Hydrothermal syntheses, crystal structures, and Photoluminescent properties of two Entangled complexes with Rigid Bis(imidazolyl) ligands

Article abstract of DOI:10.1002/zaac.201300240

Two new entangled complexes, namely, [Zn(bibp)(L1)] (1) and [Co(bib)(L ²)]·H₂O (2) [bibp = 4,4-bis(1-imidazolyl)biphenyl, bib = 1,4-bis(1-imidazolyl)-benzene, H₂L¹ = 4,4-oxydibenzoic acid and H₂L2 = 4,4-(2,2-oxybis(ethane-2,1-diyl) bis(oxy))dibenzoic acid] were synthesized hydrothermally and characterized by IR spectroscopy, elemental analyses, and single crystal X-ray diffraction tech- niques. Complex 1 presents a uninodal 4-connected dmp net with fivefold interpenetration containing left- and right-handed single-helical (ZnL1)n chains. Complex 2 displays both polyrotaxane and polycatenane characteristics. Furthermore, thermogravimetric studies of 1 and 2 and photoluminescent property of 1 were also investigated.

Full text of DOI:10.1002/zaac.201300240

ARTICLE
DOI: 10.1002/zaac.201300240
Hydrothermal Syntheses, Crystal Structures, and Photoluminescent
Properties of Two Entangled Complexes with Rigid Bis(imidazolyl) Ligands
Yan Qi,[a] Yanhui Li,*[a] and Yue Wang[b]
Keywords: Rigid bis(imidazole) ligand; Interpenetration; Polyrotaxane; Polycatenane; Topology
Abstract. Two new entangled complexes, namely, [Zn(bibp)(L1)] (1)
and [Co(bib)(L2)]·H2O (2) [bibp = 4,4Ј-bis(1-imidazolyl)biphenyl, bib
= 1,4-bis(1-imidazolyl)-benzene, H2L1 = 4,4Ј-oxydibenzoic acid and
niques. Complex 1 presents a uninodal 4-connected dmp net with five-
fold interpenetration containing left- and right-handed single-helical
(ZnL1)n chains. Complex 2 displays both polyrotaxane and polycaten-
H2L2
= 4,4Ј-(2,2Ј-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid] ane characteristics. Furthermore, thermogravimetric studies of 1 and 2
were synthesized hydrothermally and characterized by IR spec-
troscopy, elemental analyses, and single crystal X-ray diffraction tech-
and photoluminescent property of 1 were also investigated.
acids, viz. 4,4Ј-oxydibenzoic acid (H2L1) and 4,4Ј-[2,2Ј-
oxybis(ethane-2,1-diyl)bis(oxy)]dibenzoic acid (H2L2) as co-
ligands, attributed to their diverse coordination modes and high
structural stability.[9a,10] Fortunately, two novel entangled com-
plexes [Zn(bibp)(L1)] (1) and [Co(bib)(L2)]·H2O (2) were suc-
cessfully isolated. The syntheses, structures, thermal and pho-
toluminescent studies in detail are listed below.
Introduction
Particular attention has been recently devoted to entangled
systems because of their undisputed beauty and potential appli-
cations as materials for gas storage, separation, and cataly-
sis.[1,2] There are some comprehensive reviews by Robson,
Batten, and Ciani’s groups of many fascinating entangled
structures, such as the common catenated arrays (for example,
interpenetration) and the more complex rotaxane-like species,
viz. polycatenated, polythreaded, and polyknotted species.[3–5]
Conceptually, interpenetrating networks can be described as a
number of individual nets participating in interpenetration with
each other. However, polycatenation differs from interpen-
etration in that the whole catenated array has a higher dimen-
sionality than that of the component motifs and that each indi-
vidual motif is catenated only with the surrounding ones and
not with all the others. To date, although some polycatenated
coordination polymers have been reported by us and other
groups,[6,7] the topological frameworks containing two kinds
of entangled motifs in one compound are still quite rare. Only
a few fascinating structures showing both polyrotaxane and
polycatenane characters have been observed.[8] In addition, the
exploration of coordination polymer with mixed ligands (esp.
N-ligands and carboxylate ligands) continues to attract con-
siderable interest.[9]
Results and Discussion
Structure Description
Single-crystal structure analysis reveals that complex 1 crys-
tallizes in the orthorhombic space group Pnna. The asymmet-
ric unit consists of one independent ZnII ion, one (L1)2– anion,
and one bibp ligand. As shown in Figure 1a, the ZnII ion is
coordinated by two (L1)2– oxygen atoms and two bibp nitrogen
atoms to give the distorted ZnO2N2 tetrahedral arrangement.
The Zn–O bond length is 1.967(3) Å and the Zn–N bond
length is 2.001(4) Å, both consistent with corresponding bond
lengths found in the literature.[11]
The completely deprotonated (L1)2– ligands (in which the
O3/O3Ј atoms are disordered) adopt cis conformation and con-
nect the adjacent ZnII ions to form 1D left- and right-handed
(ZnL1)n helical chains along b direction (Figure 1b) and the
pitch of the helices is 22.199 Å. A width of helical tube is ca.
8.18ϫ8.13 Å (the nearest distance between two opposite
atoms in the tube). Each bibp ligand connects two neighboring
central zinc atoms to give a zigzag chain. The overall 3D net
is formed by the intersection, at the shared zinc nodes, of the
1D bibp chains and the 1D L1 left- and right-handed helices.
An analysis by using TOPOS[12] indicates that the coordination
framework of 1 represents a uninodal 4-connected net with
Schläfli symbol: (65·8), the extended one being (6·6·6·6·62·85),
assigned to the unusual dmp net according to Wells’ classifica-
tion (Figure 1c). The reported dmp nets are limited only ob-
Taking inspiration from our previous work, our synthetic
strategy is to select rigid bis(imidazole) ligand, namely, 4,4Ј-
bis(1-imidazolyl)biphenyl (bibp) and 1,4-bis(1-imidazolyl)-
benzene (bib) as organic linkers and the flexible dicarboxylic
* Dr. Y. Li
Fax: +86-532-85953693
E-Mail: liyanhui@tsinghua.org.cn
[a] College of Electromechanical Engineering
Qingdao University
Qingdao city, P. R. China
[b] College of Chemistry and Environment
Qingdao University
Qingdao city, P. R. China
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Entangled Complexes with Rigid Bis(imidazolyl) Ligands
served in several compounds so far in the Reticular Chemistry
Structure Resource (RCSR) database.[13] Interestingly, such
five nets interpenetrate (Figure 1d). Also, it is noticeable that
the structure of 1 is completely different from another zinc
complex combined with the same mixed ligands, namely,
[Zn2(obba)2(bimb)2·(DMF)2·(H2O)3.5]n [H2obba = 4,4Ј-oxydi-
benzoic acid; bimb = 4,4Ј-bis(1-imidazolyl)biphenyl], which
exhibits a 3D chiral porous framework.[11]
Single crystal X-ray analysis reveals that complex 2 crys-
¯
tallizes in the triclinic space group P1. The asymmetric unit
consists of one independent CoII ion, one (L2)2– anion, one bib
ligand, and one free water molecule. As shown in Figure 2a,
each cobalt atom is coordinated by two (L2)2– oxygen atoms
and two bib nitrogen atoms to give a distorted CoO2N2 tetra-
hedral arrangement. The Co–O/N bond lengths range from
1.9550(17) to 2.049(2) Å, which are similar to those found in
other related cobalt complexes.[14]
The completely deprotonated (L2)2– ligands also adopt cis
conformation and connect the adjacent CoII ions to form 40-
membered Co2(L2)2 ring. Each bib ligand shows trans confor-
mation with dihedral angle of two imidazole rings being
27.19°. The extension of the structure into a 1D ladder-like
chain is accomplished by linear a pair of bib ligands linking
the Co2(L2)2 loops, as shown in Figure 2b. That is to say, each
cobalt atom is connected to three others: two via single bib
bridges and a third by pairs of (L2)2– anions. Of particular
interest, the most striking feature of complex 2 is that a pair
of identical 1D single nets is interlocked with each other in a
1DǞ2D parallel fashion thus directly leading to the formation
of a 2D polycatenane-like structure containing rotaxane-like
motifs (Figure 2c). As shown in Figure 2c, the Co2(L2)2 loops
of each net are threaded by two Co–bib–Co rods of the other
nets up and down, and vice versa. Therefore, the structure of
2 shows both polyrotaxane and polycatenane characteristics.
Thermogravimetry
To study the thermal stability of 1 and 2, thermogravimetric
analysis (TGA) was performed on the single crystal samples
of 1 and 2 in a nitrogen atmosphere with a heating rate of
5 °C·min–1 (Figure 3). Compound 2 lost the free water mo-
lecules at 65–150 °C (obsd. 2.95%, calcd. 2.85%) and the
frameworks of these compounds can be stable up to ca. 240 °C
for 1 and ca. 260 °C for 2. The resulting residue of compounds
1 and 2 remain as ZnO (calcd. 13.39%, found 14.72%) and
CoO (calcd. 11.86%, found 11.65%), respectively, after the
complete decomposition of the organic ligands.
Photoluminescence
Photoluminescence experiments for 1 were performed at
room temperature in the solid state. The emission bands for
the free rigid bibp ligand is demonstrated at 355 nm and
373 nm (λex = 280 nm) which can be assigned to the ligand-
centered πǞπ* transitions of the benzene-imidazole rings.[15]
Excitation of 1 at 330 nm produces one broad emission peak at
361 nm (Figure 4), probably be attributed to intraligand charge
Figure 1. (a). Coordination around the ZnII atom in 1. All hydrogen
atoms are omitted for clarity. (b) Perspective (left) and space-filling
(middle) views of the 1D [ZnL1]n helical chain and the tubular motif
shown by the helices, with the width being ca. 8.18ϫ8.13 Å (right).
(c) Schematic view of the 3D 4-connected dmp net in 1. (d) The
fivefold interpenetrating networks in 1.
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Y. Qi, Y. Li, Y. Wang
ARTICLE
Figure 3. TG curve of compounds 1 and 2.
Figure 4. Solid-state emission spectra of 1 at room temperature.
flexible aromatic dicarboxylate anions, both adopting cis con-
formations, plays a key role on the ultimate frameworks. In 2
cobalt atoms are coordinated to (L2)2– anions to form
Co2(L2)2 loops, while in 1 zinc ions are coordinated to aro-
matic dicarboxylate anions to form a pair of 1D left- and right-
handed (ZnL1)n helical chains. As expected, compound 1 dis-
plays photoluminescence property.
Figure 2. (a) Coordination around the CoII atom in 2. All hydrogen
atoms and water molecules are omitted for clarity. (b). Perspective
views of the 1D ladder-like chain containing Co2(L2)2 loops of 2. (c)
The schematic view of the polyrotaxane and polycatenane motifs in 2.
Experimental Section
transfer of the bibp ligand, because the ZnII ion is difficult to
oxidize or to reduce due to its d10 configuration.[9c,9d,10a]
Materials and General Procedures: Solvents and all the ligands (bib,
bibp, H2L1, and H2L2) for synthesis were purchased commercially and
used as received. . C, H and N analyses were performed with a Perkin-
Elmer 240 analyzer. The IR spectrum was recorded as KBr pellets
with a Nicolet Magna-FT-IR 560 spectrometer in the 4000–400 cm–1
region. The photoluminescence measurements were carried out on
crystalline samples at room temperature, and the spectra were collected
with a Hitachi F-2500FL spectrophotometer. The thermogravimetric
analyses were investigated with a standard TG analyzer in a nitrogen
Conclusions
Two new 3D entangled coordination complexes were suc-
cessfully isolated. Complex 1 presents a fivefold interpen-
etrated uninodal 4-connected dmp net. Complex 2 displays
both polyrotaxane and polycatenane characteristics. In 1 and 2 flow at a heating rate of 5 °C·min–1 for all measurements.
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Entangled Complexes with Rigid Bis(imidazolyl) Ligands
Synthesis of 1: A mixture of Zn(NO3)2·6H2O (297 mg, 1.0 mmol),
H2L1 (258 mg, 1.0 mmol), bibp (286 mg, 1.0 mmol), and water (8 mL)
was placed in a 25-ml Teflon-lined stainless steel vessel. Subsequently
the pH value was adjusted to 6.0 with 1 m NaOH solution, the mixture
was heated at 160 °C for 3 d, and the reaction system was cooled to
room temperature. Colorless crystals were obtained in yield 65%
(based on Zn). Elemental analysis for C64H44N8O10Zn2: calcd. C
63.22, H 3.65, N 9.22%; found C 63.25, H 3.63, N 9.28%. FT-IR
(KBr, selected bands): ν˜ = 1596 (s), 1548 (s), 1521 (s), 1386(s), 1235
(s), 1011 (s), 924 (s), 835 (s), 667 (m) cm–1.
Table 2. Selected bond lengths /Å and angles /° for complexes 1 and
2.
1
Zn(1)–O(1)#1
1.963(5)
Zn(1)–N(1)#1
2.011(3)
132.5(2)
O(1)#1–Zn(1)–O(1) 99.1(3)
N(1)–Zn(1)–N(1)#1 99.3(2)
O(1)#1–Zn(1)–N(1)
2
Co(1)–O(4)#2
Co(1)–N(4)
1.9550(17) Co(1)–O(2)
1.9574(17)
2.049(2)
2.035(2)
Co(1)–N(1)#3
O(2)–Co(1)–N(4)
122.52(7) O(4)#2–Co(1)–N(1)#3 119.48(8)
Synthesis of 2: A mixture of CoCl2·6H2O (238 mg, 1.0 mmol), H2L2
(350 mg, 1.0 mmol), bib (218 mg, 1.0 mmol), and water (8 mL) was
placed in a 25-ml Teflon-lined stainless steel vessel. The pH value was
adjusted to 6.0 with 1 m NaOH solution and the mixture was heated
at 160 °C for 3 d. Afterwards the reaction system was cooled to room
temperature. Purple crystals were obtained in yield 60% (based on
Co). Elemental analysis for C30H28CoN4O8: calcd. C 57.06, H 4.47, N
8.87%; found C 57.11, H 4.40, N 8.82%. FT-IR (KBr, selected
bands): ν˜ = 3421 (s), 1610 (s), 1532 (m), 1387 (s), 1304 (s), 1248 (s),
1139 (s), 1067 (s), 1139 (s), 1067 (s), 933(m), 829 (m), 781 (s), 656
(s) cm–1.
O(2)–Co(1)–N(1)#3 95.11(6)
O(4)#2–Co(1)–N(4) 97.93(6)
N(4)–Co(1)–N(1)#3
O(4)#2–Co(1)–O(2)
101.42(6)
120.38(7)
Symmetry transformations used to generate equivalent atoms: #1 x,
–y+1/2, –z+1/2 for 1; #2 –x+1, –y+1, –z+1, #3 x+1, y, z+1 for 2.
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Formula
Fw
Crystal system
Space group
a /Å
b /Å
c /Å
α /°
β /°
C64H44N8O10Zn2
1215.81
orthorhombic
Pnna
8.5510(17)
22.199(4)
14.867(3)
90
90
90
2822.1(9)
2
1.431
C30H28CoN4O8
631.49
triclinic
¯
P1
10.169(10)
11.891(9)
12.366(11)
92.341(15)
112.077(19)
92.860(7)
1381(2)
2
γ /°
V /Å3
Z
D /g·cm–3
T /K
1.519
293
654
293
1248
F(000)
Reflections collected / 24992 / 3237 R(int) = 14585 / 6480 R(int)
unique
GOF
R1, wR2 [IϾ2σ]
0.1181
1.034
R1 = 0.0655
wR2 = 0.1543
= 0.0341
1.075
R1 = 0.0335
wR2 = 0.0815
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CrystEngComm 2008, 10, 461–464.
Acknowledgements
This work was supported by the Natural Science Foundation of Shan-
dong Province (ZR2010BQ033) and Science and Technology Basic
Research Item of Qingdao City (12-1-4-2-(24)-jch).
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Y. Qi, Y. Li, Y. Wang
ARTICLE
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Received: May 9, 2013
Published Online: July 16, 2013
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Z. Anorg. Allg. Chem. 2013, 2258–2262