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A series of planar tetracoordinate carbon molecules in cyclic semisaturated hydrocarbons resulting from the combination of the C5(2-) skeleton with saturated hydrocarbon fragments is reported. The electronic stabilization and the bonding situation are studied through the analyses of molecular orbitals and the electron localization function. The magnetic properties are also revised, giving particular attention to the induced magnetic field. These systems are the first semisaturated cycles containing a planar tetracoordinate carbon stabilized only by electronic factors.

Theoretical electronic Structure methods have been employed to study the structure and activity of certain (free) quinolones and the interaction of their Cu(II)-complexes on a DNA model (Rhodamine 6G (rhod)). As a manner of assessing the generated geometries, the nalidixic acid geometrical parameters obtained were tested against the crystallographic ones and it was found that the average error in the calculated geometries is small. The present study allows us to (1) Rationalize the observed differences in antibiotic activities through their electronic hardnesses. (2) Suggest a plausible mechanism of action for these drugs through formation of a reactive intermediate (or carrier) which would consist of a quinolone anion coordinated to an adequate metal center (Cu(II) in this study). (3) We find that, through this model of DNA (modeled with rhod) the interaction seems to be mediated by an effective π-π stacking. (4) Finally, an in vitro experiment was designed so that the intercalation process in DNA could be experimentally modeled as well. The quenching of the rhod fluorescence is proportional to the strength of the Cu(II)-complex-rhod interaction and therefore provides a quantitative measurement of the “intercalating” capacity of the quinolones and their copper complexes. These results agree well with the theoretical total adduct formation energies.

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The arene rings of W ( ~-C ~H S M ~) ~ and M o ( ~-C ~H ~) ~ are readily displaced by the fulvenes C5H4=CR2 (R = M e or Ph) giving M(q5:91-C5H4-p-CR2) (7-arene), M = Mo or W; when M = Mo and R = M e then treatment with HCI gives the binuclear [ M o ( 9-PriC5H4) (p-CI2)l2 whose crystal structure has been determined and which is a convenient precursor t o mono-cyclopentadienylmolybdenum derivatives. The compounds M(q5 :q1-C5H4-p-CRi)(q-C6H5R3) (1)-(4) conditions of an arene ring of M(q-C6H5R1)2 (M = Mo, are readily prepared in high yields by displacement under mild R1 = H or M = W, R1 = Me, respectively) by the disubsti-