Ricardo Oliveira Freire

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Twenty years ago, the landmark AM1 was introduced, and has since had an increasingly wide following among chemists due to its consistently good results and time-tested reliability--being presently available in countless computational quantum chemistry programs. However, semiempirical molecular orbital models still are of limited accuracy and need to be(More)
PM6 is the first semiempirical method to be released already parametrized for the elements of the periodic table, from hydrogen to bismuth (Z = 83), with the exception of the lanthanides from cerium (Z = 58) to ytterbium (Z = 70). In order to fill this gap, we present in this article a generalization of our Sparkle Model for the quantum chemical(More)
The recently published Parametric Method number 7, PM7, is the first semiempirical method to be successfully tested by modeling crystal structures and heats of formation of solids. PM7 is thus also capable of producing results of useful accuracy for materials science, and constitutes a great improvement over its predecessor, PM6. In this article, we present(More)
The sparkle/AM1 model for the quantum chemical prediction of coordination polyhedron crystallographic geometries from isolated lanthanide complex ion calculations, defined recently for Eu(III), Gd(III), and Tb(III) (Inorg. Chem. 2005, 44, 3299) is now extended to La(III) and Lu(III). Thus, for each of the metal ions we chose a training set of 15 complexes(More)
The recently defined Sparkle model for the quantum chemical prediction of geometries of lanthanum(III) and lutetium(III) complexes within AM1 (J. Phys. Chem. A 2006, 110, 5897) has been extended to PM3. As training sets, we used the same two groups, one for each lanthanide, of 15 high-crystallographic-quality (R factor < 0.05 A) complexes as was previously(More)
The Sparkle/PM3 model is extended to cerium(III) complexes. The validation procedure was carried out using only high quality crystallographic structures (R factor < 0.05Å), for a total of thirty-seven Ce(III) complexes. The Sparkle/PM3 unsigned mean error, for all interatomic distances between the Ce(III) ion and the directly coordinating oxygen or nitrogen(More)
New europium and gadolinium tris-beta-diketonate complexes have been prepared and incorporated in sol-gel-derived organic-inorganic hybrids, named di-ureasils. The general formula [Ln(btfa)3(4,4'-bpy)(EtOH)] (Ln=Eu, Gd; 4,4'-bpy=4,4'-bipyridine; btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione) for the complexes was confirmed by X-ray crystallography and(More)
This work presents the synthesis and spectroscopic study of new homotrinuclear (TRI) systems for photonics applications. The luminescence spectroscopy shows characteristics transitions of Eu(III) and Tb(III) ions. For the Gd(III) complexes, the triplets states were determined by phosphorescence measurement. The complexes’ coordination geometries were(More)
A novel class of efficient visible light sensitized antenna complexes of Eu(3+) based on the use of a series of highly conjugated β-diketonates, namely, 1-(1-phenyl)-3-(2-fluoryl) propanedione, 1-(2-naphthyl)-3-(2-fluoryl)propanedione, 1-(4-biphenyl)-3-(2-fluoryl) propanedione, and 2,2'-bis(di-p-tolylphosphino)-1,1'-binaphthyl oxide as an ancillary ligand(More)
In this paper, we report the hydrothermal synthesis of three lanthanide-organic framework materials using as primary building blocks the metallic centers Eu(3+), Tb(3+), and Gd(3+) and residues of mellitic acid: [Ln(2)(MELL)(H(2)O)(6)] (where Ln(3+) = Eu(3+), Tb(3+), and Gd(3); hereafter designated as (1), (2) and (3)). Structural characterization(More)