Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism

Abstract

We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(μ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and μ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and μ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact.

Combining Molecular Spintronics with Electron Paramagnetic Resonance: The Path Towards Single-Molecule Pulsed Spin Spectroscopy

“…Due to advances in fabrication methods, it is now possible to synthesize ultra-clean GNRs via an bottom-up approach [271][272][273]. This allows us to chemically bond molecules, carrying a spin centre or photoswitchable unit [23,248,274,275], and directly integrate into spintronic devices for which fabrication methods exist [276]. Recently, it has been able to clearly observe the topological edge state in graphene nanoribbons [277], which represented a mainly theoretical concept thus far and experimental hints were scarce until then.…”

Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

“…52 It is well known that solvation effects play a key role in the valence tautomerization process, and can either change the transition temperature or entirely deactivate the process. 9,[53][54][55][56] This has been attributed to intermolecular factors such as a change in polarity or lattice softness in crystalline VT compounds, which either changes the barrier or the energy difference between the two tautomers. It is likely that annealing produces one or both effects.…”

“…This class of compounds includes well studied materials such as Co-Fe Prussian Blue analogues and Co dioxolene complexes. [5][6][7][8][9] Dioxolene ligands have valence orbitals close in energy to those of third-row transition metal d orbitals, and can exist in multiple oxidation states. Previous results showed that the electronic structure of the two valence tautomers are localized, and can be thought of as electron transfer between the ligand and metal, with the metal center changing from LS Co III ↔ HS Co II .…”

Conduction mechanism of nitronyl-nitroxide molecular magnetic compounds

“…Molecular magnetic materials offer a particularly rich experimental ground, 1 where sophisticated effects can be observed with particular clarity and tuned by the means of molecular synthetic chemistry. [2][3][4][5][6][7] They have allowed, for example the observation of magnetic quantum tunnelling, [8][9][10][11] Berry phase interference, 12 and permit controlling the spin degrees of freedom by light [13][14][15][16][17][18][19][20] or via other external stimuli. [21][22][23][24][25] Recent work has highlighted in particular the relevance of molecular magnetic materials for spintronics.…”

“…, within experimental error. These compounds also dis-13 play a wider dispersion of behaviours, with a few cases14 showing exponents up to 3. This effect is actually to 15 be linked to a more limited experimental accuracy, pro-16 duced by the presence of other mechanisms, such as traps see Section V) and the limited voltage range between C and the breakdown voltage of the crystals.…”