Spectoscopic and structural studies on charge-transfer complexes of lanthanum(III)acetylacetonate with σ-acceptor iodine and π-acceptor DDQ

The interaction of the donor La(III)acetylacetonate, [La(acac)3], with iodine as a σ-acceptor and with 2,3-dichloro-5,6 dicyano-1,4-benzoquinone, (DDQ) as a π-acceptor have been studied in the solvents CH2Cl2, CHCl3 and CCl4 at room temperature. The obtained results indicate the formation of 1:1 charge-transfer complexes. The electronic and infrared absorptions and elemental analysis of the formed complexes indicate that the complexes are formulated as the triiodide [(La(acac)3)2I]+·I3- and [La(acac)3(DDQ)]. Far-infrared spectrum shows that the triiodide ion is nonlinear with C2v symmetry. The values of the equilibrium constants (K) and obsorptivities (ε) for both the formed CT-complexes are calculated and discussed in term of reaction stoichiometry values and molecular steric hindrance. Mid infrared spectra suggest that the electron donation from [La(acac)3] to the donors I2 or DDQ could mainly take place through the oxygen atoms in addition to the acac ring π-molecular orbitals.

► [La(acac)3] reacts with iodine forming the triiodide complex , [(La(acac)3)2I]+.I3-, rather than I2-product and with DDQ to form [La(acac)3 (DDQ)].
► Formation constant for [(La(acac)3)2I]+.I3- is about four times higher than that of [La(acac)3 (DDQ)] due in part to the relatively higher steric hindrance of DDQ.
► Bonding, symmetry and electronic transitions of the triiodide ion, I3-, are explained.