Spontaneous Electronic Band Formation and Switchable Behaviors in a Phase-Rich Superatomic Crystal

Abstract

Structural phase transitions run in families of crystalline solids. Perovskites, for example, feature a remarkable number of structural transformations that produce a wealth of exotic behaviors, including ferroelectricity, magnetoresistance, metal–insulator transitions and superconductivity. In superatomic crystals and other such materials assembled from programmable building blocks, phase transitions offer pathways to new properties that are both tunable and switchable. Here we describe [Co6Te8(PEt3)6]­[C70]2, a novel superatomic crystal with two separate phase transitions that drastically transform the collective material properties. A coupled structural-electronic phase transition triggers the emergence of a new electronic band in the fullerene sublattice of the crystal, increasing its electrical conductivity by 2 orders of magnitude, while narrowing its optical gap and increasing its spin density. Independently, an order–disorder transition transforms [Co6Te8(PEt3)6]­[C70]2 from a phonon crystal to a phonon glass. These results introduce a family of materials in which functional phase transformations may be manipulated by varying the constituent building blocks.

Self-Assembly of a Chiral Cubic Three-Connected Net from the High Symmetry Molecules C60 and SnI4

“…We follow this transition crystallographically by observing the appearance of reflections that are systematically absent in P 4 3 32 (h00 = 0k0 = 00l ≠ 4n) (Figure ). Pure C 60 also undergoes a phase transition upon cooling below 255–260 K where the C 60 molecules rotationally order, resulting in a change from a FCC to a primitive cubic structure and a sudden ∼0.05 Å reduction in the lattice parameter. , Similar phase transitions are detected in other fullerene intercalation compounds. , Given the nearly identical temperatures of the phase transitions in C 60 and C 60 (SnI 4 ) 2 , we hypothesize that a similar rotational ordering of C 60 occurs in C 60 (SnI 4 ) 2 , which breaks the 4 3 screw axis because the C 60 molecules no longer behave as spherical shells and become inequivalent by symmetry. However, the lattice parameter changes continuously with temperature in C 60 (SnI 4 ) 2 (Figure S8), complicating this analogy.…”

“…18,19 Similar phase transitions are detected in other fullerene intercalation compounds. 54,55 Given the nearly identical temperatures of the phase transitions in C 60 and C 60 (SnI 4 ) 2 , we hypothesize that a similar rotational ordering of C 60 occurs in C 60 (SnI 4 ) 2 , which breaks the 4 3 screw axis because the C 60 molecules no longer behave as spherical shells and become inequivalent by symmetry. However, the lattice parameter changes continuously with temperature in C 60 (SnI 4 ) 2 (Figure S8), complicating this analogy.…”

Structural order enhances charge carrier transport in self-assembled Au-nanoclusters

“…These materials exhibit larger dielectric constants than organic semiconductors with profound consequences for their excitedstate properties, such as the ability to exploit quantum confinement effects. A variety of such molecular clusters, often referred to as superatoms, has already been used for the formation of solid-state materials [14][15][16][17][18] . A special interest is thereby focused on the influence of the structure of the assembled materials onto their properties, possibly enabling the creation of materials with desired properties by design 19,20 .…”

Stepwise Assembly of an Electroactive Framework from a Co6S8 Superatomic Metalloligand and Cuprous Iodide Building Units

“…This can be achieved through intercluster charge‐transfer or via cluster‐salt metathesis . Ionic intercluster compounds derived from fullerene and metal‐chalcogenide clusters have been shown to exhibit novel physical properties such as thermal transport, ferromagnetic ordering, and switchable phase‐transitions, for example. Coordination driven assembly can also be utilized to prepare multi‐cluster crystalline solids.…”