Coordination polymers with iridium(iii) metalloligands: the effect of pore size upon luminescent cation sensing

Abstract

The chemical sensing of metal ions is important in environmental monitoring and biomedical diagnostics. Iridium(III) metalloligand-based coordination polymers (CPs) containing Cd(II): [Cd{Ir(ppy)₂(dcbpy)}₂] (1), [Cd{Ir(ppy)₂(dcbpy)}₂(H₂O)₂]·8H₂O (1-H₂O), [Cd₂{Ir(dfppy)₂(dcbpy)}₄]·DMF (2) and [Cd{Ir(bt)₂(dcbpy)}₂]·DMF (3) have been synthesised and their chemical sensing properties towards metal ions determined. Framework 1 shows selectivity for Fe³⁺ over other common metal cations with a detection limit of 32 μM and quantitation limit of 96 μM. Upon soaking in water 1 transforms into 1-H₂O, changing the coordination geometry at Cd(II) and distorting the structure of the cation sensing site. Surprisingly, the structural distortion of 1-H₂O results in improved selectivity for Fe³⁺, potentially due to the narrowing of pores inside the CP precluding the diffusion of large metal ions to the sensing site.