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We employ second-order Møller-Plesset perturbation theory level in combination with recently developed pseudopotential-based correlation consistent basis sets to obtain accurate relativistic-consistent electron densities for small coinage metal clusters. Using calculated electron densities, we employ Bader's quantum theory of atoms in molecules (QTALM) to gain insights into the nature of metal-metal bonding in the clusters M2, M4, M4,2-, and M4Na2 (M = Cu, Ag, Au). For the simplest case of the metal dimer, M2, we correlate the strength of the metal-metal bond with the value of the electron density at the bond critical point, the total energy density at the bond critical point, the sharing (derealization) index, and the values of die two principle negative curvatures. We then consider changes to the metal-metal bonding and charge density distribution upon the addition of two metal atoms to form the metal tetramer, M4 and then followed by the addition of an electron pair to form M42- and finally followed by die addition of two alkali metal (sodium) ions to form M4Na2. Using topological properties of die electron density, we present evidence for the existence of a-aromaticity in Au42- . We also report die existence of two non-nuclear attractors in the molecular in the molecular graph of Cu42- and large negative charge accumulation in the nonbonded Cu basins of this cluster. [ABSTRACT FROM AUTHOR]

Examines the synthesis of a crystalline compound containing titanium (Ti) bonded to cyclopentadienyl and dienyl fragments. Connection between Ti and carbon; Interaction between metals and saturated carbon atom; Discussion of the quantum theory of atoms in molecules.

The molecular structure can be defined quantum mechanically thanks to the theory of atoms in molecules. Here, we report a new molecular model that reflects quantum mechanical properties of the chemical bonds. This graphical representation of molecules is based on the topology of the electron density at the critical points. The eigenvalues of the Hessian are used for depicting the critical points three- dimensionally. The bond path linking two atoms has a thickness that is proportional to the electron density at the bond critical point The nuclei are represented according to the experimentally determined atomic radii. The resulting molecular structures are similar to the traditional ball and stick ones, with the difference that in this model each object included in the plot provides topological information about the atoms and bonding interactions. As a result, the character and intensity of any given interatomic interaction can be identified by visual inspection, including the noncovalent ones. Because similar bonding interactions have similar plots, this tool permits the visualization of chemical bond transferability, revealing the presence of functional groups in large molecules. [ABSTRACT FROM AUTHOR]