Superatomic Solid-State Material Structures Imitate Simple Salts

As part of a quest to prepare materials with new electronic and magnetic properties, researchers have combined molecular clusters into solid-state assemblies that have structures imitating simple molecules such as table salt. The appeal of materials made of these super­atomic components is that building blocks can be varied in size and composition to tune properties in a way that’s not possible for traditional solid-state materials. The research team, led by Columbia University’s Xavier Roy, Michael L. Steigerwald, and Colin Nuckolls, used metal clusters as one superatom building block and C₆₀ as the other (Science 2013, DOI: 10.1126/science.1236259). One of the materials is [Ni₉Te₆(P(C₂H₅)₃)₈][C₆₀], which has a crystal lattice that structurally resembles NaCl, albeit with larger dimensions. Other materials they prepared are [Co₆Se₈(P(C₂H₅)₃)₆][C₆₀]₂ and [Cr₆Te₈(P(C₂H₅)₃)₆][C₆₀]₂, which both resemble CdI₂. The products form when the metal clusters transfer electrons to C₆₀. The materials possess collective electronic and magnetic properties that are absent in their constituent parts. For example, the superatomic building blocks behave individually as insulators, whereas the combined materials are semiconductors.