Controlling interpenetration in CuCN coordination polymers by size of the pendant substituents of terpyridine ligands

Article abstract of DOI:10.1039/c1ce05565h

To systematically investigate the effect of the pendant groups of ligands on the assembly of coordination polymers (e.g, controlling interpenetration), four terpyridine ligands with bulky pendant groups, namely, 4′-(4-tolyl)- 4,2′:6′,4′′-terpyridine (L1), 4′-(4-ethylphenyl)- 4,2′:6′,4′′-terpyridine (L2), 4′-(4- isopropylphenyl)-4,2′:6′,4′′-terpyridine (L3), and 4′-biphenyl-4,2′:6′,4′′-terpyridine (L4) have been synthesized for comparative purposes. The reactions of CuCN and L1-L4 under the same solvothermal conditions provided four CuCN coordination polymers: [(CuCN)₂L1]_n (1), [(CuCN)₂L2]_n (2), [(CuCN)₂L3]_n (3), and {[(CuCN)₃L4 _1.5]·H₂O}_n) (4), respectively. Single-crystal X-ray analyses reveal that compounds 1-3 are isostructural with the same topological 4-fold interpenetrated 3D CuCN networks, and compound 4 is a non-interpenetrated CuCN network. This success demonstrates that the interpenetration is suppressed by the alteration of the size of the pendant groups of terpyridine ligands. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1ce05565h

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PAPER
Controlling interpenetration in CuCN coordination polymers by size of the
pendant substituents of terpyridine ligands†
*
Xin-Zhi Li, Xiao-Ping Zhou, Dan Li and Ye-Gao Yin
*
Received 15th May 2011, Accepted 1st August 2011
DOI: 10.1039/c1ce05565h
To systematically investigate the effect of the pendant groups of ligands on the assembly of
coordination polymers (e.g, controlling interpenetration), four terpyridine ligands with bulky pendant
groups, namely, 40-(4-tolyl)-4,20:60,400-terpyridine (L1), 40-(4-ethylphenyl)-4,20:60,400-terpyridine (L2),
40-(4-isopropylphenyl)-4,20:60,400-terpyridine (L3), and 40-biphenyl-4,20:60,400-terpyridine (L4) have been
synthesized for comparative purposes. The reactions of CuCN and L1–L4 under the same solvothermal
conditions provided four CuCN coordination polymers: [(CuCN)2L1]n (1), [(CuCN)2L2]n (2),
[(CuCN)2L3]n (3), and {[(CuCN)3L41.5]$H2O}n) (4), respectively. Single-crystal X-ray analyses reveal
that compounds 1–3 are isostructural with the same topological 4-fold interpenetrated 3D CuCN
networks, and compound 4 is a non-interpenetrated CuCN network. This success demonstrates that the
interpenetration is suppressed by the alteration of the size of the pendant groups of terpyridine ligands.
that the size and functional groups of organic ligands can be
Introduction
altered and tuned by organic synthesis.
Coordination polymers (or metal–organic frameworks, MOFs)
have attracted great interest because of their structural diversity
and potential applications as solid-state functional materials for
use in gas storage,1 sensing,2 heterogeneous catalysis3 and
magnetism.4 Compared to traditional inorganic porous materials
(e.g. zeolite), one salient feature of coordination polymers is that
the porous properties (e.g. pore size) can be easily tuned by
rationally selecting and designing organic ligands. In principle,
the high porosity of coordination polymers can be achieved by
increasing the length of bridging ligands. Unfortunately, it is not
always the case because the porosity is often severely compressed
due to the interpenetration of multiple networks. The prevention
of interpenetration in coordination polymers is extremely
important, and is still a great challenge for chemists.5 Recently,
chemists have adopted several strategies to control the degree of
interpenetration, including (i) introducing guest molecules or
anions as templates,6 (ii) changing the reaction conditions, e.g.,
temperature, solvents and concentration,7 (iii) in situ generation
of rod shaped or high connected secondary building units,8 (iv)
the ‘‘liquid-phase epitaxy’’ method,9 and (v) rational design of
organic ligands (with steric hindrance groups, or chirality).6a,10 In
comparison to these methods, the modification of organic
ligands in controlling the interpenetration may be relatively
practicable and feasible. This presumption is rooted in the fact
The metal salt CuCN is very useful to assemble unique coor-
dination polymers due to its structural diversity.11 When CuCN
reacts with exo-bidentate, or exo-tridentate ligands, CuCN
coordination polymers with multiple interpenetration networks
will probably be obtained, as with other types of coordination
polymers. A series of interpenetrated CuCN coordination poly-
mers had been reported.12 However, a systematic study on the
compression of CuCN interpenetration networks is still not
available. We, and others, are interested in research on the
coordination chemistry of the assembly of 4,20:60,400-terpyridine
ligands and metal ions.13 Herein, we report a systematic modi-
fication of the pendant substituents of 4,20:60,400-terpyridine to
control the interpenetration in CuCN coordination polymers.
The idea is that the pendant groups with larger size probably
cause steric hindrance in the formation of additional inter-
penetrated networks, and thus compress the interpenetration. A
series of 4,20:60,400-terpyridine-based ligands with alteration of
the size of the pendant groups: 40-(4-tolyl)-4,20:60,400-terpyridine
(L1), 40-(4-ethylphenyl)-4,20:60,400-terpyridine (L2), 40-(4-iso-
propylphenyl)-4,20:60,400-terpyridine (L3), and 40-biphenyl-
4,20:60,400-terpyridine (L4) (Scheme 1) were synthesized and
reacted with CuCN under the same conditions.
Experimental section
Materials and measurements
Department of Chemistry, Shantou University, Guangdong 515063, P. R.
China. E-mail: dli@stu.edu.cn; ygyin@stu.edu.cn
All starting materials were commercially available and used as
received without further purification. Infrared spectra were
obtained in KBr disks on a Nicolet Avatar 360 FTIR
† Electronic supplementary information (ESI) available. CCDC
reference numbers 826227–826230. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1ce05565h
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4-biphenylcarboxaldehyde (3.64 g, 20.0 mmol) in place of p-tol-
ualdehyde. Yield: 24%, (1.85 g, 4.8 mmol). Elemental analysis
calcd (%) for L4 C27H19N3: C 84.13, H 4.97, N 10.90; found: C
84.37, H 4.51, N 11.12. IR data (KBr, cmꢀ1) for L4: 3027 w,
1593 s, 1544 s, 1483 m, 1409 s, 1217 w, 1062 w, 1005 w, 820 s,
764 m.
Synthesis of complexes
[(CuCN)3L11.5]n (1). A mixture of CuCN (0.009 g, 0.1 mmol),
L1 (0.0323 g, 0.1 mmol) and acetonitrile (8.0 mL) was sealed in
a 15 mL Teflon-lined stainless-steel autoclave, which was heated
to 160 ꢁC and held for 72 h. After cooling to room temperature at
a rate of 5 ꢁC hꢀ1 and filtering, X-ray quality yellow block
crystals of compound 1 were obtained. Yield: 48%. Elemental
analysis calcd (%) for 1 C36H25.5Cu3N7.5: C 57.36, H 3.40, N
13.94. Found: C 56.97, H 3.17, N 14.43. IR data (KBr, cmꢀ1):
3027 w, 2913 w, 2847 w, 2124 s, 1597 s, 1556 w, 1535 m, 1515 w,
1393 m, 1061 w, 1009 w, 816 s.
Scheme 1
spectrometer in the range 4000–400 cmꢀ1. Elemental analyses of
C, H, and N were determined with a Perkin-Elmer 2400C
elemental analyzer. Thermogravimetric analysis (TGA) was
carꢁried out under an argon atmosphere with a heating rate of
10 C minꢀ1 from room temperature to 800 C, on Seiko Extar
ꢁ
6000 TG/DTA equipment.
Synthesis of ligands
[(CuCN)3L21.5]n (2). The procedure for preparing 2 was iden-
tical to that for preparing 1, except L1 was replaced with L2
(0.0337 g, 0.1 mmol). Yellow block crystals of compound 2 were
obtained. Yield: 54%. Elemental analysis calcd (%) for 2
40-(4-Tolyl)-4,20:60,400-terpyridine (L1). A mixture of p-tol-
ualdehyde (2.4 g, 20 mmol), 4-acetylpyridine (4.84 g, 40.0 mmol)
and NaOH (s, 96%) (1.67 g, 41.75 mmol) was ground using
a mortar and pestle. The viscosity rapidly strengthened to
produce a tacky solid after ca. 5 min of constant mixing, then the
yellow medium was aggregated until a yellow powder was
formed (ca. 5 min) and further ground for 20 min. The powder
was transferred to a suspension of ammonium acetate (13 g,
excess) in glacial acetic acid (40 ml, ca. 100%) and refluxed for 5
h. The resulting solution was cooled, the solvent was reduced and
treated with a mixture of ethanol (20 mL) and water (30 mL) to
give a pale yellow precipitate, which was recrystallized from
ethanol to yield colorless crystals. Yield: 29%, (1.87 g, 5.8 mmol).
Elemental analysis calcd (%) for L1 C22H17N3: C 81.71, H 5.30,
C
37.5H28.5Cu3N7.5: C 58.13, H 3.71, N 13.56. Found: C 58.39, H
3.84, N 13.31. IR data (KBr, cmꢀ1): 3040 w, 2958 w, 2925 w,
2872 w, 2120 s, 1597 s, 1532 m, 1454 w, 1393 m, 1217 w, 1066 m,
1009 m, 825 s.
[(CuCN)6L33]n (3). The procedure for preparing 3 was iden-
tical to that for preparing 1, except L1 was replaced with L3
(0.0351 g, 0.1 mmol). Yellow block crystals of compound 3 were
obtained. Yield: 54%. Elemental analysis calcd (%) for 3
C78H63Cu6N15: C 58.86, H 3.99, N 13.20. Found: C 58.42, H
4.11, N 13.36. IR data (KBr, cmꢀ1): 2953 w, 2921 w, 2864 w,
2120 m, 1601 s, 1535 w, 1450 w, 1393 m, 1217 w, 1062 w, 1012 w,
825 s.
N 12.99; found: C 81.54, H 5.25, N 13.21. IR data (KBr, cmꢀ1
)
for L1: 3032 w, 2974 w, 2913 w, 2852 w, 1593 s, 1540 m, 1516 m,
1393 m, 1213 w, 1066 w, 997 w, 809 s.
{[(CuCN)3L41.5]$H2O}n (4). The procedure for preparing 4
was identical to that for preparing 1, except L1 was replaced with
L4 (0.0385 g, 0.1 mmol), and yellow block crystals of compound
4 were obtained. Yield: 49%. Elemental analysis calcd (%) for 4
40-(4-Ethylphenyl)-4,20:60,400-terpyridine (L2). 40-(4-Ethyl-
phenyl)-4,20:60,400-terpyridine was prepared analogously to L1,
but with 4-ethylbenzaldehyde (2.68 g, 20.0 mmol) in place of
p-tolualdehyde. Yield: 24.5%, (1.65 g, 4.9 mmol). Elemental
analysis calcd (%) for L2 C23H19N3: C 81.87, H 5.68, N 12.45;
found: C 81.99, H 5.75, N 12.26. IR data (KBr, cmꢀ1) for L2:
3032 w, 2974 w, 2917 m, 2852 w, 1593 s, 1540 m, 1426 w, 1393 s,
1213 w, 1062 w, 997 w, 817 s.
C
43.5H30.5Cu3N7.5O: C 60.41, H 3.55, N 12.15. Found: C 60.65,
H 3.32, N 13.69. IR data (KBr, cmꢀ1): 3027 w, 2913 w, 2116 s,
1593 s, 1536 m, 1486 m, 1389 m, 1217 w, 1062 w, 1013 w, 825 s,
772 s.
X-ray crystallography
40-(4-Isopropylphenyl)-4,20:60,400-terpyridine (L3). 40-(4-Iso-
propylphenyl)-4,20:60,400-terpyridine was prepared analogously
to L1, but with 4-isopropylbenzaldehyde (2.96 g, 20.0 mmol) in
place of p-tolualdehyde. Yield: 32%, (2.25 g, 6.4 mmol).
Elemental analysis calcd (%) for L3 C24H21N3: C 82.02, H 6.02,
Suitable crystals of 1–4 were mounted with glue at the end of
a glass fiber. Data collections were performed on a Bruker-AXS
SMART CCD area detector diffractometer at 298(2) K using
rotation scans with a scan width of 0.3ꢁ and Mo-Ka radiation
N 11.96; found: C 82.37, H 5.51, N 12.12. IR data (KBr, cmꢀ1
)
(l ¼ 0.71073 A). A summary of the crystallography data and
ꢀ
for L3: 3023 w, 2958 m, 2925 w, 1593 s, 1536 m, 1426 w, 1397 m,
structure refinement is given in Table 1. Empirical absorption
corrections were carried out utilizing the SADABS routine. The
structures were solved by direct methods and refined by full-
matrix least squares refinements on the basis of F2. All non-
hydrogen atoms were anisotropically refined. Hydrogen atoms
1217 w, 1058 w, 993 w, 821 s.
40-Biphenyl-4,20:60,400-terpyridine (L4). 40-Biphenyl-4,20:60,400-
terpyridine was prepared analogously to L1, but with
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Table 1 Summary of the crystal data and structure refinement parameters for 1–4
1
2
3
4
Formula
Mr
C72H51Cu6N15
1507.58
Monoclinic
C2/c
22.4693(15)
14.3685(9)
21.7069(16)
90
109.1680(10)
90
6619.5(8)
4
1.513
C75H57Cu6N15
1549.59
Monoclinic
C2/c
22.7172(10)
14.5191(7)
21.7987(10)
90
108.7880(10)
90
6806.8(5)
4
1.512
1.896
17510
5983
0.0278
1.002
0.0400
0.0996
0.0631
0.1157
C78H63Cu6N15
1591.68
Monoclinic
P21/c
23.568(3)
14.2616(16)
24.342(4)
90
118.922(2)
90
7161.2(16)
4
1.476
1.805
36875
12592
0.0418
1.001
0.0604
0.1462
0.1133
0.1886
C87H61Cu6N15O2
1729.74
Orthorhombic
Pnna
32.9876(14)
15.2044(6)
15.3966(6)
90
90
90
7722.3(5)
4
1.488
1.682
37252
6811
0.0477
0.985
0.0477
0.1225
0.0885
0.1390
Cryst syst
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
a/ꢁ
b/ꢁ
g/ꢁ
V/A
Z
3
ꢀ
Dc/g cmꢀ3
m/mmꢀ1
no. of reflns collected
no. of unique reflns
Rint
1.948
17070
5812
0.0394
1.006
GOF
R1 [I > 2s(I)]a
wR2 [I > 2s(I)]b
R1 [all data]
wR2 [all data]
0.0473
0.0930
0.0887
0.1099
P
P
P
P
a
R1 ¼ (kF0| ꢀ |Fck)/ |F0|.b wR2 ¼ [ w(F0 ꢀ Fc )2/ w(F0 )2]1/2
.
2
2
2
were added geometrically and refined with a riding model;
structure solutions, refinements, and graphics were performed
with the SHELXTL-97 software package.14 Selected bond
lengths and angles for all complexes are given in Table S1.† The
bridge C/N atoms of CNꢀ are undistinguished, and were assigned
randomly as C or N atom in compounds 1–3. The C1/N1 and C4/
N4 atoms in compound 4 were refined as occupying the same site,
both the C and N atoms were refined with 0.5 site occupation.
Thermagravimetric analyses of compounds 1–4 in argon reveal
the mass loss as shown in Fig. S1 in the ESI,† indicating the
ꢁ
complexes are thermally stable up to 300–400 C.
Crystal structures of 1 and 2
X-ray crystallography studies reveal that both 1 and 2 crystallize
in the monoclinic space group C2/c with similar unit cells and
feature identical linkage of metal to ligand. Compounds 1 and 2
are isomorphous, therefore only compound 1 is described in
detail. The crystal data, and bond distances and angles of 2 are
listed in Table 1 and Table S1 (in the ESI†), respectively. The
asymmetric unit of 1 contains three independent copper(I) atoms,
three cyanide anions, and 1.5 L1 ligands (the half L1 ligand lies
on the twofold axis). All copper(I) centers adopt distorted
triangular geometry, and are coordinated by two CNꢀ and one
ligand L1 (Fig. 1a). Except for the central N atoms in L1, the
other two N atoms of 4-pyridyl groups coordinate to copper
centers, and L1 adopts a m-2 bridging mode (Cu–N: 2.031(3)–
Results and discussion
Synthesis
Solvent-free synthesis is a useful approach to reduce environ-
mental pollution, in addition to its simplicity and mild condi-
tions. The efficient synthesis of pyridines via a sequential
solventless aldol condensation and Michael addition had been
developed by Raston and co-workers.15 Herein, a similar solvent-
free method is also adopted in preparing L1–L4. Two equivalents
of the ketone to the aldehyde were ground together in the pres-
ence of a catalytic quantity of base to proceed to the 1,5-diketone
directly without any solvent. This procedure involves aldol
condensation followed by a Michael addition stage. Then,
reaction of the 1,5-diketone with ammonium acetate in the
solvent acetic acid gave rise to the formation of the pyridine ring.
All CuCN coordination polymers were synthesized with
a solvothermal method. To eliminate the influence of synthe-
sizing conditions (e.g. temperature, solvent, mole ratio) to the
resulting networks, the compounds 1–4 were synthesized under
the same solvothermal conditions (e.g. temperature, 160 ꢁC;
solvent, acetonitrile; the mole ratio of metal to ligand, 1 : 1; see
experimental section for more details). Therefore, the ligands
here are the only variable for the self-assembly of networks 1–4.
For ligands L1–L4, the differences localize on the pendant R
groups (Scheme 1), which will probably play important role in
the assembly of the coordination polymers 1–4.
ꢀ
ꢀ
2.122(3) A). Like the L1, all CN anions adopt the m-2 bridging
mode, and the Cu–C/N (CNꢀ) bond distances range from 1.837
ꢀ
(4)–1.936(4) A, and the C–Cu–N angles in the CuCN chains
range from 131.70(15)–152.22(17)ꢁ. The CNꢀ anions link the
copper centers to form a meso-helical 1D chain, in which the
ꢀ
helical pitch is 25.68 A (Fig. 1b). The CuCN chains are further
bound by the exo-bidentate L1, and a 3D network was con-
structed, as shown in Fig. 1c. The network consists of large
hexagonal-like channels, and is further interpenetrated by three
other identical networks, as shown in Fig. 1d. Therefore, the
coordination polymer 1 consists of four fold interpenetrated
CuCN–L1 3D networks. After the 4-fold interpenetration, there
is no solvent accessible void in 1 (checked by PLATON
program). To understand the whole linkage between the metal
and ligands of the complicated network of 1, the topology was
analyzed. The network of 1 can be simplified as a 3-connected
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Fig. 1 Crystal structure of complex 1: (a) coordination environment of copper(I) centers; (b) meso-helical CuCN chain in 1; (c) overview of the 3D
CuCN network with hexagonal channels (the toyl groups are omitted for clarity); (d) four interpenetrating networks in 1 (the tolyl groups are omitted for
clarity); and (e) topologic network representation of 1 (red sphere representing the copper nodes with (4.8.10) topology, cyan sphere representing the
cooper nodes with (82.12) topology, and blue and green sticks representing CNꢀ and L1, respectively). Symmetry transformations a, x ꢀ 1/2, ꢀy + 3/2,
z ꢀ 1/2; b, ꢀx ꢀ 1/2, ꢀy + 1/2, ꢀz; c, ꢀx + 1, y, ꢀz + 1/2.
topologic network, when all the copper(I) centers are rationalized
as the 3-connected nodes, and the CNꢀ anions and L1 are treated
as the linkers, as shown in Fig. 1e. The numbers of copper nodes
in the shortest path of the resulting circuits is varied, including 4,
8, 10, and 12-membered. The Cu1 and Cu2 nodes have the same
topological linkage (composing 4, 8, and 10-membered circuits),
and Cu3 is involved in one 8, and two 12-member circuits.
chain in 3. The angles around the copper centers of the CuCN
chains in 3 are 137.3(2)–148.5(2)ꢁ for the chain containing Cu1–
Cu3 copper centers, and 131.3(2)–148.0(2)ꢁ for the chain con-
taining Cu4–Cu6 copper centers (Fig. 2b). Both angle values are
slightly different to the angles in 1 (131.70(15)–152.22(17)ꢁ). The
slight angle difference leads to a large change in the whole CuCN
chain motif when compared to compound 1, as shown in Fig. 2b.
The CuCN chain seems to derive from the normal meso-helical
Therefore 1 can be treated as a 3-connected binodal network with
€
2
the short vertex Schlafli symbol of (4.8.10)2(8 .12). Lots of
ꢀ
chain. The pitch is about 24.34 A, and the value is smaller than
ꢀ
that in 1 (25.68 A). Further comparing the 3D network of 3 to
3-connected networks with varied topologies have been reported
(e.g. (83),16 (103),17 (123),18 (4.122)19 and (62.10)20). However, to the
best of our knowledge, the topology of (4.8.10)2(82.12) in 1 is
unprecedented.
that of 1, the network of 3 is relatively distorted (Fig. 2c), which
is consistent with the relative lower symmetry in 3. Albeit
compound 3 has a larger ligand L3 and lower symmetric space
group and distorted networks when compared to 1, it also
contains 4-fold interpenetrated networks, and has the same
(4.8.10)2(82.12) topology. Therefore, the increase of the pendant
group size from tolyl in L1 to isopropylphenyl in L3 do not
compress the interpenetration in these CuCN coordination
polymers.
Crystal structure of 3
Compound 3 crystallizes in monoclinic space group P21/c
(a lower symmetry than C2/c in compound 1), and features
identical topologic linkage of 1. The asymmetric unit of 3
contains 6 copper(I) centers, 6 cyanide anions, and three L3
ligands, which are double that in 1. All copper(I) centers adopt
the triangular geometry, and are coordinated by two CNꢀ and
one L3, as shown in Fig. 2a. Both of the bond distances of Cu–N
Crystal structure of 4
In a further study, we employed a more bulky ligand L4, and
obtained the non-interpenetrating CuCN coordination polymer
4. Single crystal X-ray diffraction reveals that compound 4
crystallizes in orthorhombic space group Pnna, and features
ꢀ
ꢀ
(L3) (2.051(4)–2.109(4) A) and Cu–C/N (CN ) (1.867(5)–1.938
ꢀ
(7) A) are comparable with the bond distances in compound 1.
The copper(I) centers are also bridged by CNꢀ to form the CuCN
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Fig. 2 Crystal structure of 3: (a) coordination environment of copper(I) centers; (b) view of CuCN chains (top, containing Cu4–Cu6 atoms, and bottom,
containing Cu1–Cu3 atoms); and (c) overview of the 3D CuCN network (the isopropylphenyl groups are omitted for clarity). Symmetry transformations
a: x, ꢀy + 3/2, z ꢀ 1/2; b: x + 1, ꢀy + 1/2, z ꢀ 1/2; c: x, ꢀy ꢀ 1/2, z ꢀ 1/2; d: x, ꢀy + 3/2, z + 1/2.
a non-interpenetrated 3D coordination network. The asym-
metric unit of 4 contains three independent copper(I) atoms,
three cyanide anions, and 1.5 L4 ligands (the half L4 ligand lies
on the twofold axis). Similar to compounds 1–3, each Cu(I) atom
in 2 is three-coordinated by two C/N atoms (CNꢀ, Cu–C/N 1.836
Fig. 3d. Further topological analysis found that the network of 4
can be abstracted into a (10,3)-b network17 (Fig. 3e), when both
CN anions and L4 ligands are donated as linkers and Cu(I) atoms
donated as 3-connected nodes. The major voids of coordination
polymer 4 are occupied by the pedant biphenyl group, a volume
of about 8.9% of unit cell volume is still solvent accessible in
compound 4 (calculated by PLATON program), which is occu-
pied by disordered water molecules. Thus, by increasing the
pendant group size to biphenyl, the interpenetrations were
successfully compressed in CuCN coordination polymer 4.
However, the total linkage and topology of the non-inter-
penetrated network were also changed at the same time in
comparison with those in compounds 1–3.
ꢀ
ꢀ
(4)–1.919(4) A) and one N atom (L4, Cu–N 2.094(5)–2.108(4) A),
as shown in Fig. 3a. The copper(I) centers are also linked by CNꢀ
to form a meso-helical CuCN chain (Fig. 3b). The C–Cu–N
angles in the meso-helical CuCN chain range from 138.52(6)–
ꢀ
149.77(6) A, which is slightly different when compared with the
angles of compounds 1–3. However, the meso-helical chain is
obviously different to those in compounds 1–3, and the length of
ꢀ
the helical pitch (48.63 A) is about double that in compounds 1–
3. On the other hand, the CuCN meso-helices run along two
different directions, with the CuCN chain extending along the
same direction in 1–3. The CuCN chains are further connected
by the L4 ligands to form a 3D network (Fig. 3c). Unlike the
four-fold networks in compounds 1–3, compound 4 only
contains a mono-fold network. Therefore there is no interpene-
tration in 4. Although the coordination mode of both the ligands
and copper centers in compounds 1–4 are the same, the total
linkage of the network in 4 is distinctly different when compared
to networks in 1–3. The CNꢀ and L4 ligands linking copper(I)
centers form the uniform 10-membered circuits in 4, as shown in
Effect of ligands on structures
The reaction of CuCN with L1–L4 under the same solvothermal
conditions yield three 4-fold interpenetrated 3D CuCN coordi-
nation polymers: [(CuCN)2L1]n (1), [(CuCN)2L2]n (2) and
[(CuCN)2L3]n (3), and one non-interpenetrated CuCN coordi-
nation polymer {[(CuCN)3L41.5]$H2O}n (4), respectively.
Ligands L1–L4 are similar except for the pendant groups. The
pendant groups (tolyl to biphenyl, with non-active C–H bonds)
in ligands L1–L4 are not functionalized, and they have no
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Fig. 3 Crystal structure of 4: (a) coordination environment of copper centers, (b) meso-helical CuCN chain, (c) overview of three-dimensional network
of 4 (the biphenyl groups are omitted for clarity), (d) view of the 10-membered circuits, and (e) the (10, 3)-b topologic network of 4 (red sphere, Cu; green
sticks, L4; and blue sticks, CNꢀ). Symmetry transformation a: x ꢀ 1/2, y, ꢀz + 1.
hydrogen bond sites or potential coordination sites. Additional
affecting factors including the inherent p–p interactions for
aromatic rings and steric hindrance of ligands may play impor-
tant roles in the assembly of the final structures of CuCN coor-
dination polymers 1–4. In the crystal structures of 1–4, there are
no obvious p–p interactions found between the pendant group
and adjacent ligands. Therefore, the leftover factor of steric
hindrance of pendant groups may become the sole variable in the
assembly of the structures of 1–4. As depicted above, complexes
1–3 feature identical four-fold interpenetrating 3D networks and
binodal 3-connected (4.8.10)2(82.12) topology. The networks 1–2
are almost identical, apart from the difference of tolyl and eth-
ylphenyl groups. Due to the increase in steric hindrance (after the
change to the larger isopropylphenyl), the CuCN network in 3 is
beginning to distort from the normal CuCN network 1. It makes
us contemplate that coordination polymer 3 may be an inter-
mediate state between the interpenetrated CuCN coordination
polymer and non-interpenetrated CuCN coordination polymer
in this system. The continuing increase of steric hindrances by
employing more bulky pendant biphenyl group leads to the non-
interpenetrated network 4. The change in the linkage and
topology in 4 in comparison to 1–3 may be attributed to the
inherent flexible property of CuCN coordination polymers.
study of the control over the interpenetration in other coordi-
nation polymer systems based on these ligands need to be
extended.
Acknowledgements
This work was financially supported by the National Science
Foundation for Distinguished Young Scholars of China (Grant
No. 20825102) and the National Natural Science Foundation of
China (Grant No. 20771072 and 20971083).
Notes and references
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In summary, four CuCN coordination polymers based on four
terpyridine ligands with various sized pendant substituents have
been synthesized and characterized. The control over the inter-
penetration in these CuCN frameworks was systematically
studied by carefully varying the size of the pendant group of the
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