Selective and sensitive recognition of hexafluorophosphate via an unusual equilibrium between a cationic square host and a image guest

Hyper-selective and -sensitive recognition of hexafluorophosphate via a rigid molecular square has been carried out in solution. The equilibrium of [Pd(Me4en)(Isoni)(PF6)1/4]4(PF6)3/[Pd(Me4en)(Isoni)]4(PF6)4 (Me4en = N,N,N′,N′-tetramethylethylenediamine; Isoni = isonicotinate) has been monitored via a suitable combination of electrostatic interactions and size effects between a cationic square host and a image guest.