Decorated Tetrathiafulvalene‐Based Ligands: Powerful Chemical Tools for the Design of Single‐Molecule Magnets

Abstract

This Minireview covers the design and characterization of coordination lanthanide complexes involving TTF-based ligands. The specific design of TTF-based ligands allowed the isolation of complexes with magnetic properties such as Single-Molecule Magnets (SMMs) behavior and the studies of magnetic modulations due to supramolecular interaction, molecular engineering, magnetic dilution as well as isotopic enrichment. A careful design leads to TTF-based ligands displaying several coordination sites in order to rationally elaborate polynuclear [a] 148The research activities of Olivier Cador started in 1994 in Bordeaux (France). He mainly focused on the studies of the magnetic properties of systems with various dimensionalities, from nanoparticles to isolated molecules which show quantum behavior, and finally to magnets with atypical behavior. In Rennes, his aim was at first to develop the synergy between electronic properties, such as magnetism and electrical conductivity, in new molecular edifices based on organic/inorganic networks. He orients now its research field to Single Molecule Magnets (SMMs) based on lanthanide. 149Assuming that hydrogen bonds are broken in dichloromethane solution, the first hypothesis was to attribute the nonobservation of the slow magnetic relaxation to the presence Eur.A very challenging synthetic route is the design of TTF core functionalized with stable organic radical (S = 1/2) able to realize coordination reaction with metal centers. Such strategy is promising because the organic radical plays the magnetic relay Eur.

Interplay of Electronic and Geometric Structure Tunes Organic Biradical Character in Bimetallic Tetrathiafulvalene Tetrathiolate Complexes

“…Since first being reported in the early 1970s, − tetrathiafulvalene (TTF) has been established as a valuable building block in multiple areas of chemistry and materials science. − This includes the use of TTF and its derivatives in organic conductors, ,,, metal or covalent organic frameworks, − molecular switches, , coordinating ligands in transition metal and lanthanide chemistry, ,− and macrocyclic and supramolecular structures. ,, The versatility in its applications arises from its tunable electronic structure, namely, its extended π-system that yields low-lying excitations and accessible 1+ and, more recently, 2+ oxidation states. , Promising applications of TTF-derived compounds include their roles in the development of single molecule magnets (SMMs), , molecular transistors, as well as materials for light harvesting and solar energy conversion …”

“…Recently, tetrathiafulvalene tetrathiolate (TTFtt) , has found application as a bridging ligand in bimetallic transition metal complexes. ,, Here TTFtt may be utilized as a formal TTFtt 4– , TTFtt 3– , or TTFtt 2– ligand, where the TTF core is in its neutral, 1+, or 2+ state, respectively, accessed via oxidation of the neutrally charged bimetallic parent compounds . While radical TTF 1+ ligands are well studied and have found applications in the development of SMM, , the TTFtt 2– ligand has only recently been shown to yield significant TTF-based organic biradical character as a bridging ligand in transition metal bimetallic complexes . Further TTFtt 2– bridged complexes containing different metal centers have been synthesized and demonstrated to display high photoluminescence quantum yield (PLQY), as well as high conductivity in amorphous, glassy coordination polymers…”

“…7,25,26 The versatility in its applications arises from its tunable electronic structure, namely, its extended π-system that yields low-lying excitations and accessible 1+ and, more recently, 2+ oxidation states. 14,27 Promising applications of TTF-derived compounds include their roles in the development of single molecule magnets (SMMs), 21,23 molecular transistors, 28 as well as materials for light harvesting and solar energy conversion. 11 Recently, tetrathiafulvalene tetrathiolate (TTFtt) 29,30 has found application as a bridging ligand in bimetallic transition metal complexes.…”

Rigid N3O2-Pentadentate Ligand-Assisted Octacoordinate Mononuclear Ln(III) Complexes: Syntheses, Characterization, and Slow Magnetization Relaxation

“…A single-molecule magnet (SMM) is broadly referred to the paramagnetic metal complex exhibiting magnetization blocking and slow relaxation of magnetization below a critical temperature, generally known as the blocking temperature, T B . , Due to the electronic spin-induced quantum magnetic states, SMMs inherit immense prospects in the high-impact modern technology such as high-density data storage, quantum computing, spintronics, bionics, multiferroics, and so forth. − However, the rational design and synthesis of potential SMMs are non-trivial. Since the discovery of the lanthanide (Ln) ion-based SMM behavior in phthalocyanine-sandwiched Ln­(III) mononuclear complexes by Ishikawa et al, , there has been an insurgence of research interest in the arena of molecule-based magnetism associated with Ln ions. − Notably, large spin ground state and high magnetic anisotropy originating from strong spin–orbit coupling bequeath the Ln complexes, especially the Dy­(III)-analogues, with fascinating slow magnetization dynamics when the Ln ions are complexed with appropriate crystal field (CF) environments. − Recent advances reveal that the Ln-based complexes with low coordination numbers and high CF symmetry are expected to exhibit a promising SMM behavior, especially for the lanthanide ions having oblate electrostatic potential surfaces corresponding to their ground magnetic microstates. ,− However, it is worth mentioning that the Ln ions prefer large coordination numbers, commonly 8–10, and variable coordination geometry because of their large ionic size and highly shielded valance (4 f ) orbitals. , At the same time, a subtle change in the coordination environment can influence the SMM behavior significantly. ,− ,− Therefore, having synthetic control over the inner coordination sphere with a desired CF topology is crucial in order for achieving potential SMMs rationally, especially for multinuclear SMMs.…”

Dysprosium Single-Molecule Magnets Involving 1,10-Phenantroline-5,6-dione Ligand

“…To go one step forward, more complex ligands with multi-functionality, such as the combination of redox-activity with multi coordination sites, could be used. These kind of ligands can allow the observation of multi-emission or -SMM behavior [24][25][26][27]. In this context, the 1,10-phenantroline-5,6-dione (L) appears as a promising multifunctional ligand since it combines two potential coordination sites with electro-activity [28,29], leading to the design of potential multi-properties compounds, such as a combination of spin crossover and valence tautomerism, as has recently been proposed from a computational point of view [30].…”