Zinc metal-organic frameworks based on a flexible benzylaminetetracarboxylic acid and bipyridine colinkers

Article abstract of DOI:10.1002/ejic.201402094

Three new metal-organic frameworks (MOFs), [Zn₂(L)(H ₂O)]·3DMF·1.5H₂O (1), [Zn ₂(L)(4,4-bpy)_1.5(H₂O)₂] ·2DMF·2H₂O (2), and [Zn₂(L)(2,2-bpy) ₂(DMF)₂]·2DMF·4H₂O (3) [H ₄L = 5,5-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene) bis(azanediyl)diisophthalic acid, 4,4-bpy = 4,4-bipyridine, 2,2-bpy = 2,2-bipyridine, DMF = N,N-dimethylformamide], were synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). The L^4- ligands in 1-3 display different coordination modes, and the introduction of bipyridine colinkers brings significant structural variation into the frameworks. Complex 1 is constructed from dinuclear carboxylate [Zn₂O(COO)₄] secondary building units (SBUs) and H₄L ligands and exhibits a binodal (4,4)-connected pts net with 54.6 % solvent-accessible void. Complex 2 exhibits an unprecedented tetranodal (3,4,4,4)-connected net, which is constructed from two types of crystallographically independent Zn^II ions, H₄L ligands, and the 4,4-bipyridine colinker. Complex 3 is constructed from parallel 1D molecular ladders stacked along the a axis that generate 1D channels (7.8 × 10.4 A?) and are hydrogen bonded to form 2D layers. The thermal stabilities and luminescence properties of 1-3 have also been studied in detail. Copyright

Full text of DOI:10.1002/ejic.201402094

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DOI:10.1002/ejic.201402094
Zinc Metal–Organic Frameworks Based on a Flexible
Benzylaminetetracarboxylic Acid and Bipyridine Colinkers
Chao Wang,[a,b] Sifu Tang,[a] Xiaoxia Lv,[c] Liangjun Li,[a,b] and
Xuebo Zhao*[a]
Keywords: Metal–organic frameworks / Zinc / Carboxylate ligands / Colinkers
Three new metal–organic frameworks (MOFs), [Zn2(L)-
(H2O)]·3DMF·1.5H2O (1), [Zn2(L)(4,4Ј-bpy)1.5(H2O)2]·2DMF·
2H2O (2), and [Zn2(L)(2,2Ј-bpy)2(DMF)2]·2DMF·4H2O (3)
tural variation into the frameworks. Complex 1 is constructed
from dinuclear carboxylate [Zn2O(COO)4] secondary build-
ing units (SBUs) and H4L ligands and exhibits a binodal (4,4)-
connected pts net with 54.6% solvent-accessible void. Com-
plex 2 exhibits an unprecedented tetranodal (3,4,4,4)-con-
nected net, which is constructed from two types of crystallo-
graphically independent ZnII ions, H4L ligands, and the 4,4Ј-
bipyridine colinker. Complex 3 is constructed from parallel
1D molecular ladders stacked along the a axis that generate
1D channels (7.8ϫ10.4 Å) and are hydrogen bonded to form
2D layers. The thermal stabilities and luminescence proper-
[H4L
= 5,5Ј-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methyl-
ene)bis(azanediyl)diisophthalic acid, 4,4Ј-bpy = 4,4Ј-bipyr-
idine, 2,2Ј-bpy = 2,2Ј-bipyridine, DMF = N,N-dimethylform-
amide], were synthesized under solvothermal conditions and
characterized by single-crystal X-ray diffraction analysis, el-
emental analysis, IR spectroscopy, powder X-ray diffraction
(PXRD), and thermogravimetric analysis (TGA). The L4– li-
gands in 1–3 display different coordination modes, and the
introduction of bipyridine colinkers brings significant struc- ties of 1–3 have also been studied in detail.
when coordinated to metal centers.[7] Generally, this flexibil-
ity in MOFs manifests two forms, that is, varied coordina-
tion geometries between the metal center and ligand or free
motion of the framework, such as reversible rotation and
bending.[7b,8] Additionally, the promising “mixed-ligand
strategy” has been widely used to design and construct
MOFs with desired and diverse structures and proper-
ties.[6c,6e,6f,9]
On the basis of these considerations, a benzylamine-
based tetracarboxylate ligand, 5,5Ј-(2,3,5,6-tetramethyl-1,4-
phenylene)bis(methylene)bis(azanediyl)diisophthalic acid
(H4L), has been designed and employed in the construction
of MOFs with various architectures. H4L has two terminal
isophthalic acid units linked by the central benzylamine
fragment. Four methyl groups are grafted onto the central
benzene ring to enhance the steric hindrance of the whole
ligand and ensure that the zygomorphic isophthalate groups
are roughly in the same plane. Bipyridine colinkers are
adopted to extend the structures constructed from ZnII ions
and H4L. We successfully applied the above strategy and
Introduction
From the concept of “nodes and spacers”[1] to the strat-
egy of “reticular chemistry”,[2] the feasibility of the fore-
sight design of metal–organic frameworks (MOFs) has es-
tablished a compelling rationale to target MOFs for specific
applications such as gas storage and separation, catalysis,
luminescence, sensing, microelectronics, and optics.[3] The
underlying structures obtained from given secondary build-
ing units (SBUs) with polytopic linkers can be analyzed
from the crystallographic and topological perspective.[4]
The selection of different metal centers and organic linkers
can give rise to considerable structural diversity.[5] Even for
a given metal center and ligand, the resulting MOFs can
possess varied structures and topologies under different re-
action conditions, such as reactant ratio and concentration,
pH value, solvent type and composition, and multiple li-
gand ratios.[6] Another strategy to achieve structural diver-
sity is the incorporation of flexible linkers into the frame-
work; thus, the linkers possess conformational freedom
[a] Qingdao Institute of Bioenergy and Bioprocess Technology, obtained three new MOFs, namely, [Zn2(L)(H2O)]·
Chinese Academy of Sciences,
3DMF·1.5H2O (1), [Zn2(L)(4,4Ј-bpy)1.5(H2O)2]·2DMF·
Shandong 266101, China
2H2O (2, 4,4Ј-bpy =4,4Ј-bipyridine, DMF = N,N-dimethyl-
formamide), and [Zn2(L)(2,2Ј-bpy)2(DMF)2]·2DMF·4H2O
(3, 2,2Ј-bpy = 2,2Ј-bipyridine). Their structures vary from
a 3D (4,4)-connected pts network to a 3D twofold-interpen-
etrated (3,4,4,4)-connected framework and a 2D layer.
Their syntheses, crystal structures, thermal stabilities, and
photoluminescence properties are reported herein.
E-mail: zhaoxb@qibebt.ac.cn
http://info.qibebt.cas.cn/hydrogen/6.htm
[b] University of Chinese Academy of Sciences,
Beijing, China
[c] School of Chemistry and Chemical Engineering, Qufu Normal
University,
Qufu, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402094.
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solvent-accessible void of 1 was calculated by PLATON[11]
analysis as 54.6% of the crystal volume (2670.4 out of the
4892.5 Å3 unit cell volume).
Results and Discussion
Structure of [Zn2(L)(H2O)]·3DMF·1.5H2O (1)
Complex 1 crystallizes in the monoclinic space group
C2/c, and the asymmetric unit contains one ZnII ion, half
of an L4– anion, and half of a bridging aqua ligand. The
ZnII ion is surrounded by four oxygen atoms from three
different carboxylate groups of three L4– ligands [Zn–O
1.912(3), 1.974(3), and 2.001(3) Å] and one terminal aqua
ligand [Zn–O 1.935(3) Å] to generate a distorted tetrahedral
coordination geometry (Figure 1, a). Two ZnII atoms are
connected by two carboxylate bridges from two different
L4– anions and one bridging oxygen atom to form a dinu-
clear carboxylate [Zn2O(COO)4] SBU [Zn···Zn 3.0005(8) Å;
Figure 1, b]. Each SBU bridges four L4– anions and serves
as a distorted 4-connected node. Each L4– ligand links six
ZnII ions with its four carboxylate groups, which are located
symmetrically around the center of the L4– ligand and dis-
play monodentate bridging and bidentate chelate coordina-
tion modes (Figure 1, c). Notably, the two isophthalate
units of the L4– ligand are almost parallel and form a
square-planar topological node (Figure 1, c). Thus, the
whole net of 1 can be rationalized as a binodal (4,4)-con-
nected pts net with the same (42·84) point symbols (Fig-
ure 1, d)[10] but with the different long vertex symbols of
[4.4.82.82.88.88] and [4.4.87.87.87.87] for L4– and the dinu-
clear SBU, respectively. The framework generated by the
construction of [Zn2O(COO)4] SBUs and L4– exhibits one-
dimensional (1D) channels along the crystallographic [10–
1] and [110] directions, respectively (Figure 1, e and f). The
Structure of [Zn2(L)(4,4Ј-bpy)1.5(H2O)2]·2DMF·2H2O (2)
Single-crystal X-ray diffraction analysis revealed that 2
¯
crystallizes in the triclinic space group P1, and the asymm-
etric unit consists of two ZnII ions (Zn1 and Zn2), one L4–
ligand, one and a half 4,4Ј-bpy ligands, and two coordi-
nated water molecules. The two crystallographically inde-
pendent ZnII ions, Zn1 and Zn2, are five- and four-coordi-
nate, respectively (Figure 2, a). Each Zn1 atom is five-coor-
dinate to two oxygen atoms from two L4– anions, two nitro-
gen atoms of two 4,4Ј-bpy molecules, and one aqua ligand
to form a trigonal-bipyramidal coordination geometry
[Zn1–N2 2.080(3), Zn1–O1 1.978(3), Zn1–O4i 1.969(3),
Zn1–N3 2.274(4), Zn1–O5 2.120(3)]. Similarly to Zn1, each
Zn2 atom is bonded to two L4– ligands, one H2O molecule,
and only one bpy ligand without the perpendicular bpy li-
gand that connects two layers [Zn2–N1 2.046(3), Zn2–O7
1.951(3), Zn2–O9ii 1.914(3), Zn2–O6 2.016(3); Figure 2, a].
Each L4– ligand links four Zn1 or Zn2 centers; the four
carboxylate groups are located symmetrically around the
center of the L4– ligand and all display a monodentate coor-
dination mode (Figure 2, b). Importantly, in the two crys-
tallographically independent L4– ligands, both isophthalate
units are almost parallel and form a square-planar topolog-
ical node, and the two types of L4– nodes combine with 4-
connected Zn1 and 3-connected Zn2 nodes to generate the
3D framework (Figure 2, c). From a topological point of
view, the resulting 3D net relies on the construction of tetra-
hedral Zn1, tetrahedral Zn2, and two types of square-
planar L4– building units, which serve as 3-, 4-, 4-, and 4-
connected nodes, respectively (Figure 2, b). Thus, the whole
3D framework can be rationalized as a new 4-nodal
(3,4,4,4)-connected net (Figure 2, c) with the Schläfli sym-
bol (4·62)(4·64·8)(42·64·82).
A detailed analysis shows that the framework structure
of 2 is twofold-interpenetrated and consists of two identical
crystallographically independent networks. For a single net-
work, each 2D layer is linked to the adjacent layers by bpy
linkers and is offset from two adjacent layers, which results
in the loss of porosity along the b axis (Figure 2, d and e).
The two networks are related to each other by a translation
of 14.72 Å along the b axis. Each single network consists of
infinite honeycomb 2D layers with hexagonal cavities,
which consist of a chain of ZnII ions bridged by L4– and
bpy linkers (Figure 2, f). The layers are further connected
by bpy linkers through Zn–N bonding interactions to form
a three-dimensional (3D) coordination network with the
brick-wall motif (Figure 2, g). Despite the unexpected oc-
currence of twofold interpenetration, complex 2 still pos-
sesses a solvent-accessible void space, calculated to be
761.1 Å3 by PLATON,[11] that is, 29.7% of the lattice vol-
Figure 1. (a) The coordination environment of the ZnII atoms in 1
[symmetry codes: (i) x – 1/2, y + 1/2, z; (ii) –x, y, –z + 1/2]. (b)
[Zn2O(COO)4] SBU in 1. (c) [Zn2O(COO)4] SBU and L4– ligand as
tetrahedral and square-planar 4-connected nodes, respectively. (d)
(4,4)-connected pts net topology in 1. (e,f) Channels along the crys-
tallographic [10–1] and [110] directions, respectively.
ume. In addition, the 3D framework is reinforced by Owater
–
H···Ocarboxylate, CL4––H···Ocarboxylate, Cbpy–H···Ocarboxylate
,
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gular cavity in the ladder is 7.8ϫ10.4 Å2 and is constructed
from two Zn2+ ions (Zn···Zn 16.862 Å) and two L4– ligands.
The shortest Zn···Zn distance along the b axis is 10.197 Å.
Interestingly, the ladders are connected to form 2D layers
through Cbpy–H···Ocarboxylate hydrogen bonds, which pro-
vide additional stability to the structure (Figure 3, d and
Table S3). The lattice water and DMF molecules occupy the
cavities within the ladders and interact with the framework
through hydrogen bonds. In addition, intermolecular
hydrogen bonds are also observed in the framework (Table
S3).
Figure 3. (a) The coordination environments of the ZnII ions in 3
[symmetry code: (i) x, y – 1, z]. (b) 1D molecular ladders along the
b axis and 1D channels along the a axis. (c) The parallel 1D molec-
ular ladders stacked along the a axis. (d) The 2D layer constructed
from 1D ladders through hydrogen bonds (green lines represent
hydrogen bonds).
Figure 2. (a) The coordination environments of the ZnII ions in 2
[symmetry codes: (i) x – 1, y, z; (ii) x + 1, y, z]. (b) Four types of
node in 2. (c) (3,4,4,4)-connected net topology in 2. (d,e) Adjacent
layers of a single network viewed along the b and a axes, respec-
tively. (f) Simplified adjacent layers of the two independent net-
works viewed along the b axis. (g) Simplified view of the two inde-
pendent networks in 2.
Configurations of L4–, Coordination Modes, and Effects of
Bipyridine Colinkers
and CL4––H···NL4– hydrogen bonds [2.629(4) to 3.295(7) Å]
among coordinated water molecules, L4– ligands, 4,4Ј-bpy
ligands, and carboxylate groups (Table S2).
With the introduction and variation of the auxiliary li-
gand, the tetracarboxylate ligand H4L shows different coor-
dination modes and three new MOFs with different struc-
tures are formed. In 1, dinuclear carboxylate [Zn2O-
(COO)4] SBUs are formed as the four carboxylate groups
Structure of [Zn2(L)(2,2Ј-bpy)2(DMF)2]·2DMF·4H2O (3)
In comparison to that of 2, the framework structure of of L4– link six ZnII ions through a mixed bridging-bidentate
3 shows some crystallographic similarities. Complex 3 also and monodentate coordination mode (Figure 4). In 2, the
crystallizes in the triclinic space group P1, and the asym- pyridyl N atoms of 4,4Ј-bpy replace some of the coordina-
¯
metric unit consists of one ZnII ion (Zn1), half of an L4– tion sites previously occupied by the L4– ligand, which re-
ligand, one 2,2Ј-bpy ligand, and one coordinated DMF mo- sults in the μ4-O,OЈ,OЈЈ,OЈЈЈ coordination mode. Further-
lecule. Each Zn2+ ion is six-coordinate through binding to more, the lengthened asymmetric unit leads to the emer-
the O and N atoms from one chelated carboxylate group, gence of the twofold-interpenetrated framework. In 3, both
one monodentate carboxylate group, one chelate 2,2Ј-bpy N atoms of one 2,2Ј-bpy ligand participate in the coordina-
ligand, and one DMF molecule to form a distorted octa- tion to the ZnII ions and inhibit the growth of the network
hedral geometry (Figure 3, a). Complex 3 is assembled from to a higher dimensionality. The L4– ligand in 3 presents two
1D molecular ladders that generate 1D channels (Figure 3, types of coordination mode, namely, monodentate and che-
b). The ZnII ions are linked by L4– ions to generate a 1D lating-bidentate. By comparison, we found that the intro-
ladder-type structure that is elongated along the b axis, and duction of different bipyridine colinkers can thoroughly
all of the 1D molecular ladders are stacked in a parallel change the whole structure of the MOF, including the coor-
way (Figure 3, c). The distance between two adjacent 1D dination mode, dimensionality, and number of independent
molecular ladders along the b axis is 9.000 Å. Each rectan- networks.
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Figure 4. Coordination modes of the L4– ligands in 1–3.
The flexible –CH2NH– spacer can give rise to various
configurations in MOFs.[12i] However, the four methyl
groups grafted onto the central benzene ring effectively en-
hance the steric hindrance of the whole ligand and result in
a similar configuration of the L4– ligands in 1–3, that is, the
zygomorphic isophthalate groups are roughly in the same
Figure 5. TGA profiles of 1–3.
Luminescence Properties
The photoluminescence properties of the Zn-based
plane. Despite a higher steric hindrance in the L4– ligand, MOFs have been widely studied, in consideration of their
the whole framework still possess some degree of flexibility potential applications as functional luminescent materi-
owing to the rotatable –CH2NH– spacer. Specifically, the als.[12,9d] The photoluminescence spectra of solid samples of
plane angles between the terminal benzene rings and the ligands H4L, 2,2Ј-bpy, and 4,4Ј-bpy and complexes 1–3
central one of the L4– ligands in 1–3 shows certain differ- were investigated at ambient temperature in the visible re-
ences and are 84.908° for 1, 83.240 and 80.664° for 2, and gion (Figure 6 and Table S4). For the free ligands H4L, 2,2Ј-
78.055° for 3. Furthermore, the –CH2–NH– angles also ex- bpy, and 4,4Ј-bpy, emission peaks were observed at 452 (λex
hibit differences for 1–3 (Table S1).
= 340 nm), 544 (λex = 340 nm), and 429 nm (λex = 346 nm),
respectively, and are attributed to the π*Ǟπ or π*Ǟn tran-
sitions. Compared with those of the free ligands H4L, 2,2Ј-
bpy, and 4,4Ј-bpy, apparent blue- or redshifts of the emis-
sion bands for 1–3 can be observed, and the maximum
emission wavelengths are 420 nm (λex = 350 nm) for 1,
602 nm (λex = 380 nm) for 2, and 524 nm (λex = 334 nm)
for 3. The emission of 1 is tentatively assigned to the intrali-
gand transition of the L4– ligand, whereas the emissions of
2 and 3 may be a mixture with characteristics of intraligand
and ligand-to-ligand charge transfer (LLCT) transitions, as
the ZnII ion is difficult to oxidize or reduce owing to its d10
configuration.[13,12g] The observed red- or blueshift of the
emission maxima between the complexes and ligands are
considered to mainly arise from the different coordination
Thermal Analyses
To investigate the thermal stabilities of 1–3, thermogravi-
metric analysis (TGA) was performed under a N2 atmo-
sphere, and the TGA profiles are shown in Figure 5. For 1,
the TGA profile shows a weight loss between 30 and 96 °C,
which is attributed to the loss of one and a half lattice water
molecules (found/calcd. 2.82/2.96%). The second weight
loss step between 96 and 270 °C corresponds to the loss of
three lattice DMF molecules (found/calcd. 25.5/24.0%); the
subsequent weight loss between 270 and 404 °C (8.59%) is
due to the partial decompositions of the framework. Above
404 °C, complex 1 starts to decompose rapidly. For 2, the
TGA profile shows a multistep weight loss between 30 and
145 °C on account of the loss of two lattice water molecules,
two DMF molecules, and two coordinated water molecules
(found/calcd 18.7/19.2%). The framework is stable to
257 °C with a minor weight loss (2.8%). Another weight
loss step between 257 and 425 °C (9.2%) corresponds to the
partial decomposition of the L4– and bpy ligands. Above
425 °C, complex 2 starts to decompose rapidly. The TGA
profile of 3 shows a multistep weight loss between 30 and
199 °C, which corresponds to the loss of four lattice water
molecules, two lattice DMF molecules, and two coordinated
DMF molecules, followed by a gradual weight loss between
199 and 250 °C. Above 250 °C, complex 3 starts to decom-
pose rapidly. All of the complexes formed white zinc oxide
powder after the TGA analyses.
Figure 6. Solid-state emission spectra of 2,2Ј-bpy, 4,4Ј-bpy, H4L,
and 1–3.
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modes of the ligands to the ZnII ions and the coordination
environments around the ZnII ions. The redshift of the
emission band for 2 compared with those of 1 and 3 might
be ascribed to the employment of the 4,4Ј-bpy linker, which
can expand the π-conjugation system and consequently en-
hance the delocalization of electron density from the ligand
to the metal and reduce the energy gap between the π*–π
molecular orbital of the ligands.
and then heated to 95 °C for 12 h. After that, deionized water
(100 mL) was added to the above solution. The resulting product
was collected by filtration, washed with deionized water, and air-
dried at 65 °C (26.50 g, 83%).
Tetraethyl 5,5Ј-(2,3,5,6-Tetramethyl-1,4-phenylene)bis(methylene)-
bis(azanediyl)diisophthalate [(Et)4L]: Diethyl 5-aminoisophthalate
(7.12 g, 0.03 mol) was dissolved in acetonitrile (100 mL), followed
by the addition of K2CO3 (5.53 g, 0.04 mol). Then, the solution
was cooled to less than 10 °C in an ice–water bath prior to the
dropwise addition of 1,4-bis(bromomethyl)-2,3,5,6-tetrameth-
ylbenzene (4.80 g, 0.015 mol, in 150 mL acetonitrile). After the ad-
dition, the solution was kept below 10 °C for 1 h and stirred for
16 h at room temperature. The solvent was removed under vacuum.
After that, the crude product was extracted with CHCl3 and
washed with H2O several times. The organic layer was then dried
with Na2SO4, and the solvent was removed with a rotary evapora-
tor. The resulting product was dried under vacuum at 65 °C (6.20 g,
65%). 1H NMR (600 MHz, CDCl3): δ = 8.05 (s, 2 H), 7.50 (s, 4
H), 4.40 (m, 8 H), 4.34 (d, 4 H), 3.76 (s, 2 H), 2.32 (s, 12 H), 1.41
(t, 12 H) ppm.
Conclusions
Three new zinc metal–organic frameworks constructed
from a flexible benzylaminetetracarboxylic acid and bipyr-
idine colinkers have been successfully obtained under solvo-
thermal conditions. With the introduction of different bi-
pyridine colinkers, complexes 1–3 display diverse structural
features including a 3D (4,4)-connected pts network con-
structed from [Zn2O(COO)4] SBUs (1), a new twofold-inter-
penetrated (3,4,4,5)-connected framework (2), and a 2D
layer constructed from 1D molecular ladders through
hydrogen bonds (3). The various coordination modes of the
L4– anion reveal that the presence of bipyridine colinkers
greatly influences the construction of coordination com-
plexes. The diverse structural features also engender dif-
ferent photoluminescence properties.
5,5Ј-(2,3,5,6-Tetramethyl-1,4-phenylene)bis(methylene)bis(azane-
diyl)diisophthalic Acid (H4L): A NaOH (2 m) aqueous solution
(150 mL) was added to a solution of (Et)4L (6.20 g, 0.0098 mmol)
in methanol/tetrahydrofuran (MeOH/THF, 1:1 v/v; 200 mL), and
the solution was stirred under reflux for 24 h at 100 °C. The organic
solvent was removed with a rotary evaporator at 65 °C. The pH
value was adjusted to 3–4 with concentrated HCl, and a large
amount of pale yellow precipitated appeared. The resulting solu-
tion was cooled overnight at 5 °C. The resulting pale yellow precipi-
tated was collected by filtration, washed with water and diethyl
ether, and then dried under vacuum at 65 °C (4.85 g, 95%). 1H
NMR [600 MHz, (CD3)2SO]: δ = 12.96 (s, 4 H), 7.73 (s, 2 H), 7.49
(d, 2 H), 6.11 (s, 2 H), 4.19 (s, 4 H), 2.25 (s, 12 H) ppm. IR (KBr):
Experimental Section
Materials and Methods: All reagents and solvents were commer-
cially available and used without further purification. The 1H
ν = 3409 (b), 2923 (w), 1711 (w), 1682 (m), 1606 (s), 1508 (w), 1428
˜
NMR spectra were recorded with
a Bruker AVANCE III
(w), 1382 (w), 1297 (w), 1262 (m), 1210 (w), 1096 (w), 992 (w), 798
(600 MHz) spectrophotometer. The elemental analyses for C, H,
and N were performed with an Elementar Vario EL III elemental
analyzer. The infrared (IR) spectra were acquired with a Thermo
Fisher Nicolet 6700 FTIR spectrometer. The powder X-ray diffrac-
tion (PXRD) measurements were performed with a Bruker AXS
D8 Advance θ/2θ diffractometer equipped with a Cu-Kα radiation
source (λ = 1.5418 Å) at a scan speed of 2°min–1 and a step size
of 0.02° in 2θ at room temperature. The thermogravimetric analyses
(TGA) were performed in the temperature range 30–800 °C with a
NETZSCH STA449 F3 TG-DSC analyzer under a flow of nitrogen
(20 mLmin–1) at a ramp rate of 10 °Cmin–1. The luminescence
spectra of the solid samples were recorded with a HORIBA Jobin
Yvon FluoroMax-4 fluorescence spectrometer.
(w), 762 (m), 674 (m) cm–1.
[Zn2(L)(H2O)]·3DMF·1.5H2O (1): A mixture of Zn(NO3)·6H2O
(0.059 g, 0.2 mmol), H4L (0.052 g, 0.1 mmol), H2O (2 mL), and
DMF (10 mL) was stirred for 30 min in air. The solution was
placed in a Teflon-lined stainless steel vessel (25 mL), which was
sealed and heated to 100 °C for 24 h. Cooling the vessel to room
temperature gave colorless crystals (0.031 g), yield 34% (based on
Zn). C37H51N5O13.5Zn2 (912.64): calcd. C 48.69, H 5.63, N 7.67;
found C 48.45, H 5.54, N 7.79. IR (KBr): ν = 3424 (b), 2927 (w),
˜
1659 (s), 1578 (s), 1497 (w), 1420 (m), 1384 (m), 1282 (w), 1249
(w), 1142 (w), 1099 (m), 1064 (w), 1024 (w), 997 (w), 840 (w), 780
(s), 727 (s), 662 (w) cm–1.
Diethyl 5-Aminoisophthalate: 5-Aminoisophthalic acid (18.12 g,
0.1 mol) was dissolved in ethanol (200 mL), and then concentrated
H2SO4 (20 mL) was added. After that, the solution was stirred un-
der reflux for 12 h at 100 °C. The pH value was adjusted to 7.0 by
using 10 wt.-% Na2CO3 aqueous solution, and the solution was
filtered. The solvent was removed from the filtrate with a rotary
evaporator, and the crude product was extracted with diethyl ether.
The organic layer was then dried with Na2SO4, and the solvent was
removed with a rotary evaporator. The resulting product was dried
under vacuum at 65 °C (19.50 g, 82%).
[Zn2(L)(4,4Ј-bpy)1.5(H2O)2]·2DMF·2H2O (2):
A
mixture of
Zn(NO3)·6H2O (0.059 g, 0.2 mmol), H4L (0.052 g, 0.1 mmol), 4,4Ј-
bipyridine (0.016 g, 0.1 mmol), H2O (3 mL), and DMF (9 mL) was
stirred for 30 min in air. The solution was placed in a Teflon-lined
stainless steel vessel (25 mL), which was sealed and heated to
100 °C for 24 h. Yellow plate crystals of 2 were collected (0.056 g)
in 51% yield (based on Zn). C49H56N7O14Zn2 (1097.83): calcd. C
53.61, H 5.14, N 8.93; found C 53.72, H 5.20, N 8.78. IR (KBr): ν
˜
= 3424 (b), 2925 (w), 1672 (s), 1611 (m), 1564 (s), 1492 (m), 1421
(m), 1384 (s), 1323 (w) 1280 (w) 1254 (w) 1227 (m) 1143 (w) 1093
(m) 1072 (m) 1046 (w) 1013 (w) 817 (m) 782 (s) 732 (s) 662 (w) 638
(m) cm–1.
1,4-Bis(bromomethyl)-2,3,5,6-tetramethylbenzene:
1,2,4,5-Tetra-
methylbenzene (13.44 g, 0.1 mol) and paraformaldehyde (6.00 g,
0.2 mol) were added to an aqueous solution (60 mL) of HBr/HOAc
(33 wt.-%), and the mixture was stirred at 85 °C till a white solid
precipitate was observed. The solution was kept at 85 °C for 20 min
[Zn2(L)(2,2Ј-bpy)2(DMF)2]·2DMF·4H2O (3): The preparation of 3
was similar to that of 2, except that 2,2Ј-bipyridine (0.016 g,
0.1 mmol) was used instead of 4,4Ј-bipyridine. Yellow plate crystals
Eur. J. Inorg. Chem. 2014, 3133–3139
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FULL PAPER
Table 1. Crystal data and structure refinements for 1–3.
Complex 1
Complex 2
Complex 3
Empirical formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C14H13NO4.50Zn
332.62
173(2)
0.71073
monoclinic
C2/c
15.8430(9)
11.3621(6)
28.2091(18)
90
105.531(2)
90
4892.5(5)
8
C43H38N5O10Zn2
915.52
293(2)
C30H38N5O8Zn
662.02
173(2)
0.71073
triclinic
0.71073
triclinic
¯
¯
P1
P1
9.572(2)
9.000(3)
10.197(3)
18.109(4)
100.459(7)
90.851(9)
106.781(8)
1560.7(7)
2
14.718(4)
19.571(5)
73.658(3)
77.093(3)
80.260(3)
2562.2(11)
2
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
0.903
1.187
0.988
1.409
0.844
Absorption coefficient [mm–1] 1.013
F(000)
1360
942
694
Crystal size [mm]
θ range for data collection [°]
Limiting indices
0.10ϫ0.10ϫ0.10
3.41 to 25.00
–18ϽhϽ18
–13ϽkϽ13
–33ϽlϽ33
0.20ϫ0.20ϫ0.10
2.03 to 25.00
–11ϽhϽ11
–17ϽkϽ16
–23ϽlϽ23
17944/8867 [R(int) = 0.0600]
98.1
0.26ϫ0.24ϫ0.20
1.15 to 27.52
–11ϽhϽ11,
–13ϽkϽ12,
0ϽlϽ23
4901/4901 [R(int) = 0.0000]
67.1
Reflections collected/unique
Completeness to θ = 25.00 [%] 98.3
16575/4244 [R(int) = 0.0498]
Absorption correction
Max. and min. transmission
Refinement method
semi-empirical from equivalents semi-empirical from equivalents semi-empirical from equivalents
0.9055 and 0.9055
full-matrix least squares on F2
4244/6/187
0.9076 and 0.8268
full-matrix least squares on F2
8867/4/546
0.8493 and 0.8104
full-matrix least squares on F2
4901/13/364
Data/restraints/parameters
Goodness-of-fit on F2
0.971
1.083
1.049
R1,[a] wR2[b] [IϾ2σ(I)]
0.0553, 0.1453
0.0846, 0.1591
0.0611, 0.1054
0.0964, 0.1132
1.188, –0.767
0.0767, 0.2101
0.1037, 0.2398
0.773, –0.647
[b]
R1,[a] wR2 (all data)
Largest diff. peak, hole [eÅ–3] 0.613, –0.415
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2
.
of 3 were collected (0.050 g) in 38% yield (based on Zn).
C60H76N10O16Zn2 (1324.04): calcd. C 54.42, H 5.79, N 10.58; found
Acknowledgments
C 53.37, H 5.68, N 10.44. IR (KBr): ν = 3431 (b), 2926 (w), 1660
˜
This work was supported by grants from the National Natural Sci-
ence Foundation of China (NSFC) (grant numbers 21073216 and
21173246) and the “Hundred-talent Project” (grant number
KJCX2-YW-W34) of the Chinese Academy of Sciences.
(s), 1621 (s), 1579 (m), 1494 (w), 1474 (w), 1442 (w), 1416 (w), 1386
(w), 1364 (w), 1257 (w), 1100 (m), 1059 (w), 1022 (w), 780 (s), 769
(s), 736 (w), 721 (w), 661 (w) cm–1.
Crystallography: The single-crystal X-ray diffraction data were col-
lected with a Bruker Smart CCD diffractometer by using thr ω-
scan method with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) at 293 K. Absorption corrections were applied by using
the multiscan technique. The structures were solved by direct meth-
ods and developed by difference Fourier techniques with the
SHELXTL software package.[14] The SQUEEZE routine im-
plemented in PLATON[15] was used to remove the highly disor-
dered guest molecules in 1 and 2. The crystal data as well as details
of the data collection and refinement for 1–3 are summarized in
Table 1, and selected bond lengths and angles are given in Table
S1.
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: February 22, 2014
Published Online: June 3, 2014
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