Modulation of the structural information in shape-defined heterocyclic strands: the case of a (pyridine-hydrazone)₂pyrazine ligand

Metal ions (Ag$^{+}$, Cd$^{2+}$, Eu$^{3+}$, Sm$^{3+}$) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand $L$ (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms ($H_{2}L(PF_{6})_{2}$ and $H_{2}L(CF_{3}SO_{3})_{2}$), a polymeric architecture $[AgL]_{n}(CF_{3}SO_{3})_{n}$, two rack-like complexes $([Eu_{2}H_{2}L_{3}(CF_{3}SO_{3})_{6}](PF_{6})_{2}$ and $[Sm_{2}H_{2}L_{3}(CF_{3}SO_{3})_{6}](PF_{6})_{2})$ and a grid-like structure ($[Cd_{4}L_{4}](CF_{3}SO_{3})_{8}$)

Dynamic molecular system stimuli by acidic-basic conditions

International audienc

Autoassemblage et mouvements moléculaires de brins hétérocycliques

Des brins moléculaires hétérocycliques de type polyhydrazone, s'auto-organisant sous forme hélicoïdale ou linéaire ont été préparés. La réaction de condensation d'un précurseur linéaire avec le précurseur hélicoïdal approprié conduit à un brin hétérocyclique mixte, comportant une partie hélicoïdale et une partie linéaire.Ces brins hélicoïdaux peuvent fonctionner comme ligands car la séquence pyrimidine-hydrazone-pyrimidine est équivalente au ligand terpyridine. La coordination des ions métalliques appropriés (Pb(II), Zn(II)) engendre le déroulement du ligand hélicoïdal et la formation d'un complexe polynucléaire linéaire. Ceci est une extension moléculaire. La coordination ultérieure des ions de Pb(II) par le ligand tren (tris(2-aminoéthyl)amine) régénère le ligand hélicoïdal, produisant une contraction. L'ajout d'acide triflique (3 équivalents par molécule de tren) produit la protonation du ligand tren, les ions Pb(II) sont mis en liberté et complexent à nouveau le ligand hélicoïdal, générant une nouvelle extension. L'ajout d'une quantité équivalente de base (triéthylamine) produit la déprotonation du tren triprotoné et le tren ainsi formé peut lier à nouveau les ions Pb(II) du complexe linéaire, régénérant le ligand hélicoïdal. Nous avons ainsi mis au point un système de mouvements moléculaires d'extension/contraction des ligands hélicoïdaux, modulé par l'ajout alternatif d'acide et de base. Le même principe a été appliqué aux ligands linéaires dont la coordination avec des ions de Pb(II) produit des complexes hélicoïdaux. Les ligands mixtes produisent des mouvements moléculaires où la partie linéaire devient hélicoïdale après coordination, alors que la partie hélicoïdale devient linéaire. Certains ligands à deux groupes hydrazone conduisent à des complexes dinucléaires de type [Ru2ligand (terpy)2](PF6)4. Certains brins hélicoïdaux forment avec les ions Ag(I) des complexes dinucléaires de type double hélice, dont l'un a une structure de polymère à l'état solide.Hydrazone formation reaction was used to synthesize new helical and linear molecules which were characterized by X-ray crystallography and spectroscopic methods. The condensation between a linear precursor and a helical one generates a mixed molecule, having a linear part, but also a helical one. A pyrazine derived ligand having an inversion centre was prepared by using the hydrazone-condensation method.The helical strands act as ligands yielding coordination complexes, the sequence pyrimidine-hydrazone-pyrimidine being a terpyridine-like site. The coordination of metal-ions (Pb(II), Zn(II)) produces the uncoiling of the helical ligand, forming a polynuclear linear complex. Thus, molecular extension of large amplitude can be performed. The subsequent coordination of the Pb(II) ions by tren (tris(2-aminoéthyl)amine) produces the destruction of the linear complex and the coiling of the ligand. Adding triflic acid (3 equivalents per molecule of tren) produces the protonation of tren and thus the Pb(II) ions are released and can coordinate again the helical ligand, thus producing a new extension. Adding the equivalent quantity of base (triethylamine) produces the deprotonation of the triprotonated tren and the tren thus formed can bind the Pb(II) ions of the linear complex, regenerating, once more, the helical ligand. The same molecular motion principle was applied in the case of linear ligands whose coordination of Pb(II) ions generates helical complexes. Ligands having both linear and helical parts produce combined molecular motions: the linear part becomes helical and the helical part becomes linear by coordination. These motions can also be modulated by the pH-change. Several two-sites ligands derived from pyrimidine generated dinuclear complexes [Ru2ligand(terpy)2](PF6)4. Dinuclear helical double-stranded complexes of some pyrimidine-derived ligands were prepared and the X-ray structure of one of them showed a polymeric structure in the solid state.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Coupled Nanomechanical Motions: Metal-Ion-Effected, pH-Modulated, Simultaneous Extension/Contraction Motions of Double-Domain Helical/Linear Molecular Strands

A new class of shape-enforced synthetic polyheterocyclic molecular strands, containing both a helical and a linear domain, has been designed and synthesized. On reaction with Pb­(II), under the effect of cation binding to the coordination subunits, the helical section unfolds into a linear shape in the complex and the linear domain folds into a helical ligand wrapped around the bound cations. Such double-domain ligand strands are thus able to undergo a combined unfolding–folding interconversion on binding and release of metal cations. These changes can be modulated through coupling to a competing ligand that reversibly binds and releases metal cations, when respectively unprotonated and protonated, on effecting alternate pH changes. The resulting process thus performs nanomechanical extension/contraction molecular motions of a linear motor type, which is fueled by acid–base neutralization

Modulation of the structural information in shape-defined heterocyclic strands: the case of a (pyridine-hydrazone) 2 pyrazine ligand

International audienceMetal ions (Ag+, Cd2+, Eu3+, Sm3+) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand L (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms (H2L(PF6)2 and H2L(CF3SO3)2), a polymeric architecture [AgL]n(CF3SO3)n, two rack-like complexes ([Eu2H2L3(CF3SO3)6](PF6)2 and [Sm2H2L3(CF3SO3)6](PF6)2) and a grid-like structure ([Cd4L4](CF3SO3)8)