Halogen Bonding Tripodal Metallo-Receptors for Phosphate Recognition and Sensing in Aqueous-Containing Organic Media

The anion recognition and electrochemical anion-sensing properties of halogen-bonding (XB) tripodal zinc(II) receptors strategically designed and constructed for tetrahedral anion guest binding are described. The XB tris(iodotriazole)-containing hosts exhibit high affinities and selectivities for inorganic phosphate over other more basic, mono-charged oxoanions such as acetate and the halides in a competitive CD3CN/D2O (9 : 1 v/v) aqueous solvent mixture. 1H NMR anion binding and electrochemical voltammetric anion sensing studies with redox-active ferrocene functionalised metallo-tripodal receptor analogues, reveal each of the XB tripods as superior anion complexants when compared to their tris(prototriazole)-containing, hydrogen bonding (HB) counterparts, not only exemplifying the halogen bond as a strong alternative interaction to the traditional hydrogen bond for molecular recognition but also providing rare evidence of the ability of XB receptors to preferentially bind the "harder" phosphate oxoanion over the "softer" and less hydrated halides in aqueous containing media. A series of tris(iodotriazole)-containing halogen bonding (XB) tripodal ZnII metallo-receptors, strategically designed for tetrahedral anion guest binding, are demonstrated to selectively recognise inorganic phosphate over more basic, mono-charged oxoanions and the halides in aqueous solvent media. The XB metallo-receptors display augmented anion affinities compared to their tris(prototriazole)-containing hydrogen bonding (HB) counterparts. The attachment of redox-active ferrocene moieties at the XB and HB tripodal receptor termini facilitated complementary electrochemical anion sensing capability.image