Syntheses, structures, and photoluminescence of a series of d10 coordination complexes from N,N′-bidentate imidazo[4,5-f][1,10] phenanthroline and benzene-1,3,5-tricarboxylic acid

Article abstract of DOI:10.1016/j.ica.2012.09.007

Four new d¹⁰ metal-organic complexes, [Cd(L)(HBTC)(H ₂O)]_n (1), [Cd₂Cl(L)₂(BTC)(H ₂O)₂]_n (2), [Zn(L)(HBTC)(H₂O) ₂]₂·2H₂O (3) and [Zn(L)(HBTC)(H ₂O)]_n (4) were prepared through hydrothermal reactions of L and H₃BTC (L = imidazo[4,5-f][1,10]phenanthroline and H ₃BTC = benzene-1,3,5-tricarboxylic acid). These complexes were structurally characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Complexes 1 and 4 are analogous, showing 2D network with the Schla?fli symbol of 4.8², which further linked into 3D supramolecular architecture by aromatic π-π interactions. Complex 2 possesses a 1D chain structure. Two neighboring chains of 2 are linked through the π-π interactions into a double chain supramolecular structure. Complex 3 features a dinuclear structure and further forms a 2D layer by π-π interactions. The thermal stabilities and photoluminescent properties of the coordination compounds have also been investigated.

Full text of DOI:10.1016/j.ica.2012.09.007

Inorganica Chimica Acta 394 (2013) 481–487
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Note
Syntheses, structures, and photoluminescence of a series of d10 coordination
complexes from N,N0-bidentate imidazo[4,5-f][1,10]phenanthroline
and benzene-1,3,5-tricarboxylic acid
Guang-Bo Che a,c, , Shan-Shan Wang b, Xiao-Lin Zha b, Xiu-Ying Li b,c, Chun-Bo Liu b,c, , Xing-Jing Zhang b,c
,
⇑
⇑
Zhan-Lin Xu b,c, Qing-Wei Wang b,c
a College of Environmental Science and Engineering, Jilin Normal University, Siping 136000, People’s Republic of China
b College of Chemistry, Jilin Normal University, Siping 136000, People’s Republic of China
c Key Laboratory of Preparation and Applications of Environmental Friendly Materials (Jilin Normal University), Chinese Ministry of Education, Siping 136000,
People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Four new d10 metal–organic complexes, [Cd(L)(HBTC)(H2O)]n (1), [Cd2Cl(L)2(BTC)(H2O)2]n (2),
[Zn(L)(HBTC)(H2O)2]2ꢀ2H2O (3) and [Zn(L)(HBTC)(H2O)]n (4) were prepared through hydrothermal reac-
tions of L and H3BTC (L = imidazo[4,5-f][1,10]phenanthroline and H3BTC = benzene-1,3,5-tricarboxylic
acid). These complexes were structurally characterized by elemental analysis, IR spectroscopy, and
X-ray single-crystal diffraction. Complexes 1 and 4 are analogous, showing 2D network with the Schläfli
Article history:
Received 19 December 2010
Received in revised form 12 September 2012
Accepted 12 September 2012
Available online 26 September 2012
symbol of 4.82, which further linked into 3D supramolecular architecture by aromatic
Complex 2 possesses a 1D chain structure. Two neighboring chains of 2 are linked through the
actions into a double chain supramolecular structure. Complex 3 features a dinuclear structure and
further forms a 2D layer by interactions. The thermal stabilities and photoluminescent properties
of the coordination compounds have also been investigated.
p
–
p
interactions.
inter-
Keywords:
Cadmium(II)
Zinc(II)
Imidazo[4,5-f][1,10]phenanthroline
Benzene-1,3,5-tricarboxylic acid
Complex
p–p
p–p
Ó 2012 Elsevier B.V. All rights reserved.
Crystal structure
1. Introduction
been widely used to build MOFs because of its excellent coordinat-
ing ability and large conjugated system that may provide potential
Recently, metal–organic frameworks (MOFs) have become an
area of increasing interest due to their fascinating structures with
potential applications in adsorption, catalysis, chirality, fluores-
cence and magnetism, etc. [1–5]. However, the rational design and
syntheses of MOFs with specific topologies and useful properties
still remain a significant challenge to chemists. The most effective
and facile approach for the preparation of predictable MOFs is the
skillful combination of the appropriate organic ligands or building
blocks, together with the metal centers with various coordination
preferences [6–10]. In this regard, a lot of multidentate N- or O-do-
nor ligands have been explored extensively as organic spacers in the
construction of desirable frameworks, such as 4,40-bipyridine, 1,10-
phenanthroline (phen), and related species or polycarboxylates
[11–20]. In particular, N-donor chelating ligands phen’s derivatives
such as Pyphen (Dpq) [21], DPPZ (dpdp) [22–24] or TTBT [25] have
supramolecular recognition sites for p–p interactions, but the nitro-
gen atoms of these large planar molecules can only act as hydrogen
acceptors enabling the formation of metal–organic supramolecules.
Nevertheless, another kind of building blocks derived from the
appropriate modification of phen, such as bidentate imidazo
[4,5-f][1,10]phenanthroline (L) [26] or 2-phenyl-1H-1,3,7,8-tetra-
azacyclopenta[l]phenanthrene (PTCP) [27] ligand has also received
considerable attention in which the imidazole rings are both hydro-
gen donors and hydrogen acceptors. Furthermore, O-donor ligand
benzene-1,3,5-tricarboxylic acid (H3BTC) exhibits a variety of coor-
dination fashions and holds the capability of generating the unusual
multidimensional MOFs [28–32]. Additionally, the H3BTC can also
serve as both hydrogen bond donor and hydrogen bond acceptor.
In this context, we choose L ligand incorporated with H3BTC as the
building blocks to construct four novel d10 metal Cd(II) and Zn(II)
complexes [Cd(L)(HBTC)(H2O)]n (1), [Cd2Cl(L)2(BTC)(H2O)2]n (2),
[Zn(L)(HBTC) (H2O)2]2ꢀ2H2O (3) and [Zn(L)(HBTC)(H2O)]n (4). Inter-
estingly, by varying the ratios of the reactants and pH values, four
complexes exhibit varied structural dimensionality (from 0D to
3D). The photoluminescent properties of four complexes have also
been studied.
⇑
Corresponding authors at: Key Laboratory of Preparation and Applications of
Environmental Friendly Materials (Jilin Normal University), Chinese Ministry of
Education, Siping 136000, People’s Republic of China. Tel.: +86 434 3292207.
E-mail addresses: guangbochejl@yahoo.com (G.-B. Che), liuchunbo431@yahoo.
com.cn (C.-B. Liu).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.007

482
G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
Table 1
Crystallographic data for complexes 1–4.
Compound
1
2
3
4
Formula
C
22H14CdN4O7
C35H23Cd2ClN8O8
943.86
P1
0.40 ꢂ 0.32 ꢂ 0.25
9.6373(19)
12.802(3)
14.049(3)
98.04(3)
C44H36Zn2N8O18
1095.55
P1
0.41 ꢂ 0.36 ꢂ 0.30
8.5875(17)
9.0836(18)
14.313(3)
82.15(3)
C22H14ZnN4O7
511.74
P21/c
Formula mass
Space group
Crystal size (mm)
a (Å)
b (Å)
c (Å)
558.77
P21/n
ꢀ
ꢀ
0.39 ꢂ 0.32 ꢂ 0.26
9.3200(19)
16.041(3)
14.167(3)
90
0.33 ꢂ 0.26 ꢂ 0.20
8.8932(18)
16.118(3)
14.415(3)
90
a
(°)
b (°)
107.49(3)
90
2019.9(7)
4
1.138
1.064
91.10(3)
87.49(3)
73.34(3)
1059.5(4)
1
1.226
107.75(3)
90
1967.9(7)
4
1.307
1.145
c
(°)
106.72(3)
1640.4(6)
2
1.447
1.163
V (Å3)
Z
M (mmꢁ1
)
Goodness-of-fit on F2
1.071
Reflections collected/unique
19041/4559
1.837
3.02–27.48
0.0248, 0.0587
0.0321, 0.0611
16114/7446
1.911
3.15–27.48
0.0321, 0.0953
0.0405, 0.1042
10263/4729
1.717
3.09–27.48
0.0292, 0.0772
0.0353, 0.0785
18286/4422
1.727
3.20–27.48
0.0338, 0.0876
0.0466, 0.1014
Dcalc (Mg mꢁ3
h Range (°)
)
R (I > 2r(I))
R (all data)
pellets with KBr. Powder XRD patterns of samples 1–4 were col-
2. Experimental
lected on a Bruker D8-ADVANCE X-ray diffractometer with graph-
ite monochromated Cu Ka radiation (k = 0.154 nm) and 2h ranging
2.1. Materials and general methods
from 5° to 40°. Thermogravimetric analysis (TGA) was performed
on a TA Instruments with a heating rate of 10 °C minꢁ1 under air
atmosphere. The photoluminescent behaviors of the complexes
were studied using a Perkin-Elmer LS55 spectrometer.
All analytical grade chemicals and solvents were purchased and
used as received. The chelating ligand L was synthesized according
to the literature [33]. Elemental analyses of carbon, hydrogen and
nitrogen were performed on a Perkin-Elmer 240C element ana-
lyzer. IR spectra were recorded on a Perkin-Elmer 2400LSII spec-
trometer within 4000–400 cmꢁ1 using the samples prepared as
2.2. Synthesis and characterization
2.2.1. Synthesis of complex 1
CdCl2ꢀ2H2O (0.110 g, 0.5 mmol), L (0.110 g, 0.5 mmol) and
H3BTC (0.105 g, 0.5 mmol) were dissolved in distilled water
(15 mL), and NaOH aqueous solution was added until the pH value
of the system was adjusted to about 5. The resulting solution was
sealed in a 23 mL Teflon-lined stainless autoclave and heated at
140 °C for 3 d under autogenous pressure. The reaction system
was then cooled slowly to room temperature. The obtained solid
is a mixture of yellow block crystals and powder. The crystals of
1 are picked out from the solid mixture in 62% yield based on
CdCl2ꢀ2H2O. IR (KBr, cmꢁ1): 3398 s, 2341 w, 1859 w, 1615 s,
1551 s, 1439 s, 1367 s, 1110 m, 928 m, 759 s, 735 s, 531 m. Anal.
Calc. for 1 C22H14CdN4O7: C, 47.29; H, 2.53; N, 10.03. Found: C,
47.31; H, 2.57; N, 10.02%.
Table 2
Selected bond distances (Å) and angles (°) for 1–4.
1
Cd–N(1)
Cd–O(1)
Cd–O(5)A
O(1W)–Cd–O(5)A
O(4)B–Cd–O(1)
N(2)–Cd–N(1)
2.3671(18)
2.3030(14)
2.3328(18)
161.01(7)
111.87(6)
70.75(6)
Cd–N(2)
Cd–O(1W)
Cd–O(4)B
N(2)–Cd–N(1)
O(4)B–Cd–N(1)
2.3212(19)
2.286(2)
2.1810(17)
70.75(6)
87.78(6)
2
Cd(1)–N(1)
Cd(2)–N(5)
Cd(1)–O(1)
2.325(4)
2.338(3)
2.428(3)
2.268(4)
2.271(3)
2.5657(13)
150.43(17)
130.26(9)
88.13(14)
94.69(8)
93.77(11)
Cd(1)–N(2)
Cd(2)–N(6)
Cd(1)–O(2)
Cd(2)–O(3)
Cd(2)–O(4)
Cd(2)–Cl
O(2)–Cd(1)–O(1)
O(2)–Cd(1)–Cl
O(2W)–Cd(2)–N(5)
N(6)–Cd(2)–Cl
O(3)–Cd(2)–O(4)
2.326(3)
2.327(4)
2.314(3)
2.279(3)
Cd(1)–O(1W)
Cd(2)–O(2W)
Cd(1)–Cl
O(1W)–Cd(1)–N(1)
N(2)–Cd(1)–Cl
O(1W)–Cd(1)–N(2)
O(3)–Cd(2)–Cl
N(6)–Cd(2)–O(4)
2.527(3)
2.2.2. Synthesis of complex 2
2.5130(12)
54.63(11)
89.53(9)
160.07(13)
118.01(10)
54.36(10)
CdCl2ꢀ2H2O (0.110 g, 0.5 mmol), L (0.110 g, 0.5 mmol) and
H3BTC (0.105 g, 0.5 mmol) were dissolved in distilled water
(15 mL), and NaOH aqueous solution was added until the pH value
of the system was adjusted to about 7. The resulting solution was
sealed in a 23 mL Teflon-lined stainless autoclave and heated at
140 °C for 3 d under autogenous pressure. The reaction system
was then cooled slowly to room temperature. The obtained prod-
uct is a mixture of yellow crystals and powder. The crystals of 2
are picked out from the solid mixture in 68% yield based on CdCl2-
ꢀ2H2O. IR (KBr, cmꢁ1): 3412 m, 1708 m, 1630 s, 1540 s, 1463 m,
1371 m, 1202 m, 830 s, 754 m, 727 m. 549 m. Anal. Calc. for 2 C35-
H23Cd2ClN8O8: C, 44.54; H, 2.46; N, 11.87. Found: C, 44.55; H, 2.48;
N, 11.85%.
3
Zn–N(1)
Zn–O(1)
Zn–O(1W)
O(1)–Zn–N(1)
N(2)–Zn–O(2)
O(1W)–Zn–O(2W)
2.1278(17)
2.0388(14)
2.0963(17)
173.65(5)
88.43(6)
Zn–N(2)
Zn–O(2)
Zn–O(2W)
O(1W)–Zn–N(2)
O(2W)–Zn–O(2)
2.1209(17)
2.3198(16)
2.1057(16)
94.85(6)
84.64(6)
92.34(7)
4
Zn–N(1)
Zn–O(1)
Zn–O(3)
O(1W)–Zn–O(3)
N(2)–Zn–N(1)
O(1)–Zn–O(5)
2.201(2)
Zn–N(2)
Zn–O(1W)
Zn–O(5)
O(1)–Zn–N(1)
N(2)–Zn–O(5)
2.141(2)
2.089(2)
2.2321(16)
90.09(7)
87.41(7)
2.0084(17)
2.121(2)
171.36(9)
75.64(7)
106.86(7)
2.2.3. Synthesis of complex 3
An identical procedure with 2 was followed to prepare 3 except
CdCl2ꢀ2H2O was replaced by ZnCl2ꢀ6H2O. The obtained product is
also a mixture of yellow block crystals and powder. The crystals
Symmetry code for A: x + 1/2, ꢁy + 1/2, z ꢁ 1/2; B: ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2.

G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
483
Fig. 1. (a) Crystal structure of complex 1, the hydrogen atoms are omitted for clarity. (b) 2D coordination layer of 1. The L ligands are omitted. (c) Schematic representation of
the 2D 4.82 network in 1. The L ligands are omitted and the HBTC linkers are simplified as rods for clarity. (d) The 3D framework of 1 showing the
p–p interactions between
the adjacent HBTC and L ligands.
of 3 are picked out from the solid mixture in 71% yield based on
ZnCl2ꢀ6H2O. IR (KBr, cmꢁ1): 3460 s, 3077 s, 1947 w, 1670 s, 1615
s, 1568 s, 1431 s, 1372 s, 1282 s, 1077 s, 942 m, 812 m, 759 m,
732 m, 714 m, 545 m. Anal. Calc. for 3 C44H36Zn2N8O18: C, 48.24;
H, 3.31; N, 10.23. Found: C, 48.21; H, 3.34; N, 10.21%.
m,1399 s, 1271 s, 1091 m, 933 m, 832 m, 754 m, 540 m. Anal. Calc.
for 4 C22H14ZnN4O7: C, 51.63; H, 2.76; N, 10.95. Found: C, 51.64; H,
2.80; N, 10.96%.
2.3. X-ray crystallography
2.2.4. Synthesis of complex 4
Single-crystal X-ray diffraction data for complexes 1–4 were re-
An identical procedure with 1 was followed to prepare 4 except
CdCl2ꢀ2H2O was replaced by ZnCl2ꢀ6H2O. The obtained product is
also a mixture of yellow block crystals and powder. The crystals
of 4 are picked out from the solid mixture in 87% yield based on
ZnCl2ꢀ6H2O. IR (KBr, cmꢁ1): 3331 s, 3027 w, 1694 s, 1600 s, 1547
corded on a Rigaku RAXIS-RAPID diffractometer with graphite-
monochromated Mo K
a radiation (k = 0.71073 Å) at 292(2) K using
the scan technique. All the structures were solved by direct
x
methods using the program SHELXS-97 [34] and refined by full-ma-
trix least-squares techniques against F2 using the SHELXTL-97 [35]

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G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
Fig. 2. (a) Crystal structure of complex 2, the hydrogen atoms are omitted for clarity. (b) The p–p interactions.
crystallographic software package. All of the non-hydrogen atoms
were easily found from the different Fourier map and refined
anisotropically, whereas the hydrogen atoms of the compounds
were placed by geometrical considerations and were added to
the structure factor calculation. The detailed crystallographic data
and structure refinement parameters for four complexes are sum-
marized in Table 1. Selected bond distances and angles are listed in
Table 2.
interactions between the adjacent HBTC and L ligands to stack in a
novel 3D architecture, with the shortest centroid-to-centroid dis-
tance being 3.599 Å (Fig. 1d). Otherwise, the O–Hꢀ ꢀ ꢀO, O–Hꢀ ꢀ ꢀN
and N–Hꢀ ꢀ ꢀO hydrogen bonds (see Table S1), forming among L
ligands, water molecules and oxygen atoms of the HBTC anions, play
a key role during the construction of the 3D supramolecular archi-
tecture of 1.
3.1.2. Structure description of 2
X-ray analysis reveals that 2 contains two crystallographically
3. Results and discussion
unique Cd(II) ions, two L ligands, one BTC3ꢁ ligands, one
l2-Cl ion
and two coordinated water molecules. Cd1 and Cd2 are all six coor-
dinated N2O3Cl and resides in the distorted octahedral coordination
environment: two oxygen atoms (O1, O2 or O3, O4) from one
BTC3ꢁ ligand, O1W or O2W from a coordinated water molecule,
and two nitrogen atoms (N1, N2 or N5, N6) from one L ligand
(Fig. 2a). The Cd–N, Cd–O and Cd–Cl bond lengths are in the range
of 2.325(4)–2.338(3), 2.268(4)–2.527(3) and 2.5130(12)–
2.5657(13) Å, respectively. The Cd1ꢀ ꢀ ꢀCd2 distance bridged by the
3.1. Description of crystal structures
3.1.1. Structure description of 1
The molecular structure of 1 is shown in Fig. 1a. The geometry of
each Cd(II) ion, comprising of N2O4 from one L ligand, one coordina-
tion water molecule and three different HBTC ligands, can be
described as a slightly distorted octahedron. The bond lengths of
Cd–O (2.1810(17)–2.3328(18) Å) and Cd–N (2.3212(19)–2.3671
(18) Å) are similar to previously reported results [36]. The adjacent
Cd ions are interconnected through the HBTC anions, which display
the tri-monodentate coordination mode, to yield a 2D network with
the Schläfli symbol of 4.82 with the shortest Cdꢀ ꢀ ꢀCd distance is
6.711 Å (Fig. 1b and c). This topological net is very similar to
[In(BTC)(H2O)(phen)] reported in the literature [37]. These indepen-
one
l2-Cl ion is 4.015 Å. The neighboring dinuclear Cd(II) units
are linked by BTC3ꢁ in bis-chelating mode to form an infinite 1D
chain along the [001] direction with the L ligands are all attached
to one side (Cd1ꢀ ꢀ ꢀ Cd2A 10.038 Å). The neighboring 1D chains
interact through
p–p stackings between the L ligands (centroid-
to-centroid distance ca. 3.537 Å, Fig. 2b) to yield a double chain,
which is further cross-linked by the strong O–Hꢀ ꢀ ꢀO and N–Hꢀ ꢀ ꢀO
hydrogen-bond interactions between the coordinated water
dent 2D layers are further formed by aromatic
p–p stacking

G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
485
Fig. 3. (a) Crystal structure of complex 3, the hydrogen atoms and free water molecule are omitted for clarity. (b) The 2D supramolecular layer in the ab plane via
p–p
interactions.
molecules or –NH– groups and carboxylate O atoms, thus leading to
the construction of a stable 3D network (Fig. S1). The related hydro-
gen-bonding geometries with the symmetry codes are given in
Table S1.
3.1.4. Structure description of 4
The X-ray diffraction analysis reveals that complex 4 is of anal-
ogous architectures with 1, exhibiting interesting 3D supramolecu-
lar framework. The metal center is in a distorted octahedral
geometry and coordinated by two N atoms (Zn–N1 2.201(2) Å and
Zn–N2 2.141(2) Å) of one L ligand, one water molecule (Zn–O1W
2.089(2) Å), three oxygen atom (Zn–O1 2.0084(17) Å, Zn–O3A
2.121(2) Å and Zn–O5B 2.2321(16) Å) of three HBTC ligands
(Fig. S3). Similar to 1, adjacent Zn(II) ions are bridged by the carbox-
ylate groups of the HBTC ligands to a 2D 4.82 net in the bc plane
with the shortest Znꢀ ꢀ ꢀZn distance of 6.934 Å. Moreover, there also
3.1.3. Structure description of 3
As shown in Fig. 3a, the crystal structure of 3 consists of a dis-
crete dinuclear [Zn(L)(HBTC)(H2O)2]2. The [Zn(L)(HBTC)(H2O)2]2
dimer comprises two L ligands, two HBTC ligands, four water mol-
ecules and two Zn(II) atoms. Each Zn(II) atom in 3 is coordinated by
two nitrogen atoms from a chelating L ligand, two coordinated
water molecules and two oxygen atoms from two different HBTC
ligands in a distorted octahedral geometry. The distances of the
Zn–O bond (2.0388(14)–2.3198(16) Å) and Zn–N bonds
(2.1209(17) and 2.1278(17) Å) are near to those of reported
[38,39]. The adjacent Zn(II) atoms are bridged by two HBTC ligands
to form a dimer with Znꢀ ꢀ ꢀZn distance of 4.684 Å. These discrete di-
mers are stacked to furnish a 2D supramolecular layer in the ab
exist
p–p stacking interactions between the HBTC and L ligands
(centroid-to-centroid distance ca. 3.539 Å) and intramolecular
and intermolecular hydrogen bonds (Table S1), resulting in a 3D
supramolecular network.
3.1.5. Structural comparison of 1–4 complexes
From the above structural discussion of the series of metal com-
plexes, we can see that the carboxylateligand and metal–L coordina-
tion can furnish kinds of dimensional supramolecular structures
ranging from 0D to 3D networks. Through varying the pH values of
reaction system under similar synthetic conditions, four related
complexes were successfully obtained and they exhibit some differ-
ences in their architectures. Complexes 1 and 4 are isomorphic when
pH value of the system was adjusted to about 5. In compound 1 or 4,
the neighboring Cd(II) or Zn(II) atoms are bridged by three HBTC2ꢁ
carboxylates in monodentate mode, generating a 2D network
plane (Fig. 3b) via two types of
p–p interactions: one is between
L ligands (centroid-to-centroid distance ca. 3.706 Å), and another
is between L ligand and HBTC anion (centroid-to-centroid distance
ca. 3.729 Å). In addition, the O–Hꢀ ꢀ ꢀO, O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydro-
gen bonds (Table S1) involving the water molecules, the carboxylic
groups of HBTC anions and L ligands further extend the 2D supra-
molecular arrays into an interesting 3D supramolecular structure
(Fig. S2).

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G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
Scheme 1. Three different coordination modes of H3BTC ligand found in the complexes 1 and 4 (type a), 2 (types b) and 3 (type c).
ZnO for 3, respectively. Although the compositions of these three
complexes are similar, the TGA of them are somewhat different.
We believe that different coordinated modes are the main reasons
that lead to the difference in their TGA.
3.3. Photoluminescence properties
As we all know, Cd(II) and Zn(II) can produce a variety of com-
plexes that not only exhibit appealing structures but also possess
photoluminescence (PL) properties. The PL spectra of four com-
plexes were investigated in the solid state at room temperature.
As indicated in Fig. 4, the emission peaks are 553 nm (1), 536 nm
(2), 543 nm (3) and 558 nm (4) upon excitation at 365 nm, respec-
tively. By comparison, the four complexes with L ligand shows sim-
ilar photoluminescent bahavior. In order to understand the nature
of these emission bands, the PL properties of free ligands H3BTC
Fig. 4. Solid-state photoluminescent spectra of 1–4 and L ligand at room tem-
perature.
and L were analyzed, showing they exhibit the strongest emission
peaks at about 380 nm [21a] and 460 nm [26g] from 300 to
800 nm, respectively. Compared with the PL spectra of free ligand,
the emission spectra of four complexes are obviously similar to that
of L, which might be attributable to chelating coordination of the
planar L ligand in both complexes. The PL emissions of 1–4 also
mainly originate from the intraligand fluorescent emissions of L
[22]. The reason for different emissive peak positions of four com-
plexes was presumably owing to the differences of coordination
mode of complexes.
structure. Remarkably, only two of three carboxyl groups of each
H3BTC are deprotonated, and the third protonated one also coordi-
nates to the Cd(II) or Zn(II) center, respectively. Under the same
pH value (pH 7), complex 2 adopts a one-dimensional single chain
and complex 3 is observed as discrete unit. In complex 2, H3BTC is
completely deprotonated and two of three carboxylates of each
H3BTC coordinate to the central Cd(II) atom in bidentate mode and
the third one remains free of coordination. In complex 3, two neigh-
boring Zn(II) atoms are bridged by two HBTC2ꢁ ligands, forming a
dimer. In contrast with 1 and 4, two of three carboxyl groups of each
H3BTC are also deprotonated, among of them, one carboxylate coor-
4. Conclusion
In summary, four novel d10 metal coordination complexes with
different dimensionality based on L and H3BTC have been prepared
dinates to the central Zn(II) atom in l
2-COO- mode and the other is
free of coordination. Furthermore, the third protonated one also
remains free of coordination. Coordination modes of H3BTC groups
in complexes 1–4 are shown in Scheme 1. In particular, chelating
coordination mode of L in 1–4 is different from [Cd(L3)(IP)]n [26d].
and structurally characterized. The results suggest that
p–p stac-
kings and hydrogen-bond interactions played important roles in
formation of supramolecular structures. At the same time, the
structural diversification of coordination complexes may result
from the varied pH values. In addition, complexes 1–4 exhibit in-
tense fluorescence emissions and may be candidates for fluores-
cent materials. The work may provide helpful information for the
design and construction of MOFs.
3.2. Thermal study
In order to substantiate the phase purity of the measured prod-
uct 1–4, their powder XRD were performed before their TGA and
photoluminescent properties were measured. The experimental
powder XRD patterns are in good agreement with the correspond-
ing simulated ones (Figs. S4–S7) except for the relative intensity
variation because of preferred orientations of the crystals. We
examined 1–3 using TGA. (The X-ray crystallographic study re-
vealed that complexes 1 and 4 are isostructural, so 1 represents 4
for detailed TGA) As shown in Figs. S8–S10, the first obvious weight
loss of 3.40%, 3.92% and 9.95% for 1–3 are in the range 130–210,
105–219 and 90–240 °C, assigned to the release of the water mole-
cules (calcd. 3.22%, 3.81% and 9.86%). The second sharp weight loss
of 75.73%, 67.02% and 78.15% are ascribable to the decompositon of
organic ligands HBTC2ꢁ/BTC3ꢁ and L (calcd. 76.66%, 68.61% and
78.21%) occurring from 280 to 645 °C, 305 to 690 °C and 315 to
630 °C, respectively. The final products may be CdO for 1, 2 and
Acknowledgments
The authors thank Jilin Normal University for supporting this
work.
Appendix A. Supplementary material
CCDC 796175, 796176, 796177 and 796178 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supple-
mentary data associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.ica.2012.09.007.

G.-B. Che et al. / Inorganica Chimica Acta 394 (2013) 481–487
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