In situ hydrothermal synthesis of two novel Cd(II) coordination compounds

Article abstract of DOI:10.1016/j.inoche.2011.09.029

Hydrothermal in-situ reactions of 4,4′-bis(3,3′-dicyano) pyridine (pydcy) with Cd(NO₃)₂?6H₂O under the similar reaction condition but different solvent media result in two new compounds [C₄₈H₃₂Cd₂N₈O ₁₈](1) and [C₁₇H₁₃CdN₃O ₅](2). Compound 1 features a new dimeric carboxylate bridged structure, while compound 2 gives a 3D framework with large hexagon channels embodied with water molecules. Topology analysis of 2 defines a type of {8 ³} etb topology. TGA and XRPD analysis indicated that the guest water molecules in 2 can be removed to result in a nanoporous network. Both compounds exhibit intense fluorescence at room temperature, which may originate from the ligand-to-metal charge transfer (LMCT) state.

Full text of DOI:10.1016/j.inoche.2011.09.029

Inorganic Chemistry Communications 15 (2012) 21–24
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
In situ hydrothermal synthesis of two novel Cd(II) coordination compounds
a,b,c
b
a,
Guo-Jie Yin
, Bao-Ming Ji , Chen-Xia Du ⁎
a
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, PR China
College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471022, PR China
Department of environment engineering and Chemistry, Luoyang Institute of Science and Technology,Luoyang 471023, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2011
Accepted 23 September 2011
Available online 1 October 2011
Hydrothermal in-situ reactions of 4,4′-bis(3,3′-dicyano)pyridine (pydcy) with Cd(NO ) ·6H O under the
3
2
2
similar reaction condition but different solvent media result in two new compounds [C48
and [C17 13CdN
gives a 3D framework with large hexagon channels embodied with water molecules. Topology analysis of 2
H
32Cd
2 8
N O18](1)
H
3 5
O ](2). Compound 1 features a new dimeric carboxylate bridged structure, while compound
2
3
defines a type of {8 } etb topology. TGA and XRPD analysis indicated that the guest water molecules in 2 can
be removed to result in a nanoporous network. Both compounds exhibit intense fluorescence at room tem-
perature, which may originate from the ligand-to-metal charge transfer (LMCT) state.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Coordination polymers
4,4′-bis(3,3′-dicyano)pyridine
Crystal structure
Hydrothermal synthesis
Design and synthesis of functional metal-organic frameworks
MOFs) with desired properties is a hard and challenging problem,
different topologies and properties depending on whether the solvent
is H O or H O/pyridine/ethanol. The solvent media used in the assem-
(
2
2
while introduction of the mechanism of hydro(solvo)thermal in-situ
metal/ligand reactions shades light on this scientific problem [1],
and this method has been proved to be a promising technique in
the preparation of highly stable materials that are inaccessible or
not easily obtainable by conventional methods. For example, Lin
and co-workers have synthesized a series of acentric MOFs of metal
carboxylates with second-order nonlinear optic properties based on
in-situ metal/ligand reactions, which may not be accessible from
their corresponding carboxylic acids [2]. Arshad Aijaz et al. reported
a number of interesting MOFs by using tripodal ligand 3,5-di(1H-
imidazol-1-yl)benzoxylate in situ generated from a CN-containing
precursor [3]. Also, in situ generated donor groups via slow hydrolysis
of precursor ligands under hydro(solvo)thermal conditions can provide
more intriguing network topologies than the direct reaction of metal
ions with the corresponding carboxylic acids [4].
The carboxylate functional group has been extensively used for
constructing polynuclear complexes due to its versatile coordination
modes and ability to generate metal-oxygen chains [5]. Other bridging
ligands, such as 4,4′-bipyridine, also have strong ability to form polynu-
clear compounds [6]. Therefore, the combination of carboxylate and
pyridine donor moieties in a ligand may lead to more interesting
network topologies [7]. Considering these in mind, we choose, 4,4′-bis
bling processes was found to significantly influence the structures and
properties of the resultant coordination compounds.
The ligand 4,4′-bis(3,3′-dicyano)pyridine (pydcy) was prepared
according to the procedure shown in Scheme 1.
4,4-bipyridine-N,N-dioxide was obtained according to the reference
[9]. The 4,4′-bis(3,3′-dicyano)pyridine (pydcy) ligand was easily
synthesized from the reaction of 4,4-bipyridine-N,N-dioxide, Me
and PhCOCl in CH C1 solvent under a dry nitrogen atmosphere [10].
Yellow solid was obtained with a yield of 96%. Anal. Calc. For C12
C, 69.90; H, 2.93; N, 27.17%. Found: C, 69.89; H, 2.94; N, 27.16%. 1H
NMR (400 MHz, CDCl ): δ=8.919(d, J=4.8 Hz, 2H), 7.932 (s, 2H),
7.749(d, J=2 Hz, 2H).
Synthesis of compound [C48
ligand (20.6 mg, 0.10 mmol), Cd(NO
3
SiCN
2
2
6 4
H N :
3
H
2
32Cd N
8
O18] (1). A mixture of pydcy
3
)
2
·4H O (30.9 mg, 0.10 mmol)
2
and distilled water(5 ml) was sealed in a Teflon-lined reactor and
heated at 130 °C for 3 days. After slow cooling to room temperature,
block colorless crystals were collected and dried in air (yield: 42%
(
3,3′-dicyano)pyridine (pydcy) [8] as a precursor ligand. Hydro(solvo)
thermal reaction of pydcy with cadmium(II) salt resulted in the forma-
tion of compounds [C48 32Cd 18](1) and [C17 13CdN ](2) with
H
2 8
N O
H
3 5
O
⁎
Corresponding author. Tel.: +86 371 67767896; fax: +86 371 67763390.
E-mail address: dcx@zzu.edu.cn (C.-X. Du).
Scheme 1. Schematic drawing for the synthetic route of pydcy.
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.09.029

22
G.-J. Yin et al. / Inorganic Chemistry Communications 15 (2012) 21–24
Fig. 1. The coordination environment of the Cd(II) atom in compound 1. Hydrogen
atoms are omitted for clarity.
yield based on Cd). Anal. Calc. For C48
Cd, 18.21; N, 9.06%. Found: C, 46.64; H, 2.64; Cd, 18.17; N, 9.02%.
Compound [C17 13CdN ] (2) was obtained under the same
reaction condition as that of compound 1 except that the solvent
used was H O/pyridine/ EtOH (5 ml, 1:2:2, v/v). Colorless acicular
crystals were collected and dried in air (yield: 62% yield based on
Cd). Anal. Calc. For C17 13CdN : C, 45.20; H, 2.91; Cd, 24.89; N,
.32%. Found: C, 45.16; H, 2.95; Cd, 24.84; N, 9.25%.
The single crystal X-ray structural analysis reveals that the cyano-
gen moieties of the ligand was hydrolyzed to carboxylic acid through
2 8
H32Cd N O18: C, 46.68; H, 2.61;
H
3 5
O
2
H
3 5
O
9
Fig. 3. The coordination environment of the Cd(II) atom as well as coordination mode
of pydca ligand in compound 2. Free water molecules and H atoms are omitted for
clarity.
2
-
−
2−
2−
in-situ ligand reaction (Hpydca or pydca , pydca =4,4′-bis
3,3′-dicarboxyl)pyridine). The solvent media is said to play a crucial
(
role in the assembling processes of the resulting complexes [11].
Compound 1 crystallizes in triclinic with space group P−1. As
shown in Fig. 1, each Cd(II) atom is six-coordinated by three carbox-
ylate oxygen atoms (Cd1-O1 2.269(2) Å, Cd1-O5 2.429(2) Å, Cd1-O6
structure. As a result, no free solvent molecules are enclathrated in
compound 1.
Compound 2 crystallizes in the Rhombohedral with space group
R− . There are one unique Cd(II) atom, one pydca ligand, one pyr-
idine and two free water molecules in the asymmetric unit of com-
pound 2. As illustrated in Fig. 3, each Cd(II) atom is six-coordinated
by three carboxylate oxygen atoms (Cd1-O1 2.369(5) Å, Cd1-O2
2.278(5) Å, Cd1-O3 2.296(5) Å), two nitrogen atoms (Cd1-N1 2.370
(6) Å, Cd1-N2 2.297(6) Å) from the ligand and one nitrogen atom
(Cd1-N3 2.319(6) Å) from pyridine to furnish a distorted octahedral
3
2−
2
.3225(18) Å ), two pyridyl nitrogen atoms (Cd1-N1 2.276(3), Cd1-
N3 2.293(2) Å) of the ligands and one oxygen atom of water (Cd1-
O9 2.299(2) Å). The overall geometry around the Cd(II) center is a
distorted octahedron. A typical feature of 1 is the dimeric carboxylate
bridged unit, of which eight carboxylate groups adopt three different
chelating modes. O3–O4 carboxylate group is free, while O1–O2 car-
boxylate group is in a semi-chelating fashion and O5–O6 carboxylate
coordination geometry.
1
2
2−
group adopts a syn-anti μ
2
-η :η bridge to link two metal atoms to
The two carboxylate groups of pydca
ligand adopt different
form a dimetal linkage. As shown in Fig. 2, each dicaryon was inter-
linked via hydrogen bonds {O(9)-H(2 W)…O(1)[O/O 2.676(3)A ,
chelating modes. O3–O4 carboxylate group is in a semi-chelating
˚
2
1
2
mode, while O1–O2 carboxylate group adopts a syn-anti μ -η :η
bridge to link adjacent two Cd(II) atoms. The dihedral angle between
H…O 1.99 Å, ∠OHO, 148(8)°], O(4)-H(4)…O(7) [O/O 2.890(4)Å,
H…O 2.11 Å, ∠OHO, 159(4)°]} to form a two dimensional supramo-
lecular structure. Furthermore, the two pyridyl rings of the ligand
are almost coplanar, the aromatic π–π stacking interaction between
adjacent ligands not only leads to increased thermodynamic stability
but also effectively fills the void space of this two dimensional
2
o
the two pyridyl rings of pydca – ligand is 71.5 . First, one-dimensional
(1D) helical chain subunit is formed by the operation of a threefold
screw along c-axis. The distance between adjacent Cd(II) atoms
bridged by O1–O2 carboxylate group is 5.370 Å. (Fig. 4a). The 1D
helical chains are further joined together by O3 N2 chelating atoms
(
(
Fig. 4b) to result in a 3D framework with large hexagon channels
Fig. 4c), and water molecules are embodied in the hexagon channels
via hydrogen bonds.
In order to get a better insight into the nature of this complicated 3D
framework, the topology approach can be used. From the topological
view, each Cd(II) atom coordinated with three pydca2 ligands togeth-
er with its adjacent pyridine can be considered as a 3-connecting node,
and each pydca2 ligand linked three Cd(II) atoms can be defined as an-
other 3-connecting nodal point (Fig. 5). Thus compound 2 possesses a
−
−
3
1
D 3-connected net with the ratio of these two 3-connecting nodes of
:1. The topology analysis by the TOPOS4.0 program suggests that it is
3
a 3-connected net with a Schläfli symbol of {8 }. It can be seen from
the Fig. 5b that the minimum loop through each node was a chair like
eight-membered ring configuration. The net of compound 2 defines
a type of etb topological framework which is earliest observed by
Nathaniel L. Rosi [12].
Considering the possibility of generating porous network by
removing the guest molecules, the thermal stability of compound 2
Fig. 2. Perspective view of the network of compound 1 along a axis.

G.-J. Yin et al. / Inorganic Chemistry Communications 15 (2012) 21–24
23
Fig. 4. Perspective view of the 1D helical chain structure along c-axis (a) and the 3D framework of 2 extended along the ab plane by the connection of adjacent helical chains with
O3, N2 chelating atoms (b) 3D framework of 2 showing trapped water molecules inside the large hexagon channels (c).
has been investigated. The TGA curve of compound 2 showed that
guest molecules can be easily removed by heating under nitrogen
atmosphere (Fig. 1S). The first stage weight loss of 4.017% in the
2
temperature range 54–160 °C corresponded to the release of H O
guest molecules (expected 3.988%). Interestingly, XRPD pattern for
the sample of compound 2 after removal of the included water mole-
cules remains essentially identical with that of pristine solids
(
Fig. 2S). Moreover, guest water molecules can be readily reintro-
duced into the porous network of compound 2 by exposure to the
water vapor at room temperature, which can be confirmed by TGA
analysis. This result conclusively demonstrated that the guest mole-
cules in compound 2 can be successfully removed to result in a porous
network with hexagon channels. As shown in Fig. 1S, the framework
structure of compound 2 is stable up to 300 °C.
It has been established that coordination polymers with conjugated
organic ligands are promising candidates for photoactive materials due
to their luminescent properties. Consequently, solid state fluorescent
properties of these two compounds have been investigated at room
2
temperature. As shown in Fig. 6, Na pydca shows a very broad weak
emission band centered at 445 nm upon excitation at 400 nm, which
can be attributed to the π*–π intraligand transition. However, com-
pounds 1 and 2 display apparent red-shifted strong emissions compared
with that of Na
4
5
2
pydca. Compound 1 shows a maximum emission at
67 nm, while compound 2 exhibits a strong emission band at
13 nm. The emissions of those two compounds might be attributable
to the πtz-5s ligand-to-metal charge transfer transition [13]. Interesting-
ly, the emission band of compound 2 is red-shifted 46 nm, together with
apparently enhanced emission intensity compared with that of com-
pound 1. The increased rigidity of compound 2 can effectively reduce
3
Fig. 5. View of the 3D framework of 2 along c-axis (a) and {8 } net topology (b), the chair like
eight-membered ring defined by the green line shows the minimum loop through each node.

24
G.-J. Yin et al. / Inorganic Chemistry Communications 15 (2012) 21–24
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In conclusion, two novel Cd(II) coordination compounds have
been successfully synthesized by the in-situ reaction of (pydcy)
with Cd(NO ) ·6H O under the similar reaction condition but differ-
3 2 2
ent solvent media. The single crystal X-ray structural analysis reveals
that the cyanogen moieties of the ligand were hydrolyzed to carbox-
ylic acids at this process and the resultant coordination frameworks
are profoundly influenced by the solvent media. Compound 1 forms
[
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a new dimeric structure by using H O as a solvent, while compound
3
2
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2
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[
[
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