Two New Solvent-modulated Zinc(II) Metal-Organic Hybrid Materials based on Rigid Tripodal Carboxylate Ligand and 2,2′-Bipy Co-ligand: Crystal Structures and Luminescent Properties

Article abstract of DOI:10.1002/zaac.201500154

The zinc(II) coordination polymers [Zn(Htatb)(2,2′-bipy)·(NMP)·H₂O] (1) and [Zn₃(tatb)₂(2,2′-bipy)₃·H₂O] (2) (H₃tatb = 4,4′,4′′-s-triazine-2,4,6-triyl-tribenzoic acid; 2,2′-bipy = 2,2′-bipyridyl, NMP = N-methyl-2-pyrrolidon), were synthesized hydrothermally, and characterized by infrared spectroscopy (IR), powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. Both compounds 1 and 2 possess expectant low dimensional coordination structures, which further connected into interesting 3D networks by hydrogen bond and strong π-π interactions. Moreover, the thermal stabilities and fluorescent properties of 1 and 2 were investigated.

Full text of DOI:10.1002/zaac.201500154

Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500154
Two New Solvent-modulated Zinc(II) Metal-Organic Hybrid Materials based
on Rigid Tripodal Carboxylate Ligand and 2,2Ј-Bipy Co-ligand: Crystal
Structures and Luminescent Properties
Xiao-Bin Liu,[a] Zhen-Yu Xiao,[a] Ming-Hui Zhang,[a] Liang-Liang Zhang,[a]
Rong-Ming Wang,*[a] and Dao-Feng Sun[a]
Keywords: Low-dimensional coordination polymers; π–π Interactions; Zinc; Fluorescent properties
Abstract. The zinc(II) coordination polymers [Zn(Htatb)(2,2Ј-bipy) diffraction (PXRD), and single-crystal X-ray diffraction. Both com-
·(NMP)·H2O] (1) and [Zn3(tatb)2(2,2Ј-bipy)3·H2O] (2) (H3tatb =
4,4Ј,4ЈЈ-s-triazine-2,4,6-triyl-tribenzoic acid; 2,2Ј-bipy = 2,2Ј-bipyr-
idyl, NMP = N-methyl-2-pyrrolidon), were synthesized hydrother-
pounds 1 and 2 possess expectant low dimensional coordination struc-
tures, which further connected into interesting 3D networks by
hydrogen bond and strong π–π interactions. Moreover, the thermal sta-
mally, and characterized by infrared spectroscopy (IR), powder X-ray bilities and fluorescent properties of 1 and 2 were investigated.
bipy)3·H2O] (2) are reported. The thermal behaviors, luminescent
properties and inter-ligand π–π interaction motif were studied.
1 Introduction
Coordination polymers (CPs) as one kind of solid state ma-
terials have developed exponentially over the past few decades
in terms of both crystal engineering and supramolecular chem-
istry.[1–7] In the design and synthesis of such solid state materi-
2 Experimental Section
als with new structures and varying functionalities, organic 2.1 Materials and Measurements
multi-carboxylate linkers are widely used as bridging ligands
All the reagents and solvents employed were commercially available
due to the high thermal and chemical stabilities of the carb-
and used as received without further purification except H3tatb. Infra-
oxylate-metal fragment.[8–11] Among the family of organic
red spectra were recorded with a Bruker VERTEX-70 spectrometer as
KBr pellets in the frequency range 4000–400 cm–1. Elemental analyses
(C, H, and N) were determined with a CE instruments EA 1110 ana-
carboxylate, tri-angular carboxylate, especially H3tatb
(4,4Ј,4ЈЈ-s-triazine-2,4,6-triyl-tribenzoic acid), will remarkable
improve the thermal stability and enhance the hydrogen uptake lyzer. Photoluminescence measurements were performed with a Hita-
property, which has been proved by our group.[12] In tatb3–,
chi F-7000 fluorescence spectrophotometer with solid powder on a
1 cm quartz round plate. TG curves were measured from 40 to 900 °C
the three nitrogen atoms in the central triazine ring allow a
with a Mettler Toledo TGA instrument at a heating rate 10 K·min–1 in
nearly complete delocalization of π electrons and draw the
positively charged carbon atoms, which obviously strong
a nitrogen atmosphere (100 mL·min–1).
inter-ligand interaction and lead to those superiorities charac-
ter.[13–14] For this point, research and exploration of π–π inter-
action motif is necessary between tatb ligand to guide the syn-
thesis of subsequent tatb-based CPs. However, the reported
tatb-based CPs are all three-dimension framework by search-
2.2 Synthesis of H3tatb Ligand (4,4Ј,4ЈЈ-s-Triazine-2,4,6-
triyl-tribenzoic Acid) (H3tatb)
A 500 mL three-necked flask was charged with acetic acid (72.64 g),
H2SO4 (4.4 mL), and 4,4Ј,4Љ-s-triazine-2,4,6-tri-p-tolyl (2.783 g).
ing for CCDC database, which means that tatb molecular were
Chromium oxide (7.2 g) and acetic anhydride (4.8 mL) were added
not freedom on the process of self-assembling.[15] Therefore,
with stirring, carefully keeping the temperature below 50 °C
(Scheme 1). The resulting black-brown slurry was stirred overnight,
poured into cold water (300 mL), well mixed, and filtered. The solid
was washed with water and dissolved in 2 m NaOH solution (200 mL).
co-ligand, such as 2,2Ј-bipy ligands was employed by us as
blocking agent to synthesis tatb-based low dimensional CPs.
Herein, the syntheses and structures of the low dimensional
CPs [Zn(Htatb)(2,2Ј-bipy)·(NMP)·H2O] (1) and [Zn3(tatb)2(2,2Ј-
* Prof. Dr. R.-M. Wang
E-Mail: rmwang@upc.edu.cn
[a] College of Science
China University of Petroleum(East China)
Qingdao, 266580, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201500154 or from the au-
thor.
Scheme 1. Synthesis of H3tatb.
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After the unreacted starting material was removed by filtration, the
Table 1. Crystallographic data for 1 and 2.
solution was acidified with HCl to give crude product. Recrystalli-
zation from DMF gave pure product as white solid (yield: 95%). IR
(KBr): ν˜ = 2858 (w), 2546 (w), 1684 (s), 1583 (m), 1507 (vs), 1407
1
2
Formula
M
Crystal system
Space group
a /Å
b /Å
c /Å
α /°
β /°
C39H32ZnN6O8
778.08
triclinic
C78H53Zn3N12O13
1562.43
monoclinic
P2/c
25.7542(9)
8.8192(2)
38.2868(14)
90.00
121.123(2)
90.00
1
(m), 1360 (s), 1282 (vs), 1016 (m), 790 (s), 762 (vs) cm–1. H NMR
(300 MHz, [D6]DMSO): δ = 7.5 (d, 6 H), 8.7 (d, 6 H), 12.9 (br.,
3 H).[16]
¯
P1
8.6456(5)
12.5274(6)
17.6100(10)
110.576(5)
90.640(5)
93.301(5)
1781.63(17)
2
2.3 Synthesis of Complexes 1 and 2
[Zn(Htatb)(2,2Ј-bipy)·(NMP)·H2O] (1)
γ /°
A mixture of Zn(NO3)2·6H2O (23.5 mg, 0.079 mmol), 2,2Ј-bipy
(33.2 mg, 0.21 mmol), and H3tatb (11.7 mg, 0.027 mmol) was dis-
solved in NMP/H2O mixed solvent (7 mL, v/v = 1/1). All reagents
were sealed in a pressure-resistant glass tube and slowly heated to μ /mm–1
V /Å3
Z
7444.4(4)
4
1.394
D /g·cm–3
1.450
1.492
1.030
Rint
0.0366
1.047
0.0514, 0.1354
0.0774, 0.1531
0.0741
1.023
0.0875, 0.2514
0.1555, 0.3120
120 °C from room temperature in 500 min. After keeping at 120 °C
for 3000 min, the mixture was slowly cooled to 30 °C at a rate of
7 K·h–1. Afterwards, the yellowish block crystals were collected after
washed with acetone, and dried in air. (yield: 71%, based on zinc).
C39H32N6O8Zn: calcd. C 61.22 (found 60.15); H 4.08 (4.11); N 10.99
(10.80)%. IR (KBr): ν˜ = 3422 (s), 2032 (w), 1632 (m), 1560 (m),
1514 (m) cm–1.
GOF
a)
b)
R1 / wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
2
2 2
2 2 0.5
a) R1 = ∑||Fo|–|Fc||/∑|Fo|. b) wR2 = [∑w(Fo –Fc ) /∑w(Fo ) ]
.
and 2 (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk,
http://www.ccdc.cam.ac.uk)
[Zn3(tatb)2(2,2Ј-bipy)3·H2O] (2)
Supporting Information (see footnote on the first page of this article):
PXRD patterns and selected bond lengths and angles of complexes 1
and 2.
A
mixture of Zn(NO3)2·6H2O (112.9 mg, 0.38 mmol), 2,2Ј-
bipy(67.8 mg, 0.43 mmol), and H3tatb (13.2 mg, 0.03 mmol) was dis-
solved in DMF/EtOH/H2O mixed solvent (7 mL, v/v/v = 5/2/1). All
reagents were sealed in a pressure-resistant glass tube and slowly
heated to 120 °C from room temperature in 500 min. After keeping at
120 °C for 3000 min, the mixture was slowly cooled to 30 °C at a rate
of 7 K·h–1. Afterwards, the colorless transparent crystals were col-
lected after washed with acetone, and dried in air (yield: 67%, based
on zinc). C78H53N12O13Zn3: calcd. C 60.21 (found 59.92); H 3.52
(3.39); N 10.88 (10.76)%. IR (KBr): ν˜ = 3422 (s), 2330 (w), 2016
(w), 1624 (m),1407 (w), 1342 (w), 1124 (w), 1086 (w), 766 (w), 599
(w) cm–1.
3 Results and Discussion
3.1 Crystal Structure Descriptions
[Zn(Htatb)(2,2Ј-bipy)·(NMP)·H2O] (1)
Single-crystal X-ray diffraction analysis reveals that com-
plex 1 has a 1D chain structure, crystallizing in the triclinic
¯
P1 space group. The asymmetric unit in complex 1 contains
one crystallographic independent ZnII ion, one Htatb2– anion,
one 2,2Ј-bipy ligand, one coordinated water molecule, and one
uncoordinated NMP unit. As shown in Figure 1a, the ZnII ion
in 1 adopts a distorted trigonal bipyramidal arrangement. Each
ZnII ion is five-coordinated by two carboxylate oxygen atoms
from two different Htatb2– molecules, one oxygen atom from
coordinated water molecule, and two nitrogen atoms from
one chelating 2,2Ј-bipy ligand. The Zn–O and Zn–N
distances range from 1.999(1) to 2.197(2) Å, in the order
Zn–N Ͼ Zn–Ow Ͼ Zn–OHtatb, with the O(or N)–Zn–O(or N)
bond angles varying from 75.522(5)° to 168.787(6)°, which
are comparable to those of reported ZnII coordination poly-
mers.[18,19] The carboxylate ligands in complex 1 are partly
deprotonated, adopting a monodentate mode to link two dif-
ferent central ZnII atoms, coordinated water molecules and
2,2Ј-bipy occupy the left coordinated sites of the central metal
ions, which interrupts to construct high-dimensional architec-
ture. At last, the 1D infinite chains are further stacked into a
three-dimensional supramolecular framework through π–π
stacking and weak interactions.
2.4 X-ray Single-crystal Structure Determination
Single crystals of the complexes 1 and 2 with appropriate dimensions
were chosen under an optical microscope and quickly coated with high
vacuum grease (Dow Corning Corporation) before being mounted on
a glass fiber for data collection. Data for 1 and 2 were collected with
a SuperNova diffractometer equipped with a Molybdenum micro-focus
X-ray sources (λ = 0.71073 Å) and an Eos CCD detector under 293 K.
The data were collected with a ω-scan technique and an arbitrary φ-
angle. Data reduction was performed with the CrysAlisPro package,
and an analytical absorption correction was performed. The structures
were treated anisotropically, whereas the aromatic and hydroxyl
hydrogen atoms were placed in calculated, ideal positions and refined
as riding on their respective carbon or oxygen atoms. Structure was
examined using the Addsym subroutine of PLATON [17] to assure that
no additional symmetry could be applied to the models. Crystal data
and collection and parameters are summarized in Table 1, and selected
bond lengths and angles are given in Table S1 and Table S2 (Support-
ing Information).
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
[Zn3(tatb)2(2,2Ј-bipy)3·H2O] (2)
X-ray single-crystal diffraction reveals that complex 2 has a
2D wavy framework. Complex 2 crystallizes in the monoclinic
numbers CCDC-1054255 and CCDC-1054256 for complexes
1
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Figure 1. (a) Partial view of 1 with atom labeling of the asymmetric unit and metal coordination. (b) Perspective view of the Zn-tatb chain. (c)
Perspective view of the 2D layered framework extended through O–H···O hydrogen bonds. (d) The 3D supramolecular architecture by π···π
stacking interactions and different motif of π–π stacking.
P2/c space group. The asymmetrical unit of 2 contains three powder samples perhaps caused the dissimilarities in inten-
dependent ZnII atoms, two tatb3– anion, three 2,2Ј-bipy li- sity.[10]
gands, and one lattice water molecule. The Zn2 atom is five-
The thermal behavior of compounds 1 and 2 were studied
coordinated by three carboxylate oxygen atoms from three dif- by TGA in a nitrogen atmosphere with a heating rate of
ferent tatb3– molecules and two nitrogen atoms from one che- 10 K·min–1 (Figure 3). Complex 1 experienced a weight loss
lating 2,2Ј-bipy ligand, whereas Zn3 is six-coordinated by four of 3.69% below 150 °C corresponding to the release of the
carboxylate oxygen atoms from two different tatb3– molecules coordinated water molecules (calcd. 2.32%). Finally, the re-
and two nitrogen atoms from one chelating 2,2Ј-bipy ligand. moval of uncoordinated NMP molecules and the pyrolysis of
Zn1 is four-coordinated by three carboxylate oxygen atoms organic ligands occur in the range of 150 to 900 °C. For com-
from two different tatb3– molecules and two nitrogen atoms plex 2, there are only one obvious weight loss step with the
from one chelating 2,2Ј-bipy ligand (Figure 2). The Zn–O and 16.17% mass remnant corresponding to a deposition of ZnO
Zn–N distances range from 1.929(2) to 1.948(2) Å and (15.39%).
2.022(3) to 2.027(3) Å, respectively. The carboxylate group in
compound 2 adopts μ1-η1-η0 and μ1-η1-η1 bridging modes to
link different Zn2O4, ZnO4N2, and ZnO3N2 resulting in a
3.3 Photoluminescence Properties
It is reported that the luminescent properties of d10 transition
metal have attractive fluorescence properties and potential ap-
plications in multiple fields, such as photochemistry and chem-
ical sensors.[20,21] The luminescent properties emission spectra
of complexes 1 and 2 were examined in the solid state at room
wavy-like layer structure.
3.2 X-ray Power Diffraction Analyses and
Thermogravimetric Analyses
The X-ray powder diffraction patterns of samples were re- temperature, which is shown in Figure 4. The main emission
corded for checking the phase purities of 1 and 2 at room peak of free rigid tatb is at 407 nm (λex = 247 nm), which can
temperature. As shown in Figure S1 and Figure S2 (Supporting be assigned to the intra-ligand π–π* transitions. Excitation of
Information), the experimental patterns are in good agreement compound 1 and 2 at 247 nm produces two similar emission
with simulated patterns generated from the results of single- peak at 407 nm for 1 and 410 nm for 2, probably attributed to
crystal diffraction data, demonstrating the phase purity of the intra-ligand charge transfer of the tatb, because the ZnII is diffi-
product nicely. The preferred orientation of the crystalline cult to oxidize or to reduce due to its d10 configuration.[22]
Z. Anorg. Allg. Chem. 2015, 1781–1785
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Figure 2. (a) Molecular structure of 2 with atom labeling of the asymmetric unit. (b) View of the 2D layer completed by the ZnII ions and the
tatb anions. (c) View of the 2D Zn-tatb layer simplified through topology. (d) View of the 3D supramolecular structure and π···π stacking motifs
exist in the framework.
Figure 4. Solid-state fluorescence emissions recorded at room tem-
perature for complexes 1 and 2.
Figure 3. TGA curves for complexes 1 and 2.
4 Conclusions
of π–π interaction motifs were observed in the crystal struc-
Two ZnII coordination polymers based on 4,4Ј,4ЈЈ-s-triazine- tures of 1 and 2: the “Piedfort unit” and the “X-shape unit”.
2,4,6-triyl-tribenzoic acid (tatb) and N-donor co-ligand (2,2Ј- In the case of more freedom, the intensity of π–π interaction
bipy) were obtained. Complex 1 has a 1D zigzag-like chain of the “Piedfort unit” (3.47–3.50 Å) is not stronger than that
and 2 exhibits a 2D wave-like layer. To the best of our knowl- in reported 3D frameworks, and the “X-shape staking” motif
edge, complexes 1 and 2 are the first two low-dimensional was discovered, which did not exist in reported tatb-based
coordination polymers composed by tatb ligands. Two kinds structures.
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[11] K. S. Jeong, Y. B. Go, S. M. Shin, S. J. Lee, J. Kim, O. M. Yaghi,
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This work was supported by the National Natural Science Foundation
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