Helices and Helicates: Beautiful Supramolecular Motifs with Emerging Applications

Hannon, Michael J.; Childs, Laura J.

doi:10.1080/10610270310001632386

Cited by 275 publications

(62 citation statements)

References 66 publications

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“…One of the simplest assemblies is the dinuclear doublestranded helicate, and the rules that govern the formation of this species are largely established. [1][2][3][4][5][6][7] The formation of the helicates' higher nuclearity cousin, the cyclic helicate, is conversely less well understood. One of the major problems in the formation of these higher nuclearity assemblies is that the design principles that apply to helicate formation, i.e.…”

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Controlling the formation of metallosupramolecular assemblies by metal ionic radii

et al. 2010

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The formation of either dinuclear double-stranded or pentanuclear circular helicates from a ligand containing two tridentate domains separated by a phenylene unit can be controlled by inter-ligand steric interactions which themselves are governed by the size of the metal ion.Controlling the structure of multi-component assemblies is one of the leading challenges for the supramolecular chemist. One of the simplest assemblies is the dinuclear doublestranded helicate, and the rules that govern the formation of this species are largely established. [1][2][3][4][5][6][7] The formation of the helicates' higher nuclearity cousin, the cyclic helicate, is conversely less well understood. One of the major problems in the formation of these higher nuclearity assemblies is that the design principles that apply to helicate formation, i.e. using a ligand that contains two binding domains that coordinate different metal ions, equally apply to the formation of cyclic helicates. For the larger cyclic species to preside in solution, the formation of the entropically favoured dimer has to be prevented and this can be achieved by intermolecular interactions (e.g. templation by anions) 8 or by intramolecular interactions which stabilise the formation of the cyclic species relative to its double-stranded alternative. As an example of the first of these approaches, in the work carried out by Ward et al., a ligand with two bidentate domains separated by a 1,8-naphthalenediyl spacer was reported to form a simple mononuclear species with Cu(CF 3 SO 3 ), but in the presence of tetrafluoroborate, a tetranuclear cyclic helicate [Cu 4 L 4 ] 4+ was observed. 9 Hannon et al., on the other hand, demonstrated that a metal ion's preference for different coordination geometries could affect the self-assembly outcome. In this case a bis-bidentate ligand containing a 1,3-bis(aminomethyl)phenyl spacer formed linear dimers with tetrahedral metal ions and trinuclear circular helicates with octahedral metal ions. 10 Other reports have cited inter-strand CHÁ Á Áp interactions as the principal driving force for the preferential formation of high complexity cyclic assemblies over their dimeric In this communication we describe how the formation of either dinuclear double-stranded or pentanuclear circular helicates can be controlled by inter-ligand steric interactions which, in turn, are governed by the size of the metal ion. This approach allows for the specific formation of either of the two structures and gives valuable insight into some of the factors which control the formation of cyclic helicates.The ligand L 1 , which was prepared by the reaction of 2,2 0 -bipyridine-6-thioamide with 1,3-di(a-bromoacetyl)benzene, contains two tridentate binding domains separated by a phenylene ring (Fig. 1) was confirmed by a single crystal X-ray diffraction study (Fig. 2).z In the solid-state the ligand partitions into two tridentate domains, each comprising a thiazole-pyridyl-pyridyl

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Controlling the formation of metallosupramolecular assemblies by metal ionic radii

et al. 2010

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“…Advances in the design of large metallo-supramolecular complexes, utilising metal-ligand interactions to synthesise nanoscale architectures such as universal ravels, [15] molecular knots, [16,17] cages [18] and helices [19][20][21]-not so easily accessible through the use of covalent bonds-are providing SCO complexes with increasing complexity of design [22][23][24]. The development of synthetic pathways for the construction of metallo-supramolecular SCO architectures that do not require extensive ligand synthesis, and that utilise commercially available materials, provides greater accessibility of these materials for future applications of SCO materials [25].…”

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Investigation of the Spin Crossover Properties of Three Dinulear Fe(II) Triple Helicates by Variation of the Steric Nature of the Ligand Type

et al. 2017

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Abstract:The investigation of new spin-crossover (SCO) compounds plays an important role in understanding the key design factors involved, informing the synthesis of materials for future applications in electronic and sensing devices. In this report, three bis- − counter ions and imidazole N-H were present. The three compounds displayed similar spin-transition profiles, with 2 (-S-) possessing the steepest nature. The shape of the spin transition can be altered in this manner, and this is likely due to the subtle effects that the steric nature of the central atom has on the crystal packing (and thus inter-helical Fe-Fe separation), intermolecular interactions and Fe-Fe intra-helical separations.

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“…E.g., double-stranded helicates are formed from linear ligand strands with bidentate chelating units and tetrahedrally coordinated metal ions, whereas appropriate metal centres for triple-stranded helicates possess, e.g., octahedral coordination geometry. [23][24][25] Due to the simplicity of helicates, they developed over the years to a kind of metallosupramolecular chemists ''drosophila.'' They allow the study of fundamental mechanistic principles.…”

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Symmetry Driven Self-Assembly of Metallo-Supramolecular Architectures

Albrecht¹,

Fröhlich²

2007

Bulletin of the Chemical Society of Japan

111

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The self-assembly of well-defined metallosupramolecular aggregates highly depends on the symmetry of the ligands as well as of the metals. Approaches in which symmetry considerations allow the stepwise-''hierarchical''-assembly of helicate-type complexes from very simple catechol derivatives are described. In addition helicates and meso-helicates are stereoselectively obtained by the use of linear ligands possessing the relevant symmetry element for the formation of either diastereomer (even-odd principle). In case of helicates, this allows the preparation of enantiomerically pure complexes. Finally, the self-assembly of tetrahedral M 4 L 4 complexes is described using either constrained flexible or highly predisposed rigid ligands.

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Helices and Helicates: Beautiful Supramolecular Motifs with Emerging Applications

Cited by 275 publications

References 66 publications

Controlling the formation of metallosupramolecular assemblies by metal ionic radii

Controlling the formation of metallosupramolecular assemblies by metal ionic radii

Investigation of the Spin Crossover Properties of Three Dinulear Fe(II) Triple Helicates by Variation of the Steric Nature of the Ligand Type

Symmetry Driven Self-Assembly of Metallo-Supramolecular Architectures

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