New phosphorylated calix [4]resorcinarene and cavitands were synthesized. Their extrac tion ability toward La III , Gd III , and Yb III ions was studied. The cavitands are more efficient extracting agents than octasubstituted calix [4]resorcinarenes. The nature of substituents at the nitrogen atom at the upper rim and hydrophobic substituents at the lower rim exerts a substan tial effect on the solubility of the extracted complex in chloroform. Coordination of two lanthanide ions with an extragent molecule results in their efficient but non selective extrac tion. The literature and our spectral ( 31 P NMR) data suggested that the ligand in the extracted complex has most probably a "kite" conformation.Increasing interest in selective and efficient methods for extraction of ions of 4(5)f elements is caused by their use in nuclear fuel or radioactive waste processing. 1 Due to similarity of the electronic properties of 4f and 5f atoms, lanthanide ions represent a convenient model of radioactive actinides, whose handling is hazardous and requires special care.Separation of lanthanide ions is a complicated prob lem, because their thermodynamic parameters of com plex formation are similar due to the ionic character of bonding. 2 Unlike alkaline and alkaline earth metals, high selectivity of lanthanide extraction is hardly attainable, because the change in the stability constants along the series is determined by the result of opposite effects of different factors: size, solvation, metal ion charge, ligand mobility, etc. 3 High coordination numbers of lanthanides are a prerequisite for their coordination by macrocycles. 4 Efficient extraction is achieved in the case of macrocyclic compounds that actually and selectively bind specific metal ions through the polycentered interaction, when the bind ing sites of the macrocycle and substrate are in geometric correspondence. High lipophilicity of the most part of metal ion complexes with calixarenes in combination with high efficiency serves as a reason for the use of calixarenes in liquid extraction. 4,5 The highest efficiency and selectiv ity of extraction were observed for functionalization of calixarenes by substituents containing the P=O groups. 6 It is known 4,7-15 that immobilization and pre organization of phosphineoxide, carbamoyloxide, and carbamoyl phosphate groups at the rim of the calixarene or cavitand matrix enhance the efficiency and selectivity of extraction. The degree of lanthanide extraction by the carbamoyl phosphineoxide extracting agents decreases in the order La III ≈ Eu III > Yb III . 10 Calix[4]resorcinarenes are conve nient platforms for extracting agents because make it pos sible to change simultaneously both the complexation properties and hydrophobicity. Since the pre organiza tion of donor centers affects the selectivity of complex formation with lanthanide ions, it is natural to expect that the complexation properties would change substantially on going from the calix[4]resorcinarene matrix to related cavitand structures. Examples for using pho...