Two diverse nitrogen-site-directed 3D cobalt coordination polymers with Bi-/penta-nuclear subunits exhibiting multi-functional electrochemical and fluorescent sensing activities

Abstract

Two new cobalt coordination polymers (CPs), [Co2(3-dpyh)0.5(dcppa)(H2O)3]·2H2O (1) and [Co5(μ3-OH)2(4-dpyh)(dcppa)2(H2O)2] (2) [3-dpyh = N,N'-di(3-pyridinecarboxamide)-1,6-hexane, 4-dpyh = N,N'-di(4-pyridinecarboxamide)-1,6-hexane, H4dcppa = 3-(3′,5′-dicarboxylphenoxy)phthalic acid] have been prepared under hydrothermal conditions by using two flexible bis-pyridyl-bis-amide ligands with different N site of pyridyl and same auxiliary ligand. Single crystal X-ray diffraction (XRD) analysis of CPs 1–2 reveals that both CP 1 and CP 2 exhibit completely different 3D structures stemmed from different pyridine N sites of bis-pyridyl-bis-amide ligands. The electrochemical properties of CP 1 and CP 2 were investigated, which show good electrocatalytic effect on the reduction of nitrite and oxidation of ascorbic acid. Fluorescence sensing behaviors of CP 1 and CP 2 were investigated, which exhibit obvious quenching effect for Fe3+ ions and Cr2O72– ions in water and good selectivity. In addition, CP 2 containing penta-nuclear Co clusters is magnetic.