The electronic properties and chemical bonding of the C6H6:LnO (Bz:LnO) adducts have been investigated by density functional theory (DFT) calculations. Two types (I and II) of Bz:LnO adducts are formed upon trapping LnO by the benzene molecule. In type I, the benzene molecule is coordinated to the Ln atom in a η6-coordination mode with the LnO perpendicular to the ring center, while in type II the LnO is inclined with respect to the ring plane. In type II adducts, the benzene molecule undergoes significant structural distortions adopting a boat conformation facing the Ln atom of LnO. In the bending conformation of benzene, the bond length equalization is lifted up with the 1,2- and 4,5-double bonds shortened by 0.01 Å with respect to the CC double bond in the “free” benzene molecule while the remaining bonds are lengthened by about 0.04 Å, thus coordinated benzene exhibits a 1,4-diene type π-localization within the ring. The effect of adduct formation on the structural, spectroscopic, and magnetotropic properties of the coordinated benzene have been explored using electronic structure computational techniques. The main features of the Time Dependent DFT (TD-DFT) simulated absorption spectra of the LnOs and C6H6:LnO adducts are analyzed and assignments of the electronic transitions are given. © 2012 Wiley Periodicals, Inc.