Gilberto F. de Sá

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.

Energy levels of Nd3+ in LiYF4

High‐resolution absorption spectra of Nd3+ in LiYF4 were recorded between 3900 and 40 200 cm−1 at temperatures from 10 to 300 K. The levels were obtained by diagonalizing a Hamiltonian that describes the free ion parameters, including two and three‐body configuration interactions, as well as the crystal field operator. Calculations were performed using the complete basis of 364 ‖αSLJMj〉 kets of the 4f3 configuration of Nd3+. A set of free ion and crystal field parameters were calculated which fitted energy levels with an rms deviation of 22 cm−1 with respect to 134 experimentally determined levels.

Single-Shot Biodiesel Analysis: Nearly Instantaneous Typification and Quality Control Solely by Ambient Mass Spectrometry

Using a simple and easily implemented desorption/ionization mass spectrometry technique, a tiny droplet of biodiesel placed on the surface of a sheet of paper is analyzed directly and nearly instantaneously under ambient conditions. No pre-separation or sample preparation is required, and clean mass spectra are obtained with great simplicity. In the positive ion mode, easy ambient sonic-spray ionization mass spectrometry, EASI(+)-MS, provides typical profiles of the major components of biodiesel samples, that is, either methyl esters (FAME) or ethyl esters (FAEE) of the natural fatty acids and triglycerides (TAG) from residual oil or oil from adulteration. Each FAME (FAEE) or TAG molecule is detected as a single sodiated molecule, [M + Na] (+) with relative intensities that correlate well with the known fatty acid profiles of the oil. Using EASI(-)-MS, typical and complementary profiles of free fatty acids (FFA) are obtained, which are detected in their deprotonated forms [FAA - H] (-). A general, single-shot approach for biodiesel analysis is therefore described, and samples from different feedstocks, from blends with petrodiesel, or from either methanol or ethanol trans-esterification are readily typified and major parameters of quality accessed.

A novel fluorinated Eu(III) β-diketone complex as thin film for optical device applications

Abstract We discuss the synthesis and spectroscopic characteristics of a thin film (∼30–90 nm) based on lanthanide europium (III) complexes as the emitter layers, to shift the UV portion of light spectrum into the visible region. The complex presents high quantum efficiency (∼65%), is highly volatile and thermodynamically stable. In addition, the thin film is used as an alternative antireflection coating on a silicon solar cell, allowing for an improvement of about 21% on cell efficiency. The high absorption and luminescence properties in the UV–visible region and its compatibility with device fabrication processes make this material of great potential for use in advanced optical device technologies.

Modeling, Structural, and Spectroscopic Studies of Lanthanide-Organic Frameworks

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 encompasses single-crystal X-ray diffraction studies, thermal analysis, and vibrational spectroscopy, plus detailed investigations on the experimental and predicted (using the Sparkle/AM1 model) photophysical luminescent properties. Crystallographic investigations showed that the compounds are all isostructural, crystallizing in the orthorhombic space group Pnnm and structurally identical to the lanthanum 3D material reported by the group of Williams. (2) is highly photoluminescent, as confirmed by the measured quantum yield and lifetime (37% and 0.74 ms, respectively). The intensity parameters (Omega(2), Omega(4), and Omega(6)) of (1) were first calculated using the Sparkle/AM1 structures and then employed in the calculation of the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield derived from the Sparkle/AM1 structures was approximately 16%, and the experimental value was 8%. We attribute the registered differences to the fact that the theoretical model does not consider the vibronic coupling with O-H oscillators from coordinated water molecules. These results clearly attest for the efficacy of the theoretical models employed in all calculations and open a new window of interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Europium(III) mixed complexes with β-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devices

The new complex tris(4,4,4-trifluoro-1-phenyl-1,3-butanedionate)(1,10-phenanthroline-N-oxide)-europium(III) shows a remarkable luminescence quantum yield at room temperature (66%) upon ligand excitation and a long 5D0 lifetime (670 µs), which makes it a promising light-conversion molecular device.

THEORETICAL MODEL FOR THE PREDICTION OF ELECTRONIC SPECTRA OF LANTHANIDE COMPLEXES

A technique is introduced for the theoretical prediction of electronic spectra of lanthanide complexes by replacing the metal ion by a point charge with the ligands held in their positions as determined by the SMLC/AM1, and by computing the theoretical spectra via the intermediate neglect of differential overlap/spectroscopic-configuration interaction (INDO/S-CI). As a test case, we report the absorption spectrum of tris(picolinate-N-oxide)(2,2′: 6′,2″-terpyridine) of EuIII complex which has been synthesized in our laboratory. The predicted absorption spectra (complex and free ligands) compare well with the UV region experimental data. Moreover, the computed triplet energy levels display transitions near 470 and 560 nm which are due to the N-oxide and which may be relevant for the luminescence.

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the effects of polarizable drift gases and ionic charge distribution

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM-MS) using drift-gases with varying masses and polarizabilities. Despite the reduced length of the cell (18 cm), a pair of constitutional isomers, N-butylaniline and para-butylaniline, with theoretical collision cross-section values in helium (ΩHe ) differing by as little as 1.2 Å(2) (1.5%) but possessing contrasting charge distribution, showed baseline peak-to-peak resolution (Rp-p ) for their protonated molecules, using carbon dioxide (CO2), nitrous oxide (N2O) and ethene (C2H4 ) as the TWIM drift-gas. Near baseline Rp-p was also obtained in CO2 for a group of protonated haloanilines (para-chloroaniline, para-bromoaniline and para-iodoaniline) which display contrasting masses and theoretical ΩHe , which differ by as much as 15.7 Å(2) (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans-oleic acid and cis-oleic acid possessing nearly identical theoretical ΩHe and ΩN2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift-times were observed for the 1,3-dialkylimidazolium ions when comparing He, N2 and N2O. Using density functional theory as a means of examining the ions electronic structure, and He and N2-based trajectory method algorithm, we discuss the effect of the long-range charge induced dipole attractive and short-range Van der Waals forces involved in the TWIM separation in drift-gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift-gases could improve separation and the overall success of TWIM-MS analysis.

Separation of isomeric disaccharides by traveling wave ion mobility mass spectrometry using CO2 as drift gas

The use of CO(2) as a massive and polarizable drift gas is shown to greatly improve peak-to-peak resolution (R(p-p) ), as compared with N(2) , for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline R(p-p) was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (R(p-p)  = 0.76), maltose and sucrose (R(p-p)  = 1.04), and maltose and lactose (R(p-p)  = 0.74). Ion mobility mass spectrometry using CO(2) as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides.

Analysis of fuels via easy ambient sonic-spray ionization mass spectrometry.

The desorption and ionization of analytes directly from surfaces or natural matrices under ambient conditions has greatly simplified chemical analysis by mass spectrometry. Among the currently available set of such techniques, easy ambient sonic-spray ionization (EASI) is one of the simplest and most easily implemented. Fuels are among the most important and most complex classes of chemical mixtures and a challenge for fast and comprehensive chemical analysis. This review summarizes the applications of EASI-MS for fast, simple and nearly sample-preparation-free analysis of various fuels, focusing in typification, adulteration and quality control.