Correlating the magic numbers of inorganic nanomolecular assemblies with a {Pd84} molecular-ring Rosetta Stone.

Molecular self-assembly has often been suggested as the ultimate route for the bottom-up construction of building blocks atom-by-atom for functional nanotechnology, yet structural design or prediction of nanomolecular assemblies is still far from reach. Whereas nature uses complex machinery such as the ribosome, chemists use painstakingly engineered step-by-step approaches to build complex molecules but the size and complexity of such molecules, not to mention the accessible yields, can be limited. Herein we present the discovery of a palladium oxometalate {Pd(84)}-ring cluster 3.3 nm in diameter; [Pd(84)O(42)(OAc)(28)(PO(4))(42)](70-) ({Pd(84)} ≡ {Pd(12)}(7)) that is formed in water just by mixing two reagents at room temperature, giving crystals of the compound in just a few days. The structure of the {Pd(84)}-ring has sevenfold symmetry, comprises 196 building blocks, and we also show, using mass spectrometry, that a large library of other related nanostructures is present in solution. Finally, by analysis of the symmetry and the building block library that construct the {Pd(84)} we show that the correlation of the symmetry, subunit number, and overall cluster nuclearity can be used as a "Rosetta Stone" to rationalize the "magic numbers" defining a number of other systems. This is because the discovery of {Pd(84)} allows the relationship between seemingly unrelated families of molecular inorganic nanosystems to be decoded from the overall cluster magic-number nuclearity, to the symmetry and building blocks that define such structures allowing the prediction of other members of these nanocluster families.