Evans-Showell-type polyoxometalate-based metal-organic complexes with novel 3D structures constructed from flexible bis-pyrazine-bis-amide ligands and copper metals: syntheses, structures, and fluorescence and catalytic properties

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-02, Vol.48 (6), p.216-2169
• Main Authors: Li, Feng-Cai, Li, Xi-Li, Tan, Li-Kun, Wang, Jin-Tang, Yao, Wei-Zhong
• Format: Article
• Language: English
• Subjects: Benzoic acid; Benzyl alcohol; Catalysts; Catalytic activity; Catalytic converters; Chemical analysis; Coordination compounds; Copper; Crystal structure; Crystallography; Fluorescence; Infrared analysis; Infrared spectroscopy; Ligands; Metal-organic frameworks; Oxidation; Polyoxometallates; Selectivity; Single crystals; Spectrum analysis; X ray powder diffraction; X-ray diffraction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt04698k

Two new Evans-Showell-type polyoxometalate (POM)-based metal-organic complexes, namely {Cu 3 (L 1 ) 1.5 (H 2 O) 5 [Co 2 Mo 10 H 4 O 38 ]}·5H 2 O ( 1 ), {[Cu(L 2 ) 0.5 (H 2 O) 2 ] 2 [Co 2 Mo 10 H 4 O 38 ]}·6H 2 O ( 2 ) ( L 1 = N , N ′-bis(2-pyrazinecarboxamide)-1,4-butane, L 2 = N , N ′-bis(2-pyrazinecarboxamide)-1,6-hexane), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1 , the adjacent [Co 2 Mo 10 H 4 O 38 ] 6− polyoxoanions are linked by Cu II ions to form a 1D Cu-[Co 2 Mo 10 H 4 O 38 ] 6− inorganic chain, which is further linked by ligand L 1 and [Co 2 Mo 10 H 4 O 38 ] 6− polyoxoanions, forming a 3D metal-organic framework. In complex 2 , the adjacent [Co 2 Mo 10 H 4 O 38 ] 6− polyoxoanions link the Cu II ions to generate a 2D Cu-[Co 2 Mo 10 H 4 O 38 ] 6− inorganic layer, which is further connected with bidentate ligands L 2 to obtain a 3D metal-organic framework. The structural diversities of compounds 1 and 2 showed that the spacer lengths of the flexible bis-pyrazine-bis-amide ligands play important roles in tuning the structures of the title complexes. Compounds 1 and 2 represent the first examples of 3D frameworks based on the Evans-Showell-type polyoxoanions and Cu-bis-pyrazine-bis-amide coordination complexes. Moreover, the ligand L 1 was first successfully introduced into the POM system. The electrochemical and fluorescence properties of compounds 1 and 2 were discussed. As heterogeneous catalysts, compounds 1 and 2 have good catalytic activity for the oxidation of benzyl alcohol. Moreover, compound 2 has higher catalytic performance with 100% conversion and 98.0% selectivity for benzoic acid at 10 h. The difference in their catalytic performance may be mainly due to the difference of their structures. The catalysts can be recovered and reused without displaying any significant loss of activity. Two 3D Evans-Showell-type POM-based copper-bis-pyrazine-bis-amide complexes show good heterogeneous catalytic activity for the oxidation of benzyl alcohol.