A new six-connected double-layer metal-organic framework directed by carboxylate and N-containing donor Co-ligands

Article abstract of DOI:10.1080/15533174.2011.591876

A new polymer, [Co(fipbb)(bpt).DMF]_n (1) (H₂fipbb = 4,4'- (hexafluoroisopropylidene)bis(benzoic acid) and bpt = 2,5-bis (4-pyridyl)-1,3,4-thiadiazole), has been synthesized and characterized. The polymer presents a two-dimensional (2D) bilayer structure containing dimeric [Co2(COO)4] units. In the 2D network, each Co(II) atom is coordinated by four carboxylate oxygen atoms from three different fipbb ligands and two nitrogen atoms from two bpt ligands. The thermogravimetric (TG) and magnetic properties of the compound are also discussed. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2011.591876

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:1240–1243, 2011
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591876
A New Six-Connected Double-Layer Metal-Organic
Framework Directed by Carboxylate and N-Containing
Donor Co-Ligands
Jian-Qiang Liu
Guangdong Medical College, School of Pharmacy, Dongguan, P. R. China
ring and two more potential N-donor atoms inducing flexible
A new polymer, [Co(fipbb)(bpt).DMF]n (1) (H2fipbb = 4,4ꢀ-
(hexafluoroisopropylidene)bis(benzoic acid) and bpt = 2,5-bis
(4-pyridyl)-1,3,4-thiadiazole), has been synthesized and character-
ized. The polymer presents a two-dimensional (2D) bilayer struc-
ture containing dimeric [Co2(COO)4] units. In the 2D network,
each Co(II) atom is coordinated by four carboxylate oxygen atoms
from three different fipbb ligands and two nitrogen atoms from two
bpt ligands. The thermogravimetric (TG) and magnetic properties
of the compound are also discussed.
coordination modes, which favor constructing unexpected, un-
predictable, and interesting frameworks.[8–10] In our previous
work, we demonstrated the role of secondary ligands on the
resultant MOFs.[8b] Herein, we report on having synthesized a
new compound of [Co(fipbb)(bpt).DMF]n (1), which presents a
two-dimensional (2D) bilayer structure containing ring dimeric
[Co2 (COO)4] units. Moreover, the thermogravimetric (TG) and
magnetic properties of the compound are also discussed.
Keywords bilayer, magnetism, metal-organic framework, structure
MATERIALS AND INSTRUMENTS
All reagents were purchased from commercial sources and
used as received. Infrared (IR) spectra were recorded with
a Perkin–Elmer Spectrum One spectrometer in the region
4000–400 cm−1 using KBr pellets. TGA were carried out with a
Metter–Toledo TA 50 in dry dinitrogen (60 mL min−1) at a heat-
ing rate of 5◦C min−1. X-ray powder diffraction (XRPD) data
were recorded on a Rigaku RU200 diffractometer at 60 kV, 300
mA, for Cu Kα radiation (λ = 1.5406 Å), with a scan speed of
2◦C/min and a step size of 0.02◦ in 2θ. Magnetic susceptibility
data of powdered samples restrained in parafilm was measured
on Oxford Maglab 2000 magnetic measurement system in the
temperature range 300–2 K and at field of 1 kOe. Diamagnetic
correction was applied using Pascal’s constant.[11]
INTRODUCTION
Synthesis and characterization of metal–organic frame-
works (MOFs) are of great current interest because of their
intriguing structures and potential applications on gas ad-
sorption/separation, microelectronics, nonlinear optics, ion ex-
change, heterogeneous catalysis, and so on.[1–5] In this regard,
MOFs on the basis of polycarboxylate connectors have been
widely focused on due to their versatile coordination capability
as well as their sensitivity to acidity of such building blocks,
which will be responsible for structural diversity of resulting
MOFs.[6] In contrast to the rigid organic carboxylate ligands,
the conformation of flexible ones is variable; thus, they can
meet the coordination geometrical requirement of metal ions
through changing their conformation, which may provide more
possibilities for the construction of novel architectures.[7] On
the other hand, as for the dipyridyl bridging ligands, some
analogous sets derived from the proper modification of the
classical 4,4ꢁ-bipyridine ligand have been employed. Unlike
the more commonly used tethering 4,4ꢁ-bipyridine ligand, 2,5-
bis(4-pyridyl)-1,3,4-thiadiazole(bpt) has an angular disposition
of its terminal pyridyl spacers because of its central thiadiazole
Synthesis of the Complex
To a mixture of DMF solution (5 mL) containing H2fipbb
(0.1 mmol) and bpt (0.1 mmol) was added Co(NO3)2·4H2O
(0.15 mmol) in water at 30◦C. The pH of the resulting solution
was adjusted to 5.5 using dilute NaOH (0.1 mol/L) and kept
at 160◦C for 96 h to prepare compound 1. From that solution,
pink crystals suitable for x-ray measurements were obtained.
Yield: 40%. Anal.: Calc. (%) for C32H23CoF6N8O5S: C, 50.46;
N, 9.02; H, 3.22. Found (%): C, 50.40; N, 9.18; H, 3.40. IR
(KBr cm−1): 2950 (w), 1688 (s), 1522 (w), 1460(s), 1195 (m),
866(m). CCDC: 800682.
Received 12 December 2010; accepted 16 February 2011.
This work was supported by the Guangdong Medical College.
Address correspondence to Jian-Qiang Liu, Guangdong Medical
College, School of Pharmacy, Dongguan 523808, P. R. China. E-mail:
jianqiangliu2010@126.com
RESULTS AND DISCUSSION
Compound 1 displays an interesting double-layer frame-
work. As shown in Figure 1, each distorted octahedral Co(II)
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NEW DOUBLE-LAYER MOF DIRECTED BY CO-LIGANDS
1241
TABLE 1
Crystallographic data for 1
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C32H23CoF6N8O5S
762.54
298(2)
0.71073
triclinic
P-1
a = 8.3070(9) Å
b = 13.6280(15) Å
c = 14.8286(15) Å
α = 86.2070(10)
β = 79.3410(10)◦
γ = 83.8640(10)
1638.4(3) Å3, 2
1.546
Unit cell dimensions
Volume, Z
Calculated density (kg/m3)
Crystal size (mm3)
0.26 × 0.20×0.13
2.01–25.22
8288
θ Range for data collection (◦)
Reflections collected
Independent reflection
Final R indices [I > 2σ (I)]
R indices (all data)
FIG. 1. The coordinated geometry of Co(II) ion in 1 (symmetry codes: i = x,
y, z + 1; ii = –x + 2, –y + 1, –z + 1, iii = x + 1, y – 1, z) (color figure available
online).
5751
R1 = 0.0489, wR2 = 0.1255
center is defined by four carboxylate oxygen atoms from three
different fipbb ligands and two nitrogen atoms from two bpt
ligands. The two carboxylate groups adopt bidentate chelating
and bridging bidentate modes. The Co–O distances fall in
R1 = 0.0635, wR2 = 0.1416
the range 2.011(2)–2.182(3) Å, and Co–N bond lengths are binuclear subunits and bpt ligands (Figure 4). The porous sizes
2.175(3)–2.178(3) Å (Table 1), similar to those in others Co- are 8.8 × 9.1 Å (window A) and 12.2×10.2 Å (window B),
carboxylate coordination polymers.[12] Each pair of Co(II) ions respectively. A calculation by PLATON indicates that the free
is connected by a pair of syn-syn fipbb carboxylate groups to volume of channels occupies 15% of the crystal volume.[14]
A
form a binuclear subunit, and these are doubly interlinked by the fascinating type of 2D → three-dimensional (3D) polythreaded
fipbb ligands into an infinite ribbon (Figure 2), which is similar motif with different side arms involving nine polymeric units at
to that observed in [Co(fipbb)(dpp)].MeOH.[13] The bpt ligand a time was directed by flexible dicarboxylate and bpt coligands
serves as double bridges connecting [Co(fipbb)]n ribbons into under mild condition.[15] A three-dimensional, microporous
2D (4,4) noninterpenetrating double layers with two kinds of MOF exhibiting reversible water adsorption is constructed from
windows when viewed along the crystallographic a axis (Figure hexagonal Co(II) atoms-dicarboxylate layers and N,Nꢁ-pillars
3). The 2D bilayer framework can also be considered as being of bpt ligands.[16]
constructed by two puckering layers of [Co(fipbb)(bpt)] linked
The temperature-dependent molar magnetic susceptibility of
by carboxylato groups of fipbb ligands. This structure is very 1 was measured at 1000 Oe in the range 2–300 K on a polycrys-
similar to that of the polymer of [Co(fipbb)(dpp)].MeOH.[13] talline powder sample (Figure 5). At room temperature, χMT
The lattice DMF molecule is located at void region. There exist is 12.19 cm3 mol−1 K, which is larger than the spin-only value
two windows porous. Window A is directed by two binuclear for S = 3/2, indicating the important orbital contribution arising
subunits and two fipbb ligands and window B consists of two from the high-spin Co(II).[17] χM−1 obeys the Curie–Weiss law
FIG. 2. View of the 1D ribbon chain along the bc plane (color figure available online).

1242
J.-Q. LIU
FIG. 5. Plots χMT and χM−1 of versus T for 1; solid lines represent fits to the
data.
ligands and indicates the network is thermally stable below these
temperatures. The pattern that was simulated from the single-
crystal X-ray data of compound 1 was in agreement with those
that were observed (Figure 7), which indicates that compound
1 was obtained as a single phase (minor differences can be seen
in the positions, intensities, and widths of some peaks).
FIG. 3. View of Co atoms interlinked by fipbb and bpt co-ligands to generate
a 2D bilayer network parallel to (100) plane (color figure available online).
with a Curie constant of 9.88 cm3 K mol−1 and a Weiss constant
of θ = −0.28 K. The negative θ value is indicative of a dominant
antiferromagnetic interaction between Co2+ centers.[18]
Crystallographic Data Collection and Structure
Determination
Single-crystal data were collected at 298(2) K on a
Compound 1 has stability in air and retains its crystalline Bruker Smart Apex II diffractometer equipped with graphite-
integrity at ambient conditions. Thermogravimetric analysis of monochromated Mo Kα radiation. The structure was solved
compound 1 shows loss of the DMF molecule (9.9%) within using direct methods and successive Fourier difference syn-
the temperature range of 35–255◦C (calcd. 9.5%) (Figure 6). thesis (SHELXS-97),[19] and was refined using the full-matrix
Further weight loss was observed in the range of 290–510◦C, least-squares method on F2 with anisotropic thermal parameters
which is in agreement with the removal of the fipbb and bpt for all nonhydrogen atoms (SHELXL-97).[20] Metal atoms in
FIG. 4. Schematic representation of the double-layer network (color figure available online).

NEW DOUBLE-LAYER MOF DIRECTED BY CO-LIGANDS
1243
TABLE 2
Selected bond lengths (Å) and angles (◦) for 1
Co1–O4#1a
Co1–O2
Co1–O3
Co1–N4#3
Co1–N1
Co1–O2
2.011(2)
2.184(2)
2.030(2)
2.175(3)
2.178(3)
2.184(2)
O4–Co1–O3
O3–Co1–N1
N1–Co1–N4
O4–Co1–O2
O2–Co1–N1
O3–Co1–O2
114.29(10)
90.24(10)
177.00(11)
155.98(10)
90.24(10)
88.95(9)
aSymmetry codes: #1: x, y, z + 1; #2: –x + 2, –y + 1, –z + 1; #3:
x + 1, y – 1, z.
data is given in Table 1. Selected bond distances and angles data
are given in Table 2.
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all the complexes were located from the E-maps and other non-
hydrogen atoms were located in successive difference Fourier
syntheses. All other hydrogen atoms were included in calculated
positions and refined with isotropic thermal parameters riding
on those of the parent atoms. A summary of the crystallographic

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