Examinando por Autor "Ponce Vargas, Miguel Armando"

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    Metallacycles capabilities in host-guest chemistry
    (2014) Ponce Vargas, Miguel Armando; Muñoz Castro, Álvaro
    Metallacycles offer structural diversity and interesting properties based on their highly symmetric frameworks and host-guest chemistry. They can be used as molecular recognition agents, photochromic devices, catalysts, and surface patterning structures, just to mention a few applications. The aim of this work is to gain a deeper understanding into the coupling forces within metallacycle complexes possessing metal centers acting as binding sites, by using density functional calculations. We focus on the electrostatic contribution to total interaction energy, which can be divided in ion-dipole, ion-quadrupole, dipole-dipole, dipolequadrupole, etc., according to the multipole expansion of the electrostatic potential. We choice two representative case studies: halide-centered hexanuclear copper(II) pyrazolate- and di-halide cyclic pentameric perfluoroisopropylidenemercury complexes, due to the presence of metal centers capable of interacting directly with the guest entities. The current approach, allows us to determine the role of certain Coulombic terms in the electrostatic nature of the coupling forces, leading to a clear rationalization of the soft-soft or hard-soft preferences into the formation of the host-guest entities. The non-covalent forces involving the hexanuclear copper(II) pyrazolate complexes and a halide guest [trans-Cu6{μ -3 ,5-(CF3)2pz}6(μ-OH)6X]- (X = F, Cl, Br, 1), describe an electrostatic character (about 70% of the stabilizing terms) where the ion-dipole and ionquadrupole contributions to the electrostatic term range from 95.0% to 77.0%, going from f - to r-, describing the increasing role of higher arder interactions, such as quadrupoledipole and quadrupole-quadrupole into the coupling as the guest becomes softer. In di-halide cyclic pentameric perfl uoroisopropylidenemercury complexes, [(HgC(Cf3)2)s2X]2- (X = Cl, Br, 1), our results revea! an interesting case where the expected soft acid-soft base pair is not the more stable situation. Instead, a surprising hardsoft pair arises as the preferred species, with stronger forces towards Cl- than those corresponding to J- by about 24 kcal/mol. The almost linear mercury local geometry and the Dsh molecular symmetry determine the shape of the local quadrupole moments at the binding sites leading to an in-plane distribution, preventing the arise of a significant quadrupole component perpendicular to the Hgs plane, that could contribute to higher order electrostatic terms such as quadrupole-quadrupole, which is related to the soft-soft preference. In summary, the results here presented suggest that metallacycles hosts with metal centers acting as binding sites, can offer great advantages in comparison to their organic counterparts, prompted by the versatility of such centers, which can modulate their electron density according to the incoming guest. This work was made possible by the CONICYT 63130036 Doctoral fellowship, and the financia! support of UNAB-DI-403-13/I Interna! Project, 1140358 FONDECYT Grant and RCl20001 MILLENNIUM Project.