Sensitive Current Sensor Based on a Lanthanide Framework with Lewis Basic Bipyridyl Sites for Cu²⁺ Detection

Abstract

A new Yb-based three-dimensional metal-organic framework with free Lewis basic sites, [Yb₂(ddbpdc)₃(CH₃OH)₂] (referred to as ACBP-6), from YbCl₃ and (6<i>R</i>,8<i>R</i>)-6,8-dimethyl-7,8-dihydro-6<i>H</i>-[1,5]dioxonino[7,6-<i>b</i>:8,9-<i>b</i>']dipyridine-3,11-dicarboxylic acid (H₂ddbpdc) was synthesized by a conventional solvothermal method. Two Yb³⁺ are connected by three carboxyl groups to form the [Yb₂(CO₂)₅] binuclear unit, which is further bridged by two carboxyl moieties to produce a tetranuclear secondary building unit. With further ligation of the ligand ddbpdc^2-, a 3-D MOF with helical channels is constructed. In the MOF, Yb³⁺ only coordinates with O atoms, leaving the bipyridyl N atoms of ddbpdc^2- unoccupied. The unsaturated Lewis basic sites make this framework possible to coordinate with other metal ions. After growing the ACBP-6 in situ into a glass micropipette, a novel current sensor is formed. This sensor shows high selectivity and a high signal-to-noise ratio toward Cu²⁺ detection with a detection limit of 1 <i>μ</i>M, due to the stronger coordination ability between the Cu²⁺ and the bipyridyl N atoms.