The symmetry, structure and formation mechanism of the structurally self-complementary {Pd84} = [Pd84O42(PO4)42(CH3CO2)28](70-) wheel is explored. Not only does the symmetry give rise to a non-closest packed structure, the mechanism of the wheel formation is proposed to depend on the delicate balance between reaction conditions. We achieve the resolution of gigantic polyoxopalladate species through electrophoresis and size-exclusion chromatography, the latter has been used in conjunction with electrospray mass spectrometry to probe the formation of the ring, which was found to proceed by the stepwise aggregation of {Pd6}(-) = [Pd6O4(CH3CO2)2(PO4)3Na(6-n)H(n)](-) building blocks. Furthermore, the higher-order assembly of these clusters into hollow blackberry structures of around 50 nm has been observed using dynamic and static light scattering.
Molecular self-assembly has often been suggested as the ultimate route for the bottom-up construction of building blocks atom-byatom 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 fPd 84 g-ring cluster 3.3 nm in diameter; ½Pd 84 O 42 ðOAcÞ 28 ðPO 4 Þ 42 70− (fPd 84 g ≡ fPd 12 g 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 fPd 84 g-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 fPd 84 g 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 fPd 84 g 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.polyoxopalladates | {M84} cluster | noble metals | inorganic chemistry | self assembly F unctional nanotechnology requires control of nanomolecular architectures (1-3) that probably can only be achieved by selfassembly from the bottom up (4, 5) but this process itself is very difficult to predict, rationalize, or control. In self-assembly, the observation of symmetrically favored numbers of metal nuclearity ("magic numbers") (6) or shapes with high symmetry, such as icosahedra (7) and rings (8-10), may provide a theoretical basis for the reliable and controlled fabrication of complex molecular architectures. In this respect we hypothesized that it is important to design minimal systems that use only a small number of chemical components, but with a vast library of possible architectures, and to use the techniques of structural and analytical chemistry to probe the range of accessible molecular architectures. By conducting such solution studies, combined with structural analysis, our aim has been to understand the overall cluster nuclearity and structure to reveal the underlying principles that link symmetry to structure with the overall grand aim of the a priori design of molecular nanosystems from the bottom up using self-assembly.Here, we present the discovery of a complex self-assembled system in which the architectural beauty and molecular complexity are orchestrated by symmetry and a library of dynamic subuni...
A high-nuclearity polyoxopalladate compound, [Pd(II)(2)⊂{H(7)Pd(II)(15)O(10)(PO(4))(10)}](9-) {Pd(II)(17)}, comprising a {Pd(15)} host occupied by a {Pd(2)} guest and the parent pristine "empty" [H(7)Pd(II)(15)O(10)(P(V)O(4))(10)](13-) {Pd(15)} cluster have both been prepared and characterized by single-crystal X-ray crystallography, (31)P NMR, CSI-MS, and XPS. The encapsulated {Pd(2)} has a short Pd(II)-Pd(II) distance within the {Pd(15)} host. Solution studies indicate that the empty host and filled guest complex are in equilibrium with each other, and UV titrations revealed a binding constant of ca. 10(3) for the guest Pd(II) ions, with a binding stoichiometry of almost 2.
The {Pd84}Ac wheel, initially discovered serendipitously, is the only reported giant palladium macrocycle—a unique structure that spontaneously assembles from small building blocks. Analogues of this structure are elusive. A new modular route to {Pd84}Ac is described, allowing incorporation of other ligands, and a new screening approach to cluster discovery. Structural assignments were made of new species from solution experiments, overcoming the need for crystallographic analysis. As a result, two new palladium macrocycles were discovered: a structural analogue of the existing {Pd84}Ac wheel with glycolate ligands, {Pd84}Gly, and the next in a magic number series for this cluster family—a new {Pd72}Prop wheel decorated with propionate ligands. These findings confirm predictions of a magic number rule for the family of {Pdx} macrocycles. Furthermore, structures with variable fractions of functional ligands were obtained. Together these discoveries establish palladium clusters as a new class of tunable nanostructures. In facilitating the discovery of species that would not have been discovered by orthodox crystallization approaches, this work also demonstrates the value of solution‐based screening and characterization in cluster chemistry, as a means to decouple cluster formation, discovery, and isolation.
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