Synthesis and structure of a new fluorescent sensor based on Ba(II)‐multicarboxylate for detection of Cu 2+ ion

A novel barium(II) coordination polymer (CP), [Ba 3 (L) 2 (H 2 O) 4 ] n 1 , has been firstly isolated based on organic ligand 1‐[(2′‐carboxybiphenyl‐4‐yl)methyl]‐2‐propylimidazole‐4,5‐dicarboxylic acid (H 3 L=(HO 2 C) 2 (C 3 N 2 )(C 3 H 7 )CH 2 (C 6 H 4 )(C 6 H 3 )CO 2 H) by hydrothermal technique, and determined by single‐crystal X‐ray diffractions, elemental analysis, IR, powder X‐ray diffractions (PXRD). The Ba(II)‐CP 1 belongs to a novel 2‐D layer structure created from 1‐D serrated chain containing secondary building unit (SBU) [Ba(1)Ba(2)Ba(3)] via carboxylate group linkage. In 1 , the ligand L 3− gives a variety of coordinated styles, nonadentate: μ 2 :( η 1 η 1 ), μ 2 :( η 1 η 1 ), μ 3 :( η 2 η 2 ) and decadentate: μ 1 :( η 1 η 1 ), μ 3 :( η 2 η 2 ), μ 3 :( η 1 η 2 ), μ 3 :( η 1 η 2 ), which is the first reported example. Moreover, the room‐temperature fluorescent measurements show that the Ba(II)‐CP 1 has specific ability to recognize copper(II) ion in aqueous solution by means of fluorescence quenching effect, corresponding obtained quenching constant K sv =1.18×10 2  M −1 and the limit of detection LOD=0.274 μM. Fluorescence titration experiment reveals that there is a good linear relationship between copper ion concentration and fluorescence intensity in the concentration range of 2.0×10 −6 ∼5.3×10 −6  mol ⋅ L −1 . The corresponding linear equation: y =402.41897–0.70486 x , and linear correlation coefficient: R 2 =0.99866 ( λ ex =310 nm and λ em =412 nm).