Highnuclearity

High-nuclearity is a term used to describe metal-containing species in which a large number of metal atoms constitute a single cluster, core, or nanoparticle. In coordination chemistry, cluster chemistry, and materials science, nuclearity reflects the number of discrete metal centers that share ligands and a common framework. The threshold for "high" is not fixed and depends on context, but clusters with dozens or more metal centers are commonly described as high-nuclearity.

Nuclearity is typically determined by X-ray crystallography when crystals are available; otherwise, mass spectrometry and elemental analysis combined with structural models. For polycrystalline materials, indirect methods may estimate nuclearity. High-nuclearity clusters can be homometallic (all same metal) or heterometallic.

Synthesis often relies on self-assembly from metal salts and multidentate ligands, templating or lacunary building blocks, and specialized solvothermal or hydrothermal conditions. Soft-chemistry approaches and polyoxometalate chemistry are notable for producing very high-nuclearity clusters, such as Keplerates with around 132 metal centers.

Properties of high-nuclearity clusters are governed by metal–metal interactions and electronic structure; they can exhibit interesting magnetic behavior (e.g., exchange coupling, single-molecule magnet behavior), redox activity, catalytic sites, and tunable optical properties. Their large cores can provide multiple active sites and cooperative effects in catalysis.

A well-known family is polyoxometalate Keplerates, e.g., Mo132 and related W132 clusters, which contain about 132 metal centers interconnected by oxide ligands. Other high-nuclearity systems include metal-organic cages with M24L24 scaffolds and larger metal clusters formed by other transition metals.

Despite scientific interest, challenges remain: controlling stoichiometry and topology, stability in solution, crystallization, and scalable synthesis.