Synthesis, crystal structure and fluorescent property of two-dimensional Cu(I) coordination polymers with cyanide, thiocyanate and triazole bridges

Article abstract of DOI:10.1016/j.molstruc.2007.03.055

Hydrothermal reaction of CuCN, K₃[Fe(CN)₆] with 4-(6-amino-2-pyridyl)-1,2,4-triazole (apt) afforded a coordination polymer [Cu₇(CN)₇(apt)₂]_n (1), while solvothermal reaction of CuSCN with apt in acetonitrile afforded a coordination polymer [Cu₂(SCN)₂(apt)]_n (2). Complex 1 shows two-dimensional polymeric network with large hexagonal channels constructing by CuCN chains and tridentate apt ligands. Complex 2 shows two-dimensional polymeric framework assembled by ladder-like [Cu(SCN)]_n chains and bidentate apt ligands, in which thiocyanate acts as a tridentate bridging ligand. Both polymers are thermal stable and strong fluorescent in the solid state.

Full text of DOI:10.1016/j.molstruc.2007.03.055

Available online at www.sciencedirect.com
Journal of Molecular Structure 875 (2008) 17–21
www.elsevier.com/locate/molstruc
Synthesis, crystal structure and fluorescent property
of two-dimensional Cu(I) coordination polymers with cyanide,
thiocyanate and triazole bridges
a
a,
b
a
Sheng-Wen Liang , Ming-Xing Li *, Min Shao , Xiang He
a
Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, PR China
Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, PR China
b
Received 1 March 2007; accepted 27 March 2007
Available online 12 April 2007
Abstract
Hydrothermal reaction of CuCN, K3[Fe(CN)6] with 4-(6-amino-2-pyridyl)-1,2,4-triazole (apt) afforded a coordination polymer
[Cu7(CN)7(apt)2]n (1), while solvothermal reaction of CuSCN with apt in acetonitrile afforded a coordination polymer [Cu2(SCN)2(apt)]n
(2). Complex 1 shows two-dimensional polymeric network with large hexagonal channels constructing by CuCN chains and tridentate
apt ligands. Complex 2 shows two-dimensional polymeric framework assembled by ladder-like [Cu(SCN)]n chains and bidentate apt
ligands, in which thiocyanate acts as a tridentate bridging ligand. Both polymers are thermal stable and strong fluorescent in the solid
state.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Cu(I) complex; Cyanide; Thiocyanate; 4-(6-Amino-2-pyridyl)-1,2,4-triazole; Crystal structure; Fluorescence
1. Introduction
Analogous to cyanide, thiocyanate is a linear anion and a
potential worthy bridging ligand in constructing coordina-
tion polymer. A few transition metal thiocyanate-contain-
ing coordination polymers have been reported which
show interesting structural diversity and properties [8–11].
We report herein two interesting Cu(I) coordination poly-
mers formulated as [Cu7(CN)7(apt)2]n (1) and [Cu2(SC-
N)2(apt)]n (2), wherein an aminopyridyl-1,2,4-triazole
(apt) is used as connector between Cu(I)-cyanide and
Cu(I)-thiocyanate polymeric chains, which is different with
previous monodentate or chelating N-donor groups used
as co-ligands in preparing copper cyanide coordination
polymers.
The design, synthesis and crystal engineering of coordi-
nation polymers continue to be a quite active research field
because of their intriguing structural motifs and potential
applications as functional materials [1–3]. The diversity in
the structures of coordination polymers was attributed to
the selection of metal centers and organic bridging ligands
as well as synthetic methods. Recently, there has been a
growing interest in copper cyanide coordination polymers
incorporating organodiimine and N-heterocycle as co-
ligands [4–6]. Cu(I) ion is in favor of trigonal or tetrahedral
coordination in the presence of cyanide and aromatic N-
donor ligands gives the possibility of promoting the forma-
tion of metal-organic frameworks because of the strong
coordinating nature of these ligands and their ability to
act as connectors between different copper centers [7].
2. Experimental
2.1. Materials and measurements
*
All chemicals were of reagent grade and used as received
without further purification. Apt was prepared as literature
Corresponding author. Tel.: +86 21 66132401; fax: +86 21 66132797.
E-mail address: mx_li@mail.shu.edu.cn (M.-X. Li).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.03.055

18
S.-W. Liang et al. / Journal of Molecular Structure 875 (2008) 17–21
method [12]. C, H and N analyses were performed on a
Vario EL III elemental analyzer. Infrared spectra were
recorded with a Nicolet A370 FT-IR spectrometer in
KBr pellets in the 4000–400 cmÀ1 region. TG-DSC analy-
ses were completed on a Netzsch STA 449C thermal ana-
lyzer at a heating rate of 10 ꢁC minÀ1 in air. Fluorescent
(m), 3319 (m), 2138 (s), 2119 (s), 1620 (s), 1570 (w), 1529
(s), 1451 (s), 1247 (m), 788 (m), 615 (w).
2.3. Crystal structure determination
Single crystal X-ray diffraction measurements for com-
plexes 1 and 2 were carried out on a Bruker Smart Apex-II
CCD diffractometer with graphite monochromatic Mo Ka
spectra were recorded on
spectrophotometer.
a
Shimadzu RF-5301
˚
radiation (k = 0.71073 A) using both u and x-scan modes
at 273(2) K. Data reductions were made with SAINT pack-
age. Absorption corrections were performed using SADABS
program. The structures were solved by direct method with
SHELXS-97 program and refined on F2 by full-matrix least
squares techniques with SHELXL-97 program [13]. All non-
hydrogen atoms were refined anisotropically, and hydrogen
atoms were treated by mixture of independent and con-
strained refinement. The crystal data and structure refine-
ment results are summarized in Table 1. The selected bond
lengths and angles are given in Table 2.
2.2. Synthesis
[Cu7(CN)7(apt)2]n (1): A mixture of CuCN (0.5 mmol),
K3[Fe(CN)6] (0.5 mmol), apt (0.5 mmol), and water
(10 mL) was sealed in a 15 mL Teflon-lined stainless-steel
reactor, which was heated at 180 ꢁC for 24 h under autog-
enous pressure. Upon cooling to room temperature at a
rate of 10 ꢁC hÀ1, colorless block crystals suitable for X-
ray structure study were obtained in 65% yield based on
Cu. Anal. Found: C, 26.57; H, 1.50; N, 24.82. Calc. for
C21H14Cu7N17: C, 26.51; H, 1.48; N, 25.03. IR (KBr,
cmÀ1): 3330 (m), 3129 (m), 2118 (s), 1617 (m), 1572 (w),
1531 (s), 1459 (s), 1246 (m), 786 (m), 718 (w).
3. Results and discussion
[Cu2(SCN)2(apt)]n (2): A mixture of CuSCN (0.5 mmol),
apt (0.5 mmol), and acetonitrile (5 mL) was sealed in a
15 mL Teflon-lined stainless-steel reactor, which was
heated at 140 ꢁC for 72 h under autogenous pressure. Upon
cooling to room temperature at a rate of 10 ꢁC hÀ1, yellow
rod-like crystals suitable for X-ray structure study were
obtained in 40% yield based on Cu. Anal. Found: C,
27.05; H, 1.76; N, 24.11. Calc. for C9H7Cu2N7S2: C,
26.73; H, 1.74; N, 24.23. IR (KBr, cmÀ1): 3422 (m), 3311
3.1. Description of crystal structures
X–ray structure analysis revealed that complex 1
assumes a two-dimensional polymeric network construct-
ing by CuCN chains and tridentate apt ligands. As shown
in Fig. 1, the molecular structure of [Cu7(CN)7(apt)2]n is
central symmetric, and the center locates at Cu(4) atom.
Each asymmetric structure unit contains four crystallo-
graphically independent copper(I) atoms. Cu(1) atom
Table 1
Crystallographic data and structure refinement for 1 and 2
Complex 1
Complex 2
Empirical formula
Formula weight
Crystal system
Space group
C
951.27
Triclinic
P1
8.2529(11)
9.7052(13)
10.3996(14)
67.298(2)
69.518(2)
79.187(2)
718.52(17)
1
21H14Cu7N17
C9H7Cu2N7S2
404.42
Monoclinic
P21
5.7255(9)
12.1360(19)
9.3084(14)
90
94.792(2)
90
644.53(17)
2
2.084
3.621
400
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dc (Mg mÀ3
)
2.198
5.129
463
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm3)
Measured reflections
Independent reflections
Data/restraints/parameters
Goodness-of fit on F2
R [I > 2r(I)]
0.40 · 0.30 · 0.10
3727
2501 [Rint = 0.0405]
2501/0/210
0.40 · 0.30 · 0.30
3360
2168 [Rint = 0.0170]
2168/1/181
1.093
1.092
R1 = 0.0526, wR2 = 0.1474
R1 = 0.0594, wR2 = 0.1523À3
R1 = 0.0242, wR2 = 0.0515
R1 = 0.0272, wR2 = 0.0531À3
R (all data)
Largest diff. peak and hole
˚
˚
0.772 and À1.043 e A
0.236 and À0.241 e A

S.-W. Liang et al. / Journal of Molecular Structure 875 (2008) 17–21
19
Table 2
structed by the coordination of N(1), N(2) and N(6). The
bond lengths of Cu(1)–N(1), Cu(1)–N(2) and Cu(1)–N(6)
are 2.052(4), 2.007(4), 1.909(7) A, respectively, while the
˚
Selected bond lengths (A) and angles (ꢁ) for 1 and 2
˚
Complex 1
Cu(1)–N(1) 2.052(4)
Cu(1)–N(2) 2.007(4)
Cu(1)–N(5) 2.434(5)
Cu(1)–N(6) 1.909(7)
Cu(2)–N(8) 1.945(6)
N(1)–Cu(1)–N(2) 104.76(16)
N(1)–Cu(1)–N(6) 117.2(2)
N(2)–Cu(1)–N(6) 130.4(2)
N(5)–Cu(1)–N(2) 93.32(16)
Cu(2)–N(9) 1.905(5)
Cu(2)–C(9) 1.905(5)
Cu(3)–N(7) 1.865(6)
Cu(3)–C(8) 1.834(5)
Cu(4)–C(10) 1.842(5)
N(5)–Cu(1)–N(6) 108.5(2)
C(9)–Cu(2)–N(9) 120.1(2)
C(9)–Cu(2)–N(8) 123.0(2)
C(8)–Cu(3)–N(7) 177.1(3)
bond angles of N(1)–Cu(1)–N(2), N(1)–Cu(1)–N(6) and
N(2)–Cu(1)–N(6) are 104.76(16), 117.2(2), 130.4(2)ꢁ,
respectively. The amino N(5) atom occupies the axial posi-
˚
tion with the Cu(1)–N(5) bond distance of 2.434(5) A and
the N(5)–Cu(1)–N(1) bond angle of 93.38(18)ꢁ. This bond
distance is significantly longer than those of other three
Cu–N bonds, indicating a weak coordination behavior
between amino group of apt and Cu(1) atom. Cu(2) atom
is planar trigonally coordinated by three cyanide bridges.
The bond angles of C(9)–Cu(2)–N(9), C(9)–Cu(2)–N(8)
and N(9)–Cu(2)–N(8) are 120.1(2), 123.0(2), 116.6(2)ꢁ,
respectively. Cu(3) and Cu(4) atoms are typically two-coor-
dinated by bridging cyanide groups in linear fashion. Bond
angles C(8)–Cu(3)–N(7) and C10–Cu(4)–C(10A) are
177.1(3), 179.998(1)ꢁ, respectively.
Complex 2
Cu(1)–S(1) 2.4279(11)
Cu(1)–S(2) 2.6236(11)
Cu(1)–N(4) 1.982(3)
Cu(2)–S(1) 2.8068(11)
Cu(2)–S(2) 2.3378(11)
Cu(2)–N(5) 1.970(3)
Cu(1)–N(6) 1.906(3)
Cu(2)–N(7) 1.907(3)
Cu(1)–S(1)-Cu(2) 69.53(3)
S(1)–Cu(1)-S(2) 109.74(4)
N(6)–Cu(1)-N(4) 143.76(13)
N(6)–Cu(1)-S(1) 103.88(9)
Cu(1)–S(2)–Cu(2) 74.19(3)
S(2)–Cu(2)–S(1) 106.55(4)
N(7)–Cu(2)–N(5) 134.66(13)
N(7)–Cu(2)–S(2) 105.97(9)
In structure of 1, all cyanide groups play l2-bridge. The
structure can be described as that both Cu3(CN)3 pieces are
linked to central Cu(4) atom through a cyanide group to
form a Cu7(CN)7 unit, which is further polymerized to
form [Cu7(CN)7]n zigzag chain. These [Cu7(CN)7]n chains
adopts a distorted trigonal-pyramidal geometry, coordi-
nated by four N atoms from two triazoles, one amino
group and one cyanide group. The basal plane is con-
Fig. 1. Views of asymmetric structural unit and 2D polymeric network of 1.

20
S.-W. Liang et al. / Journal of Molecular Structure 875 (2008) 17–21
are connected by apt via its two triazole nitrogen atoms
N(1) and N(2), leading to the formation of a 2D polymeric
network with large hexagonal channels. In previous
reports, monodentate and chelating N-donor ligands were
frequently used as co-ligands in preparing copper cyanide
coordination polymers. Such designs often led to the for-
mation of one-dimensional chains [14,15]. The complex 1
is exampled that 2D or 3D copper cyanide coordination
polymers can be expected when multidentate bridging
ligand is selected as co-ligand.
between two adjacent [Cu(SCN)]n ladder-like chains, which
extends the structure to a two-dimensional polymeric
framework. Such structure is rare in previous reports.
Using apt as ligand, only tetranuclear Ag(I) complex is pre-
pared and structurally characterized to date [17].
3.2. Thermal stability and fluorescent properties
Thermal analyses for complexes 1 and 2 were performed
in the temperature range of 20–800 ꢁC. As shown in Fig. 3,
the complexes 1 and 2 are stable up to 250 ꢁC without
weight-loss. Complex 1 decomposed rapidly near 300 ꢁC
with 5.70% weight-loss, and then decomposed continuously
to 800 ꢁC with 36.89% weight-loss. The final residue is CuO
(found: 57.41%, calc.: 58.53%). Complex 2 showed an
endothermic maximum at 255.7 ꢁC without weight-loss
indicated a phase transfer process happened. This phenom-
enon is also observed in [Cu3(CN)3(phen)]n complex [5]. In
the temperature range of 270–800 ꢁC, complex 2 decom-
posed successively with the final 56.01% residue left, which
may be a mixture of CuO and CuSO4 [18].
The complex 2 exhibits two-dimensional polymeric
structure as shown in Fig. 2. The asymmetric structure unit
consists of two crystallographically independent copper(I)
atoms, one apt, and two thiocyanate ligands. Both cop-
per(I) atoms adopt distorted tetrahedral geometry, coordi-
nated by one nitrogen atom and two bridging sulfur atoms
from three l3-thiocyanate groups, and one nitrogen atom
from the triazole group of apt. The bond lengths of
˚
Cu(1)–S(1) and Cu(1)–S(2) are 2.4279(11), 2.6236(11) A,
while those of Cu(2)–S(1) and Cu(2)–S(2) are 2.8068(11),
˚
2.3378(11) A, respectively. Cu(1) and Cu(2) atoms are
linked by two bridging S atoms to form a Cu2S2 dimmer.
The bond angles of Cu(1)–S(1)–Cu(2) and Cu(1)–S(2)–
Cu(2) are 69.53(3), 74.19(3)ꢁ, while S(1)–Cu(1)–S(2) and
S(1)–Cu(2)–S(2) are 109.74(4), 106.55(4)ꢁ, respectively.
Such Cu2S2 dimmers are further linked by linear thiocya-
nate groups to form ladder-like [Cu(SCN)]n chains. The
bond lengths of Cu(1)–N(6) and Cu(2)–N(7) are 1.906(3),
In the solid state, complexes 1 and 2 show strong fluo-
rescent emission bands centered at 387 and 525 nm, respec-
tively, under photoexcitation of 356 nm (Fig. 4). Generally,
metal-to-ligand charge transfer (MLCT) is the most com-
mon assignment for the fluorescent emission of copper(I)
cyanide complexes [6]. The fluorescent emission of complex
1 is assigned to metal-to-ligand charge transfer where the
electron is transferred from Cu(I) ion to p* orbital of cya-
nide group [19]. The emission band of complex 2 is obvi-
ously different with the one of complex 1. This
phenomenon is observed in several copper(I) thiocyanate
coordination polymers such as [Cu2(SCN)2(dmpz)]n
(582 nm) and [Cu2(SCN)2(dps)]n (538 nm), and the most
possible assignment for these emissions originates from
ligand-to-metal charge transfer (LMCT) [8,9].
˚
1.907(3) A, respectively. Generally, thiocyanate acts as
counter anion or monodentate ligand in metal complexes
[16]. Thiocyanate acting as tridentate ligand is rarely
observed and only found in copper(I) complexes [8,9].
On the other hand, apt acts as bidentate ligand in com-
plex 2. Amino nitrogen atom of apt is uncoordinated,
which is different with the structure of complex 1. The
triazole group of apt binds to two copper(I) centers
Fig. 2. Views of asymmetric structural unit and 2D polymeric network of 2.

S.-W. Liang et al. / Journal of Molecular Structure 875 (2008) 17–21
21
DTA /(mW/mg)
TG /%
TG /%
100
DTA /(uV/mg)
255.7oC
exo
exo
0
0.5
110
100
90
-5.70%
-3.03%
90
80
70
60
0.0
-10
-20
-30
-36.89%
-40.96%
-0.5
-1.0
-1.5
298.0oC
80
70
60
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
600
700
800
Temperature oC
/
Temperature /oC
Fig. 3. Thermal analysis curves of 1 and 2.
450
400
350
300
250
200
150
100
50
387nm
525nm
450
400
350
300
250
200
633nm
375
380
385
390
395
400
405
400
450
500
550
600
650
700
Wavelength /nm
Wavelength /nm
Fig. 4. Fluorescent emission spectra of 1 (left) and 2 (right).
[4] X. He, C.Z. Lu, C.D. Wu, L.J. Chen, Eur. J. Inorg. Chem. 12 (2006)
2491.
4. Supplementary material
[5] S.W. Liang, M.X. Li, M. Shao, Z.X. Miao, Inorg. Chem. Commun. 9
(2006) 1312.
[6] E. Colacio, R. Kivekas, F. Lloret, M. Sunberg, J. Suarez-Varela, M.
Bardaji, A. Laguna, Inorg. Chem. 41 (2002) 5141.
[7] X. He, C.Z. Lu, D.Q. Yuan, S.M. Chen, J.T. Chen, Eur. J. Inorg.
Chem. 11 (2005) 2181.
[8] C. Na¨ther, J. Greve, I. Jeb, C. Wickleder, Solid State Sci. 5 (2003) 1167.
[9] Z.M. Hao, X.M. Zhang, Crystal Growth Des. 7 (2007) 64.
[10] T. Rottgers, W.S. Sheldrick, Z. Anorg. Allg. Chem. 627 (2001) 1976.
[11] C.F. Wang, Z.Y. Zhu, X.G. Zhou, L.H. Weng, Q.S. Shen, Y.G. Yan,
Inorg. Chem. Commun. 9 (2006) 1326.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Center, CCDC-619857 for complex 1 and CCDC-636040
for complex 2. Copies of the data can be obtained free of
charge from CCDC, 12 Union Road, Cambridge, CB2IEZ,
UK. E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
[12] R.H. Wiley, A.J. Hart, J. Org. Chem. 18 (1953) 1368.
[13] G.M. Sheldrick, SHELX-97 Program for Crystal Structure Solution
Financially supported by the Research Foundation for
Returned Chinese Scholars Overseas of Chinese Education
Ministry (7A14219), and the Development Foundation of
Shanghai Education Commission (03AK35).
¨
and Refinement, University of GOttingen, Germany, 1997.
[14] J.H. Yu, J.Q. Xu, Q.X. Yang, L.Y. Pan, T.G. Wang, C.H. Lu, T.H.
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