Syntheses and host-guest properties of tetrabridged phosphorylated cavitands in their iiii (4i) configurations are described. The tetraphosphonato cavitands 2 and 3, with the four P=O bonds oriented inwards (4i stereoisomer) were prepared in 25% and 53% yields respectively, from the corresponding resorc[4]arenes, dichloro(phenyl)phosphane oxide and base. The formation of the 4i stereoisomers is solventdependent and is attributable to the capability of an ammonium guest to form an inclusion complex. Only the iiio (3io) stereoisomer of 3 was isolated otherwise, in low yield. These phosphonato cavitands, in their 4i configurations, are particularly efficient extractants for metal ions. The free energies of complexation of 3 with alkali metal and ammonium cations