Influences of Hard Donor on Cation Selectivities Closing to Soft Selenium Donor in Tweezer-like Calix[4]arene Receptors

Three novel 25,27‐dihydroxy‐26,28‐bis(3‐benzylselenopropoxy)‐5,11,17,23‐tetra‐tert‐butylcdix4]‐arene (2), 25,27‐dihydroxy‐26,28‐bis3‐(2‐hydroxyethylseleno)propoxy]‐5,11,17,23‐tetra‐tert‐butyl‐calix4]arene (3) and 25,27‐dihydroxy‐26,28‐bis(3‐propylselenopropoxy)‐5,11,17,23‐tetra‐tert‐butyI‐calix4]arene (4) were synthesized for the comparison of their ion‐selectivity in ion‐selective electrodes (ISE). X‐ray structure of the CH/π complex of 4·CH₂Cl₂ was elucidated. ISEs based on 2‐4 as neutral ionophores were prepared, and their selectivity coefficients for Ag+ (log K) were investigated against some main group metal ions and transition metal ones using the fixed interference method (FZM). These ISEs showed excellent Ag' selectivity over most of the interfering cations examined. It is evident that the stronger Hg²⁺ interference may not be produced while hard donors (hydroxy) are close to the soft selenium donors.