Structure characterization of two new three-dimensional piperazine-bridged metal-halo coordination polymers

Article abstract of DOI:10.1016/j.ica.2008.12.025

By the simple hydro/solvothermal reaction, two new 3-D metal-halo cluster polymers, [NiCl₂(pip)] (pip = piperazine) (1) and [Cu₂I₂(pip)] (2) were obtained and characterized by IR spectroscopy, CHN analysis and TG analysis.

Full text of DOI:10.1016/j.ica.2008.12.025

Inorganica Chimica Acta 362 (2009) 2802–2806
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Structure characterization of two new three-dimensional piperazine-bridged
metal–halo coordination polymers
*
*
Qin Hou, Jie-Hui Yu , Jia-Ning Xu, Qing-Feng Yang, Ji-Qing Xu
College of Chemistry, State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, 2519 Jie Fang Road, Changchun 130023, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
By the simple hydro/solvothermal reaction, two new 3-D metal–halo cluster polymers, [NiCl2(pip)]
(pip = piperazine) (1) and [Cu2I2(pip)] (2) were obtained and characterized by IR spectroscopy, CHN anal-
ysis and TG analysis. Single-crystal X-ray analysis reveals that, the 3-D network of compounds 1 and 2 are
constructed from the 1-D zigzag NiCl2 chains and the 1-D castellated Cu2I2 chains bridged by pip mole-
Received 11 September 2008
Accepted 27 December 2008
Available online 3 January 2009
cules respectively. The leff versus T curve indicates that compound 1 is ferromagnetic when T > 14 K. The
photoluminscent spectrum shows that compound 2 possesses the fluorescent property with a broad
emission peak at 567 nm upon excision at 397 nm.
Keywords:
Metal–halo cluster polymer
Subunit
Fluorescence property
Magnetic property
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
strategy has been extensively adopted when preparing high-D
poly-acids [27–31]. Some recent reports show that it is being ex-
In the past decade, the study on the design and synthesis of no-
vel cluster polymers achieved considerable attention due to the
structural unpredictability (i.e., which cluster will form and what
is the linking mode between the clusters and organic moieties)
and potential functional properties in some fields as optics (con-
taining groups IB, IIB or rare-earth metal), electrochemistry based
on the metals with many oxidation states, catalysis (poly-acid, zeo-
lite or zeolite-like materials), electrical conductivity (containing
group IVA metal) and magnetism [1–6]. As far as the construction
of cluster polymers is concerned, on the one hand, the inorganic
salts being prone to form the clusters, such as oxides, halides or
sulfides are usually used as the inorganic precursors to form inor-
ganic subunits (SUs) [7–15]. On the other hand, the literature show
that three types of bridges can extend the inorganic SUs into poly-
nuclear or high-dimensional (D) cluster polymers: (i) inorganic
bridge. With various organic ammines as guest species or organic
templating agents, the SUs interact with each other through cova-
lent M–O (X or S) bonds (or through sharing the corner, edge or/
and face) between the SUs, producing new polymeric clusters. This
is the basic constructing conception of zeolite and zeolite-like
materials [16–19]. (ii) Organic bridge, the most common method.
Up to now, lots of bridging organic ligands with N/O/S donors have
been chosen to extend the SUs into the 1-D, 2-D, 3-D cluster poly-
mers via covalent interactions or a combination of covalent and
non-covalent interactions [20–26]. (iii) Metal complex bridge. This
tended to the construction of metal–halo cluster polymers [32–36].
Since 2001, one of the investigations in our group is focused on
the synthesis and property of metal–halo cluster polymers based
on these three construction strategies stated above. Some interest-
ing compounds such as the 3-D [CuX2(1,4-btzb)] [Xꢀ = Clꢀ, Brꢀ;
1,4-btzb = 1,4-bis(tetrazol-1-yl)butane] [37], 2-D [Cu4(OH)4(-
phen)4][Cu8Br12] (phen = 1,10-phenanthroline) [38] and decanu-
clear [Ni(phen)3]2[Cu10HI15] [39] have been obtained. Herein, we
report the syntheses and characterization of two new 3-D metal–
halo cluster polymers: [NiCl2(pip)] 1 and [Cu2I2(pip)] 2 obtained
by the simple hydro/solvothermal technique.
2. Experimental
2.1. Materials and general methods
The chemicals used to prepare the title compounds include
NiCl2 ꢁ 6H2O, CuI, KI, pip ꢁ 6H2O, H2C2O4 ꢁ 2H2O, succinic acid and
ethanol without further purification. The synthesis was carried
out in 30 mL Teflon-lined stainless steel vessels under autogenous
pressure. Elemental (CHN) analysis was performed with a Perkin–
Elmer 2400LS II elemental analyzer. Infrared (IR) spectrum was re-
corded with a Perkin–Elmer Spectrum 1 spectrophotometer in the
4000–400 cmꢀ1 region using a powdered sample on a KBr plate.
Data were collected with Mo Ka radiation (k = 0.71073 Å) on a
Rigaku R-AXIS RAPID IP diffractometer for 1 and on a Siemens
SMART CCD diffractometer for 2. With SHELXTL program, compound
1 was solved with heavy-atom method and compound 2 with di-
rect methods. Then both were refined by full-matrix least-squares
* Corresponding authors. Tel.: +86 431 88499132; fax: +86 431 85168624.
E-mail addresses: jiehuiyu@yahoo.com.cn (J.-H. Yu), xjq@mail.jlu.edu.cn (J.-Q.
Xu).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.12.025

Q. Hou et al. / Inorganica Chimica Acta 362 (2009) 2802–2806
2803
Table 1
[Cu2I2(pip)] (2). To a mixture of CuI (0.24 g, 1.2 mmol) and KI
(0.2 g, 1.2 mmol) in 10 mL water, a solution of pip ꢁ 6H2O (0.12 g,
0.6 mmol) and H2C2O4 ꢁ 2H2O (0.04 g, 0.3 mmol) in 5 mL ethanol
was added. The following process is similar to that 1, but before
the autoclave being sealed, the mixture was adjusted to pH 9 with
dilute KOH. After being washed with water, the orange crystals
were obtained with a yield of ca. 25% based on Cu. IR (cmꢀ1):
3230 m, 2942 w, 1445 w, 1413 w, 1243 w, 1095 m, 1046 m,
1002 w, 989 s, 866 s, 369 w. Anal. Calc. for C4H10N2Cu2I2: C,
10.29; H, 2.16; N, 5.99. Found: C, 10.35; H, 2.10; N, 5.91%.
Crystal data and structure refinement for the title compounds.
Compound
1
2
Formula
Formula weight
Crystal system
Space group
T (K)
a (Å)
b (Å)
c (Å)
C4H10N2NiCl2
215.75
monoclinic
C2/c
C4H10N2Cu2I2
467.02
monoclinic
C2/c
293(2)
293(2)
9.2889(19)
12.895(3)
6.3072(13)
92.48(3)
754.8(3)
4
1.899
3.189
440
3.16–27.47
3652
9.309(2)
15.436(4)
7.0974(16)
103.604(4)
991.3(4)
4
3.129
10.456
848
3.52–28.37
3259
b (°)
V (Å3)
Z
3. Results and discussion
D (g cmꢀ3
)
l
(mmꢀ1
F(000)
)
3.1. Structural description
h Range for data collection (°)
Reflections (measured)
Goodness-of-fit (GOF) on F2
Rint
So far, the report on nickel–halo coordination polymer with the
bridging N-donor ligand is rather rare. The classical cases are com-
pounds [NiX2(4,40-bpy)] (Xꢀ = Clꢀ, Brꢀ; bpy = bipyridine) [40],
which show a 2-D layered topology consisting of the 1-D NiX2
chains bridged by 4,40-bpy ligands.
1.124
0.0315
0.0258/0.0509
0.332, ꢀ0.447
1.027
0.0883
0.0298/0.0601
1.052, ꢀ1.645
R1/wR2
Largest difference in peak and hole (e Åꢀ3
)
[a] R =
R
||Fo| ꢀ |Fc||/
R
|Fo|. [b] Rw = |
R
w(|Fo|2 ꢀ |Fc|2)|/
R
|w(Fo2)2|1/2
,
where w = 1/
Using the pip in place of the 4,40-bpy, the title 3-D compound 1
with a different topology from the former was synthesized. With
the pip, NiCl2 ꢁ 6H2O forms a 1-D chained SU. The Ni(II) center with
an octahedral geometry is coordinated by four Clꢀ ions and two N
atoms from the different pip. The Ni–N bond length [2.118(2) Å]
and the average Ni-Cl bond length [2.475 Å] are similar to those
[r
2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3.
techniques. The non-hydrogen atoms for both were assigned aniso-
tropic displacement parameters in the refinement. For compound
1, the hydrogen atoms were obtained from difference Fourier
map, and for compound 2, the hydrogen atoms were treated with
a riding model except ones on N atoms being obtained from differ-
ence Fourier map. The structures were then refined on F2 using
SHELXL-97. Basic information pertaining to the crystal parameters
and structure refinement of the title compounds is summarized
in Table 1. Selected bond lengths and bond angles are listed in Ta-
ble 2.
found in reported [NiCl2(4,40-bpy)] [40]. Through the
l2-Cl bridges,
all of the Ni(II) centers are linked into a zigzag chain, which can be
described as an infinite extension of edge-shared NiCl4N2 octahe-
dra. The Ni(pip)2+ unit adopts a cis-type arrangement. It is notice-
able that compound 1 displays the different porous shapes in
different directions. As shown in Fig. 1, in [100] direction, it takes
on a trigonal channel with base 6.3 Å and height 6.6 Å. While in
[001] direction, it displays a square hydrophobic channel with
the size of 7.9 ꢂ 7.9 Å2.
2.2. Synthesis of complex
Comparing the topology of 1 with one of [NiX2(4,40-bpy)], we
can find that the different organic ligands lead to the different
[NiCl2(pip)] (1). To
a
16 mL ethanol, NiCl2 ꢁ 6H2O (0.24 g,
2+
topologies. The reason is that NiL2 unit adopts the different geo-
1 mmol), pip ꢁ 6H2O (0.19 g, 1 mmol) and succinic acid (0.12 g,
1 mmol) were added in succession. After being stirred for 4 h, the
mixture (pH = 6) was sealed in a 30 mL Teflon-lined autoclave,
and then heated in an oven at 170 °C. After 3 days, green needle
crystals were obtained, being washed with ethanol and dried in
ambient temperature. Yield: ca. 30% based on Ni. IR (cmꢀ1): 3206
s, 2976 w, 2942 w, 1447 w, 1421 m, 1136 s, 1085 w, 1027 m,
1002 w, 855 s, 664 w, 397 w. Anal. Calc. for C4H10N2NiCl2: C,
22.27; H, 4.67; N, 12.98. Found: C, 22.35; H, 4.59; N, 12.90%.
metric configuration duing to the different bulk of organic ligand.
In compound 1, Ni(pip)2 is cis-pattern, which helps to extend
2+
NiCl2 chains into
a
3-D network, while in [NiX2(4,40-bpy)],
2+
2+
Ni(4,40-bpy)2 is trans-pattern. In addition, the different NiL2
type has an effect on NiX2 chain arrangement: zigzag type in 1; lin-
ear-type in [NiX2(4,40-bpy)].
Compared with the Ni(II), the structure of copper–halo clusters
is richer due to the diversity of coordination geometry of Cu(I).
With bridging N-donor ligands, CuX can form various neutral olig-
omeric and polymeric clusters, namely so-called SUs. The most re-
ports are rhombic dimer, cubane tetramer, zigzag-type and
staircase chains [41]. Further, these SUs are extended by organic
bridges into the 1-D, 2-D or 3-D networks. It was reported that
the size of organic ligands determines the mode of the SUs. In gen-
eral, the bulky ligands as 4,40-bpy favor the formation of discrete
SUs, whereas the small ones favor the polymeric SUs. In compound
[Cu2Br2(tri)] (tri = 1,3,5-triazine) [41], the castellated CuI single
chain was reported, while in compound 2, a new castellated CuI
double chain was observed in reaction with the pip.
X-ray analysis reveals that the structure of compound 2 features
a new 3-D framework constructed from the 1-D Cu2I2 chains
bridged by the pip molecules. With the pip, CuI forms a 1-D castel-
lated Cu2I2 chain as shown in Fig. 2a. The Cu(I) ion adopts a dis-
torted tetrahedral geometry [the angles around Cu(I) ion being
from 103.52(9) to 117.373(19)°] and is coordinated by three equiv-
alent I- ions and one N atom from the pip. The Cu–I bond lengths,
ranging from 2.6569(8) to 2.6876(8) Å, are comparable with those
Table 2
Selected bond lengths (Å) and angles (°) for the title compounds.
Compound 1
Ni(1)–N(1)
Ni(1)–Cl(1)#2
N(1)#1–Ni(1)–Cl(1)
Cl(1)–Ni(1)–Cl(1)#1
Cl(1)#2–Ni(1)–Cl(1)#3
Ni(1)–Cl(1)–Ni(1)#3
2.118(2)
2.5050(8)
94.48(6)
176.87(3)
87.50(4)
95.67(2)
Ni(1)–Cl(1)
2.4455(9)
Cl(1)–Ni(1)–Cl(1)#3
Cl(1)–Ni(1)–Cl(1)#2
N(1)–Ni(1)–N(1)#1
N(1)–Ni(1)–Cl(1)
84.33(2)
93.40(2)
105.73(12)
87.41(6)
Compound 2
Cu(1)–N(1)
Cu(1)–I(1)#1
Cu(1)–Cu(1)#2
N(1)–Cu(1)–I(1)
I(1)–Cu(1)–I(1)#1
I(1)–Cu(1)–I(1)#2
2.088(3)
Cu(1)–I(1)
Cu(1)–I(1)#2
Cu(1)–Cu(1)#1
N(1)–Cu(1)–I(1)#1
N(1)–Cu(1)–I(1)#2
I(1)#1–Cu(1)–I(1)#2
2.6569(8)
2.6876(8)
2.7707(11)
106.10(8)
103.52(9)
106.74(2)
2.6636(7)
2.7294(10)
104.38(9)
117.23(2)
117.373(19)

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Q. Hou et al. / Inorganica Chimica Acta 362 (2009) 2802–2806
Fig. 1. 3-D networks of [NiCl2(pip)] (1) in [100] (a) and [001] (b) directions.
Fig. 2. A 1-D castellated Cu2I2 SU (a) together with 3-D networks in [100] (b) and [001] (c) directions in 2.
observed in the reported similar compounds [8,23,42,43]. The dis-
tances of Cuꢁ ꢁ ꢁCu [2.7294(10)–2.7707(11) Å] are less than twice
the van der Waals radius of the Cu (2.8 Å), which implies that there
exist the weaker Cuꢁ ꢁ ꢁCu interactions within the inorganic chains.
The Iꢀ ions with a trigonal pyramidal geometry link the tetrahedral
Cu(I) to form a castellated Cu2I2 chain, which is obviously different
from the known zigzag chain and the staircase chain. Next, the pip
molecules protrude out from the inorganic chains, bridging them
into a 3-D framework with the 1-D channels in different directions.
In [100] direction, the channel is rectangular with the size of
2.7 ꢂ 9.0 Å2 (see Fig. 2b), while in [001] direction the channel is
a diamondoid structure with the size of 7.5 ꢂ 13.9 Å2 (see Fig. 2c).
Based on the title compounds and the documents, it is easy to
find that the structure of copper(I)–halo cluster is richer than that
of nickel–halo cluster. Perhaps it is due to the flexibility of the me-
tal ion. Generally, the X- ion has a tendency to exhibit the multi-
types of bridging-modes with the flexible metal. For example, in
the reported Cu(I)–X cluster compounds, the Xꢀ ions take on
3.2. Synthetic analysis
It deserves to note that the pH level of the system plays a key
role in the course of crystal growth. The optimal pH values are 6
for 1 and 9 for 2, respectively. The reasonable explanation may
be: (i) in a acid condition, the Cu+ ion will be disproportionated
to the Cu2+ ion and the Cu metal. (ii) In a basic condition, the
Ni2+ ion exists in the Ni(OH)2 form.
As literature reported, the bridging organic acid can be used as
one of the precursors when preparing hybrid metal–halo coordina-
tion polymers. Sometimes, organic acid appeared in the final prod-
uct as the reported Na[Cd2Cl4(C2O4)0.5] ꢁ 4H2O [44] and
Na3[Cd5(C4H4O4)6X] (Xꢀ = Clꢀ, Brꢀ; C4H4O4 = succinate) [45].
Sometimes, organic acid didn’t appear in the final product. Just
as Rao has ever mentioned, the real role of organic acids is still un-
clear, but the target products can’t be obtained without them [45].
3.3. TG analysis
the
l2-, l3-, l4- and l5-bridging modes with linear, trigonal
pyramidal, tetrahedral, planar rectangular, tetragonal pyramidal,
Thermogravimetric (TG) behavior was investigated on a SHIMA-
DZU DTG-60 instrument in a temperature range of 25–800 °C with
a heating rate of 10 °C minꢀ1 in air. As shown in Fig. 3, compound 1
pentagonal pyramidal and umbrella-like (l4-) geometric configu-
rations [38].

Q. Hou et al. / Inorganica Chimica Acta 362 (2009) 2802–2806
2805
110
100
90
(1)
(2)
567
593
80
70
60
50
40
30
20
500
550
600
650
700
750
0
200
400
600
800
Wavelength/nm
Temperature/oc
Fig. 5. Solid-state fluorescence emission spectrum of 2 (kex = 397 nm).
Fig. 3. TGA curves of the title compounds.
exhibits one-step continuous weight-loss in the temperature range
of 310–575 °C. The final residue is proved to be NiO (calc.: 34.62%;
found: 33.15%), which suggests that the pip molecule and the Clꢀ
ion released simultaneously, meanwhile, the Ni(II) ion combined
with the O2 to form the NiO. Compound 2 underwent two steps
of the weight loss. The first step from 210 °C to 440 °C should cor-
respond to the loss of the pip, meanwhile, part Cu(I) transformed
into CuO (calc.: 18.43%; found: 12.67%). The second stage should
correspond to the sublimation of the I- ion and the oxidation of
the residual Cu(I) (calc.: 54%; found: 51%).
tion of metal ion. Based on both stated above, the observed
behavior is thus characteristic of the occurrence of ferromagnetic
interactions within the NiCl2 chains due to a plus h value, whereas
the drop below 14 K can be related to antiferromagnetic coupling
between the chains as well as the effect of zero-field splitting. A
1-D chain model was used to fit the magnetic data of compound
1, unluckily no ideal result was obtained [46].
3.5. Photoluminescent property
The photoluminescent spectrum of compound 2 was measured
on a LS 55 florescence/phosphorescence in the solid state at room
temperature. As displayed in Fig. 5, the emission spectrum of com-
pound 2 shows a strong band at 567 nm with a shoulder at 593 nm
when excited at 397 nm. The emission may be from a triplet ‘‘clus-
ter centered” (3CC*) excited state, which should be assigned to a
combination of iodide to copper charge transfer (IMCT*) and ‘‘metal
cluster centered” [(3MCC*), dCu ? (s,p)Cu] transition. The weak
Cuꢁ ꢁ ꢁCu interactions with an average distance of 2.75 Å within
the Cu2I2 chain, as literature reported, will be responsible for a
3MCC* excited solid [47,48].
3.4. Magnetic property
Magnetic susceptibility data were determined on the basis of a
10.3 mg sample over the temperature of 2–300 K at a magnetic
field of 1 kG on a Quantum Design MPMS-7 SQUID magnetometer.
The leff versus T plot is shown in Fig. 4 (left) [
The experimental leff value at 300 K is 3.11
the theoretically expected value of 2.83 lB for a d8 Ni(II) ion with
an octahedral geometry. Upon cooling down, eff increases contin-
uously up to a maximum of 4.8 B at 14 K, then drops rapidly down
to a value of 1.4 lB at 2 K. The 1/vM versus T curve is close to be
linear when T > 150 K [see Fig. 4 (right)], being well fitted by using
the Curie Weiss law with C = 1.014 emu K molꢀ1, and h = 53.97 K.
On the other hand, zero-field splitting is known to occur for Ni(II)
ions, and for isolated ions may induce either an increase or a de-
l
eff = 2.83 (
v
MT)1/2].
l
B, comparable with
l
l
4. Conclusion
Two new metal–halo cluster polymers based on the pip ligand
have been obtained, which show the 3-D network structures com-
prising the 1-D zigzag NiCl2 SUs and the 1-D castellated Cu2I2 SUs,
respectively. Compound 1 possesses the ferromagnetism, whereas
compound 2 displays the fluorescence due to the existence of the
weaker Cuꢁ ꢁ ꢁCu interaction. The interrelated work is still going
on, aiming at getting more compounds and exploring the relation-
ship between the structure and the property.
crease of
leff value at rather low temperature due to the site distor-
6
250
200
150
Acknowledgement
4
2
This research was supported by the National Natural Science
Foundation of China (No. 20571032).
χ
100
50
0
Appendix A. Supplementary data
CCDC 672190 and 672191 contain the supplementary crystallo-
graphic data for 1 and 2. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2008.12.025.
0
50
100
150
T/K
200
250
300
Fig. 4. leff vs. T curve (left) and 1/vM vs. T curve (right) of 1.

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Q. Hou et al. / Inorganica Chimica Acta 362 (2009) 2802–2806
[27] R. Cao, S.X. Liu, L.H. Xie, Y.B. Pan, J.F. Cao, Y.H. Ren, L. Xu, Inorg. Chem. 46
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