[en] The peculiarities of interaction of lithium cations with sorbents phosphate groups (titanium and zirconium phosphates) are studied quantum-chemically in the framework of the MOLCAO method. Supposing, that the ion introduction into the sorbent at the stage of synthesis contributes to the formation of a porous structure corresponding to cation parameters, samples of titanium and zirconium phosphates are synthesized in the presence of lithium cations. The theoretical and experimental investigations into sorption peculiarities of alkaline metal cations with amorphous titanium and zirconium phosphates have shown, that the nature of ion selectivity is largely regulated by the factor of cation diameter correspondence to the effective ultrapore size. The steric correspondence conditions both the selective nature of ion-exchange adsorption and the peculiarities of ion transport inside sorbent ultrapore