Sensitive Current Sensor Based on a Lanthanide Framework with Lewis Basic Bipyridyl Sites for Cu

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 (6R,8R)-6,8-dimethyl-7,8-dihydro-6H-[1,5]dioxonino[7,6-b:8,9-b']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 ddbpdc2-, a 3-D MOF with helical channels is constructed. In the MOF, Yb3+ only coordinates with O atoms, leaving the bipyridyl N atoms of ddbpdc2- 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 μM, due to the stronger coordination ability between the Cu2+ and the bipyridyl N atoms.