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 sigma-acceptor and with 2,3-dichloro-5,6 dicyano-1,4-benzoquinone, (DDQ) as a pi-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))(2)I](+)center dot I-3(-) and [La(acac)(3)(DDQ)]. Far-infrared spectrum shows that the triiodide ion is nonlinear with C-2v symmetry. The values of the equilibrium constants (K) and obsorptivities (epsilon) 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 I-2 or DDQ could mainly take place through the oxygen atoms in addition to the acac ring pi-molecular orbitals. (c) 2011 Elsevier B.V. All rights reserved.