On the nature and importance of the transition between molecules and nanocrystals: towards a chemistry of “nanoscale perfection”

Abstract

This paper discusses the importance of the transition between molecular compounds and nanocrystals. The boundary between molecular and nanocrystals/nanoclusters can be defined by the emergence of the bulk phase; atoms in the core of the nanoclusters that are not bound to ligands. This transition in dimensions and structural organization is important because it overlaps with the boundary between atomically defined moieties (molecules can be isolated with increasing purity) and mixtures (nanocrystals have a distribution of sizes, shapes, and defects; they cannot be easily separated into batches of structurally identical species). Passing through this boundary, as the size of a structure increases beyond a few nanometres, the information about the position of each atom gradually disappears. This loss of structural information about a chemical structure fundamentally compromises our ability to use it as a part of a complex chemical system. If we are to engineer complex functions encoded in a chemical language, we will need pure batches of atomically defined (truly monodisperse) nanoscale compounds, and we will need to understand how to make them and preserve them over a broad range of length scales, compositions, and timeframes. In this review we survey most classes of monodisperse nanomaterials (mostly nanoclusters) and highlight the recent breakthroughs in this area which might be spearheading the development of a chemistry of "nanoscale perfection".

Structure & bonding of the gold-subhalide cluster I-Au144Cl60[z]

“…The enormous reduction in complexity may mean that an understanding of the structure, bonding, and electronic properties of ligand-protected noble-metal clusters, in the crucial size-range where the characteristically ‘metallic’ properties emerge, may not be so distant, after all. 29 …”

Bottom-up assembly of photonic crystals

“…For instance, intrinsically non-chiral colloids, such as nanoprisms, stabilized with chiral ligands were shown to assemble into helical columnar colloidal crystals resembling chiral liquid crystal mesophases. 27 Given intrinsic chirality of clusters stabilized with chiral ligands, 25 their supramolecular assembly into colloidal particles with preservation of chirality can be envisaged. Another relevant system concerns helical supramolecular self-assembled structures templated by inorganic materials, such as silica, for creation of chiral CBBs.…”

“…24 An advantage of silicon colloidal stabilization is in facile formation of an oxidized surface layer of silica that is commonly utilized in Si-NCs. 25 Inorganic oxides are among the most commonly used dielectric materials of CBBs for PCs due to their usually low light absorption in the visible and NIR and the relative ease of electrostatic stabilization in polar solvents. Two typical examples of stabilizing surfactants/ligands used for oxides are siloxanes and phosphonates.…”

“…thiols, phosphines, amines) in order to counteract aggregation. 25 Self-assembly of anisotropic CBBs permits versatile control over the dimensionality of colloidal photonic crystals. For instance, 1D PCs can be prepared using 2D colloidal building blocks (e.g.…”

Using shape for self-assembly

“…In artificial systems, our reliance on 'imperfect' building blocks may severely limit the potential complexity of future self-assembled systems. There is therefore an interest in developing a chemistry of nanoscale 'perfection' (and of 'self-correction'), which strives to create and characterize atomically defined building blocks at the nano-and microscale [15]. -Understanding and controlling the interactions.…”