At the edge of covalency: metallic nanotubes, low-dimensional metals and clusters

Abstract

Abstract One of the main classifications of materials uses the categories of metals, semiconductors and insulators. However, the boundaries are vague. In so-called confined metals the mobility of conduction electrons is restricted by at least one of the following circumstances: (a) Tendency towards electronic localization in covalent bonds, on ions or in lone-pairs (chemical confinement). (b) Contrast of bonding interactions in adjacent parts of the structure, i.e. separation of metallic and non-metallic domains (structural confinement). (c) Reduced size of metallic particles (size confinement). One playground for the investigation of the properties of matter at the limit of the metallic state is the chemistry of low-valent bismuth compounds, from which metallic nanotubes and nanorods, crystalline metal/salt hybrids, low-dimensional metals and unique clusters emerge. Strange physical effects, like coexistence of ferromagnetism and superconductivity, are found.