Synthesis, Crystal Structure, and Fluorescence Sensing Property in Water by a Two-Dimensional Cobalt Metal-Organic Framework

doi:10.16553/j.cnki.issn1000-985x.2025.0063

Abstract

Abstract: A new two-dimensional cobalt-based metal-organic framework （Co-MOF） with the formula ｛［Co（IPA）（TIB）］·2H₂O｝ _n， was successfully synthesized through solvothermal method using isophthalic acid （H₂IPA） and 1，3，5-tris（1-imidazolyl）benzene （TIB） as mixed ligands， and cobalt nitrate as metal source. Its crystal structure and properties were fully characterized by single-crystal X-ray diffraction （SCXRD）， powder X-ray diffraction （PXRD）， infrared spectroscopy （IR）， thermogravimetric analysis （TGA）， and fluorescence spectroscopy. The SCXRD determination reveals that the Co-MOF crystallizes in the monoclinic system with space group P2₁/c， and with the unit cell parameters of a=0.964 28（7） nm， b=1.282 98（10） nm， and c=1.783 32（14） nm. The asymmetric unit of Co-MOF contains a Co（Ⅱ） ion， a deprotonated IPA^2- anion ligand， a neutral TIB ligand， and two crystalline H₂O molecules. Notably， both IPA^2- and TIB ligands were observed to coordinate two Co²⁺ by a μ₂-η¹：η¹ bridging mode， forming a distorted tetrahedral CoN₂O₂ secondary building unit. These structural units were further interconnected via inversion-related IPA^2- and TIB ligands， resulting in a two-dimensional ladder-type framework. Topologically， the 2D network of Co-MOF can be simplified as a （4，4）-connected sql network with a Schläfli symbol of （4⁴.6²）. Furthermore， the adjacent 2D layers were extended to a three-dimensional supramolecular architecture with strong π-π stacking interactions between the symmetry-related imidazole rings of TIB ligand. The fluorescence investigations indicate that this Co-MOF exhibits high selectivity and sensitivity for detecting three polyoxoanions （Cr₂O₇^2-， CrO₄^2-， and S₂O₈^2-） and Fe³⁺ in aqueous solutions， with the calculated detection limits of 2.007×10^-4， 2.514×10^-4， 8.331×10^-4， and 2.709×10^-4 mol/L， respectively. The Co-MOF has excellent thermal stability and fluorescence sensing performance， which may be accounted for the presence of open metal sites and uncoordinated imidazole groups of TIB ligand. These combined characteristics suggest that the Co-MOF possesses significant potential for environmental pollutant detection applications.

Key words: cobalt（II） metal-organic framework; crystal structure; fluorescence sensing; quenching constant; polyoxoanion recognition; iron （Ⅲ） ion

CLC Number:

O641.4

CHEN Wentao, ZHUANG Xingyi, AN Hangyi, LAI Zhongjie, WANG Airong, LUO Yani, SHI Zhongfeng, LI Jiaming. Synthesis, Crystal Structure, and Fluorescence Sensing Property in Water by a Two-Dimensional Cobalt Metal-Organic Framework[J]. Journal of Synthetic Crystals, 2025, 54(9): 1642-1653.

Figures/Tables 15

Table 1 Crystallographic data parameters of Co-MOF

Complex	｛［Co（IPA）（TIB）］·2H₂O｝ _n
Empirical formula	C₂₃H₂₀CoN₆O₆
Formula weight	535.38
T/K	298.15
Crystal system	Monoclinic
Crystal size	0.520 mm×0.240 mm×0.120 mm
Space-group	P2₁/c
a/nm	0.964 28（7）
b/nm	1.282 98（10）
c/nm	1.783 32（14）
α/（°）	90
β/（°）	90.001（1）
γ/（°）	90
V/nm³	2.206 2（3）
Z	4
ρ_calc/（g·cm^-3）	1.612
μ/mm^-1	0.834
F（000）	1 100.0
2θ range for data collection/（°）	4.568 to 50.054
Index ranges	-10≤h≤11， -14≤k≤15， -13≤l≤21
Reflections collected	6 943
Independent reflections， R_int， R_sigma	3 797，0.030 8，0.048 3
Data/restraints/parameters	3 797/0/307
Goodness-of-fit on F²	1.035
R₁， wR₂ ［I≥2σ（I）］	0.041 7， 0.111 1
R₁， wR₂ ［all data］	0.056 2， 0.121 9
CCDC/ICSD	2434500

Table 2 Selected bond lengths and bond angles of Co-MOF

Bond	Length/nm	Bond	Angle/（°）
Co1—N6	0.201 5（3）	N6—Co1—O2	109.81（10）
Co1—O2	0.195 0（2）	N1^ⅱ—Co1—O2	117.01（11）
Co1—N1^ⅱ	0.203 0（3）	O3ⁱ—Co1—O2	119.10（9）
Co1—O3ⁱ	0.197 6（2）	O3ⁱ—Co1—N6	107.23（10）
Co1^ⅳ—N1	0.203 0（3）	O3ⁱ—Co1—N1^ⅱ	96.38（10）
Co1^ⅲ—O3	0.197 6（2）	N1^ⅱ—Co1—N6	105.86（10）

Table 3 Hydrogen bonds lengths and bond angles of Co-MOF

Bond	d（D—H）/nm	d（H…A）/nm	d（D…A）/nm	Angle/（°）
C3—H3…O4^ⅷ	0.093	0.242	0.313 3（5）	134
C20—H20…O1^ⅹ	0.093	0.243	0.325 5（5）	148
C13—H13…N4^ⅰ	0.093	0.254	0.344 2（4）	163

Fig 1 Coordination environment diagram of Co（Ⅱ） in Co-MOF （Symmetry codes：（i） -1+x， y， z；（ⅱ） x， 0.5-y， -0.5+z；（ⅲ） 1+x， y， z；（ⅳ） x， 0.5-y， 0.5+z）

Fig.2 2D network and view of topological diagram of Co-MOF

Fig.3 Stacking diagram of the complex. （a） 2D planar structure；（b） offset face-to-face π—π stacking interactions （symmetry codes：（v） -x， -0.5+y， 0.5-z；（vi） -x， -y， 1-z）；（c） 3D diagram of π—π stacking

Fig.4 XRD patterns and TGA pattern of Co-MOF

Fig.5 Solid state fluorescence spectra of H2IPA， TIB and Co-MOF

Fig.6 Fluorescence intensities of the complex in salt solutions containing anions and salt solutions containing cations

Fig.7 Fluorescence spectra of Co-MOF suspension changing with Cr2O72- concentration and the fluorescence quenching linearity relationship at low concentration

Fig.8 Fluorescence spectra of Co-MOF suspension changing with CrO42- concentration and the fluorescence quenching linearity relationship at low concentration

Fig.9 Fluorescence spectra of Co-MOF suspension changing with S2O82- concentration and the fluorescence quenching linearity relationship at low concentration

Fig.10 Fluorescence spectra of Co-MOF suspension changing with Fe3+ concentration and the fluorescence quenching linearity relationship at low concentration

Fig.11 Fluorescence intensity of Co-MOF after cycling with Cr2O72-， CrO42-， S2O82- and Fe3+

Fig.12 XRD patterns and FT-IR spectra after treatment with Cr2O72-， CrO42-， S2O82- and Fe3+

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