Nivan B. da Costa

Sparkle model for the quantum chemical AM1 calculation of europium complexes

Abstract Considering that the bonds between a lanthanide and its ligands essentially possess an electrostatic character, we propose the representation of rare-earth elements within AM1 as sparkles. To parametrize the sparkle model we have used the known geometry of the complex tris (acetylacetonate) (1,10-phenantroline) of europium (III). Interatomic distances for the coordination polyhedron, averaging 2.81 A, could be predicted with an average deviation of 0.13 A. In short, this is a simple lanthanide-ligand electrostatic model which simultaneously treats the organic ligands and their interactions with the powerful AM1 method, yielding results of useful accuracy.

Sparkle model for the quantum chemical AM1 calculation of europium complexes of coordination number nine

Abstract Recently, we have proposed the representation of lanthanides within AM1 as sparkles for the purpose of obtaining ground state geometries of their complexes. In the present work we tested our quantum chemical sparkle model for the prediction of the crystallographic structure of tris (dipivaloylmethanato) (2,2′:6′,2′-terpyridine) of europium(III), a complex with coordination number nine. Considering the coordination polyhedron, the interatomic distances averaging 2.83 A and the bond angles could be predicted with an average deviation of 0.12 A and 5° respectively. This finding reinforces our model and consequently the notion that the lanthanide-ligand interaction is essentially electrostatic.

Would the pseudocoordination centre method be appropriate to describe the geometries of lanthanide complexes

The correct prediction of the ground-state geometries of lanthanide complexes is an important step in the development of efficient light conversion molecular devices (LCMD). Considering this, we evaluate here the capability of semiempirical approaches and ab initio effective core potential (ECP) methodology in reproducing the coordination polyhedron geometries of lanthanide complexes. Initially, we compare the facility of two semiempirical approaches: Pseudocoordination centre method (PCC) and Sparkle model. In the first step, we considered only high-quality crystallographic structures and included 633 complexes, and in the last step, we compare the capability of two semiempirical approaches with ab initio/ECP calculations. Because this last methodology was found to be computationally very demanding, we further used a subset containing 91 high-quality crystallographic structures. A total of 91 ab initio full geometry optimizations were performed. Our results suggest that only the semiempirical Sparkle model (hundreds of times faster) present accuracy similar to what can be obtained by present-day ab initio/ECP full geometry optimization calculations on such lanthanide complexes. In addition, it further indicates that the PCC approach has a poor prediction related to the coordination polyhedron geometries of lanthanide complexes.

An IR spectral measure of classical aromaticity in five-and six-membered ring heterocycles: an ab initio study

Abstract The carbon—hydrogen IR frequencies and intensities obtained from 4-31G molecular orbital calculations for 15 five- and six-membered ring heterocycles are subjected to a principal component analysis. The first principal component (PC) is found to discriminate between five- and six-membered ring compounds. The first PC scores are found to be correlated with a recently proposed measure of classical aromaticity. In consequence, the first PC score is suggested as a measure of classical aromaticity, entirely based on quantities that can be observed. The relative contributions of the IR intensities to the first PC indicate increasing charge localization in the less aromatic compounds.

Infrared intensity parameters for furan and thiophene

Determination of atomic charges and charge fluxes, derived from the charge-charge flux-overlap modified (CCFOM) model by using 4-31G ab initio calculations for furan and thiophene.