Nanostructures of III-V (III: Ga, In; V: N, P, As) and II-VI (II: Zn, Cd; VI: S, Se, Te) semiconductor materials have attracted a great deal of interest due to their fascinating properties, which usually differ from their bulk counterparts. There are two main reasons responsibles for such a deviation. On the one hand, the confinement of electrons (and holes) in nanostructures gives rise to a size- and shape- dependent structure of electronic levels. On the one hand, the number of atoms forming the surface of a nanostructure is a significant fraction of the total. The unsaturated surface atoms tend to reorganize in order to minimize the surface energy, favouring certain crystalline phases and eventually leading to fancy atomic arrangements. Again, the stability of each polymorph depends on the size and the morphology of the nanostructure.

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Nanostructures are characterized by their high surface-to-volume ratio. Unsaturated surface atoms tend to rearrange their position in order to saturate the dangling bonds and minimize the surface energy. Such a reconstruction penetrates deep inside the nanostructure and determines, to a large extent, the morphology of the material. Solvent and surface attached ligands modify the surface energy and exert a strong influence on the atomic structure of the nanomaterial, which in turn, defines the electronic and optical structure of the material. Furthermore, surface attached ligands modify important properties of nanomaterials, including photophysics, charge transport, catalysis and magnetism. Tayloring nanostructures’ character by means of surface attached ligands has aroused the interest of chemists and physicists. Chemical functionalization has been proven to be very useful in designing materials with specific electrical and optical properties. Moreover, the application of nanomaterials in biology and medicine is based on the ability to make them water soluble and to cap them with specific surfactants in order to facilitate selective binding to target biomolecules or subcellular structures.

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Designing new chemical compounds is one of the most ambitious goals of every chemist. Nonetheless, efforts made for the understanding of the chemistry of new chemical compounds often yield new paradigms which open unexpected research areas. All-metal aromatic molecules, recently synthesized by Li et al, constitute one such an example. Indeed, rationalizing the unexpected large resonance energy of Al4(2-) has yield the concept of multiple-fold aromaticity, as that present in molecules that posses more than one independent delocalized bonding system, either σ-type or π-type, each of them satisfying the 4n+2 electron counting rule of aromaticity.

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The study of small nanoclusters may serve as a bridge between bulk materials and atomic structures. In these nanoclusters, the coexistence of different type of metals may give rise to interesting electronic, structural, chemical or catalytical properties. The study of the chemical bond in small clusters is a crucial issue to understand and predict the behaviour of nanomaterials of more realistic sizes.

Contact person: Jon M. Matxain. email: jonmattin.matxain@ehu.es