COVALENT BONDING OF CROWN-ETHERS TO GAMMA-ZIRCONIUM PHOSPHATE - NEW LAYERED ION-EXCHANGERS SHOWING SELECTIVE RECOGNITION

The topotactic exchange reactions of gamma-zirconium phosphate and gam ma-zirconium phosphate/methylphosphonate with phosphonic acids derived from aza-crown ethers of different sizes was examined. Prior intercal ation of hexylamine was necessary in most cases to attain the maximum exchange level predicted by molecular modeling. Materials with imbrica ted or nonimbricated layers were obtained depending on crown size and exchange level, Exchange of methylphosphonates in gamma-zirconium phos phate/methylphosphonate was only observed when hexylamine had previous ly been intercalated. The exchange with the bisphosphonic acid derived from 1,10-diaza[18]crown-6 gave a material with an interlayer distanc e compatible with pillaring of the gamma-phase, The materials obtained from the exchange reactions of gamma-zirconium phosphate with phospho nic acids derived from [12]crown-4 and [18]crown-6 showed thermodynami c selectivities towards Na+ and K+, respectively, that were much highe r than those observed for the simple crowns in solution, This observat ion suggests that the inorganic molecular framework enhances molecular recognition by minimization of solvation effects.