Symmetry‐Based Metal Complex Cluster Formation

Abstract

There are examples of non-covalently linked molecular clusters in nature of stunning symmetry and beauty. Two are shown in Figure 1. The 24 individual protein subunits of apoferritin['.21 (the elipsoid-shaped subunits on the left of Fig. 1) cluster Fig. 1. Models of theapoferritin 24-mer (left) and human rhinovirus 60-mer (right). The view of ferritin IS down one of the C, axes. the other two C, axes of the octahedral cluster are horizontal and vertical, respectively. Along the body diagonal (between three of the elipsoid ends marked N) lies the C, axis of the octahedral cluster. The view, of the virus is down the C, axis, and the regions related by symmetry through the C2 axis and the Cj axis are shown in green and blue. respectively.together to form only this polymeric assemblage (symmetry group 0). The approximately spherical cavity can hold over 4000 iron atoms in the form of FeO(OH).['] When the apoprotein is dissociated into the individual protein subunits and then allowed to reassemble only the highly symmetrical 24-mer of apoferritin forms. Something similar happens with many viruses, in which non-covalently linked protein clusters of virus coats are used to protect the viral nucleic acid. The protein cluster coat of the human rhinovirus ( Fig. 1 contains 60 protein subunits, which spontaneously assemble to give an icosahedron (symmetry group I ) . Once again, it is generally true that dissociation and reassembly of the protein coat does not give a random polymer assembly but instead only the highly symmetrical 60-mer.What is it that leads to the high symmetry of such clusters? What is the relationship of this symmetry to the specificity seen in the formation of a single cluster type with unique cavity size and properties? In each case the individual molecular fragments (the protein subunits) are asymmetric units-the order of the pure rotation groups 0 and I are 24 and 60, respectively. Can this process be mimicked by using metal -ligand interactions as the driving force? This paper addresses these questions and shows that highly symmetrical clusters can be systematically designed by using the principles of symmetry-driven reactions deduced from natural structures.In considering the interaction of molecular subunits to make supramolecular assemblages[41 a useful, if extreme, simplification is to consider each intermolecular interaction around the symmetry axis as a molecular lock and key interaction.[5361 Such interactions that require different symmetries are incommensurate-they require different stoichiometries a t the site of interaction. A useful analogy can be made here with the interaction of incommensurate lattices (Fig. 2). As occurs with some natural silicates, the superposition of one layer upon another which has a slightly different lattice spacing soon results in a mismatch of the unit cells due to the incommensurate lattice spacings.171 The two spacings can be kept in register only by curling them, as shown in Figure 2. Similarly, two incommensurate coordination numbers can coexist only by a ...

Anion-templated self-assembly of tetrahedral cage complexes of cobalt(II) with bridging ligands containing two bidentate pyrazolyl-pyridine binding sites

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“…A notable feature of many such complexes is that the central cavity can accommodate guest species, with the nature of the guest depending on the charge carried by the surrounding complex cage. Thus, neutral cages tend to have either no guests (15) or solvent molecules as guests (17) in the cavity, anionic cages are found to contain tetraalkylammonium (19,21) (23,24). The twin facts that some cages can form without a guest (15,22) and that some guests can be freely exchanged with other species (19) suggest that in these cases, the assembly of the cage arises from an ideal match between the symmetry properties of the ligands and the coordination preferences of the metal ions, and that no templating effect is necessary.…”

Stereochemical Communication within Tetrahedral Capsules

“…21 One of the first examples is a [Ga 4 (3) 6 ] (4) structure based on C 2 -symmetric bishydroxamate ligands 3 ( Figure 3). 44 1 H NMR studies showed 4 to exist in solution as a mixture of the T, C 3 , and S 4 diastereomers having ≡ Figure 1. The subcomponent self-assembly of an octahedral metal ion (M 2+ ), 2-formylpyridine and an amine (commonly an aromatic amine, as shown) leads to a chiral, octahedral metal complex with C 3 symmetry; such complexes can form the vertices of tetrahedral supramolecular structures.…”

Properties of N,N-Bis[2-(isonicotinoyloxy)ethyl]-p-toluenesulfonamide. Structures of Its Silver(I) Complexes via Anion Effects

“…[1][2][3][4][5] In particular, various metallamacrocycles have been studied as important building blocks in the construction of functional supramolecular materials that can be utilized for molecular recognition, selective transformation, drug delivery systems, catalysts, storage, and biomimics. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Facile synthetic methods are either the ring-expansion [21][22][23] by means of labile metalligand coordination or the ring-formation via appropriate tectonics.…”