Abstract: Molecular dynamics method and semi-empirical quantum chemistry method havebeen used to study the geometric and electronic structure of seven isopropylphosphonate rareearth extractants.The geometry of each extractant was first obtained through MolecularAnnealing; then basd on the most stable structure optimized by Molecular Annealing, thegeometry was further optimized by using PM3 method.The results show that thesubstituent on the alkoxy group exhibits a stronger space obstacle effect than the main chain.The phosphonyl oxygen atom, which is the coordinate atom with the rare earth atom, hasthe largest component in HOMOorbitals.The LUMOorbitals consist of the contribution ofnon-coordinate orbitals.This results indicate that the HOMOof isopropylphosphonate mightplay an important role in the complex compound.The calculated atomic charges ofphosphorus atom, phosphoryl oxygen atom, hydroxy oxygen atom and hydroxy hydrogen atom varyregularly with the change of the size and position of substituents.We have found that thecharges of hydroxy oxygen atom and phosphorus atom have a linear relationship with theacid dissociation constants (pK_a) of the extractants.

Key words: Isopropylphosphonate, Extractants, Molecular dynamics, Semi-empirical quantum chemistry method