Co−MOFs with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) and aromatic carboxylates as coligands: synthesis, structure, and spectroscopic and thermal characterizations
Creators: name: Li, Xia
name: Ruiying Wang
name: Zhao, Hong
name: Benlai Wu
Publisher: name: Taylor & Francis
Year: 2016
Subjects: subject: Biophysics
subject: Biochemistry
subject: 29999 Physical Sciences not elsewhere classified
subject: FOS: Physical sciences
subject: FOS: Physical sciences
subject: Cell Biology
subject: Molecular Biology
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: 69999 Biological Sciences not elsewhere classified
subject: FOS: Biological sciences
subject: FOS: Biological sciences

description: Four cobalt(II) compounds, [Co(Bim)(IA)(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub>·0.5nH<sub>2</sub>O (<b>1</b>), [Co(Bim)(MA)(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub> (<b>2</b>), [Co<sub>2</sub>(Bim)<sub>2</sub>(MA)<sub>2</sub>]<sub><i>n</i></sub>·nH<sub>2</sub>O (<b>3</b>), and [Co<sub>3</sub>(Bim)<sub>4</sub>(TA)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub>·2.5nH<sub>2</sub>O (<b>4</b>), have been synthesized by solvothermal reactions of cobalt(II) salts with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) [Bim] and aromatic polycarboxylic acids (H<sub>2</sub>IA = isophthalic acid, H<sub>2</sub>MA = 5-methylisophthalic acid, and H<sub>3</sub>TA = trimesic acid) as coligands. The four complexes were characterized by IR and UV−vis spectra, elemental analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses (TGAs). <b>1</b> features a zigzag polymeric macrocycle chain containing a nanotubular channel, which is constructed by bridging the folded 20-membered macrocyclic [Co<sub>2</sub>(Bim)<sub>2</sub>] subunits with IA ligands. <b>2</b> represents a double-chain structure containing 18-membered macrocyclic [Co<sub>2</sub>(Bim)(MA)] subunits. Both <b>3</b> and <b>4</b> are 2-D porous coordination polymers but have different architectures. In <b>3</b>, cage-like [Co<sub>4</sub>(Bim)<sub>2</sub>(MA)<sub>4</sub>] subunits are 4-connected nodes that are further bridged by another half-set of Bim ligands to form a 2-D helical structure containing one-dimensional achiral channels and alternately arranged left- and right-handed helical tubular channels. In <b>4</b>, Bim ligands bridge three crystallographically independent Co centers into sharply distorted left- and right-handed helices which are further connected by TA ligands to form a meso layer about 3.0 nm monolayer thickness with a unique (3,4)-connected topology. The structural diversities of coordination polymers <b>1</b>–<b>4</b> are tuned by the flexible coordination number of Co and coligand polycarboxylates. Thermal analyses show that the main frameworks of all compounds remain stable to 352 °C. Moreover, the interesting color changes of crystals <b>1</b>–<b>4</b>, varying from pink to purple and dark blue, result from the d → d* transitions of chromophoric Co<sup>2+</sup> in different coordination geometries as determined by the UV–vis spectra in combination with crystal structure analyses.