The acetylene cyclotrimerization reaction mediated by the left-hand-side bare transition metal atoms Y, Zr, Nb, and Mo has been studied theoretically, employing DFT in its B3LYP formulation. The complete reaction mechanism has been analyzed, identifying intermediates and transition states. Both the ground spin state and at least one low-lying excited state have been considered to establish whether possible spin crossings between surfaces of different multiplicity can occur. Our results show that the overall reaction is highly favorable from a thermodynamic point of view and ground state transition states lie always below the energy limit represented by ground state reactants. After the activation of two acetylene molecules and formation of a bis-ligated complex, the reaction proceeds to give a metallacycle intermediate, as the alternative formation of a cyclobutadiene complex is energetically disfavored. All the examined reaction paths involve formation of a metallacycloheptatriene intermediate that in turn generates a metal−benzene adduct from which finally benzene is released. Similarities and differences in the behaviors of the considered four metal atoms have been examined.
The discovery of a stable decagonal QC phase in Al Cu Co by He et. al. [1] produced an importante research on these phases in the system Al Cu Co (Si). Moreover, QC phases obtained in this system were also reported with special electrical properties [2-4]. It is important to not , that these QC systems show a strong variation of the conductivity with a very slighhht change in composition. In agreement with differents authors, the electrical conductivity of the decagonal quasi-crystalls of the Al Cu Co (Si) alloy shows metallic behavior along to periodic direction and nonmetallic behavior along to quasiperiodic direction. In this work we show some HRTEM results that indicate a different behavior of the electrical conductivity for decagonal phase af the Al 62 Cu 20 Co 15 Si 3 alloy that was produced using a double elliptic mirror furnace with slow thermal inertial.We confirmed the decagonal structure of the Al Cu Co Si grains by a tilting series of salected area diffraction patterns, Fig. 1. We obtained, that the quality of their atomic resolution electron microscope images is modify drastically with the composition of the alloy. Therfore, we find that the HRTEM images from our alloy were almost impossible to obtain because the lack of electrical conductivity of the sample produced too much astigmatism. The best images obtained are present in figure 2. Campare these with those obtained by Reyes-Gasga et al. [5] in a sample with different composition. In that case, this kind of aberration was not present. The sample was ground and supported in cooper grids for the their trasmision electron microscope analysis. Electron difraction patterns, tilting experiments were obtained using a JEOL 100CX analytical electron microscope equipped with ± 60 0 goniometer. Chemical analysis were carried out using a JEOL 2010F analytical electron microscope equipped with a ± 22 0 goniometer and a NORAN energy-dispersive X-ray analyzer For high resolution observation a JEOL 4000EX high resolution electron microcope was used.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.