Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Catalysis & Coupling constant. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

The Ligand Field of the Azido Ligand: Insights into Bonding Parameters and Magnetic Anisotropy in a Co(II)–Azido Complex

Abstract: The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)-azido complex (1), which has been characterized experimentally (magnetically and by electronic d-d absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = -10.7 cm(-1), E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying d-d transitions. Calculations were performed on 1 and a related four-coordinate Co(II)-azido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3(-) ligand is shown to behave as a strong σ and π donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the Co-N bond distances) of the axial ligand on the N3(-) site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results.

Effect of mixed titania-alumina supports on the phase composition of NiMo/TiO2Al2O3 catalysts

Abstract: NiMo catalysts supported on mixed TiO2Al2O3 oxides containing between 0 and 22 wt.−% TiO2 have been prepared and characterized by temperature-programmed reduction (TPR), infrared (IR) and diffuse reflectance (DR) spectroscopy, BET and ammonia adsorption measurements. The samples have been tested in hydrodesulphurization (HDS) of thiophene. The spectral results show that the proportion of weakly bonded MoO42− groups is higher for NiMo/TiO2Al2O3 catalysts compared to catalysts contained only molybdenum. The increase in TiO2 content in the mixed supports leads to a decrease of inactive NiAl2O4 spinel. An increase of Ni2+ ions in octahedral surroundings, included in a structure analogous to NiTiO3 is observed. Acidity shows the nickel-molybdenum surface interaction to be a result of the formation of a precursor of NiMoO4-like structure. The TPR results demonstrate that addition of titania into the support facilitates the Mo6+ reduction to Mo5+ and Mo4+. The influence of nickel on the molybdenum reducibility is revealed by a decrease of the temperature of reduction of the molybdenum species. The HDS activity of NiMo/TiO2Al2O3 catalysts reaches a maximum at 17 wt.−% TiO2 due to formation of an active phase with an optimal composition of the oxidic precursors.

Structure and Physical Properties of Tailor‐Made Ce,Zr‐Doped Carbon Aerogels

Abstract: Carbon aerogels with controlled porosity can be obtained by doping the resorcinol–formaldehyde reaction mixture with Ce and/or Zr. As highlighted here, the concentration of metal dopant and the pH of the initial reaction mixture can have a profound effect on the structure, porosity, and physical properties of the resulting aerogel. The Figure shows the morphology of a Ce,Zr-doped carbon aerogel synthesized at pH 7.