Solvent- and temperature-driven synthesis of three Cd(II) coordination polymers based on 3,3′-azodibenzoic acid ligand: Crystal structures and luminescent properties

Article abstract of DOI:10.1016/j.ica.2012.11.021

Solvothermal reactions of Cd(OAc)₂·2H₂O with 3,3′-azodibenzoic acid (H₂L) in N,N′-dimethylformamide (DMF) or DMF/MeOH at 100 °C or 120 °C gave rise to three cadmium(II) coordination polymers {[CdL(DMF)₂]·0.5DMF}_n (1), [CdL(DMF)(MeOH)]_n (2) and {[Cd₃L₃(DMF) ₄]·0.5DMF}_n (3). Complexes 1-3 were characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffraction. In 1-3, dinuclear [Cd₂L₄(DMF)₄] (1) or [Cd₂L₄(DMF)₂(MeOH)₂] (2) unit and trinuclear [Cd₃L₆(DMF)₄] (3) unit acts as a four-connecting node to link its equivalent ones via sharing L ligands to form 2D layers, which are further connected through the C-H?π (1) or hydrogen-bonding interactions (2-3) to afford 3D networks with the 4 ¹²6³ topology. The network of 1 allows other one to be penetrated for the formation of twofold interpenetrating pcu net. The formation of 1-3 provided an interesting insight into solvent and temperature effects on the construction of coordination polymers under solvothermal conditions. In addition, the photoluminescent properties of 1-3 in solid state at ambient temperature were also investigated.

Full text of DOI:10.1016/j.ica.2012.11.021

Inorganica Chimica Acta 397 (2013) 75–82
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Solvent- and temperature-driven synthesis of three Cd(II) coordination
polymers based on 3,30-azodibenzoic acid ligand: Crystal structures
and luminescent properties
⇑
Lei-Lei Liu , Lin Liu, Jun-Jie Wang
College of Chemistry and Chemical Engineering, Anyang Normal University, Anyang 455000, Henan, PR China
a r t i c l e i n f o
a b s t r a c t
Solvothermal reactions of Cd(OAc)2ꢀ2H2O with 3,30-azodibenzoic acid (H2L) in N,N0-dimethylformamide
(DMF) or DMF/MeOH at 100 °C or 120 °C gave rise to three cadmium(II) coordination polymers
{[CdL(DMF)2]ꢀ0.5DMF}n (1), [CdL(DMF)(MeOH)]n (2) and {[Cd3L3(DMF)4]ꢀ0.5DMF}n (3). Complexes 1–3
were characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffrac-
tion. In 1–3, dinuclear [Cd2L4(DMF)4] (1) or [Cd2L4(DMF)2(MeOH)2] (2) unit and trinuclear [Cd3L6(DMF)4]
(3) unit acts as a four-connecting node to link its equivalent ones via sharing L ligands to form 2D layers,
Article history:
Received 10 October 2012
Received in revised form 24 November 2012
Accepted 26 November 2012
Available online 3 December 2012
Keywords:
which are further connected through the CꢁHꢀ ꢀ ꢀp (1) or hydrogen-bonding interactions (2–3) to afford
Solvent and temperature effects
3,30-Azodibenzoic acid
Cd(II) coordination polymers
Crystal structure
3D networks with the 41263 topology. The network of 1 allows other one to be penetrated for the forma-
tion of twofold interpenetrating pcu net. The formation of 1–3 provided an interesting insight into sol-
vent and temperature effects on the construction of coordination polymers under solvothermal
conditions. In addition, the photoluminescent properties of 1–3 in solid state at ambient temperature
were also investigated.
Photoluminescent properties
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
directly or indirectly influences the coordination behavior of the
metal ions: it participates in the coordinated reactions or influ-
The rational design and assembly of metal–organic frameworks
(MOFs) have attracted much more attention in past few decades
owing to their intriguing topologies and crystal packing motifs
[1] as well as potential applications in gas storage/adsorption [2],
catalysis [3], separations [4], drug delivery [5] and so on. Crystal
engineering affords us a powerful tool for the design and construc-
tion of coordination frameworks [6]. And chemists and material
scientists have been focusing their research on exploring the corre-
lation between structures and functions of crystalline materials
from 1990s, and huge efforts toward understanding the structural
diversities and fascinating topologies associated with coordination
polymers have promoted many meaningful results [7]. Generally, it
is viable to select appropriate metal centers and organic linkers to
form networks with predetermined structures and desired proper-
ties. However, in real chemical reactions, the environments, such
as pH value, solvent, temperature, and reagent concentration, have
an unpredictable impact on the crystallization of MOFs [8,9]. Minor
changes of such environmental factors may lead to different archi-
tectures originated from differences in atomic connectivity or net-
work catenation [10]. Solvent as one of the important factor often
ences the overall frameworks without participating in coordination
[11]. As for temperature, its effect on forming the coordination
polymers has been intensively explored, and some reports de-
scribed how the reaction temperature affects the generation of dif-
ferent coordination polymers [12]. However, the studies of solvent
and temperature factors acting on the same reaction components
are rare [13].
On the other hand, azobenzenecarboxylic compounds such as
azobenzene-dicarboxylic, azobenzene-tricarboxylic and azoben-
zene-tetracarboxylic acids were utilized to construct functional
MOFs [14]. For example, Yaghi used 4,40-azodibenzoic acid
(H2ADB) to react with Tb(NO3)3ꢀ5H2O to get an interpenetrating
network of {Tb2(ADB)3[(CH3)2SO]4ꢀ16[(CH3)2SO]}n with large free
volume [15]. Recently, Lu and co-workers reported three porous
MOFs constructed by using azobenzene-3,5,40-tricarboxylic acid
(H3ABTC) and Cd(NO3)2ꢀ4H2O/MnCl2ꢀ4H2O as building blocks
[14b]. Qiu et al. used 3,30,5,50-azobenzenetetracarboxylic acid
(H4ABTC) as a building block to construct three 3D microporous
MOFs with NbO and PtS topologies, which show hydrogen storage
and luminescent properties [16]. To our best knowledge, the coor-
dination chemistry of 3,30-azodibenzoic acid has attracted little
attention, with exception of the recent report on the assembly of
3,30-azodibenzoic acid with Zn(OAc)2/Co(OAc)2/PbI2 and 1,10-phe-
nanthroline [14a]. Moreover, studies engaged in solvent- and/or
⇑
Corresponding author. Fax: +86 372 2900040.
E-mail address: liuleileimail@163.com (L.-L. Liu).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.021

76
L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
Scheme 1.
temperature-dependent construction of coordination polymers
containing 3,30-azodibenzoic acid have not been reported so
far. In this work, the solvothermal reactions of Cd(OAc)2ꢀ2H2O
with 3,30-azodibenzoic acid (H2L) in DMF or DMF/MeOH at 100
or 120 °C gave rise to three Cd(II) coordination polymers
with different structures {[CdL(DMF)2]ꢀ0.5DMF}n (1), [CdL(DMF)
(MeOH)]n (2) and {[Cd3L3(DMF)4]ꢀ0.5DMF}n (3). The results indi-
cated that solvent and temperature significantly affect the for-
mation of these cadmium(II) coordination polymers. Herein we
describe the solvent- and temperature-oriented reactions along
with the crystal structures and photoluminescent properties of
1–3 (Scheme 1).
2.2. Synthesis of complexes 1–3
2.2.1. {[CdL(DMF)2]ꢀ0.5DMF}n (1)
A mixture of Cd(OAc)2ꢀ2H2O (13 mg, 0.05 mmol), H2L ligand
(7 mg, 0.025 mmol), and DMF (4 mL) was sealed in a 10 mL Pyr-
ex glass tube and heated at 100 °C for 4 days, then cooled to
room temperature at a rate of 5 °C hꢁ1. The yellow blocks of 1
were collected and washed thoroughly with DMF and
dried in air. Yield: 11 mg (40%, based on Cd). Anal. Calc. for
C21.5H23N4.5CdO6.5: C, 46.04; H, 4.13; N, 11.24. Found: C, 46.50;
H, 4.38; N, 11.01%. IR (KBr disc): 3352 (m), 3272 (m), 3071
(w), 2931 (w), 1652 (s), 1591 (s), 1549 (s), 1475 (m), 1439
(m), 1394 (s), 1311 (w), 1253 (w), 1225 (w), 1155 (m), 1109
(m), 1075 (m), 936 (w), 811 (m), 781 (m), 684 (m), 538 (w),
2. Experimental
411 (w) cmꢁ1
.
2.1. Materials and general methods
2.2.2. [CdL(DMF)(MeOH)]n (2)
3,30-azodibenzoic acid (H2L) was prepared according to the
literature methods [17]. All chemicals and reagents were ob-
tained from commercial sources and used as received. The IR
spectra were recorded as KBr pellets on a Varian 800 FT-IR spec-
trometer in the 4000–400 cmꢁ1 region. Powder X-ray diffraction
(PXRD) measurements were performed on a Bruker Ultima III
Compound 2 (orange flakes) was prepared in the same way as
1, except using mixed solvent DMF/MeOH (4 mL, 1:1, V/V) in-
stead of solvent DMF (4 mL). Yield: 8 mg (35%, based on Cd).
Anal. Calc. for C18H18N3CdO6: C, 44.60; H, 3.74; N, 8.67. Found:
C, 44.21; H, 4.13; N, 8.55%. IR (KBr disc): 3386 (m), 3300 (m),
3065 (w), 2932 (w), 1645 (s), 1592 (s), 1545 (s), 1477 (w),
1398 (s), 1221 (w), 1154 (w), 1111 (m), 1075 (w), 1024 (m),
936 (w), 866 (w), 810 (m), 779 (m), 680 (m), 536 (w), 416 (w)
X-ray diffractometer with Cu
Ka (k = 1.5418 Å). Luminescent
spectra were recorded with a Rigaku RIX 2000 fluorescence
spectrophotometer.
cmꢁ1
.
Table 1
Summary of crystallographic data for 1–3.
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
43H44Cd2N9O13
C18H19CdN3O6
485.77
monoclinic
P21/c
9.3878(19)
10.051(2)
21.113(4)
C55.5H38Cd3N10.5O16.5
1453.19
1119.69
monoclinic
C2/c
28.608(6)
9.3713(19)
20.496(4)
triclinic
ꢀ
P1
11.476(2)
12.089(2)
12.476(3)
01.21(3)
95.16(3)
106.49(3)
1608.5(7)
1
b (Å)
c (Å)
a
(°)
b (°)
119.26(3)
102.85(3)
c
(°)
V (Å3)
Z
4794(2)
4
1942.3(7)
4
T (K)
296(2)
1.551
2260.0
0.958
24430
4218
3410
319
0.0613
0.1582
1.139
296(2)
1.661
976.0
1.164
47686
4632
3887
255
0.0471
0.1164
1.068
296(2)
1.500
720.5
1.053
16521
5671
4837
393
0.0388
0.1171
0.972
qcalc (g/cm3)
F(000)
l
(Mo K
a
, mmꢁ1
)
Total reflections
Unique reflections
No. of observations
No. of parameters
a
R1
b
wR2
Goodness-of-fit (GOF)c
a
b
c
R1
wR2 = {
GOF = {
=
R
||Fo| ꢁ |Fc|/
R|Fo|.
2
R
w(Fo ꢁ Fc2)2/
R .
w(Fo2)2}1/2
w(Fo ꢁ Fc2)2/(n ꢁ p)}1/2, where n = number of reflections and p = total numbers of parameters refined.
2
R

L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
77
2.2.3. {[Cd3L3(DMF)4]ꢀ0.5DMF}n (3)
at 296 K for 1–3. Diffraction data were collected at f and
x
modes
Compound 3 (orange blocks) was prepared in a manner similar
to that described for 1, using the same components in the same
molar ratio except the reaction temperature was fixed at 120 °C.
Yield: 13 mg (46%, based on Cd). Anal. Calc. for C55.5H51N10.5Cd3-
O16.5: C, 45.46; H, 3.51; N, 10.03. Found: C, 45.15; H, 3.08; N,
10.35%. IR (KBr disc): 3383 (m), 3302 (m), 3101 (w), 2957 (w),
1672 (s), 1611 (s), 1565 (s), 1500 (m), 1469 (m), 1420 (s), 1335
(w), 1276 (w), 1250 (w), 1180 (m), 1141 (m), 1100 (m), 960 (w),
with a detector distance of 35 mm to the crystals. Cell parameters
were refined by using the program Bruker SAINT. The collected data
were reduced by using the program Bruker SAINT A, and the absorp-
tion corrections (multi-scan) were applied. The reflection data
were also corrected for Lorentz and polarization effects.
The crystal structures of 1–3 were solved by direct method re-
fined on F2 by full-matrix least-squares techniques with the SHEL-
XTL-97 program [18]. In 3, one coordinated DMF solvent molecule
was found to be disordered over two positions with an occupancy
factor of 0.700/0.300 for O8/O8A, N5/N5A, C25–C27/C25A–C27A.
Hydrogen atoms of the DMF solvent molecules in 1 (C21ꢁC23)
and 3 (C25ꢁC30) were not located. All other H atoms in 1–3 were
placed in geometrically idealized positions and constrained to
ride on their parent atoms. The site occupation factors for O7,
N5, C21ꢁC23 atoms in 1 and O9, N6, C28ꢁC30 atoms in 3 were
fixed at 0.5 and 0.25, respectively, which were maybe due to
the partial evaporation of the DMF solvent molecules. A summary
of the key crystallographic information for 1–3 is tabulated in
Table 1 and their selected bond lengths and angles are given in
Table 2.
841 (m), 801 (m), 721 (m), 569 (w), 440 (w) cmꢁ1
.
2.3. X-ray crystallographic studies
Single crystals of 1–3 were obtained directly from the above
preparations. All measurements were made on a Bruker Smart
Apex-II CCD area detector by using graphite monochromated Mo
Ka (k = 0.071073 nm). These crystals were mounted on glass fibers
Table 2
Selected bond lengths (Å) and angles (°) for 1–3.a
Complex 1
Cd(1)–O(3)
Cd(1)–O(1A)
Cd(1)–O(2)
Cd(1)–O(4)
2.257(6)
2.320(5)
2.335(5)
2.568(6)
1.234(14)
91.6(2)
90.0(2)
101.6(2)
88.4(3)
85.7(2)
90.8(3)
90.2(2)
53.0(2)
Cd(1)–O(6)
Cd(1)–O(5)
Cd(1)–O(1)
N(1)–N(1B)
2.316(9)
2.325(7)
2.486(6)
1.235(13)
91.1(3)
3. Results and discussion
3.1. Synthesis consideration and general characterization
N(2)–N(2C)
O(3)–Cd(1)–O(6)
O(6)–Cd(1)–O(1A)
O(6)–Cd(1)–O(5)
O(3)–Cd(1)–O(2)
O(1A)–Cd(1)–O(2)
O(3)–Cd(1)–O(1)
O(1A)–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
O(6)–Cd(1)–O(4)
O(5)–Cd(1)–O(4)
O(1)–Cd(1)–O(4)
N(2C)–N(2)–C(11)
In all solvothermal reactions reported here, the molar ratio of
Cd(OAc)2ꢀ2H2O to H2L was kept at 2:1. Reactions of Cd(OAc)2ꢀ2H2O
with H2L in DMF for four days at 100 °C and cooled to ambient
temperature at a rate of 5 °C hꢁ1 produced yellow crystals of 1
(40% yield). When the reaction temperature was raised up to
120 °C, the orange crystals of 3 (46% yield) were generated through
the similar manners to those described for 1. Analogous reactions
except using mixture solvent DMF/MeOH (4 mL, 1:1, V/V) instead
of solvent DMF (4 mL, 1 and 3) at 100 °C afforded orange crystals
of 2 (35% yield). Notice that even the reaction temperature was
raised up to 120 °C, but only compound 2 was obtained. We also
attempted to crystallize at other mixture solvents, but always
failed to form any crystals. When the reaction temperature fell to
90 °C, crystals of 1 and 2 were obtained with relatively lower
yields. However, increasing the temperature to 140 °C, only orange
precipitates were isolated and the PXRD pattern was inconsistent
with those of 1–3.
O(3)–Cd(1)–O(1A)
O(3)–Cd(1)–O(5)
O(1A)–Cd(1)–O(5)
O(6)–Cd(1)–O(2)
O(5)–Cd(1)–O(2)
O(6)–Cd(1)–O(1)
O(5)–Cd(1)–O(1)
O(3)–Cd(1)–O(4)
O(1A)–Cd(1)–O(4)
O(2)–Cd(1)–O(4)
N(1B)–N(1)–C(4)
86.4(3)
171.8(3)
140.9(2)
127.32(19)
165.30(18)
73.92(19)
53.76(18)
85.4(3)
88.8(2)
141.65(18)
113.3(9)
143.5(2)
87.96(19)
115.1(8)
Complex 2
Cd(1)–O(4A)
Cd(1)–O(3B)
Cd(1)–O(2)
2.214(4)
2.301(4)
2.346(4)
1.246(6)
106.38(15)
80.27(16)
169.92(14)
96.05(14)
86.07(15)
149.73(13)
100.84(17)
112.9(5)
Cd(1)–O(6)
Cd(1)–O(5)
Cd(1)–O(1)
2.266(4)
2.341(5)
2.377(4)
N(1)–N(2)
O(4A)–Cd(1)–O(6)
O(6)–Cd(1)–O(3B)
O(6)–Cd(1)–O(5)
O(4A)–Cd(1)–O(2)
O(3B)–Cd(1)–O(2)
O(4A)–Cd(1)–O(1)
O(3B)–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
N(1)–N(2)–C(8)
124.28(14)
85.78(15)
84.19(15)
135.24(15)
93.99(15)
85.92(13)
87.36(15)
55.08(12)
113.9(5)
O(4A)–Cd(1)–O(3B)
O(4A)–Cd(1)–O(5)
O(3B)–Cd(1)–O(5)
O(6)–Cd(1)–O(2)
O(5)–Cd(1)–O(2)
O(6)–Cd(1)–O(1)
O(5)–Cd(1)–O(1)
N(2)–N(1)–C(6)
Compounds 1–3 were stable towards oxygen and moisture, and
almost insoluble in common organic solvents. The IR spectra of 1–3
showed peaks in the range of 1645–1672 and 1394–1420 cmꢁ1
,
which is indicative of the existence of coordinated carboxylic
groups [19a]. The middle peaks in the range of 1591–1611 cmꢁ1
were assigned to the asymmetric N@N vibration of complexes 1–
3 [8g]. The identities of 1–3 were further confirmed by single-crys-
tal diffraction analysis. The PXRD patterns of 1–3 were matched
with the simulated patterns generated from their single crystals
data (Fig. S1).
Complex 3
Cd(1)–O(5)
Cd(1)–O(8)
Cd(1)–O(1A)
Cd(2)–O(6B)
Cd(2)–O(2A)
N(3)–N(3D)
O(1A)–Cd(1)–O(2A)
O(5)–Cd(1)–O(8)
O(5)–Cd(1)–O(7)
O(8)–Cd(1)–O(7)
O(3)–Cd(1)–O(1A)
O(7)–Cd(1)–O(1A)
O(3)–Cd(1)–O(2A)
O(6B)–Cd(2)–O(4B)
O(4B)–Cd(2)–O(2C)
O(2C)–Cd(2)–O(4)
O(4B)–Cd(2)–O(6)
N(2)–N(1)–C(6)
2.188(4)
2.272(14)
2.358(4)
2.232(3)
2.340(3)
1.238(8)
55.18(11)
83.8(4)
Cd(1)–O(3)
Cd(1)–O(7)
Cd(1)–O(2A)
Cd(2)–O(4B)
2.231(4)
2.302(4)
2.381(3)
2.268(3)
1.246(6)
96.58(15)
156.97(14)
170.8(4)
85.35(15)
158.56(13)
91.6(4)
N(1)–N(2)
O(5)–Cd(1)–O(3)
O(7)–Cd(1)–O(2A)
O(3)–Cd(1)–O(8)
O(3)–Cd(1)–O(7)
O(5)–Cd(1)–O(1A)
O(8)–Cd(1)–O(1A)
O(5)–Cd(1)–O(2A)
O(8)–Cd(1)–O(2A)
O(6B)–Cd(2)–O(2C)
O(6B)–Cd(2)–O(2A)
O(6B)–Cd(2)–O(6)
N(3D)–N(3)–C(16)
N(1)–N(2)–C(8)
98.69(15)
85.5(4)
3.2. Description of the crystal structures
91.22(16)
101.83(14)
93.35(13)
91.33(14)
94.50(12)
85.50(12)
88.67(14)
113.1(4)
104.29(12)
95.4(4)
3.2.1. {[CdL(DMF)2]ꢀ0.5DMF}n (1)
Compound 1 crystallizes in the monoclinic space group C2/c,
and its asymmetric unit contains one [CdL(DMF)2] molecule, half
of a DMF solvent molecule. As shown in Fig. 1a, each Cd atom
adopts a pentagonal bipyramidal coordination geometry, is coordi-
nated by four O (O1, O2, O3 O4) atoms of chelating carboxylate
groups from two different L ligands, one O (O1A) atom of bridging
carboxylate groups from third L ligands and two O (O5, O6) atoms
from two different DMF molecules. The carboxylate groups of the L
88.01(14)
91.99(14)
180.000(1)
114.8(5)
114.2(4)
a
Symmetry codes for 1: (A) ꢁx + 1/2, ꢁy + 1/2, ꢁz; (B) –x, ꢁy, ꢁz; (C) –x, ꢁy + 1,
ꢁz ꢁ 1; for 2: (A) x + 1, ꢁy + 1/2, z ꢁ 1/2; (B) ꢁx + 1, y + 1/2, ꢁz + 3/2; for 3: (A) x, y,
z + 1; (B) ꢁx + 1, ꢁy + 1, ꢁz + 2; (C) ꢁx + 1, ꢁy + 1, ꢁz + 1; (D) ꢁx, ꢁy, ꢁz + 1.

78
L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
Fig. 1. (a) View of the coordination environments of Cd center in 1 with labeling schemes. Symmetry codes: (A) ꢁx + 1/2, ꢁy + 1/2, ꢁz; (B) ꢁx, ꢁy, ꢁz; (C) ꢁx, ꢁy + 1, ꢁz ꢁ 1;
(D) x + 1/2, y + 1/2, z. (b) View of one dinuclear [Cd2L4(DMF)4] unit of 1. (c) View of a 2D layer in 1 extending along the ac plane. (d) View of a 3D structure in 1 looking along
the c axis. (e) View of the twofold interpenetration model in 1. Each single net represents a pcu topology with a Schläfli symbol 41263. Atom color codes: Cd, cyan pentagonal
bipyramid; O, red; N, blue; and C, green. All H atoms except those related to H-bonding interactions and uncoordinated DMF molecules are omitted for clarity. (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
ligand in 1 display the chelating and chelating/bridging coordi-
nation modes. Cd1 and its symmetry-related Cd1A are bridged
by two L ligands to generate a dinuclear [Cd2L4(DMF)4] unit
(Fig. 1b). Each dinuclear unit serves as a planar fourfold node,
which links its four equivalent ones via sharing L ligands to form
a 2D layer with parallelogram meshes extending along the ac
plane (Fig. 1c). Each mesh in this 2D layer has a dimension of
15.05 ꢂ 15.19 Å2. Furthermore, this layer is connected to neigh-
3.2.2. [CdL(DMF)(MeOH)]n (2)
Compound 2 crystallizes in the monoclinic space group P21/c,
and its asymmetric unit contains one [CdL(DMF)(MeOH)] mole-
cule. The coordination environment of Cd2+ in 2 is different from
that of in 1. Each Cd atom in 2 adopts a disordered octahedral coor-
dination geometry, is coordinated by two O (O3A, O4B) atoms of
two bridging carboxylate groups from two L ligands, two O (O1,
O2) atoms of one chelating carboxylate groups from third L ligands
as well as two O (O5, O6) atoms from DMF and MeOH molecules
(Fig. 2a). The mean CdꢁO bond length (2.307(5) Å) is shorter than
that of 1 (2.372(4) Å), while the N@N (1.246(6) Å) bond length of 2
is slightly longer than that observed in 1 (1.234(13) Å, Table 2). In
contrast, the carboxylate groups of the L ligand in 2 display
the bridging and chelating coordination modes. Two [CdL(DMF)
(MeOH)] subunits are bridged by two L ligands to generate a
dinuclear [Cd2L4(DMF)2(MeOH)2] unit (Fig. 2b). Each dinuclear
[Cd2L4(DMF)2(MeOH)2] unit also serves as a fourfold node, which
boring layers via Hꢀ ꢀ ꢀ
p
interactions [C19Aꢀ ꢀ ꢀCg(x, y + 1,
z) = 2.965 Å, where Cg is the centroid of the C2/C3/C4/C5/C6/C7
ring], thereby completing a 3D network extending along the ab
plane (Fig. 1d) [19b]. This network was big enough to allow
the other network to penetrate to form a twofold interpenetrat-
ing pcu net with a Schläfli symbol of 41263 (Fig. 1e) [20].
Although the interpenetration in 1 occurs, there is still approxi-
mately 11.4% of the crystal volume accessible to the solvents
[21].

L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
79
Fig. 2. (a) View of the coordination environments of Cd center in 2 with labeling schemes. Symmetry codes: (A) 1 ꢁ x, ꢁy + 1/2, ꢁz + 3/2; (B) x + 1, ꢁy + 1/2, z ꢁ 1/2; (b) View
of one dinuclear [Cd2L4(DMF)2(MeOH)2] unit of 2. (c) View of a 2D network in 2 extending along the bc plane. (d) View of a 3D structure in 2 looking along the b axis. Atom
color codes: Cd, cyan pentagonal bipyramid; O, red; N, blue; and C, green. All H atoms except those related to H-bonding interactions and DMF molecules are omitted for
clarity. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

80
L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
Fig. 3. (a and b) View of the coordination environments of Cd1 and Cd2 centers in 3 with labeling schemes. Symmetry codes: (A) ꢁx, ꢁy, ꢁz + 1; (B) x, y, z + 1; (C) –x + 1,
ꢁy + 1, ꢁz + 1; (D) –x + 1, ꢁy + 1, ꢁz + 2; (E) x + 1, y + 1, z + 1. (c) View of one trinuclear [Cd3L6(DMF)4] unit of 3. (d) View of a 2D network in 3 extending along the bc plane. (e)
View of a 3D structure in 3 looking along the b axis. Atom color codes: Cd, cyan; O, red; N, blue; and C, green. All H atoms except those related to H-bonding interactions and
DMF molecules are omitted for clarity. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
links its four equivalent ones via sharing four L ligands to form a 2D
network with parallelogram meshes (13.81 ꢂ 16.10 Å2) extending
along the bc plane (Fig. 2c). Each 2D network is further intercon-
nected with neighboring ones via intermolecular hydrogen bond
(Fig. 3b). For Cd1 and Cd2, their mean CdꢁO bond length
(2.285(5) Å) is shorter than that of (2.372(4) Å) and
1
2
(2.307(5) Å). And the mean N@N (1.242(7) Å) bond length of 3 is
comparable that of 2 (1.246(6) Å), but is slightly longer than that
observed in 1 (1.234(13) Å, Table 2). The carboxylate groups of
the L ligand in 3 show the bridging and chelating/bridging coordi-
nation modes. Cd2, Cd1 and its symmetry-related Cd1A are bridged
by four L ligands to generate a trinuclear [Cd3L6(DMF)4] unit
(Fig. 3c). The trinuclear unit links its neighboring four equivalent
ones via sharing L ligands to form a 2D network with parallelogram
grids (12.48 ꢂ 16.63 Å2) extending along the bc plane (Fig. 3d).
Adjacent networks are interconnected by H-bonding interactions
between O atoms of carboxylate groups and H atoms of the phenyl
group with C18 [C18–H18ꢀ ꢀ ꢀO1, 3.342 Å, Table S1] to afford a 3D
architecture (Fig. 3e) with the effective solvent accessible volume
of 214.3 Å3 per unit cell (13.3% of the total cell volume) filled with
DMF solvent molecules. Similar to that of in 1–2, compound 3 also
show a 41263 topological structure (based on each [Cd3L6(DMF)4]
unit as a six-connecting node) (Fig. S3).
ꢁ
between the coordinated MeOH molecule and a CO2 group in
other network (O5–H5Aꢀ ꢀ ꢀ2, 2.681 Å, Table S1) to form a 3D struc-
ture extending along the ac plane (Fig. 2d). If the [Cd2L4(DMF)2
(MeOH)2] unit is considered as six-connecting nodes, the whole
structure of 2 also display a 41263 topological net (Fig. S2). The PLA-
TON program analysis of 2 suggests that there is no residual solvent
accessible void in the unit cell.
3.2.3. {[Cd3L3(DMF)4]ꢀ0.5DMF}n (3)
ꢀ
Compound 3 crystallizes in the triclinic space group P1, and its
asymmetric unit contains half a [Cd3L3(DMF)4] unit, one quarter of
DMF solvent molecule. The coordination environment of Cd(II) in 3
is different from that of in 1, but is similar with that of in 2. Cd1
atom is six-coordinated by two O (O3, O5) atoms of bridging car-
boxylate groups from two different L ligands, two O (O1A, O2A)
atoms of chelating carboxylate groups from third L ligands, and
The formation of different structures of 1–3 at different solvents
and temperatures deserves comments. Compounds 1 and 3 were
produced in DMF at 100 °C and 120 °C, respectively, while com-
pound 2 was generated in the mixed solvent DMF/MeOH at
two
O (O7, O8) atoms from two different DMF molecules
(Fig. 3a). Cd2 atom is also octahedrally coordinated by six O (O3,
O5) atoms of bridging carboxylate groups from six L ligands

L.-L. Liu et al. / Inorganica Chimica Acta 397 (2013) 75–82
81
100 °C. As described earlier in this article, the structures of 1–3 are
Appendix A. Supplementary material
greatly different in the following aspects. Firstly, Cd atoms in 1
adopt pentagonal bipyramidal coordination geometry, while those
of in 2–3 show octahedral coordination geometry. Secondly, com-
pounds 1–2 adopted a dinuclear [Cd2L4(DMF)4] (1) or [Cd2L4
(DMF)2(MeOH)2] (2) unit while compound 3 had a trinuclear
[Cd3L6(DMF)4] unit, which implied that higher nuclear units (3)
may be stable than the lower nuclear units (1) at the higher tem-
perature [22]. Moreover, each dinuclear or trinuclear unit serves
as a fourfold node, which links its four equivalent ones via sharing
four (1–2) or six (3) L ligands to generate a 3D structure. Thirdly,
compound 1 possessed one twofold interpenetrating 3D network
while 2–3 hold non-interpenetrating 3D structures. This suggests
that at lower temperatures the interpenetrating 3D structures of
1 may be not stable than the non-interpenetrating 3D networks
of 3 and may be converted directly into the structures of 3, which
was consistent with those reported previously [23]. Fourthly, com-
pounds 1–3 exhibited different crystal volume accessible to the
solvents of 1 (11.4%), 2 (0%) and 3 (13.4%), respectively. The differ-
ence between 1 and 2 indicated that solvent did work in the con-
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.11.021.
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