RESUMEN
Zn(II), Pd(II), and Cd(II) complexes, [L TH MCl 2 ] (M = Zn, Pd; X = Br, Cl) and [L TH Cd(µ-X)X] n (X = Cl, Br; n = n, 2), supported by the (E)-N 1,N 1-dimethyl-N 2-(thiophen-2-ylmethylene)ethane-1,2-diamine (L TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl- or Br-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L TH MCl 2 ]/LiO i Pr (M = Zn, Pd) and [L TH Cd(µ-Cl)Cl] n /LiO i Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L TH ZnCl 2 ]/LiO i Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L TH ZnCl 2 ]/LiO i Pr producing PLA with higher heterotactic bias (P r up to 0.74 at 0 °C).
RESUMEN
For the first time, lonsdaleite-rich impact diamonds from one of the largest Popigai impact crater (Northern Siberia) with a high concentration of structural defects are investigated under hydrostatic compression up to 25 GPa. It is found that, depending on the nature of a sample, the bulk modulus for lonsdaleite experimentally obtained by X-ray diffraction in diamond-anvil cells is systematically lower and equal to 93.3-100.5% of the average values of the bulk moduli of a diamond matrix. Density functional theory calculations reveal possible coexistence of a number of diamond/lonsdaleite and twin diamond biphases. Among the different mutual configurations, separate inclusions of one lonsdaleite (001) plane per four diamond (111) demonstrate the lowest energy per carbon atom, suggesting a favorable formation of single-layer lonsdaleite (001) fragments inserted in the diamond matrix. Calculated formation energies and experimental diamond (311) and lonsdaleite (331) powder X-ray diffraction patterns indicate that all biphases could be formed under high-temperature, high-pressure conditions. Following the equation of states, the bulk modulus of the diamond (111)/lonsdaleite (001) biphase is the largest one among all bulk moduli, including pristine diamond and lonsdaleite.