Theoretical study on the strength of interaction between hydrated lanthanide cations and some organic aromatic compounds has been reported. At first, the interactions of two hydrated metal cations, ]M(H2O)9[3+ (M=La3+, Lu3+),with π-system of a number of benzene derivatives including electron donating and electron withdrawing substituentswere studied. The results confirmthat ]Lu(H2O)9[3+ hasmore affinity to adsorb on benzene ring and its derivatives than [La(H2O)9[3+. Then the interactions of above cations with carbon atoms of the benzene ring were compared with those between the [La(H2O)9]3+ cation and C80H20 armchair single-wall carbon nanotubes (SWCNTs) and also fullerene molecule. The results showed that, the interaction in two latter systems is considerably larger than those in corresponding complexes of benzene and its derivatives. It seems that the curvature of the surface of SWCNT and fullerene molecules provides an excellent location for landing of [La(H2O)9]3+ cation on the organic aromatic compounds through its fourH2O molecules. Also the study on bond critical points (BCPs) between ]La(H2O)9[3+ cation and the SWCNT, fullerene and benzene and its derivatives indicates that among all systems investigated here the {[La(H2O)9]3+……SWCNT} has the greatest values of electron density (ρ).
