Hydrothermal synthesis of copper complexes of 4′-pyridyl terpyridine: From discrete monomer to zigzag chain polymer

Article abstract of DOI:10.1016/j.ica.2006.04.035

Seven copper complexes [Cu(L1)I₂] (1), [Cu₂(L1)₂I₂]₂[Cu₂(μ-I)₂I₂] (2), [Cu(L2)I₂] (3), [Cu₂(L2)(μ-I)I(PPh₃)] (4), [Cu₄(L2)₂(μ-I)₂I₂] (5), {[Cu(L2)I]₂[Cu₂(μ-I)₂I₂]}_n (6) and [Cu₂(L2)(μ-I)₂]_n (7) have been prepared by reactions of ligands: 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine (L1) and 4′-(3-pyridyl)-2,2′:6′,2″-terpyridine (L2) with CuI in hydrothermal conditions, respectively. By alternating the oxidations states of the metal centers, increasing stoichiometric metal/ligand ratio and introducing a second ligand, the compounds, were successfully developed from mononuclear (1 and 3) to multinuclear (2, 4 and 5) and polymers (6 and 7). The synthesis of these compounds may provide an approach for the construction of coordination compounds of 4′-pyridyl terpyridine with different nuclearity.

Full text of DOI:10.1016/j.ica.2006.04.035

Inorganica Chimica Acta 359 (2006) 4027–4035
www.elsevier.com/locate/ica
Hydrothermal synthesis of copper complexes of 40-pyridyl
terpyridine: From discrete monomer to zigzag chain polymer
a
a
a
a,
a
b
Hua Feng , Xiao-Ping Zhou , Tao Wu , Dan Li *, Ye-Gao Yin , Seik Weng Ng
a
Department of Chemistry, Shantou University, Daxue Road, Shantou, Guangdong 515063, PR China
b
Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
Received 25 February 2006; accepted 25 April 2006
Available online 3 May 2006
Abstract
Seven copper complexes [Cu(L1)I2] (1), [Cu2(L1)2I2]2[Cu2(l-I)2I2] (2), [Cu(L2)I2] (3), [Cu2(L2)(l-I)I(PPh3)] (4), [Cu4(L2)2(l-I)2I2] (5),
{[Cu(L2)I]2[Cu2(l-I)2I2]}n (6) and [Cu2(L2)(l-I)2]n (7) have been prepared by reactions of ligands: 40-(2-pyridyl)-2,20:60,200-terpyridine
(L1) and 40-(3-pyridyl)-2,20:60,200-terpyridine (L2) with CuI in hydrothermal conditions, respectively. By alternating the oxidations states
of the metal centers, increasing stoichiometric metal/ligand ratio and introducing a second ligand, the compounds, were successfully
developed from mononuclear (1 and 3) to multinuclear (2, 4 and 5) and polymers (6 and 7). The synthesis of these compounds may pro-
vide an approach for the construction of coordination compounds of 40-pyridyl terpyridine with different nuclearity.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Terpyridine; Hydrothermal reaction; Copper mixed-valent complex; Copper iodide; Coordination polymer
1. Introduction
further derivative reactions, as well as to introduce terpyri-
dine complexes into polymers [5].
The design of complex molecular architectures is an
important goal for synthetic chemistry as it provides the
opportunity to control or encode the properties of a mate-
rial at the molecular level [1]. Chemists have great interest
in the design, synthesis and exploring the properties of
coordination polymers. 2,20:60,200-Terpyridine (terpy) and
its derivatives have been intensively explored because of
their versatility as building blocks for supramolecular
assembles and polymers [2,3] and the interesting electronic,
photonic, magnetic, reactive and structural properties
shown by the transition metal complexes of these ligands
[4]. In the last decades, special attention has been drawn
to the 40-functionalized terpyridine ligands, since the
appended substituents may be utilized not only to tailor
the electronic properties of the ligand and its metal com-
plexes, but also to incorporate new functionalities through
For 40-functionalized terpyridines, the pyridyl-substi-
tuted 40-pyridyl terpyridines (pyterpy) have been essentially
ignored and scarcely reported [6,7]. As an oligopyridine
ligand with multi-domain, 40-pyridyl terpyridine is a poten-
tially bridging ligand, incorporating a tridentate 2,20:60,200-
terpyridine functionality and an isolated monodentate
pyridyl group. When the terpyridine is bonded to a metal,
it isomerizes to a cis-configuration (Scheme 1, left), though
preferably to cis–cis-configuration (Scheme 1, right). At the
same time, the different N-donor pyridyl attached to the
C(40) position of a 2,20:60,200-terpyridine ligand may result
in different coordination modes (Scheme 2). Constable [7]
has reported that the 40-pyridyl substituent is very weakly
electron withdrawing when placed in the C(40) position of
a 2,20:60,200-terpyridine ligand and the extended conjugation
make pyterpy a better p-acceptor ligand than terpyridine,
such that it stabilizes the lower oxidation states. The
pyterpy may be used in the assembly of coordination com-
pounds because of their diverse coordination modes and
bridging ability.
*
Corresponding author. Tel.: +86 754 290 3154; fax: +86 754 290 2767.
E-mail addresses: dli@stu.edu.cn (D. Li), ygyin@stu.edu.cn (Y.-G.
Yin).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.04.035

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H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
ences of the metal ions can lead to different fantastic poly-
nuclear complexes such as molecular helicates, grids, rings
and boxes [8–10]. Sauvage [11] have reported that the coor-
dination preferences of copper in different oxidation states,
e.g. four-coordinate copper(I), five- or six-coordinate cop-
per(II), may be used to drive supramolecular systems. On
the other hand, copper(I) halide were commonly selected
as the metal source due to their ability to form neutral
arrays [12], and the strong coordination nature of the
halide anion which can bridge two or more copper centers
and can be connected to form coordination polymers using
diverse bridging ligands. It is reasonable to predict that the
copper compounds based on pyterpy and an appropriate
linkers, such as halide and pseudo-halide X (Cl, Br, I,
SCN or CN), can be developed from monomers to poly-
mers as shown in Scheme 3.
Scheme 1. The different configurations of terpyridine.
On the basis of our pervious work [13,14], we report the
hydrothermal preparation of several compounds of 40-(2-
pyridyl)-2,20:60,200-terpyridine (L1) and 40-(3-pyridyl)-
2,20:60,200-terpyridine (L2) with copper(I) iodide. By chang-
ing the reaction conditions (temperature, stoichiometry,
additives), the valence of copper varied form bivalence to
mixed-valence and monovalence, the compounds devel-
oped from mononuclear to multinuclear and polymers.
The result shows that it is an effective way to achieve coor-
dination polymers of pyterpy by controlling the oxidation
states of metal centers and selecting appropriate linkers.
2. Experimental
2.1. General
Scheme 2. Coordination modes of pyterpys.
All chemicals and reagents are commercially available
and were used as received without further purification.
The ligand L1 and L2 were synthesized by a modified liter-
ature method [26,42]. FT-IR spectra (KBr pellets) were
recorded on a Nicolet Avatar 360 FTIR spectrometer in
the range 4000–400 cmꢀ1 region. Elemental analyses of
C, H, and N were determined with a Perkin–Elmer
2400 C elemental analyzer.
Our studies were induced by the interest in the develop-
ment of different polynuclear complexes of the 40-pyridyl
terpyridine, in which the discrete complex entities are fur-
ther assembled into larger entities or arrays of defined
architectures. Self-assembly processes controlled by the
multidentate ligands and the coordinated geometry prefer-
Scheme 3. Topologies of some pyterpy compounds.

H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
4029
2.2. Preparation of ligands and complexes
C20H14CuI2N4: C, 38.27; H, 2.25; N, 8.93. Found: C,
38.11; H, 2.15; N, 8.98%.
2.2.1. 40-(2-Pyridyl)-2,20:60,200-terpyridine (L1)
A solution of 2-acetylpyridine (3.64 g, 0.03 mol), and
pryridine-3-carboxaldehyde (1.61 g, 0.015 mol) was stirred
in basic aqueous ethanolic solution for 15 h at room tem-
perature. After this period either a white solid or an orange
gum was precipitated. The reaction of the solid or gum
with an excess of ammonium acetate in ethanol resulted
in the formation of the desired ligand pyterpy L1 in 25%
yield as a yellow crystalline solid. m.p. 232 °C. Anal. Calc.
for C20H14N4: C, 77.40; H, 4.55; N, 18.05. Found: C, 77.42;
H, 4.53; N, 18.02%. IR (cmꢀ1, KBr): 1581s, 1548m, 1467m,
1393m, 993m, 780m.
2.2.4. [Cu2(L1)2I2][Cu(l-I)I] (2)
The mixture of CuI (0.0380 g, 0.2 mmol), ligand L1
(0.0155 g, 0.05 mmol), saturated KI solution (2.5 ml),
4,40-bipyridyl (0.0192 g, 0.1 mmol) and water (8 ml) were
placed and sealed in a 10 ml Teflon-lined stainless steel
reactor and heated to 180 °C for 72 h, then cooled down
to room temperature at a rate of 5 °C/1 h. Red block single
crystals suitable for X-ray diffraction were obtained in ca.
40% yield. Anal. Calc. for C40H28Cu3I4N8: C, 47.97; H,
2.82; N, 11.19. Found: C, 47.70; H, 3.07; N, 10.87%.
2.2.5. [Cu(L2)I2] (3)
The mixture of CuI (0.0190 g, 0.1 mmol), ligand L2
(0.0155 g, 0.05 mmol), saturated KI solution (3 ml) and
water (6 ml) were placed and sealed in a 10 ml Teflon-lined
stainless steel reactor and heated to 140 °C for 72 h, then
cooled down to room temperature at a rate of 2 °C/
20 min. Black bar single crystals suitable for X-ray diffrac-
tion were obtained in ca. 40% yield. Anal. Calc. for
C20H14CuI2N4: C, 38.27; H, 2.25; N, 8.93. Found: C,
38.11; H, 2.15; N, 8.98%.
2.2.2. 40-(3-Pyridyl)-2,20:60,200-terpyridine (L2)
It was prepared analogously to L1 by replacing 2-acetyl-
pyridine with 3-acetylpyridine in the same mole ratio. As a
result, yellow crystalline solid was obtained in 35% yield.
m.p. 232 °C. Anal. Calc. for C20H14N4: C, 77.40; H, 4.55;
N, 18.05. Found: C, 77.42; H, 4.53; N, 18.02%. IR
(cmꢀ1, KBr): 1581s, 1548m, 1467m, 1393m, 993m, 780m.
2.2.3. [Cu(L1)I2] (1)
The mixture of CuI (0.0190 g, 0.1 mmol), ligand L1
(0.0155 g, 0.05 mmol), saturated KI solution (3 ml) and
water (6 ml) were placed and sealed in a 10 ml Teflon-lined
stainless steel reactor and heated to 140 °C for 72 h, then
cooled down to room temperature at a rate of 2 °C/
20 min. Black bar single crystals suitable for X-ray diffrac-
tion were obtained in ca. 60% yield. Anal. Calc. for
2.2.6. [Cu2(L2)(l-I)I(PPh3)] (4)
The mixture of CuI (0.0190 g, 0.1 mmol), ligand L2
(0.0155 g, 0.05 mmol), saturated KI solution (2.5 ml), tri-
phenylphosphine (PPh3) (0.0262 g, 0.1 mmol) and water
(6 ml) were placed and sealed in a 10 ml Teflon-lined stain-
less steel reactor and heated to 180 °C for 72 h, then cooled
down to room temperature at a rate of 5 °C/1 h. Red block
Table 1
Crystal data and structure refinement parameters for complexes 1–7
Parameter
1
2
3
4
5
6
7
Formula
Mr
C
627.69
295(2)
0.71073
triclinic
20H14CuI2N4 C40H28Cu3I4N8 C20H14CuI2N4 C38H29Cu2I2N4P C20H14Cu2I2N4 C20H14Cu2I3N4 C20H14Cu2I2N4
1318.92
295(2)
0.71073
triclinic
627.69
295(2)
0.71073
orthorhombic
Pca21
19.136(1)
14.9546(8)
13.7467(7)
90
90
90
3934.0(4)
8
953.50
295(2)
0.71073
monoclinic
P21/n
14.081(3)
14.931(3)
18.061(4)
90
108.98(3)
90
3590.7(12)
4
691.23
295(2)
818.13
295(2)
0.71073
triclinic
691.23
295(2)
0.71073
triclinic
T (K)
˚
Wavelength (A)
Crystal system
Space group
0.71073
monoclinic
P21/n
9.3094(6)
16.6148(11)
13.6598(9)
90
101.5710(10)
90
2069.9(2)
4
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
˚
a (A)
8.4785(5)
9.4286(6)
12.5448(8)
82.771(1)
85.006(1)
87.183(1)
990.4(1)
2
9.888(2)
11.090(2)
19.121(4)
90.62(3)
99.06(3)
93.28(3)
2066.7(7)
2
7.7388(15)
9.5312(19)
16.777(3)
90.02(3)
100.42(3)
111.17(3)
1132.0(4)
2
9.5014(19)
9.992(2)
11.427(2)
69.52(3)
81.39(3)
89.00(3)
1004.1(3)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
2.105
4.232
2.119
2.120
1.764
2.218
2.400
2.286
l (mmꢀ1
)
4.557
4.262
2.981
5.051
5.984
5.206
Reflections collected
Unique reflections
Rint
8587
4427
0.016
10874
7168
0.0184
1.012
0.0424, 0.0967
0.0599, 0.1070
23912
6808
0.041
30175
8170
0.0340
1.059
12799
4691
0.0237
1.051
0.0312, 0.0669
0.0399, 0.0702
8211
3958
0.0191
1.062
0.0326, 0.0661
0.0390, 0.0708
7345
3525
0.0168
1.033
0.0565, 0.1345
0.0655, 0.1420
Goodness-of-fit on F2 1.10
1.031
R1,a wR2 [I > 2r(I)]
0.030, 0.075
0.035, 0.087
0.0409, 0.0886 0.0359, 0.0793
0.0511, 0.0958 0.0551, 0.0928
b
R1,a wR2 (all data)
b
P
P
a
R1 = ||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2 1=2
b
wR2 ¼ ½ wðF 2o ꢀ F c2Þ = wðF 2oÞ ꢁ
.

4030
H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
Table 2
single crystals suitable for X-ray diffraction were obtained
in ca. 50% yield. Anal. Calc. for C38H29Cu2I2N4P: C,
47.86; H, 3.07; N, 5.88. Found: C, 46.70; H, 3.01; N, 5.67%.
a
˚
Selected bond lengths (A) and bond angles (°) for 1–7
Complex 1
Cu(1)–I(1)
Cu(1)–I(2)
Cu(1)–N(1)
Cu(1)–N(2)
2.5850(5)
2.8323(5)
2.062(3)
1.955(3)
2.061(3)
100.36(2)
98.57(8)
162.65(9)
I(1)–Cu(1)–N(3)
I(2)–Cu(1)–N(1)
I(2)–Cu(1)–N(2)
I(2)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
99.19(8)
95.53(9)
96.98(8)
98.35(8)
79.0(1)
2.2.7. [Cu4(L2)2(l-I)2I2] (5)
The mixture of CuI (0.0380 g, 0.2 mmol), ligand L2
(0.0155 g, 0.05 mmol), copper powder (0.0128 g,
0.2 mmol), saturated KI solution (2.5 ml), acetonitrile
(2 ml) and water (6 ml) were placed and sealed in a 15 ml
Teflon-lined stainless steel reactor and heated to 140 °C
for 72 h, then cooled down to room temperature at a rate
of 5 °C/1 h. Brown bar single crystals suitable for X-ray
diffraction were obtained in ca. 45% yield. Anal. Calc. for
C20H14Cu2I2N4: C, 34.75; H, 2.04; N, 8.11. Found: C,
34.70; H, 2.01; N, 8.06%.
Cu(1)–N(3)
I(1)–Cu(1)–I(2)
I(1)–Cu(1)–N(1)
I(1)–Cu(1)–N(2)
155.1(1)
78.8(1)
Complex 2
I1–Cu3
2.4888(14)
N1–Cu1–N2
N2–Cu1–N3
N1–Cu1–N3
N5–Cu1–N6
N6–Cu1–N7
N5–Cu1–N7
N2–Cu1–N5
N2–Cu1–N7
N2–Cu1–N6
N1–Cu1–N7
N1–Cu1–N5
N3–Cu1–N5
N3–Cu1–N7
N3–Cu1–N6
N1–Cu1–N6
N3–Cu2–I4
N4–Cu2–I4
I3–Cu2–I4
75.51(18)
74.93(17)
150.44(17)
79.57(19)
79.08(19)
158.03(19)
98.13(18)
103.84(18)
165.51(19)
97.10(18)
88.54(18)
95.33(19)
90.17(18)
90.96(18)
118.52(18)
119.52(16)
110.42(16)
130.06(5)
I2–Cu3
2.5733(14)
2.5960(13)
2.636(2)
2.296(5)
2.036(4)
2.332(5)
2.063(5)
1.939(5)
2.060(5)
2.057(6)
2.4990(14)
2.5057(14)
I2–Cu3#1
Cu3–Cu3#1
N1–Cu1
N2–Cu1
N3–Cu1
N5–Cu1
N6–Cu1–
N7–Cu1
N4–Cu2
I3–Cu2
I4–Cu2
I1–Cu3–I2
I1–Cu3–I2#1
I2–Cu3–I2#1
Cu3–I2–Cu3#1
I1–Cu3–Cu3#1
2.2.8. {[Cu(L2)I]2[Cu2(l-I)2I2]}n (6)
The mixture of CuI (0.0380 g, 0.2 mmol), ligand L2
(0.0155 g, 0.05 mmol), saturated KI solution (2.5 ml), ace-
tonitrile (2 ml) and water (6 ml) were placed and sealed in
a 15 ml Teflon-lined stainless steel reactor and heated to
140 °C for 72 h, then cooled down to room temperature
at a rate of 5 °C/1 h. Brown bar single crystals suitable
for X-ray diffraction was obtained in ca. 25% yield. Anal.
Calc. for C20H14Cu2I3N4: C, 29.36; H, 1.72; N, 6.85.
Found: C, 29.30; H, 1.70; N, 6.80%.
120.31(5)
120.98(5)
118.68(5)
61.32(5)
178.27(7)
Complex 3
Cu1–N1
Cu1–N2
Cu1–N3
Cu1–I1
2.053(5)
1.953(5)
2.065(6)
2.560(1)
2.862(1)
2.047(6)
1.951(6)
2.036(6)
2.572(1)
2.806(1)
N1–Cu1–N2
N2–Cu1–N3
N1–Cu1–N3
I1–Cu1–I2
N5–Cu2–N6
N6–Cu2–N7
N5–Cu2–N7
I3–Cu2–I4
79.2(2)
79.2(2)
157.2(2)
104.57(4)
78.8(3)
78.9(2)
157.4(3)
110.77(4)
2.2.9. [Cu2(L2)(l-I)2]n (7)
The mixture of CuI (0.0190 g, 0.1 mmol), ligand L2
(0.0155 g, 0.05 mmol), saturated KI solution (2 ml),
bis(diphenylphosphanyl)methane (dppm) (0.0192 g) and
water (10 ml) were placed and sealed in a 15 ml Teflon-
lined stainless steel reactor and heated to 180 °C for 72 h,
then cooled down to room temperature at a rate of 5 °C/
1 h. Rufous block single crystals suitable for X-ray diffrac-
tion were obtained in ca. 50% yield. Anal. Calc. for
C20H14Cu2I2N4: C, 34.75; H, 2.04; N, 8.11. Found: C,
34.70; H, 2.01; N, 8.15%.
Cu1–I2
Cu2–N5
Cu2–N6
Cu2–N7
Cu2–I3
Cu2–I4
Complex 4
I1–Cu2
I1–Cu1
I2–Cu2
Cu1–N1
Cu1–P1
Cu1–N2
Cu1–Cu2
Cu2–N3
Cu2–N2
2.6137(8)
2.6617(8)
2.4870(7)
2.062(3)
2.2106(10)
2.231(3)
2.6791(9)
2.041(3)
2.464(3)
125.96(9)
111.75(7)
118.81(4)
140.49(3)
I1–Cu1–N1
I1–Cu1–N2
N1–Cu1–N2
N1–Cu1–Cu2
N2–Cu1–Cu2
N2–Cu2–N3
N3–Cu2–I2
N3–Cu2–I1
N3–Cu2–Cu1
Cu1–I1–Cu2
I1–Cu2–I2
98.92(8)
117.72(7)
77.11(10)
91.28(8)
59.39(7)
74.26(10)
133.18(8)
105.98(8)
84.48(8)
61.03(3)
118.74(2)
2.3. Crystallography
Suitable crystals of the compounds were mounted with
glue at the end of a glass fiber, respectively. Diffraction
data were collected at 295(2) K with a Bruker-AXS
SMART CCD area detector diffractometer using x rota-
tion scans width of 0.3° and Mo Ka radiation
P1–Cu1–N1
P1–Cu1–N
P1–Cu1–I1
P1–Cu1–Cu2
˚
(k = 0.71073 A). The crystal parameters and experimental
details of the data collection are summarized in Table 1.
The data collections covered the full spheres of the recipro-
cal space of the complexes. Empirical absorption correc-
tions were carried out utilizing SADABS routine. The
structures were solved by the direct method and refined
by full-matrix least-squares refinements based on F2. All
non-hydrogen atoms were refined with anisotropic thermal
parameters, and all hydrogen atoms were included in calcu-
lated positions and refined with isotropic thermal parame-
ters riding on those of the parent atoms. Structure
Complex 5
Cu1–N1
Cu1–N2
Cu2–N3
Cu2–N4#1
I1–Cu1
2.046(3)
2.241(2)
1.990(3)
1.979(3)
2.5036(6)
2.6515(5)
2.6102(5)
N1–Cu1–N2
N1–Cu1–I1
N2–Cu1–I1
N1–Cu1–I2
N2–Cu1–I2
I1–Cu1–I2
N3–Cu2–I2
77.17(10)
119.34(8)
105.21(7)
105.87(8)
118.78(7)
122.351(18)
108.11(8)
I2–Cu1
I2–Cu2
(continued on next page)

H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
4031
Table 2 (continued)
Complex 5
values [24]. The terpyridine of L1 are approximately planar
(interannular torsion angles: 4.2°, 8.7°), the pendent pyr-
idyl has rotated slightly and formed a dihedral angle with
the central pyridyl ring of 12.5°.
Cu2–Cu1
2.6626(7)
N4#1–Cu2–I2
N4#1–Cu2–N3
Cu2–I2–Cu1
118.97(8)
131.40(11)
60.794(15)
Complex 6
Cu1–N1
Cu1–N2
Cu1–N3
Cu1–N4#1
Cu1–I1
Cu2–I2
Cu2–I3
Cu2–I2#2
Cu2–I2#2
Cu2–Cu2#2
3.2. Structure of [Cu2(L1)2I2][Cu(l-I)I] (2)
2.024(4)
1.949(4)
2.027(4)
2.124(4)
2.6365(10)
2.5833(14)
2.4856(10)
2.5799(13)
2.5799(13)
2.5752(15)
N1–Cu1–N2
N2–Cu1–N3
N3–Cu1–N1
N2–Cu1–N4#1
N2–Cu1–I1
N4#1–Cu1–I1
I2–Cu2–I3
79.10(16)
79.39(16)
158.39(16)
124.06(16)
131.95(12)
103.92(11)
119.86(4)
120.16(4)
119.97(4)
Complex 2 is mixed-valent. The asymmetric unit of 2
contains three crystallographically independent metal cen-
ters in the crystal structure (Fig. 2). The bivalence Cu(1)
atom has a distorted octahedron geometry and was che-
lated by two ligands to form a CuN6 polyhedron. The
equatorial positions of the octahedron are occupied by
three N atoms from a terpyridine and a N atom of the cen-
tral pyridyl ring from another terpyridine. The remaining
two apical positions are occupied by the terpyridine side
pyridyls. As a result of the ligand geometry constraint
and the Jahn-Teller effect of Cu2+ ion [27,28], the Cu–N
I2–Cu2–I2#2
I3–Cu2–I2#2
Complex 7
N1–Cu1
N2–Cu1
N3–Cu1
N4#1–Cu2
I1–Cu1
I2–Cu1
I1–Cu2
I2–Cu2
Cu1–Cu2
2.404(9)
2.121(7)
2.252(8)
2.025(7)
2.6307(16)
2.781(2)
2.5281(17)
2.5576(18)
2.754(3)
N1–Cu1–N2
N2–Cu1–N3
N3–Cu1–N1
N2–Cu1–I1
N2–Cu1–I2
I1–Cu1–I2
71.4(3)
74.9(3)
144.5(3)
142.6(2)
107.6(2)
109.69(6)
120.96(7)
116.5(2)
110.0(2)
˚
distances vary from 1.939(5) to 2.332(5) A and the angels
around Cu(1) vary from 74.93(17)° to 165.51(19)°.
The monovalence Cu(2) has a slightly distorted trigonal
planar geometry and was coordinated by two independent
iodine atoms and the pendant pyridyl ring of pyterpy. The
I1–Cu2–I2
N4#1–Cu2–I1
N4#1–Cu2–I2
˚
a
Cu–I distances were 2.4990(14) and 2.5057(14) A; the Cu–
Symmetry codes: (#1) ꢀx, ꢀy + 2, ꢀz ꢀ 1 for 2; (#1) ꢀx + 1, ꢀy + 1,
ꢀz + 2 for 5; (#1) x ꢀ 1, y ꢀ 1, z (#2) ꢀx + 3, ꢀy, ꢀz for 6; (#1) x,
y + 1,z ꢀ 1 for 7.
˚
N distance was 2.057(6) A, comparable with the distances
in other complexes in this work. The angles around Cu(2)
vary from 110.42(16)° to 130.06(5)°, deviated from the idea
value 120°.
Interestingly, the positive charge of the mixed-valence
species is balanced by a counteranion [Cu2I4]2ꢀ, in which
two Cu(I) ions are symmetrically bridged by two Iꢀ ions
and coordinated by two Iꢀ ions, leading to a dimer of trian-
gularly coordinated Cu(I) with the three angles of 120.31(5)°,
120.98(5)° and 118.68(5)°, respectively. The two symmetric
solutions, refinements and graphics were performed with
the SHELXL-97 [43] package. Selected bond lengths and
angles are given in Table 2.
3. Results
3.1. Structure of [Cu(L1)I2] (1)
˚
copper atoms have a shorter distance of 2.636(2) A, which
is comparable with the distances of the analogues reported
[21,29–33], indicating a strong interaction between them.
There is only one copper(II) metal center in the crystal
structure of complex 1 (Fig. 1). The copper(II) atom dis-
played a distorted square pyramidal geometry and was
coordinated by a tridentate terpyridine, in a cis–cis-config-
uration, and two independent iodine atoms to form a
monomer. In the monomer, one iodine atom was in the
apical site while the terpyridine and the other one iodine
atom were at the equatorial positions. The distances of
3.3. Structure of [Cu(L2)I2]2 (3)
X-ray diffraction proved that complex 3 is a racemic
twin with Flack parameter refined to be 0.49(3) and two
˚
Cu–I varied from 2.5850(5) to 2.8323(5) A and Cu–N from
1.955(3) to 2.062(3) A, respectively; the angles around the
˚
distorted pyramidal copper atom vary from 78.8(1)° to
162.65(9)° (Table 1), which are all similar to the reported
Fig. 2. View of complex 2, containing CuI dinuclear and CuI–CuII
dinuclear fragments (Hydrogen atoms are omitted for clarity.). Symmetry
codes: (A) ꢀx, ꢀy + 2, ꢀz ꢀ 1.
Fig. 1. View of complex 1, a CuII mononuclear structure (Hydrogen
atoms are omitted for clarity.).

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H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
Fig. 3. View of complex 3, a twin CuII mononuclear structure (Hydrogen
atoms are omitted for clarity.).
independent copper metal centers in the crystal structure
have shown +2 oxidation states (Fig. 3). The copper(II)
atoms have shown the same configurations as complex 1
and formed a pair of monomers: Cu(L)I2. The distances
Fig. 4. View of Complex 4, a CuI dinuclear structure (Hydrogen atoms are
omitted for clarity.).
˚
of Cu–I vary from 2.560(1) to 2.862(1) A and Cu–N from
˚
1.951(6) to 2.065(6) A; the angles around the distorted
tances. The fact that the sum of the angles around Cu(2),
I(1)–Cu(2)–I(2), I(1)–Cu(2)–N(3) and I(2)–Cu(2)–N(3) of
357.9°, close to 360°, and the Cu(2) atom rising from the
pyramidal copper atom vary from 78.8(3)° to 157.4(3)°
(Table 1), similar to those in complex 1 and the reported
values [24].
˚
I(1)–I(2)–N(3) basal plane by 0.1933 A, indicates Cu(2),
The terpyridines are also approximately planar (interan-
nular torsion angles: 3.2°, 5.6°; 4.2°, 7.6°), but the pendent
pyridyl has rotated and formed a dihedral angle with the
central pyridyl ring of 29.3° and 29.9°, respectively. Weak
intermolecular face-to-face p–p stacking is found within
the two pendant pyridyls (centroid–centriod distance
I(1), I(2), N(3) in an approximately coplanar. Thus, there
may have no or only a weak interaction between Cu(2)
and N(2). If the interaction between Cu(2) and N(2) could
be ignored, the coordination geometry of Cu(2) were more
like the trigonal planar than the tetrahedron geometry. The
angles around Cu(1) from 77.11(10)° to 125.96(9)° deviate
from the ideal value 109.5°. These may be attributed to the
geometric constraints imposed by the twisting of ligand L2.
˚
3.820 A), which may resulted in the formation of the
dimeric structure. The dimers aggregate into a pair of lay-
ers supported by p–p stacking with intra- and interlayer
hydrogen bonds. In the pair of layers, the underlayer has
shown a network of C–Hꢂ ꢂ ꢂI and C–Hꢂ ꢂ ꢂN hydrogen
bonds, while the layer over it has shown pairs of hydrogen
bonded parallel zigzag chains. This is quite different from
3.5. Structure of [Cu4(L2)2(l-I)2I2] (5)
The asymmetric unit of 5 contains two crystallographi-
cally independent copper(I) metal centers in the crystal
structure (Fig. 5). The Cu(1) and Cu(2) have a distorted tet-
rahedron and a slightly distorted trigonal planar geometry,
respectively. The terpyridine of L2 has shown a cis-config-
uration and acts as a bidentate and a monodentate ligand
coordinated to the copper(I) atoms, respectively. Cu(1) is
coordinated by the bidentate part and two independent
the hydrogen bonding of
1
and the complex
[Cd(L)(H2O)(NO3)2] [L = 40-(4-pyridyl)-2,20:60,200-terpyri-
dine] [6]. The pairs of layers are packed in a parallel man-
ner and extended to a three-dimensional structure.
3.4. Structure of [Cu2(L2)(l-I)I(PPh3)] (4)
The asymmetric unit of 4 contains two crystallographi-
cally independent copper(I) metal centers in the crystal
structure (Fig. 4). Both of the copper atoms have shown
distorted tetrahedron geometry. The two side rings and
the pendant ring of ligand L2 have twisted to form three
interplanar angles with the central ring: 21.2°, 33.1° and
35.6°, respectively. Therefore, the terpyridine of L2 has
shown a cis-configuration, acting as two bidentate ligands
coordinated to the copper atoms. Cu(1) is coordinated by
N(1), N(2), I(1) and P(1) at the four apical positions, while
Cu(2) is coordinated by N(2), N(3), I(1) and I(2). Here, the
N(2) and I(1) act as two double bridging between the two
copper metal centers. The two copper(I) atoms have a dis-
I
I
˚
tance of 2.6791(9) A indicating a strong Cu –Cu interac-
tion, which is comparable with CuI–CuI distance found
previously [25,26]. To be noticeable, the Cu(2) and N(2)
Fig. 5. View of complex 5, a tetranuclear CuI structure (Hydrogen atoms
are omitted for clarity.). Symmetry codes: (A) ꢀx + 1, ꢀy + 1, ꢀz + 2.
˚
distance of 2.464(3) A is longer than normal Cu(I)–N dis-

H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
4033
iodine atoms: I(1) and I(2); Cu(2) is coordinated by the
monodentate part with the pendent pyridyl group of
another pyterpy and I(2). I(2) doubly bridges the two cop-
per(I) metal centers. The two monovalent copper(I) atoms
atoms from the terpyridine of L2 and a nitrogen atom from
the pendent pyridyl group of another pyterpy at the equa-
torial positions. The remaining apical position is occupied
by an independent iodine atom. As a result, a cation unit
[Cu(L)I]+ was formed. The Cu–I has a distance of
˚
have a distance of 2.6626(7) A and is comparable with that
in 4, indicating a strong CuI–CuI interaction. The Cu–N
2.6365(10) A and the Cu–N distances vary from 1.949(4)
˚
˚
˚
distances vary from 1.979(3) to 2.241(2) A and Cu–I dis-
to 2.124(4) A. The angles around Cu(1) from 79.10(16)°
tances from 2.5036(6) to 2.6515(5) A. The angles around
to 158.39(16°) are comparable with those in the CuII mono-
mers 1 and 3. The counteranion [Cu2I4]2ꢀ is similar to that
in complex 2 with different angles and distance between
˚
Cu(1) of 77.17(10)–122.351(18)° and the angels around
Cu(2) of 108.11(8)–131.40(11)° have deviated from the
ideal value 109.5° and 120°, respectively. These may be
attributed to the differences of coordination geometry
and the geometric constraints imposed by the twisting of
ligand L2.
I
˚
both Cu atoms. The Cu–Cu distance of 2.5752(15) A is
shorter than those in 2, 4 and 5, indicating a stronger
interaction.
The ligand L2 bridges the bivalent copper atoms, prop-
agated to afford an infinite one-dimensional zigzag chain
(Fig. 7) with the counterions [Cu2I4]2ꢀ along it. The two
closest zigzag chains, in an approximate inversion pattern,
supported by weak aryl-aryl stacking interactions (centroid
The interplanar angles of the two side rings with the cen-
tral ring of them were 9.7° and 42.1°, respectively. At the
same time, there was a rotation about the interannular
bond C(8)-C(16), given place to a dihedral angle of 46.0°
between the planes of the pendant 40-pyridyl group and
the central pyridyl ring. This rotation is significant larger
than those of the complexes in this work and the approxi-
mate magnitude 39.5° [6], 40.64° [34]. Furthermore, this
twisting of the aromatic rings resulted in the formation of
a tetranuclear grid-like dimer. The central pyridyl ring
and the pendant pyridyl ring of another ligand have a cen-
˚
distance 3.978 A) and weak C–Hꢂ ꢂ ꢂI hydrogen bonds
˚
˚
(Hꢂ ꢂ ꢂI = 3.058 A, 3.158 A), resulting in the formation of
a 2D grid-like motif. The grids were connected by the
[Cu2I4]2ꢀ units with C–Hꢂ ꢂ ꢂI hydrogen bonds propagated
to form a three-dimensional network.
3.7. Structure of [Cu2(L2)(l-I)2]n (7)
˚
troid–centroid distance of 4.586 A in the dimer, indicating
aryl–aryl interaction is absent.
The structure of 7 consists of two crystallographically
independent copper(I) atoms (Fig. 7). The Cu(1) has a dis-
torted square pyramidal geometry and is coordinated by a
terpyridine part of L2 and I(1) at the equatorial position,
the apical position is occupied by I(2). The Cu–N bond
3.6. Structure of {[Cu(L2)I]2[Cu2(l-I)2I2]}n (6)
The asymmetric unit of 6 contains two crystallographi-
cally independent metal centers in the crystal structure
(Fig. 6). The bivalent Cu(1) atom is five-coordinated and
its distorted square pyramidal sites include three nitrogen
˚
lengths vary from 2.121(7) to 2.404(9) A and the angles
around the metal center range from 71.4(3)° to 144.5(3)°.
Compared with the above complexes, the differences of
bond lengths and angels may be due to the unusual five-
coordinated copper(I) geometry. The two iodine atoms
also act as two double bridging atoms between the two
copper atoms forming a Cu2I2 connector as reported
[35,36]. The Cu–Cu distance of the Cu2I2 connector is
˚
2.754(3) A, which is comparable with those in the above
complexes, indicating a strong interaction.
Cu(2) bears a distorted trigonal planar geometry and is
coordinated by two iodine atoms and a pendant pyridyl
group of another terpyridine ligand. The Cu–I bond
˚
lengths from 2.5281(17) to 2.781(2) A are comparable with
Fig. 6. View of the CuII zigzag chain polymer and CuI counterions
[Cu2I4]2ꢀ in complex 6 (Hydrogen atoms are omitted for clarity.).
Symmetry codes: (A) x ꢀ 1, y ꢀ 1, z; (B) ꢀx + 3, ꢀy, ꢀz.
those in the above complexes and other previously reported
I-bridged copper(I) complexes [12,26,35].
Fig. 7. View of the CuI zigzag chain of complex 7 (Hydrogen atoms are omitted for clarity.) Symmetry codes: (A) x, y + 1, z ꢀ 1.

4034
H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
Fig. 8. View of the Cu4I4 moiety and a section of 2D grid formed by weak interactions (Hydrogen atoms are omitted for clarity.).
The copper(I) atoms are bridged by ligand L2 and are
the terpyridyl sites. In this context, several compounds
were successfully developed from mononuclear to polymers
as predicted in Scheme 3.
propagated to form a zigzag chain. Interestingly, the
Cu2I2 units of the two approximately parallel zigzag chains
were connected by Cuꢂ ꢂ ꢂCu and Cuꢂ ꢂ ꢂI interactions to con-
struct a Cu4I4 motif, a polymeric staircase of CuI (Fig. 8b).
The Cuꢂ ꢂ ꢂCu and Cuꢂ ꢂ ꢂI distances are 3.200(9) and
Mononuclear 1 containing L1 with terpyridine chelating
copper(II) center was obtained by the reaction of CuI and
L1 in a 2:1 ratio. When the ratio increases to 4:1 and in the
presence of 4,40-pyridine, a complex [Cu2(L1)2I2][Cu(l-I)I]
containing a mixed-valent dinuclear [Cu2(L1)2I2] cation
and a monovalent [Cu(l-I)I] anion was obtained. The
reduction of Cu(II) to Cu(I) under hydrothermal condi-
tions by the reducing agents, such as 4,40-bipyridyl or pyr-
idine derivatives, has been reported previously [17–20]. The
formation of counterion [Cu2(l-I)2I2] may be attribute to
the excessive CuI. Similar [Cu2(l-I)2I2] species have also
been found in other coordination compounds [30–32].
The result indicates that the higher CuI/ligand ratio benefit
the coordination of pendent pyridyl.
˚
3.319(9) A, significant larger than the distances in above
complexes and their analogues[37–39], however, compared
with the typical values of Cuꢂ ꢂ ꢂCu distances range 2.53–
˚
3.58 A [40,41], implying weak interactions. The Cu4I4 units
are combined by weak aryl-aryl staking interactions (cen-
˚
troid distance 4.078 A) and weak C–Hꢂ ꢂ ꢂI hydrogen bonds
˚
(Hꢂ ꢂ ꢂI distance range 3.228–3.339 A), resulting in the for-
mation of a two-dimensional grid (Fig. 8a). The grids are
arranged in a parallel fashion and connected by weak C–
Hꢂ ꢂ ꢂI hydrogen bonds to form a three-dimensional
network.
Both 1 and its analogue 3 have shown cis–cis-configura-
tion and the copper atoms of them have shown square pyra-
midal geometries and +2 oxidation states. In each monomer,
the pendent 40-pyridyl was not coordinated to any metal cen-
ters. Obviously, the six-coordinate feature of copper(II)
determine the chelating preference in the formation of the
structures. Changing the oxidations states of copper atoms
may give chances to construct different compounds.
4. Discussion
It is understandable that terpyridine prefer to chelate
metal ions to form mononuclear compounds. For pyr-
idyl-substituted terpyridine, the variability of the 40-pyrid-
yls may increase the possibility of forming multinuclear
complexes. Tuning up the terpyridine chelate effect and
activating the substituted 40-pyridyls are very important
to develop complexes from mononuclear to polymers. To
increase the nuclearity of the complexes, the following
strategies may be feasible: (1) alternating the oxidations
states of the metal centers; (2) increasing stoichiometric
metal/ligand ratio; (3) introducing a second ligand. Differ-
ent oxidation states of metal centers will result in different
coordination preferences [11] and coordination molecular
architecture can be directly constructed by coordination
bonds using metal ions existing in varied coordination
geometries to combine with multifunctional ligands into
multi-dimensional frameworks [15]. For example, it is easy
to form a chelating compound by two terpyridines with a
six-coordinate copper(II), but it hard to form the same
structure with a four-coordinate copper(I). Therefore, for
pyterpy, monovalent copper(I) will provide more possibil-
ity for the 40-pyridyls to participate in the reactions. To
increase metal/ligand ratio or introduce a second ligand
is also to increase the possibility of developing the com-
pounds with higher nuclearity. At the same time, it will
help to prevent the chelation of two different pyterpys with
Other reducing agents such as PPh3, copper powder or
dppm were employed. Addition of PPh3 results in a binu-
clear compound [Cu2(L2)I2PPh3] (4). In 4, the ligand has
shown cis-configuration and the metal centers have shown
+1 oxidation states. Though the 40-pyridyl was still not
coordinated to any metal centers, it seems that the lower
oxidation states of copper atoms can drive the ligand form-
ing a different configuration. The compound 4 proved that
the additive PPh3 participating in the reactions will give
more variability. The similar strategy using different cat-
ions, anions, ligands even some unusual additives to alter
the thermodynamic and kinetic factors, had been used to
synthesize complexes of 3,5-dimethyl-1,2,5-triazolate [16].
Using a higher metal-to-ligand ratio 4:1, [Cu4(L2)2(l-
I)2I2] (5) was obtained in 140 °C by adding reducing agent
copper powder. The ligands in it have twisted into a cis–cis-
configuration and coordinated to four copper(I) metal cen-
ters to form a tetranuclear grid-like dimmer (Fig. 5). In
contrast, {[Cu(L2)I]2[Cu2(l-I)2I2]}n (6), containing a cop-
per(II) zigzag chain and counterions [Cu2(l-I)2I2] was
obtained in absence of reducing agents. [Cu2(L2)(l-I)2]n

H. Feng et al. / Inorganica Chimica Acta 359 (2006) 4027–4035
4035
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Up to now, the copper-pyterpy compounds were suc-
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the higher temperature stabilize the Cu+ under hydrother-
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agents or solvents, the compounds had been developed
from discrete monomers to zigzag polymeric chains. These
results proved that it was an effective way to synthesize dif-
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processes, metal coordination geometry may play an
important role in the formations of the complexes. For
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achieved from the reduction of copper valence states
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We gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Nos.
20571050 and 20271031) and the Natural Science Founda-
tion of Guangdong Province of China (No. 021240). S.W.
Ng thanks the support from University of Malaya.
Appendix A. Supplementary data
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Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.ica.2006.04.035.
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