n : hexagonal, space group P65, a
= 12.352(3) Ǻ, b = 12.352(3) Ǻ, c = 27.999(6) Ǻ, α = 90.00°, β = 90.00°, γ =
120.00°, V = 3699.8(13) Å3, Z = 6, Dc = 1.487 mg∙cm–3, μ = 1.487 mm–1, 3.30 <
θ< 25.15°, F(000) = 1698, T = 293(2) K. 5730 reflection collected, 3476 unique.
The final R1 and ωR2 were 0.0421 and 0.0971, respectively [I > 2σ(I)]. Detailed
crystallographic data has been deposited at Cambridge Crystallographic Data
Center (CCDC 971506). The crystal data and structure refinement are
summarized in Table S1. The selected bond lengths and bond angles are listed in
Table S2.
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Graphical abstract
A 3D non-interpenetrated chiral coordination polymer [Cu(OPY)(1,3-bdc)]n has been
solvothermally synthesized by using V−shaped N-containing and muti−carboxylate
ligands simultaneously without any chiral precursors. The structure of the complex is
composed by the exclusively left-handed helical chains and each single chain is
generated around the crystallographic 65 axis with a long pitch of 27.99 Å.
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Highlights
We are prompted to ask publication of our results for the following reasons:
• A homochiral Cu(II) coordination polymer has been synthesized and characterized.
• The complex represents one of a few examples of chiral complexes constructed by
two achiral V−shaped ligands.
• The topology of this 3D complex represents a simple yet unreported 75∙8 topology.
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