Synthesis and characterization of zinc di(O-2,2-dimethylpentan-3-yl dithiocarbonates) bearing pyridine or tetramethylethylenediamine coligands and investigation of their thermal conversion mechanisms towards nanocrystalline zinc sulfide

Laser-Induced Thermal Decomposition of Uranium Coordination Compounds with Non-oxidic Ligands to Produce Nitride and Carbide Materials

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds─UI4(TMEDA)2, UCl4(TMEDA)2, UCl3(pyridine)x, and UI3(pyridine)4. Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 °C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

Theoretical studies of Zn2+ complexes with alkyl xanthate ligands: a thermochemical, electronic energy decomposition, and natural bond orbital analysis

CONTEXT

Xanthates are organic compounds that present great interest for coordination chemistry, because they can bond in different ways to the metal ion. Thus, these compounds have several applications, being best known for their environmental application. In fact, xanthates are recognized for their application as heavy metal collector agents in aqueous environments. In view of this application, this study is aimed at showing the thermochemical and electronic parameters obtained for the reactions of substitution water molecules in the aqua zinc complexes, by xanthate ligands (n-propyl, n-butyl, and n-pentyl xanthates). In addition to their environmental application, xanthates have shown biological properties, such as anti-bacterial and anti-cancer. In recent years, xanthates have also been used in the technological area, where it participates as a precursor of sulfides for the manufacture of thin films. Our results showed complexes with distorted octahedral geometries and with negative values of enthalpy and Gibbs free energy, indicating exothermic and spontaneous processes. For all the complexes, it was observed that Zn²⁺ complexes have both an ionic and covalent character. However, the monosubstituted complexes showed a predominance of the ionic character. In addition, high donor-acceptor interaction energies were obtained, indicating a good superposition between the s and p orbitals involved in the Zn-S bond.

METHODS

This work consists in theoretical studies of Zn²⁺ complexes with alkyl xanthate ligands, with different structures, where optimization and normal modes calculations were performed at different DFT levels: M06L, M06-2X, wB97XD, and B3LYP/6-311++G**+LANL2TZ, with Gaussian09 program. The process of substitution of two aqua by two xanthate ligands was analyzed in stages, forming cationic and neutral complexes, in the first and second stages, respectively. In addition, electronic energy decomposition (EDA) and natural bond orbital (NBO) analysis were performed at level M06L/6-311++G**+LANL2TZ with Gamess program.