Abstract: The solid complex of lithium perchlorate with4-tert butylbenzo-15-crown-5(4-t-BB15C5) has been prepared in iodobenzene.The composition of the solid was determined as Li(4-t-BB15C5)ClO₄and its melting point was119_121 ℃. The far IRshift of the complex is obvious.The far IRabsorption band of the complex containing100% ⁶Li can be found by extrapolation, resolving the difficulty in obtaining a sample of100% ⁶Li up to now.Arelative reduced partition function ratio, [( s/s′)f ] _org, being1.045 is calculated.Since the [ (s/s′)f ] _aqof lithium perchlorate in solid state had been obtained as_1.025and may act as that in aqueous phase, the phase equilibrium separation factor α may be obtained as 1.019 by the quotient of 1.045/1.025 for the extractive system of (4-t-BB15C5) C₆H₅I/LiClO₄H₂oThe value of α is just equal to the value of intrinsic separation factor (¹⁺ε_p) described previously

Key words: 4-tert Butylbenzo-15-crown-5, Complex of lithium perchlorate with 4-tert-butylbenzo-15-crown-5, Far infrared shift, Theoretical calculation of separation factor of lithium isotope