Ru^II Multinuclear Metallosupramolecular Rack‐Type Architectures of Polytopic Hydrazone‐Based Ligands: Synthesis, Structural Features, Absorption Spectra, Redox Behavior, and Near‐Infrared Luminescence

Abstract

A novel class of polytopic hydrazone-based ligands was synthesized. They gave heteroleptic Ru(II) polynuclear rack-like complexes of formula [Ru(n)terpy(n)(bridging molecular strand)](2n+) (terpy=2,2':6',2''-terpyridine). The new rack-like systems can be viewed as being made of two identical or roughly identical peripheral subunits separated by several similar metal-containing spacer subunits. The presence of pyrazine or pyrimidine units within the molecular multitopic strands introduces additional chemical diversity: whereas a pyrimidine unit leads to appended orthogonal subunits that are on the same side with regard to the main molecular strand, a pyrazine unit leads to orthogonal subunits that lie on different sides. Mixing pyrazine and pyrimidine units within the same (bridging) molecular strand also allows peculiar and topographically controlled geometries to be obtained. Redox studies provided evidence that each species undergoes reversible redox processes at mild potentials, which can be assigned to specific subunits of the multicomponent arrays. Non-negligible electronic coupling takes place among the various subunits, and some electron delocalization extending over the overall bridging molecular strand takes place. In particular, oxidation data suggest that the systems can behave as p-type "molecular wires" and reduction data indicate that n-type electron conduction can occur within the multimetallic framework. All the multinuclear racks exhibit (3)MLCT emission, both at 77 K in rigid matrix and at 298 K in fluid solution, which takes place in the near-infrared region (emission maxima in the 1000-1100 nm region), and is quite structured. Rigidity of the molecular structures and delocalization within the large bridging ligands are proposed to contribute to the occurrence of the rather uncommon MLCT infrared emission, which is potentially interesting for optical communication devices.

Dondorff Rings: Synthesis, Isolation, and Properties of 60°‐Directed Bisterpyridine‐Based Folded Tetramers

“…These intricate ensembles have revolutionized the field of supramolecular chemistry. The work of Lehn,5, 6 Stoddart,7, 8 Schmittel,9–11 and others12–22 continues to introduce increased complexity into multicomponent systems; however, most self‐assembly techniques rely on the target compound having the most thermodynamic stability leading to the desired structure. Less stable products must be synthesized by kinetic control, utilizing structural factors such as steric or ionic effects to achieve the desired macromolecular targets.…”

Crystal structure of (E)-phenylacetaldehyde phenylhydrazone, C14H14N2

“…They are also employed in coordination reactions with metal ions [1], in cycloaddition reactions [2], and have promising antimicrobial, anticonvulsant, antiinflammatory, antitubercular and antitumoral properties [3]. In addition, good enough chargetransporting properties of polymeric arylaldehyde hydrazones caused increasing studies on them as optoelectronic devices [4].…”

Dichloridobis[2-(1-hydrazinylideneethyl)pyrazine-κN1]zinc

“…2-(1-hydrazinylideneethyl)pyrazine (Stadler et al, 2010) (0.1 mmol, 0.0136 g) was dissolved in 20 ml absolute ethanol, then ZnCl 2 .2H 2 O (0.2 mmol, 0.0268 g) was added, and after 0.5 h of stirring at 333 K, the mixture was filtered and held at room temperature to allow slow evaporation of solvent. Shiny pale yellow crystals suitable for X-ray diffraction were collected after one week (Yield = 64%).…”