Novos desenvolvimentos e aplicaÃÃes de mÃtodos de quÃmica quÃntica para compostos de coordenaÃÃo com Ãons lantanÃdeos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Theoretical studies on lanthanide compounds were performed, and divided into three parts: (i) generalization of the Linderberg-Seamans equations for an s-p-d-f basis set; (ii) study of the ligand-to-lanthanide ion charge transfer transitions (LMCT) with the ZINDO98 program using the INDO/S semiempirical hamiltonian and (iii) a study of point charge and charge density models to simulate a Ln(III) ion in ligand centered electronic structure in complexes. In the part (i), from the Heisenberg equation of motion, using the second quantization formalism and the closure relationship for the one particle basis set, a system with 256 equations was obtained describing relations between matrix elements over the linear momentum, the position and the two center one electron hamiltonian (resonance integrals - β âs) operators. New matrix elements including, for instance, functions of ϕ-type symmetry have been found as well as a new type of interaction, namely, between π and ϕ-type symmetry orbitals. In the part (ii), an approach to the LMCT transitions in terms of differences between ionization potentials and electron affinities, using Fock operators as well as Koopmans expressions generalized for open shells. The Rumer technique for construction of spin adapted configurations eigenfunctions was used to obtain general expressions for the LMCT transitions energies, without configuration interaction. This approach allows the prediction of new types of LMCT states of spin multiplicities (septets and quintets) different from nine (nonets), and it was shown that the Hundâs rule is obeyed. Also, calculations of LMCT transitions on Eu3+ containing compounds with the ZINDO98 program were performed, now with Rumer configuration interaction (Rumer CI). This was accomplished by two routes: via SOCI (configuration interaction with spin-orbit coupling) and ΔE(SOCI) (one SOCI ground state calculation and another independent one, for LMCT states, whose reference orbitals were optimized for a specific LMCT state). The following compounds were studied: the cryptate [Eu ⊂ 2.2.1]3+ (2.2.1 = 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane), with and without coordinated water molecules and/or fluoride ions, the aqua-complex [Eu(H2O)9]3+ and its hydrolyzed complexes [Eu(H2O)9−m(OH)m]3−m; the tri-halide compounds EuX3 (X = F−, Cl−, Br−, I−) and the doped solids YOCl: Eu3+ and LaF: Eu3+. It was found that the calculations performed with relaxation on the excited LMCT states, ΔE(SOCI), are in better agreement with the experimental results than those obtained directly by the SOCI method. This pronounced relaxation effect (ranging from 5000 to 15000 cm−1) was ascribed to the largely localized character of the 4f orbitals. The complexes Eu(tan)3⋅bipy and Eu(btfa)3⋅bipy (tan = 4,4,4-trifluoro-1-(1-naphthyl)-2,4-butanedionate; btfa = 4,4,4-trifluoro-1-phenyl-2,4-butanedionate; bipy = 2,2â-dipyridyl) were treated only by the SOCI method due to the variational collapse occurring in the ΔE(SOCI) approach. In general, the calculations of the low lying LMCT states indicate that these states have a low spin contamination through the spin-orbit coupling and, contrary to the Hundâs rule predictions, very often they are not nonets, but septets with some mixture with quintets. In the part (iii), it was proposed a distance dependent effective charge model, q(r) = 3 +14e− Ar2 , for describing the Eu3+ ion, and implemented into the ZINDO98 program. Alternatively, other point charge values (+3,5e and +4,0e) were tested. INDO/S-CI calculations of the absorption electronic spectra of the complexes Eu(btfa)3⋅bipy, Eu(btfa)3⋅2H2O, Eu(bzac)3⋅bipy and Eu(bzac)3⋅2H2O (bzac = 1-phenyl-2,4-butanedionate) were performed and used for fitting the A parameter. It was found that the q(r) model as well as the +3,5e and +4,0e point charges yielded better results than that obtained by the simple use of a +3e point charge, in spite of the more intuitive appealing of this choice

ASSUNTO(S)

quÃmica quÃntica compostos de coordenaÃÃo quimica Ãons lantanÃdeos

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