Self-assembly of metallomacrocycles with dipyrazole ligands and anion sensing of [Pd₄Fe₂] macrocycle with ferrocene-based dipyrazole ligand

By employing dipalladium corners [(bpy)₂Pd₂(NO₃)₂](NO₃)₂ or [(phen)₂Pd₂(NO₃)₂](NO₃)₂ (where bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline) to bridge ferrocene-based dipyrazole ligand (L¹) and m-phenylene-based dipyrazole ligands (L^2–3) in aqueous solution, a series of positively-charged [M₄L₂]⁴⁺ metallomacrocycles were obtained. Their structures were characterized by¹H NMR, electrospray ionization mass spectrometry (ESI-MS), elemental analysis, and single crystal X-ray diffraction analysis for 1·4NO₃ (([(bpy)Pd]₄ L¹₂)(NO₃)₄) and 4·4NO₃ (([(phen)Pd]₄ L²₂)(NO₃)₄). In their single crystal structures, NO₃⁻ anions are located at the dipalladium corners by C–H⋯O hydrogen bonds. Importantly, the anion-sensing properties of ferrocene functionalized [Pd₄Fe₂] hetero-metallomacrocycle 1 were investigated in acetonitrile by SWV, CV and NMR analysis, showing promise for Br⁻ sensing.