Syntheses, structures, and fluorescence properties of cadmium(II) and zinc(II) complexes based on 1,1′-binaphthalenyl-2,2′-diamine-N,N, N′,N′-tetraacetic acid

Article abstract of DOI:10.1016/j.poly.2012.10.042

Solvothermal reaction of Cd(II)/Zn(II) salts with 1,1′- binaphthalenyl-2,2′-diamine-N,N,N′,N′-tetraacetic acid (H ₄L) ligand results in the formation of five interesting complexes [Cd₂(L)(phen)₂(H₂O)]·2H₂O (1), [Cd₄(L)₂(phen)₂(H₂O) ₇]·CH₃OH·10H₂O (2), {[Cd ₅(L)₂(H₂O)₃(OH)₂] ·H₂O}_n (3), [Zn₂(L)(phen) ₂(H₂O)]·2H₂O (4) and {[Zn ₂(L)(H₂O)₄]·2.25H₂O} _n (5), where phen = 1,10-phenanthroline. The structure of 1 is dinuclear, and that of 2 is tetranuclear. The structural difference of 1 and 2 indicates a temperature-dependence of the formation of two complexes. 3 Is a 2D polymer with a (6,3) network constructed by a novel asymmetrical pentanuclear Cd clusters with bridging hydroxyl and carboxylate groups as secondary building units, which have never been employed before in the construction of 2D networks. 4 Is a dinuclear compound with a structure similar to that of 1. Complex 5 exhibits a zigzag chain structure bridged by L^4- ligand. A variety of coordination modes of the H₄L ligand were found, some of them are unprecedented for these type of compounds. The fluorescence properties of the compounds were studied, and strong fluorescent emissions were observed.

Full text of DOI:10.1016/j.poly.2012.10.042

Polyhedron 50 (2013) 1–9
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Polyhedron
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Syntheses, structures, and fluorescence properties of cadmium(II) and zinc(II)
complexes based on 1,10-binaphthalenyl-2,20-diamine-N,N,N0,N0-tetraacetic acid
Wan-Yun Huang a,b, Zi-Lu Chen b, Hua-Hong Zou b, Dong-Cheng Liu b, Fu-Pei Liang b,
⇑
a State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
b State Key Laboratory Cultivation Base for the Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry & Chemical Engineering of Guangxi
Normal University, Guilin 541004, PR China
a r t i c l e i n f o
a b s t r a c t
Solvothermal reaction of Cd(II)/Zn(II) salts with 1,10-binaphthalenyl-2,20-diamine-N,N,N0,N0-tetraacetic
acid (H4L) ligand results in the formation of five interesting complexes [Cd2(L)(phen)2(H2O)]ꢀ2H2O (1),
[Cd4(L)2(phen)2(H2O)7]ꢀCH3OHꢀ10H2O (2), {[Cd5(L)2(H2O)3(OH)2]ꢀH2O}n (3), [Zn2(L)(phen)2(H2O)]ꢀ2H2O
(4) and {[Zn2(L)(H2O)4]ꢀ2.25H2O}n (5), where phen = 1,10-phenanthroline. The structure of 1 is dinuclear,
and that of 2 is tetranuclear. The structural difference of 1 and 2 indicates a temperature-dependence of
the formation of two complexes. 3 Is a 2D polymer with a (6,3) network constructed by a novel asymmet-
rical pentanuclear Cd clusters with bridging hydroxyl and carboxylate groups as secondary building units,
which have never been employed before in the construction of 2D networks. 4 Is a dinuclear compound
with a structure similar to that of 1. Complex 5 exhibits a zigzag chain structure bridged by L4ꢁ ligand. A
variety of coordination modes of the H4L ligand were found, some of them are unprecedented for these
type of compounds. The fluorescence properties of the compounds were studied, and strong fluorescent
emissions were observed.
Article history:
Received 27 August 2012
Accepted 29 October 2012
Available online 5 November 2012
Keywords:
Polycarboxylic acid ligand
Cadmium complexes
Zinc complexes
Crystal structure
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
focused our attention on the reactions of various metal salts with
N-containing polycarboxylic acid ligands, and investigated the
The crystal engineering of coordination complexes (CCs) at-
tracts intense attention because controlling the molecular organi-
zation in the solid state can lead to the construction of novel
materials with desired structure and promising function [1,2].
Despite a number of CCs were obtained by various synthetic strat-
egies [3] such as secondary building units (SBUs), controlling the
hydrolysis of the metal ions to construct metal-hydroxy cluster,
template-directed, it is still a labyrinth for chemists to design
and synthesize a desired architecture in a truly predictable manner
because many factors can have an unpredictable impact on the
final product structures, such as (a) the coordination geometry pre-
ferred by the metal, the counter ion, and functionality, flexibility
and symmetry of the ligand; (b) reaction conditions such as sol-
vent, temperature, different kinds of base, pH value of the solution,
the ratio of the reactants, and method of crystallization; (c) the
influences of different bases, different kinds of metal salts and
reaction temperature on the structure of the complexes.
Iminodiacetic acid containing a flexible group on the N-atom
has attracted much attention and has been extensively used in
the preparation of all kinds of functional complexes owing to their
numerous coordination sites and flexible connection modes [7,8].
However, the ligands connecting directly a rigid ring on the N-
atom of iminodiacetic acid are relatively rarely investigated, espe-
cially for the ligands connecting a rigid aromatic ring with four or
more flexible CH2COOꢁ groups [9,10]. To investigate the influence
of the bulky aromatic skeletons of such ligands on the structures
and properties of their coordination complexes, we designed and
synthesized
a
new ligand, 1,10-binaphthalenyl-2,20-diamine-
N,N,N0,N0-tetraacetic acid (H4L). This ligand exhibits remarkable
features such as (a) it contains two iminodiacetic acid units with
four carboxylate groups, which would be able to provide a variety
of coordination modes by partially or completely deprotonating;
(b) it possesses both rigidity and flexibility due to the presence
of the naphthyl ring and the C–C single bond at the 1,10-positions
of the binaphthyl framework, and the flexible acetic moiety, which
may induce subtle effect on the formation of the complexes under
different reaction conditions; (c) the presence of aromatic groups
non-covalent forces such as hydrogen-bonding,
p–p stacking
[4–6]. Therefore, considerable elaborate and systematic work is
necessary to comprehend aforementioned factors that determine
the aggregation fashions of molecular structure in the solid state.
Taking into account of the factors mentioned above, we have
⇑
Corresponding author. Tel.: +86 773 5856302; fax: +86 773 5846837.
E-mail address: fliangoffice@yahoo.com (F.-P. Liang).
and the carboxylate groups could offer plenty of p–p and hydrogen
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.042

2
W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
bonding interactions, which will be helpful for the formation of
various supramolecular structures.
(s); Anal. Calc. for C28H24N2O8: C, 65.11; H, 4.68; N, 5.42. Found:
C, 65.29; H, 4.53; N, 5.36%.
In this paper, we report the syntheses and characterizations of
five cadmium(II) and zinc(II) complexes with H4L ligand, namely
2.3. Synthesis of complexes 1–5
[Cd2(L)(phen)2(H2O)]ꢀ2H2O
(1),
[Cd4(L)2(phen)2(H2O)7]ꢀCH3-
OHꢀ10H2O (2), {[Cd5(L)2(H2O)3(OH)2]ꢀH2O}n (3), [Zn2(L)(phen)2(H2-
O)]ꢀ2H2O (4) and {[Zn2(L)(H2O)4]ꢀ2.25H2O}n (5). These complexes
display a variety of structures varying from discrete dinuclear, tet-
ranuclear structure to chain and 2D network. Various coordination
modes for the H4L ligand in the compounds are observed.
2.3.1. [Cd2(L)(phen)2(H2O)]ꢀ2H2O (1)
A
solution of Cd(NO3)2ꢀ4H2O (27.8 mg, 0.09 mmol), H4L
(30.7 mg, 0.06 mmol), phen (11.9 mg, 0.06 mmol), and NaOH
(7.2 mg, 0.18 mmol) in CH3OH/H2O (1:8, 9 mL) was stirred for
20 min in air, then sealed in a 15 mL Teflon-lined stainless steel
vessel and heated at 95 °C for 72 h. The vessel was then taken
out from the oven and cooled down naturally at ambient temper-
ature. After cooling to room temperature, colorless block crystals of
1 suitable for X-ray diffraction analysis were obtained in 34% yield
(based on Cd). Anal. Calc. for C52H42N6O11Cd2: C, 54.23; H, 3.68; N,
7.30. Found: C, 54.29; H, 3.53; N, 7.12%. IR data (KBr pellet, cmꢁ1):
3415 (s), 1596 (s), 1514 (m), 1405 (m), 1385 (w), 1306 (m), 1193
(w), 1144 (w), 848 (m), 729 (m).
2. Experimental
2.1. Materials and measurements
Racemic 1,10-binaphthalenyl-2,20-diamine was purchased from
Alfa-aesar. Other reagents were commercially available and used
as received without further purification. Infrared spectra were re-
corded as KBr pellets using a Nicolet 360 FT-IR spectrometer. Ele-
mental analyses (C, H and N) were performed on a Vario EL
analyser. Thermogravimetric analyses were recorded with a Per-
kin-Elmer Pyris Diamond TG analyzer at a rate of 10 °C/min from
room temperature to 1000 °C under nitrogen atmosphere. The
powder X-ray diffraction (PXRD) data were collected on a Rigaku
2.3.2. [Cd4(L)2(phen)2(H2O)7]ꢀCH3OHꢀ10H2O (2)
Similar procedure as that for 1 was performed, except that the
reaction temperature was set at 120 °C. Colorless block crystals
of 2 were obtained in 26% yield (based on Cd). Anal. Calc. for C81-
H94N8O34Cd4: C, 44.77; H, 4.36; N, 5.16. Found: C, 44.94; H, 4.46;
N, 5.21%. IR data (KBr pellets, cmꢁ1): 3423 (s), 1596 (s), 1514
(w), 1407 (m), 1306 (w), 1193 (w), 848 (w), 746 (w), 727 (w).
D/max 2200 diffractometer with Cu K
a radiation. Luminescence
spectra were recorded on an Edinburgh Analytical Instrument
FLS920 Luminescence spectrometer at room temperature.
2.3.3. {[Cd5(L)2(H2O)3(OH)2]ꢀH2O}n (3)
A solution of Cd(NO3)2ꢀ4H2O (27.8 mg, 0.09 mmol) and H4L
(30.7 mg, 0.06 mmol) in H2O (8 mL) was stirred for 10 min in air,
and then placed in Parr Teflon-lined stainless steel vessel
(15 mL). After addition of triethylamine (0.1 mL), the vessel was
sealed, heated at 120 °C for 96 h, and then taken out from the oven
and cooled down naturally at ambient temperature. After cooling
to room temperature, colorless block crystals of 3 suitable for X-
ray diffraction analysis were obtained in 42% yield (based on Cd).
Anal. Calc. for C56H50N4O22Cd5: C, 39.73; H, 2.98; N, 3.31. Found:
C, 39.54; H, 2.79; N, 3.12%. IR data (KBr pellet, cmꢁ1): 3437 (s),
1593 (s), 1507(w), 1409 (s), 1310 (m), 1189 (w), 934 (w), 818
(w), 746 (w).
2.2. Synthesis of 1,10-binaphthalenyl-2,20-diamine-N,N,N0,N0-
tetraacetic acid (H4L)
Racemic 1,10-binaphthalenyl-2,20-diamine (2.84 g, 10 mmol)
was dissolved in freshly distilled acetonitrile (60 mL), then potas-
sium carbonate (13.82 g, 100 mmol) and potassium iodide
(1.33 g, 8.0 mmol) were added. The reaction mixture was heated
to reflux under nitrogen atmosphere. Then ethyl bromoacetate
(8.35 g, 50 mmol) was added dropwise and the reaction mixture
was refluxed for 72 h. The mixture was then cooled, diluted with
water (200 mL) and extracted with ethyl acetate (3 ꢂ 60 mL). The
combined organic layer was washed with water (60 mL), dried
with MgSO4, and then filtered and evaporated under reduced pres-
sure to remove the solvent. The residue was purified by flash chro-
matography on silica using ethyl acetate-petroleum ether (v/v 1:6)
as eluent to give light yellow solid. (yield 54%): 1H NMR (500 MHz,
DMSO-d6): 7.86–7.90 (m, 4H), 6.90–7.34 (m, 8H), 3.68–3.85 (m,
16H), 1.02 (t, 12H, J = 7.1 Hz).
A mixture of above resulted solid product (3.15 g, 5 mmol), eth-
anol (50 mL) and 2 M aqueous solution of NaOH (8 mL) was re-
fluxed under nitrogen atmosphere for 24 h. The solution was
then evaporated to remove most solvent, and then cooled in ice-
water, 3 M hydrochloric acid was added until pH 3–4. The crude
product was extracted with ethyl acetate (2 ꢂ 60 mL). The organic
layers were combined and washed with brine (80 mL), dried with
Na2SO4, and filtered. The solvent was then removed under reduced
pressure. The residue was purified by flash chromatography on sil-
ica using ethyl acetate as eluent, from which a yellowish solid of
H4L ligand was collected in 76% yield. Mp: 172–173 °C; 1H NMR
(500 MHz, DMSO-d6) 7.91 (d, 2H, J = 9.0 Hz), 7.86 (d, 2H,
J = 8.0 Hz), 7.42 (d, 2H, J = 8.0 Hz), 7.31 (t, 2H, J = 8.0 Hz); 7.19 (t,
2H, J = 8.0 Hz); 6.88 (d, 2H, J = 8.6 Hz); 3.66 (s, 8H); 13C NMR
(125.77 MHz, DMSO-d6):172.67, 147.89, 134.27, 130.18, 128.89,
128.38, 126.85, 125.10, 124.47, 124.16, 123.24, 53.13; IR (KBr,
cmꢁ1), 3418 (w), 3056 (w), 2929 (m), 1719 (s), 1619 (m), 1594
(m), 1507 (s), 1407 (w), 1375 (w), 1211 (s), 969 (s), 816 (s), 750
2.3.4. [Zn2(L)(phen)2(H2O)]ꢀ2H2O (4)
A
solution of Zn(NO3)2ꢀ4H2O (26.8 mg, 0.09 mmol), H4L
(30.7 mg, 0.06 mmol), phen (11.9 mg, 0.06 mmol), and NaOH
(7.2 mg, 0.18 mmol) in CH3OH/H2O (1:8, 9 mL) was stirred for
20 min in air, and then sealed in a 15 mL Teflon-lined stainless
steel vessel and heated at 90 °C for 72 h. The vessel was then taken
out from the oven and cooled down naturally at ambient temper-
ature. After cooling to room temperature, light-yellow block crys-
tals of 4 were obtained in 30% yield (based on Zn). Anal. Calc. for
C
52H42N6O11Zn2: C, 59.05; H, 4.00; N, 7.94. Found: C, 59.19; H,
4.13; N, 8.06%. IR data (KBr pellet, cmꢁ1): 3421 (s), 1624 (s),
1514 (s), 1424 (w), 1385 (w), 1199 (w), 848 (w), 727 (s).
2.3.5. {[Zn2(L)(H2O)4]ꢀ2.25H2O}n (5)
H4L
(51.6 mg,
0.10 mmol),
Zn(NO3)2ꢀ4H2O
(29.8 mg,
0.10 mmol), CH3OH (0.8 mL), 2.7% ammonia solution (0.05 mL),
and H2O (0.30 mL) were placed in a thick Pyrex tube (ca 20 cm
long). The tube was frozen using liquid N2, evacuated under vac-
uum and flame-sealed. It was then allowed to warm to room tem-
perature and heated at 90 °C for 72 h. The tube was then taken out
from the oven and cooled down naturally at ambient temperature.
After cooling to room temperature, colorless block crystals of 5
were obtained in 45% yield (based on Zn). Anal. Calc. for C28H32.5N2-
O14.25Zn2: C, 44.50; H, 4.40; N, 3.71. Found: C, 44.63; H, 4.49; N,
3.62%. IR data (KBr pellet, cmꢁ1): 3395 (s), 1596 (s), 1508 (m),

W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
3
1409 (s), 1347(w), 1306 (m), 1196 (m), 938 (w), 887 (w), 819 (w),
748 (m).
instead of Cd(NO3)2ꢀ4H2O. Different from the reaction system of
Cd(NO3)2, reaction of Zn(NO3)2 with H4L did not show a tempera-
ture-dependent result. The reaction in a temperature range of
90–125 °C gave only the same product of 4, which was certified
by the IR and PXRD. The similar reaction of Zn(NO3)2 with H4L as
that for 3 give only unidentified powder samples rather than crys-
tals. However, a modified reaction, carrying in a sealed Pyrex tube
with CH3OH and H2O as solvent in the presence of ammonia, gave
crystals of 5. The phase purity of all five complexes has been veri-
fied by powder X-ray diffraction analysis, in which the patterns of
the bulk samples were in agreement with the simulated pattern
from the corresponding single crystal data (Fig. S1).
2.4. X-ray crystallography
Suitable single crystals of 1–5 were selected and mounted onto
thin glass fibers. Measurements of 2, 3, 5 were taken at 185(2) K
using a Bruker CCDArea Detector with graphite-monochromated
Mo Ka radiation (k = 0.71073 Å). Measurements of 1 and 4 were ta-
ken at 153(2) K using a Agilent CrysAlisPro Detector in the same
radiation. All the structures were solved by direct methods using
the SHELXS-97 program package and refined against F2 by full-matrix
least-squares methods with SHELXL-97 [11] with anisotropic thermal
parameters for all the non-hydrogen atoms. Hydrogen atoms at-
tached to carbon were placed in geometrically idealized positions
and refined by using a riding model. Hydrogen atoms in water mol-
ecules were located from difference Fourier maps and refined by
using a riding model. For 2, restraints were used to maintain chem-
ically sensible bond lengths for the disordered water molecule and
a guest methanol molecule. A summary of crystallographic and
structural refinement data for 1–5 is given in Table 1. Selected
bond lengths and bond angles are listed in Table S1. Hydrogen
bonds are listed in Table S2.
3.2. Description of the crystal structures
3.2.1. [M2(L)(phen)2(H2O)]ꢀ2H2O [M = Cd (1), Zn (4)]
X-ray diffraction studies reveal that complexes 1 and 4 exhibit
similar dinuclear structure with almost identical framework. Here,
the structure of 1 is discussed in detail as a representative. The
asymmetric unit of 1 is composed of two Cd atoms, one L4ꢁ ligand,
two phen ligands, one coordinated water molecule, and two lattice
water molecules. As shown in Fig. 1, both Cd atoms in 1 are six-
coordinated. The Cd1 atom displays a severely distorted octahedral
coordination geometry completed by one carboxylate oxygen atom
(O3) from one L4ꢁ ligand, four nitrogen atoms (N3, N4, N5, N6)
from two phen ligands and one oxygen atom (O9) from one water
molecule. The Cd2 atom exhibits a slightly distorted octahedral
geometry with N1, O4, O6, O8 atoms from one L4ꢁ ligand locating
at the basal plane and the N2, O2 atoms from the same L4ꢁ ligand
at the apices. The coordination bond lengths and angles around the
Cd atoms are in the range of 2.1710(18)–2.4937(19) Å and
70.34(7)–168.54(8)°, respectively, as listed in Table S1, which
resemble closely to those reported in the literature [12]. Cd1 and
Cd2 atoms are bridged by one carboxylate group of the ligand in
a syn-anti bridging mode to give the dinuclear structure of the
complex (Fig. 1). The Cd1ꢀ ꢀ ꢀCd2 distance is of 5.0061(6) Å. The
naphthyl rings of the (Ra)-L4ꢁ and (Sa)-L4ꢁ ligand in 1 subtend a
dihedral angle of 82.881(49)° and 82.880(51)°, which is consistent
with the reported values in related complexes [13].
3. Results and discussion
3.1. Syntheses
Solvothermal reaction of Cd(NO3)2ꢀ4H2O, H4L and phen in a
mixed solvent of CH3OH and H2O at 90 °C led to the formation of
dinuclear 1. With the same starting materials as that for 1, the tet-
ranuclear 2 was obtained at a higher temperature of 120 °C, indi-
cating a temperature-dependence of the formation of 1 and 2.
Complex 3 was obtained by a hydrothermal reaction of Cd(NO3)2
and H4L in the presence of Et3N. The success in the formation of
3 by using the weak base of Et3N in the reaction may be ascribed
to that the base here plays not only the function in the deprotona-
tion of the ligand, but also an important role in directing the
construction of cadmium-hydroxy units through controlling the
hydrolysis rate of the metal ions. Complex 4 was obtained under
the same condition as that of 1 except using Zn(NO3)2ꢀ4H2O
The dinuclear [Cd2(Ra-L)(phen)2(H2O)] and [Cd2(Sa-L)(phen)2(-
H2O)] in one unit cell are assembled into a supramolecular dimer
via a cyclic R44(16) hydrogen-bonding motif (Fig. S2) formed by
Table 1
Crystallographic data and structure refinement summary for complexes 1–5.
Complex
1
2
3
4
5
Formula
Formula weight
T (K)
C
1152
153(2)
0.71
52H42Cd2N6O11
C81H94Cd4N8O34
2173
185(2)
C56H50Cd5N4O22
1693
185(2)
0.71
C52H42N6O11Zn2
1058
153(2)
C28H32.5N2O14.25Zn2
756
185(2)
0.71
k (Å)
0.71
0.71
Cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
monoclinic
P2(1)/c
17.8488(10)
20.9067(12)
15.3851(9)
90
107.8770(10)
90
5463.9(5)
4
triclinic
orthorhombic
Pbca
ꢀ
ꢀ
ꢀ
P1
P1
P1
13.4883(6)
14.7030(9)
15.0480(11)
62.083(7)
74.341(5)
63.374(5)
2350.5(2)
2
9.663(3)
20.744(5)
23.176(5)
95.562(4)
94.179(5)
102.706(5)
4489.0(19)
2
13.3998(4)
14.4935(5)
14.5449(5)
103.285(3)
104.830(3)
117.301(4)
2219.47(18)
2
10.5254(7)
14.8582(10)
38.821(3)
90
90
90
6071.2(7)
8
1.65
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.63
0.98
1.61
1.02
2.06
2
1.58
1.16
l
(mmꢁ1
)
1.66
F (000)
Goodness-of-fit (GOF) on F2
R1 (I > 2 (I))
wR2 (I > 2 (I))
1160
1.05
0.03
0.07
2200
1.05
0.06
0.16
3320
1.03
0.02
0.05
1088
1.05
0.03
0.08
3108
1.09
0.03
0.08
r
r
R1 (all data)
0.03
0.09
0.03
0.04
0.04
wR2 (all data)
0.07
0.17
0.06
0.08
0.08

4
W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
unit containing four Cd centers, two L4ꢁ ligands, two phen ligands,
seven coordinated water molecules, ten guest water molecules and
one non-coordinated methanol molecule. As shown in Fig. 3, the
tetranuclear structure shows an arcuate geometry, in which the
four cadmium centers are linked by the bridging coordination of
the ligand carboxylate groups. The Cd1 and Cd2 atoms are bridged
by a carboxylate from one ligand in a l2- :
g2 g1 chelating-bridging
mode, and the Cd1 and Cd3 atoms are linked by a carboxylate from
another ligand in the same mode. However, the Cd3 and Cd4 atoms
are bridged by a carboxylate in a l2- :
g1 g1 syn-anti bridging mode.
Four cadmium centers are located in different coordination envi-
ronments. Cd1 adopts an eight-coordinated polyhedron (Fig. S4)
completed by four carboxylate oxygen atoms (O7, O8, O15, O16)
from two different L4ꢁ ligands, two nitrogen atoms (N5, N6) from
one phen ligand, and two coordinated water molecules (O17,
O18). Cd2 and Cd3 are both seven-coordinated by two N atoms
and four carboxylate O atoms from one L4ꢁ ligand, and an O atom
from one water molecule in a geometry which may be described as
a roughly capped trigonal prism (Fig. S4). The Cd4 center is six-
coordinated in a slightly distorted octahedral geometry by two
nitrogen atoms (N7, N8) of one phen ligand, three oxygen atoms
(O21, O22, O23) of three water molecules, and one oxygen atom
(O1) from one carboxylate of the L4ꢁ ligand. In 2, the Cd–O and
Cd–N bond distances are in the range of 2.242–2.600 and 2.324–
2.605 Å, respectively, which is comparable to the reported values
[14]. The naphthyl rings of the L4ꢁ ligand subtend a dihedral angle
of 72.086(132)° and 75.650(125)°, which is obvious smaller than
the value of 82.88° in 1, indicating that the two naphthyl rings of
the ligand can adjust their relative degrees by themselves to meet
the requirement for a preferred coordination geometry.
Fig. 1. The coordination environment of Cd(II) in 1 drawn with ellipsoids at the 30%
probability level. Hydrogen atoms on carbon atoms are omitted for clarity.
intermolecular hydrogen bonds O9–H9Aꢀ ꢀ ꢀO7D (O9ꢀ ꢀ ꢀO7D,
2.694(3) Å, symmetry code D: ꢁx + 1, ꢁy + 1, ꢁz + 1) between one
coordinated water molecule (O9) on Cd1 and one oxygen atom
(O7) of one carboxylate group, and intramolecular hydrogen bonds
O9–H9Bꢀ ꢀ ꢀO2 (O9ꢀ ꢀ ꢀO2, 2.910(3) Å) between one coordinated
water molecule (O9) on Cd1 and one carboxylato oxygen atom
(O2). Meanwhile, the neighboring hydrogen-bonded dimers are
held together through intermolecular hydrogen bonds O10–
H10Aꢀ ꢀ ꢀO1C, O10–H10Bꢀ ꢀ ꢀO5B between guest water molecule and
carboxylate oxygen atom to give a hydrogen-bonded chain along
the a axis (Fig. S3). The adjacent chains are linked further together
to form a supramolecular layer through the p–p stacking interac-
Interestingly, one arcuate [Cd4(Ra-L)2(phen)2(H2O)7] unit and
one arcuate [Cd4(Sa-L)2(phen)2(H2O)7] unit in 2 are linked into a
supramolecular dimer (Fig. S5) with an elliptic motif in the
head-to-end fashion by intermolecular hydrogen bond O21–
H21Cꢀ ꢀ ꢀO13D (Oꢀ ꢀ ꢀO: 2.695(9) Å, symmetry code D: ꢁx + 2,
ꢁy + 1, ꢁz) and O22–H22Bꢀ ꢀ ꢀO14D (Oꢀ ꢀ ꢀO: 2.842(9) Å) between
the coordinated water molecule (O21 and O22) on Cd4 and
carboxylato oxygen atom (O13 and O14) of the ligand. The
supramolecular dimer displays an elliptic cavity with a long axis
tions between the phenyl rings of the phen ligands from the adja-
cent dimers with a centroidꢀ ꢀ ꢀcentroid separation of 3.46 Å (Fig. 2).
3.2.2. [Cd4(L)2(phen)2(H2O)7]ꢀCH3OHꢀ10H2O (2)
Complex 2 was obtained with a similar procedure as that for 1
except that the reaction temperature was increased to 120 °C.
However, 2 displays a different structure from that for 1, indicating
a temperature control for the structures of the complexes 1 and 2.
Complex 2 exhibits a tetranuclear structure with the asymmetric
Fig. 2. The supramolecular layer in 1 constructed by
p–p stacking interactions between the two adjacent chains in the ab plane. Hydrogen bonds and p–p stacking are
indicated by dashed lines.

W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
5
Fig. 3. The tetranuclear structure of 2 drawn with ellipsoids at the 30% probability level. Solvent molecules and hydrogen atoms on carbon atoms are omitted for clarity.
of 15.52 Å and a short axis of 11.04 Å. The guest water molecules
and one disordered methanol molecule exist in the cavity via a
number of hydrogen bond interactions, such as O22–H22Aꢀ ꢀ ꢀO29
and O17–H17Aꢀ ꢀ ꢀO27 hydrogen bonds between guest water mole-
cules and coordinated water molecules; O29–H292ꢀ ꢀ ꢀO26 and
O27–H27Cꢀ ꢀ ꢀO25 hydrogen bonds between different guest water
molecules; and weak O35–H35Aꢀ ꢀ ꢀO26 hydrogen bond between
coordinated water molecule and guest methanol molecule
(Table S2). The intramolecular hydrogen bond interactions
between coordinated water molecules and carboxylate oxygen
atoms of the ligand (O18–H18Bꢀ ꢀ ꢀO12 and O17–H17Bꢀ ꢀ ꢀO4) are
also observed in the supramolecular dimer. The neighbor elliptic
supramolecular dimers are further linked into a supramolecular
(O18–H18Aꢀ ꢀ ꢀO25A,
O19–H19Aꢀ ꢀ ꢀO32A,
O20–H20Bꢀ ꢀ ꢀO34B);
between different guest water molecules (O25–H25Fꢀ ꢀ ꢀO32); and
between guest water molecules and carboxylato oxygen atoms of
the
ligand
(O27–H27Dꢀ ꢀ ꢀO11E,
O26–H26Bꢀ ꢀ ꢀO5E,
O32–
H321ꢀ ꢀ ꢀO6E) to give a final 3D supramolecular framework struc-
ture (Fig. S6).
3.2.3. {[Cd5(L)2(H2O)3(OH)2]ꢀH2O}n (3)
The structure of 3 is a two-dimensional polymer constructed
from novel pentanuclear cadmium cluster units [Cd5(
l2-OH)
(l
3-OH)( 2-RCOO)( 3-RCOO)3]. To our best knowledge, only a
l
l
few cadmium carboxylate MOFs [15–17] are constructed by high
nuclearity cluster (>4 Cd2+ ions) as secondary building units
layer in the bc plane by
p–p interactions among the phen mole-
(SBUs). Such asymmetrical pentanuclear cluster containing l2
-
cules with the values of the centroidꢀ ꢀ ꢀcentroid separation of
3.67 and 3.96 Å, respectively (Fig. 4). Furthermore, the supramolec-
ular layers are stacked along a direction by hydrogen bond interac-
tions between coordinated water and guest water molecules
OH, 3-OH and carboxylic bridges with different bridging mode
used for the construction 2D network has never been presented
before. In the pentanuclear unit (Fig. S7), Cd1 is connected to an-
l
other four Cd centers by three
l3-carboxylate groups and two
Fig. 4. View of the 2D supramolecular network of 2. Part hydrogen atoms are omitted for clarity. Hydrogen bonds and p–p stacking are indicated by dashed lines.

6
W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
OHꢁ groups with the
l
2-OH (O17) group bridging Cd1 and Cd3, the
reference is linked to its neighboring pentanuclear Cd(II) unit
(marked with turquiose color) via two symmetry related Cd atoms
(Cd3 and Cd3B) by the bridging of two carboxylate groups in l2
g2 chelating-bridging mode. From Fig. S8b, we can see that
l
l
3-OH (O18) group linking Cd1, Cd4 and Cd5 atoms, and the three
3-carboxylate groups connecting Cd1–Cd2–Cd3, Cd1–Cd2–Cd5,
-
and Cd1–Cd3–Cd4, respectively. In addition, Cd2 is further linked
g1
:
to Cd4 by a
g
2-oxygen atom (O12) of the other carboxylate group.
the referenced purple pentanuclear Cd(II) unit connects to another
neighboring pentanuclear Cd(II) unit (marked with orange color)
by the bridging of three carboxylate groups, in which two carbox-
The nonbonding Cdꢀ ꢀ ꢀCd distances are 3.5313(3)–5.7477(4) Å. The
five cadmium centers are in different coordination environment
(Fig. 5). Cd1 is six-coordinated by four carboxylate oxygen atoms
O4, O8, O10 and O5A (symmetry code A: x, ꢁy + 3/2, z ꢁ 1/2) from
three different L4ꢁ ligands and two hydroxyl oxygen atoms (O17,
O18) in a severely distorted octahedral coordination environment
with the twist angle h of 22.18° (30° for standard octahedral
[18]). Cd2 is seven-coordinated by four carboxylate oxygen atoms
(O2, O4, O6, O8) and two nitrogen atoms (N1, N2) from one L4ꢁ li-
gand and one carboxylate oxygen atom (O12) from the other L4ꢁ
ligand in a capped distorted trigonal prismatic coordination envi-
ronment. Cd3 is also seven-coordinated by four carboxylate oxygen
aotms from three different L4ꢁ ligands and one hydroxyl oxygen
atom (O17) and two oxygen atoms of two water molecules (O19,
O20), but in a distorted pentagonal-bipyramidal coordination envi-
ronment. The equatorial atoms (O3, O9, O13B, O14B, O19) deviate
slightly from the pentagonal plane, the maximum deviation from
the mean equatorial plane being 0.135 Å at O(13B). The range of
the equatorial chelating angles is 51.76(7)–79.58(7)°, some of them
are far from the value of 72° for the ideal pentagonal bipyramid
polyhedron. Cd4 is seven-coordinated by four carboxylate oxygen
atoms (O12, O14, O16, O10) and two nitrogen atoms (N3, N4) from
ylate groups act in l3- : - :
g1 g2 bridging mode and one in l2 g2 g0
mode. In the same connecting mode, the referenced purple penta-
nuclear Cd(II) unit is linked to the third neighboring pentanuclear
Cd(II) unit (marked with green color, Fig. S8c). As a whole, the con-
nection of the referenced purple pentanuclear Cd(II) unit to its
three neighboring pentanuclear Cd(II) units is shown in Fig. S8d.
Topologically, if the pentanuclear Cd(II) SBUs are viewed as nodes,
the 2D structure of 3 can be described as a (6,3)-connected net-
work with the Schläfli symbol 63, as shown in Fig. 6. To the best
of our knowledge, it is the first 2D (6,3) network based on cad-
mium cluster SBUs built from ligands containing N,N-diacetic acid
units.
3.2.4. {[Zn2(L)(H2O)4]ꢀ2.25H2O}n (5)
Complex 5 is a 1D coordination polymer consisting of dinuclear
Zn(II) unit [Zn2(L4ꢁ)(H2O)4]. As shown in Fig. 7, two Zn atoms in the
dinuclear Zn(II) unit are in different coordination environments.
The Zn1 atom is six-coordinated in a distorted octahedral geome-
try. The best equatorial plane is defined by the O1, O3, O6, N2
atoms from one L4ꢁ ligand, and the metal deviated by 0.076 Å to-
ward O7 from the mean plane. The axial positions are occupied
by a nitrogen atom (N1) and an oxygen atom (O7) from the same
L4ꢁ ligand. The Zn2 center is coordinated by four oxygen atoms
(O9, O10, O11, O12) from four water molecules and two oxygen
atoms (O4A, O8) from two carboxylates of the ligand in a slightly
distorted octahedral geometry. The Zn1 and Zn2 atoms are bridged
one L4ꢁ ligand, one
l3-OH oxygen atom (O18) in a capped distorted
trigonal prism coordination environment. The Cd4–N4 bond
(2.774 Å) is significantly longer than the other bonds (2.224–
2.605 Å) around Cd4 (Table S1). The coordination polyhedron
around Cd5 center formed by four carboxylate oxygen atoms
(O2A, O6A, O7, O11A) from two L4ꢁ ligands, one hydroxyl oxygen
atom (O18) and one oxygen atom of coordinated water molecule
(O21) could be defined as a slightly distorted octahedral with the
twist angle h of 27.1°. In 3, the Cd–O and Cd–N bond distances
are in the range of 2.177–2.658 and 2.450–2.774 Å, respectively.
The naphthyl rings of the L4ꢁ ligand containing C10, C11 and
C38, C39 atom subtend a dihedral angle of 70.964(42)° and
73.817(60)°, respectively.
The 2D structure of 3 is constructed via the connection of the
pentanuclear Cd(II) cluster units by the bridging of the carboxylate
groups of the ligand. Every pentanuclear Cd(II) cluster unit in the
compound is connected to other three ones (Fig. S8). The pentanu-
clear Cd(II) unit (marked with purple color) which we take as
by a carboxylate of the ligand in a l2- :
g1 g1 trans–trans bridging
mode with a Zn1ꢀ ꢀ ꢀZn2 separation of 5.9622(5) Å. The neighboring
dinuclear Zn(II) units are linked by a carboxylate group of the
ligand in a l2
-
g1
:
g1 syn-trans bridging mode with a Zn(II)ꢀ ꢀ ꢀZn(II)
distance of 5.1730(5) Å, which results in the formation of a chain
along the b axis (Fig. 8). A number of hydrogen bonds between
coordinated water molecules and guest water molecules (O9–
H9Bꢀ ꢀ ꢀO13, O11–H11Bꢀ ꢀ ꢀO13A, O12–H12Bꢀ ꢀ ꢀO14E) and between
coordinated water molecules and carboxylato oxygen atom (O9–
H9Aꢀ ꢀ ꢀO2C, O10–H10Aꢀ ꢀ ꢀO1C, O11–H11Aꢀ ꢀ ꢀO3A), and so on
(Table S2) are observed, which resulted in the formation of 2D
network (Fig. S9).
The Zn–N and Zn–O bond lengths in 5 are in the range of
2.243(2)–2.285(2) and 2.0264(19)–2.177(2) Å, respectively, which
are comparable to those reported in the literatures [19]. The
naphthyl rings of the L4ꢁ ligand subtend a dihedral angle of
78.626(53)°.
3.3. Coordination modes of the H4L ligand
The H4L ligand contains two aminodicarboxylic acid groups
with ten coordination atoms. All carboxylate groups of H4L in the
five complexes are found to be completely deprotonated and in-
volved in coordination. Total six coordination modes for the car-
boxylates in L4ꢁ anion were observed in five complexes, that is
l1
l2
mode, l2
-
-
g1
:
:
g0 monodentate mode, l2
g1 trans–trans bridging mode, l2
g0 bidentate bridging mode and l3 g1
- :
-
g1
:
g1 syn-anti bridging mode,
g2 chelating-bridging
g2 tridentate
g1
-
g1
:
-
g2
:
bridging mode. Both two N atoms of the L4ꢁ ligand coordinate to
metal ion in chelating mode in all cases. As a whole, the L4ꢁ ligand
exhibits a variety of coordination fashions due to various coordina-
tion modes of carboxylates. Six distinct kinds of coordination
fashions for the L4ꢁ ligands have been found in complexes 1–5,
Fig. 5. The coordination environment of Cd(II) in 3 drawn with ellipsoids at the 30%
probability level. Hydrogen atoms on carbon atoms are omitted for clarity.
Symmetry codes: (A) x, ꢁy + 3/2, z ꢁ 1/2; (B) ꢁx + 1, ꢁy + 2, ꢁz + 1.

W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
7
Fig. 6. View of the 2D framework of 3 constructed by pentanuclear cadmium SBUs and simplified (6,3)-connected network with pentanuclear Cd(II) core as a node.
four carboxylate groups in a l1- :
g1 g0 monodentate mode, one in
l2- : - :
g1 g2 chelating-bridging mode and the other two in l3 g1 g2
bridging modes (Fig. 9d). The other L4ꢁ anion coordinates in l6
bridging fashion with one of the four carboxylate groups in a l2
-
-
g2
:
g0 bridging mode and the other three in l3
-
g1
:
g2 bridging
modes (Fig. 9e). In complex 5, the L4ꢁ anions act as a octadentate
ligand in a 3-bridging fashion with one of the four carboxylate
groups in l2
g1 trans–trans bridging mode, one in l2
syn-anti bridging mode, and the other two in l1
g0 monoden-
l
-
g1
:
- :
g1 g1
-
g1
:
tate mode (Fig. 9f). To the best of our knowledge, four coordination
modes (Fig. 9b–e) have never been observed in other metal com-
plexes with aminopolycarboxylic acids ligand. The diversity of
the coordination mode of the H4L ligand may be ascribed to its
characteristics with both rigidity and flexibility.
Fig. 7. The dinuclear Zn(II) unit in 5 drawn with ellipsoids at the 30% probability
level. Symmetry codes: (A) ꢁx + 1/2, y ꢁ 1/2, z; (B) ꢁx + 1/2, y + 1/2, z.
3.4. Thermal stability of the complexes 1–5
The thermal behaviors of complexes 1–5 were studied by ther-
mogravimetric analysis (TGA) under a N2 atmosphere (Fig. S10).
Compound 1 lost its water molecules in the range of 28–106 °C,
the weight loss of 5.0% corresponding to the loss of guest water
and one coordinated water molecule per formula unit (calc.
4.7%). The dehydration process is followed by a plateau of stability
from 106 to 329 °C, and then the compound decomposes rapidly
with a two-step weight loss. The TGA curve of 2 shows a weight
loss from room temperature to 198 °C, corresponding to the loss
of guest molecules and seven coordinated water molecules (ob-
served 14.8%, calculated 15.6%). The dehydrated solid shows no
weight loss until 263 °C. Further heating leads to the final decom-
position of the compound 2. For the TG curve of 3, the first weight
loss of 4.2% in the temperature range of 99–211 °C corresponds to
the loss of guest H2O and three coordinated H2O molecules (calc.
as shown in Fig. 9. In complexes 1 and 4, the L4ꢁ anion acts as a
heptadentate ligand in a
carboxylate groups in a l2
other three in l1
g0 monodentate modes (Fig. 9a). In complex
2, one L4ꢁ anion acts as heptadentate ligand in a
2-bridging fash-
ion with one of the four carboxylate groups in a l2
1 chelating-
bridging mode, and the other three in l1
g0 monodentate
modes (Fig. 9b). The other L4ꢁ anion in 2 acts as octadentate ligand
in a 3-bridging mode with one of the four carboxylate groups in a
1 syn-anti bridging mode, one in a l2 1 chelating-bridg-
ing mode, and the other two in l1
g0 monodentate mode
(Fig. 9c). In complex 3, all L4ꢁ anions act as nonadentate ligand.
One L4ꢁ anion coordinates in
6-bridging fashion with one of the
l
2-bridging fashion with one of the four
-
g1
:
g1 syn-anti bridging mode, and the
-
g1
:
l
-
g2
:g
-
g1
:
l
:
l2
-
g1
g
-
g2
:g
-
g1
:
l
Fig. 8. Zigzag chain structure of 5 along the b axis drawn with ellipsoids at the 30% probability level. Symmetry codes: (A) 0.5 ꢁ x, y ꢁ 0.5, z; (B) 0.5 ꢁ x, 0.5 + y, z.

8
W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
Fig. 9. Coordination modes of L4ꢁ in complexes 1–5 (a in 1 and 4, b and c in 2, d and e in 3, f in 5).
4.3%). The dehydrated solid shows no weight loss until 296 °C. Fur-
ther heating leads to the final collapse of the framework of the
compound. For complex 4, there is a 4.7% weight loss in the tem-
perature range 29–108 °C, which is attributed to the loss of one
coordinated and two guest water molecules (calculated 5.1%).
The compound began to decompose at above 176 °C with a sharp
weight loss. Compound 5 showed a weight loss from room temper-
ature to 203 °C, corresponding to the release of guest and coordi-
nated water molecules (observed weight loss 14.0%, calculated
14.9%). Further heating leads to the final collapse of the skeleton
of the compound by the decomposition of the ligand.
Zn2+ ions are difficult to be oxidized or reduced due to their d10
configuration, the emissions of their compounds cannot be attrib-
uted to either a metal-to-ligand charge transfer (MLCT) or a ligand-
to-metal charge transfer (LMCT) [21]. For complexes 3 and 5, they
can probably be assigned to the intraligand charge transfer due to
their resemblance to the emission of the H4L ligand. The emissive
blue-shifts relative to the free H4L ligand probably originate from
the coordination interactions between the metal atom and the li-
gand [22]. Conversely, for complex 1 and 4, obvious red shifts com-
pared with the emission spectra of the H4L ligand and phen ligand
have been observed. A possible explanation is that the cooperative
association of coordination interactions as well as hydrogen bonds
and p–p packing interactions compared with those of other related
3.5. Fluorescence properties
complexes [19,23]. It is noteworthy that there is no emission ob-
served for complex 2 for excitation wavelengths between 250
and 400 nm, which is a sharp contrast to the complex of 1.
Although more detailed theoretical and spectroscopic studies
may be necessary for better understanding of the luminescent
mechanism, the strong fluorescence emissions of those complexes
make them potentially useful photoactive materials.
The luminescent properties of complexes with d10 metal centers
are of great interest for their potential applications in photochem-
istry, chemical sensors, and electroluminescent display [5e,20].
Therefore, the luminescence properties of 1–5, as well as the free
H4L ligand and phen ligand, were investigated in the solid state
at room temperature. As shown in Fig. 10, intense emission bands
were observed at 428 nm (kex = 363 nm) for the H4L ligand, 415
and 436 nm (kex = 370 nm) for the phen ligand, 500 nm (kex = 366 -
nm) for 1, 403 nm (kex = 356 nm) for 3, 520 nm (kex = 360 nm) for 4,
and 389 nm (kex = 346 nm) for 5, respectively. Since the Cd2+ and
4. Conclusion
In summary, five new Zn(II)/Cd(II) complexes with a new
polycarboxylic acid ligand, 1,10-binaphthalenyl-2,20-diamine-
N,N,N0,N0-tetraacetic acid (H4L), have been synthesized and
structurally characterized. The five complexes are found to display
various architectures from 0D to 2D, and the ligands in the
compounds are found to show a variety of coordination modes.
The diversity of the coordination mode of the ligand may be
ascribed to its characteristics with both rigidity and flexibility. A
wealth of coordination mode for the ligand results in the structural
diversity of the complexes, which implies the significance of the
rational design and selection of the ligand in the construction of
the complexes with novel structure. In the work, two tempera-
ture-dependent coordination compounds of 1 and 2 were obtained.
These two complexes are found to display total different fluores-
cence properties, in which complex 1 shows a strong fluorescence
emission, while complex 2 shows no signal. Such a phenomenon is
of interesting for the study of the structure–property relationship,
although more investigations are needed for understanding the
essential reason for this difference. Further elaborate studies on
Fig. 10. The emission spectra of H4L, phen and the complexes 1, 3, 4, 5 in the solid
state at room temperature.

W.-Y. Huang et al. / Polyhedron 50 (2013) 1–9
9
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the synthesis and properties of the metal complexes with this H4L
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Acknowledgements
The authors thank the financial support by National Natural Sci-
ence Foundation of China (No. 20971029) and Guangxi Natural Sci-
ence Foundation (No. 2010GXNSFD013018 and 2010GXNSFF01
3001).
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CCDC 874703-874707 contain the supplementary crystallo-
graphic data for complexes 1–5, respectively. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2012.10.042.
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