A nanometre-sized hexahedral coordination capsule assembled from 24 components

199

182

An important problem in designing any large network is the assembly of systems that are resilient to change. From a chemical point of view, an analogy can be used where one requires supramolecular assemblies to maintain their dimensionality combined with limited structural perturbation in response to variation in its intermolecular framework. The identification of hydrogenbonded framework patterns within experimentally known supramolecular assemblies that are structurally robust to disruption and selective hydrogen substitution are envisioned to act as a supramolecular blueprint or template for metal-ion retroinsertion. Here, we report the formation of a large neutral discrete pseudo-spherical coordination capsule assembled from 6 pyrogallol[4]arene ligands and 24 Cu(II) metal ions. Amazingly, this coordination capsule is structurally analogous to its hydrogenbonded counterpart. This result shows a robust ability of pyrogallol[4]arene molecules to self-assemble into large hexameric cage structures from either the hydrogen-bonding or metal-ligand coordination process. The identification of robust supramolecular assemblies that conserve their structure in response to interchangeability between hydrogen-bonded networks for metal coordination, or inversely, represents an important advancement in supramolecular design.coordination ͉ self-assembly ͉ hexamer I nspired by the architectural beauty and robustness found within nature, the design of large multicomponent spheroid cage assemblies on the nanometer scale is becoming increasing feasible. These large supramolecular architectures often resemble and conform to the simple geometrical shapes described by Platonic or Archimedean solids (1). Indeed, such structural morphologies have attracted tremendous interest because of their practical applications for encapsulating various guest molecules (2). Synthetic chemists have principally relied on various self-assembly methods in their construction, such as hydrogen bonds (3) or metal-ligand coordination (4), although some notable covalent methods have recently been reported (5).A popular strategy for designing large multicomponent cage assemblies is the metal-directed self-assembly approach, advocated chiefly by Fujita and coworkers (6-9) and Stang and coworkers (10-12). This method has mainly focused on the geometrical permutation of various triangular pyridine-like bridging ligands driven by coordination to cis-protected Pd metal centers. Nevertheless, for the construction of discrete assemblies with large molecular cavities, the molecular paneling approach by Fujita and coworkers (13) has received the most success. Indeed, an amazingly large discrete functionalized spherical coordination network assembled from 12 metal ions and 24 exo-multidentate ligands was recently reported (14). However, an inherent complication of using n-dimensional pyridine-like spacer multidentate ligands in coordination is the resultant high positive charge combined with porous surfaces within these supramolecular assemblies. The counterions us...

mentioning

confidence: 99%

Supramolecular blueprint approach to metal-coordinated capsules

McKinlay

Cave

Atwood

2005

199

182

“…We choose Pd(II) in this study for two main reasons: Firstly, it has a well-known controllable and spontaneous behavior in metal-directed assembly, such as molecular capsules, due to its smaller coordination number and greater preference for square-planar geometry than other transition metal ions (11,12); and secondly the recent discovery of polyoxopalladates (13,14). In 2011 we reported a fPd 17 g cluster compound, Na 6 ½H 9 Pd 17 O 10 ðPO 4 Þ 10 , which is formed by heating a system of Pd 3 ðOAcÞ 6 in NaH 2 PO 4 -Na 2 HPO 4 solution for 90 min (14).…”

mentioning

confidence: 99%

Correlating the magic numbers of inorganic nanomolecular assemblies with a {Pd ₈₄ } molecular-ring Rosetta Stone

Miras²,

Scullion³

et al. 2012

105

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...

“…Rebek and colleagues (11)(12)(13)(14) have pioneered the use of self-assembly to produce a variety of entities seamed together by hydrogen bonds. Multicomponent systems also have been assembled by means of transition metal-based coordinate bonds (15)(16)(17)(18)(19)(20). The synthesis of hosts capable of housing a wide variety of guests has further been achieved by the use of the principles of crystal engineering (21,22).…”

mentioning

confidence: 99%

Organization of the interior of molecular capsules by hydrogen bonding

Atwood

Barbour

Jerga

2002

210

The enclosure of functional entities within a protective boundary is an essential feature of biological systems. On a molecular scale, free-standing capsules with an internal volume sufficiently large to house molecular species have been synthesized and studied for more than a decade. These capsules have been prepared by either covalent synthesis or self-assembly, and the internal volumes have ranged from 200 to 1,500 Å 3 . Although biological systems possess a remarkable degree of order within the protective boundaries, to date only steric constraints have been used to order the guests within molecular capsules. In this article we describe the synthesis and characterization of hexameric molecular capsules held together by hydrogen bonding. These capsules possess internal order of the guests brought about by hydrogen bond donors within, but not used by, the framework of the capsule. The basic building blocks of the hexameric capsules are tetrameric macrocycles related to resorcin[4]arenes and pyrogallol[4]arenes. The former contain four 1,3-dihydroxybenzene rings bridged together by -CHR-units, whereas the latter contain four 1,2,3-trihydroxybenzene rings bridged together. We now report the synthesis of related mixed macrocycles, and the main focus is on the macrocycle composed of three 1,2,3-trihydroxybenzene rings and one 1,3-dihydroxybenzene ring bridged together. The mixed macrocycles self-assemble from a mixture of closely related compounds to form the hexameric capsule with internally ordered guests.