The electronic structure and magnetic properties of neptunyl(VI), NpO2(2+), and two neptunyl complexes, [NpO2(NO3)3](-) and [NpO2Cl4](2-), were studied with a combination of theoretical methods: ab initio relativistic wavefunction methods and density functional theory (DFT), as well as crystal-field (CF) models with parameters extracted from the ab initio calculations. Natural orbitals for electron density and spin magnetization from wavefunctions including spin-orbit coupling were employed to analyze the connection between the electronic structure and magnetic properties, and to link the results from CF models to the ab initio data. Free complex ions and systems embedded in a crystal environment were studied. Of prime interest were the electron paramagnetic resonance g-factors and their relation to the complex geometry, ligand coordination, and nature of the nonbonding 5f orbitals. The g-factors were calculated for the ground and excited states. For [NpO2Cl4](2-), a strong influence of the environment of the complex on its magnetic behavior was demonstrated. Kohn-Sham DFT with standard functionals can produce reasonable g-factors as long as the calculation converges to a solution resembling the electronic state of interest. However, this is not always straightforward.

Schiff bases show a wide variety of applications of great importance in medicinal researchdue to their range of biological activities. In this article we describe the electronic structure, optical, redox and antifungal properties of (E)-2-{[(2-aminopyridin-3-yl)imino]-methyl}-4,6-ditert-butyl-phenol (L1) and (E)-2-{[(3-aminopyridin-4-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (L2), two isomers phenol derivatives Schiff bases exhibiting a strong intramolecular hydrogen bond (O-H•••N). These compounds were characterized by their 1 H, HHCOSY, 13 C-NMR, FT-IR spectra, and by cyclic voltammetry. All the experimental results were complemented with theoretical calculations using density functional theory (DFT) and time-dependent DFT (TDDFT). The antimicrobial activity of the compounds described herein was assessed by determining the minimal inhibitory concentration (MIC) and by a modification of the Kirby-Bauer method. We tested Salmonella enterica serovar Typhi (S. Typhi, Gram-negative bacteria), Cryptococcus spp. (yeast), and Candida albicans (yeast). We found that neither L1 nor L2 showed antimicrobial activity against S. Typhi or Candida albicans. On another hand, L2, in contrast to L1, exhibited antifungal activity against a clinical strain of Cryptococcus spp.(MIC: 4.468 µg/mL) even better than ketoconazole antifungal medicaments. We mentioned above that L1 and L2 are isomer species, because the amino groups is in ortho-position in L1 and in para-position in L2, however no significant differences were detectable by UV-vis, FT-IR, oxidation potentials and TDDFT calculations, but importantly, the antifungal activity clearly discriminated between these two isomers.LUMO) and 74% (HOMO-3 → LUMO) for L1 and 74% (HOMO-4 →LUMO) and 26% (HOMO-2 →LUMO) for L2 in all the solvents and in gas phase. The bands assigned like π→π* transitions involve the HOMO→ LUMO for L1 and L2. The comparison between the solvent spectra with the gas phase showed no significant shift in the UV-vis spectra when the solvent polarity changes. Figure 3. Calculated UV-vis absorption spectra for (E)-2-{[(2-aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (L1) in different implicit solvents and gas phase.

A theoretical protocol to study the sensitization and emission mechanism in lanthanide compounds on the basis of multireference CASSCF/PT2 calculations is proposed and applied to [Eu(NO)(dppz-CN)] and [Eu(NO)(dppz-NO)] compounds synthesized and characterized herein. The method consists of a fragmentation scheme where both the ligand and the lanthanide fragments were calculated separately but at the same level of theory, using ab initio wave-function-based methods which are adequate for the treatment of quasi-degenerate states. This is based on the fact that the absorption is ligand-localized and the emission is europium-centered. This characteristic allowed us to describe the most probable energy transfer pathways that take place in the complexes, which involved an ISC between the S to T ligand states, energy transfer to D in the lanthanide fragment, and further D → F emission. For both compounds, the triplet and D states were determined at the CASPT2 level to be around ∼26000 and ∼22400 cm, respectively. This difference is in the optimal range for the energy transfer process. Finally, the emissive state D was found at ∼18000 cm and the emission bands in the range 550-700 nm, in quite good agreement with the experimental results.

Schiff bases exhibit a broad range of applications, including their use as catalysts, stabilizers, dyes, and intermediates in organic synthesis; and biological activities, such as antifungal properties.

The simple system of tetraammonium octafluorouranate is employed to derive a fundamental understanding of the uranium–fluorine interaction. The structure is composed of isolated molecules, enabling a detailed examination of the U4+ (f 2) ion. Characterization of single-crystals by X-ray diffraction, absorption spectroscopy, and magnetic analysis up to 45 T is combined with extensive theoretical treatment by CASSCF. The influence of different active spaces and representations of the structure is examined in the context of the experimental evidence. The Interacting Quantum Atoms method (IQA) is used to examine the nature of the U–F bond, concluding that there is a non-negligible degree of covalent character (9% of the total bond energy) in [UF8]4−. For the structural and theoretical reasons discussed herein, it is proposed that the structure of (NH4)4UF8 may be appropriately employed as a benchmark compound for future theoretical characterization of U­(IV).