Helicates as Versatile Supramolecular Complexes

Piguet, Claude; Bérnardinelli, Gerald; Hopfgartner, Gérard

doi:10.1021/cr960053s

Cited by 1,710 publications

(985 citation statements)

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“…1) 4 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 Fig.…”

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confidence: 79%

“…In both structures this central phenylene ring is sandwiched between the internal pyridyl rings of the two thiazole-pyridine-pyridine tridentate domains, but in the pentanuclear helicate this packing motif is more compact, with an average centroidÁ Á Ácentroid distance of 3.9(1) Å (cf. 4 respectively. Conversion of these values into meaningful hydrodynamic radii is not trivial since microfrictional and shape effects can profoundly influence the apparent relationship between diffusion constant and molecular size.…”

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confidence: 98%

“…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

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“…The systematic diastereotopicity of all methylene protons (H12 ± H16) (observed as pseudo-sextets because J 2 % 2 J 3 , Figure 4a) excludes a D 3h symmetrical arrangement of the three strands (i.e., a nonhelical arrangement or a fast helical interconversion), but it is compatible with a non-interconverting racemic mixture of 1) helicates PPP-[Ln 3 (L7) 3 ] 9 and MMM-[Ln 3 (L7) 3 ] 9 or 2) side-by-side complexes PMP-[Ln 3 (L7) 3 ] 9 and MPM-[Ln 3 (L7) 3 ] 9 belonging to the D 3 point group. [34] The large upfield complexation shifts of the protons bound to the 4-position of the benzimidazole rings (H5,H6) in [La 3 (L7) 3 ] 9 (Dd 1.83 ± 1.93 ppm), [Y 3 (L7) 3 ] 9 (Dd 2.21 ± 2.37 ppm), and [Lu 3 (L7) 3 ] 9 (Dd 2.32 ± 2.50 ppm, Table 4) are diagnostic for a regular helication that puts these protons in the shielding region of the connected benzimidazole ring [22] in agreement with the crystal structure of [Eu 3 (L7) 3 ] 9 (Figure 6), but in complete contradiction with amphiverse PMP (or MPM) conformers. The observation of weak but significant interstrand NOE effects involving protons of the terminal and central binding units (for instance H4 ± H18) points to three strands tightly wrapped about the helical axis; [22] this rules out complexes that possess a central lanthanide with no helicity such as the racemic mixture of PP-[Ln 3 (L7) 3 ] 9 and MM-[Ln 3 (L7) 3 ] 9 (D 3 symmetry) or the side-by-side complex PM-[Ln 3 (L7) 3 ] 9 (C 3h symmetry).…”

Section: Introductionmentioning

confidence: 99%

The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity

Floquet

Ouali

Bocquet

et al. 2003

Chemistry A European J

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by paramagnetic NMR spectroscopy and linear correlations for Ln Ce ± Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN 6 O 3 and LnN 9 sites with respect to the parameters extracted for Eu III from luminescence data, suggests that the geometry of the central LnN 9 site is somewhat relaxed in solution.

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“…The chemistry of helical structures based on metal coordination has been initiated from the self-assembled double helicates that are obtained by complexation of oligobipyridine ligands with metal ions [12]. To date, various kinds of helical structures including single-, double-, and triple-helicates have been synthesized by metal complexation from the appropriate organic structures containing multiple coordination sites and linkers [13,14].…”

Section: Dynamic Helical Structuresmentioning

confidence: 99%

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

Akine

2018

Inorganics

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Much attention has recently focused on helical structures that can change their helicity in response to external stimuli. The requirements for the invertible helical structures are a dynamic feature and well-defined structures. In this context, helical metal complexes with a labile coordination sphere have a great advantage. There are several types of dynamic helicity controls, including the responsive helicity inversion. In this review article, dynamic helical structures based on oligo(salamo) metal complexes are described as one of the possible designs. The introduction of chiral carboxylate ions into Zn 3 La tetranuclear structures as an additive is effective to control the P/M ratio of the helix. The dynamic helicity inversion can be achieved by chemical modification, such as protonation/deprotonation or desilylation with fluoride ion. When (S)-2-hydroxypropyl groups are introduced into the oligo(salamo) ligand, the helicity of the resultant complexes is sensitively influenced by the metal ions. The replacement of the metal ions based on the affinity trend resulted in a sequential multistep helicity inversion. Chiral salen derivatives are also effective to bias the helicity; by incorporating the gauche/anti transformation of a 1,2-disubstituted ethylene unit, a fully predictable helicity inversion system was achieved, in which the helicity can be controlled by the molecular lengths of the diammonium guests.

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Helicates as Versatile Supramolecular Complexes

Cited by 1,710 publications

References 228 publications

Controlling the formation of metallosupramolecular assemblies by metal ionic radii

Controlling the formation of metallosupramolecular assemblies by metal ionic radii

The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

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