Biomedical subjects

G Aullón

Publications and source records attributed to G Aullón.

3 recordsLinked to original sources

PubMed2001

Molecular structures of edge-sharing square-planar dinuclear complexes with unsaturated bridges.

The dinuclear complexes of transition metal ions of type [M(2)(mu,eta(1)-XY)(2)L(4)], where XY is an unsaturated ligand that can act as a four-electron or a two-electron donor through the X atom, appear in two molecular conformations depending on whether the coordination planes around the two metal atoms are coplanar or bent. In both structures the geometry of the X atom is planar, corresponding to an sp(2) hybridization. An ab initio theoretical study on 43 representative complexes, complemented with a structural database analysis, provides a rationale for the experimentally observed structures.

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PubMed2000

Through-ring bonding in edge sharing dimers of octahedral complexes.

A study of the preferred structures for the M2X2 rings in the binuclear complexes of types [M2(mu-XR2)2L8] and [M2(mu-XR3)2L8] is presented, based on qualitative orbital arguments supported by extended Hückel calculations on Cr compounds. The main conclusions are confirmed by DFT calculations on key compounds of Cr and Mn and agree well with the results of a structural database analysis. With the simplified electron counting scheme deduced, complexes with six or four electrons available for bonding of the M2X2 framework are predicted to have two possible minimum energy structures, with either a short M-M or X-X distance, whereas compounds with eight framework electrons are expected to present no short through-ring distance. Such a behavior is consistent with the framework electron rules reported earlier for compounds with different coordination spheres and provides a general description of the structure and bonding in a variety of compounds with M2X2 diamonds. Metal-metal bonding across the ring can be equally predicted taking into account only the bonding characteristics of the t2g-like orbitals for the XR2- but not for the XR3-bridged complexes. In addition, the framework electron counting scheme has the advantage of being independent of the formal oxidation state assigned to the metal atom.

Journal Article↗

PubMed2000

Structural correlations and conformational preference in edge-sharing binuclear d8 complexes with XR2 bridges. A theoretical study.

The binuclear complexes of d8 transition metal ions of the type [M2(mu-XR2)2L4] (where M = RhI, IrI, NiII, PdII, PtII, or AuIII; X = S, N, P, or As) appear in a variety of molecular conformations in which the coordination planes around the two metal atoms are sometimes coplanar, sometimes bent. For the bent compounds with asymmetric bridges, XR1R2, the substituents adopt different orientations relative to the metal framework and to each other. Ab initio theoretical studies on the different conformers of 30 representative complexes, complemented with a structural database analysis, have allowed the establishment of structural correlations in this family of compounds. The conformational choice results from a delicate balance of different interactions which are qualitatively analyzed, such as the changes in bond angles around the bridging atoms, the existence of weak metal...metal bonding in the bent structures, and steric interactions involving the terminal ligands and the substituents at the bridging atoms.

Journal Article↗