Valence Tautomeric Transitions in Cobalt‐dioxolene Complexes

Thermal and optical control of electronic states in a single layer of switchable paramagnetic molecules

“…Proper chemical tuning of the reduction potentials of Co 3+/2+ couple allows to prepare structurally related systems with different charge distributions, either ls-Co III Cat (ls = low-spin, Cat = catecholato), hs-Co II SQ (hs = high-spin, SQ = semiquinonato radical), or exhibiting VT. 27 In the latter case, at low temperatures the diamagnetic ls-Co III Cat redox isomer is the ground state, but entropy driven intramolecular electron transfer triggers the reversible formation of the paramagnetic hs-Co II SQ species upon heating the system ( Scheme 1 ). 25 At cryogenic temperatures the same interconversion can be induced by visible 17 and soft X-ray irradiation; 28 once the stimulating source is removed, a slow decay to the ls-Co III Cat ground state occurs with a temperature dependent characteristic time. 29 DFT calculations have recently proposed that switching can be induced by the application of an electric field, suggesting that detection and modulation of the magnetic state of these complexes can be obtained at the single molecule level by using Scanning Tunnel Microscopy-based techniques.…”

“… 17 This class of materials includes cyano-metallates 18 – 21 and metal complexes showing Valence Tautomerism (VT from now on), an interconversion between redox isomers caused by electron transfer between the metal ion and an organic ligand. 22 – 24 In order to investigate the VT behaviour on a metallic surface, we focused our interest on cobalt–dioxolene complexes, 25 which can be considered as class II mixed valence systems, according to Robin and Day classification. 26 These coordination compounds are the simplest and most widespread molecular systems displaying VT and rely on a [CoL diox ] core, L being a tetradentate N-donating ancillary ligand and diox a chelating ligand belonging to the ortho -quinone (dioxolene) family.…”

Long-Sought Redox Isomerization of the Europium(III/II) Complex Achieved by Molecular Reorientation at the Interface

“…Redox isomerization is typically achieved by thermal action, application of high hydrostatic pressure or magnetic field, irradiation with light or X-rays, and so forth. This process is accompanied by alteration of optical and magnetic properties of the complexes, which can be read-out by physical–chemical measurements in order to form the basis of their practical applications. , This phenomenon is commonly studied on the examples of complexes formed by d-metals that are characterized by several accessible redox states, typically, vanadium, manganese, iron, cobalt, nickel, copper, and so forth, with non-innocent ligands such as diimines, dioxolenes, phenoxyls, tetrapyrrolic macrocycles, and so forth. Since the first publication in 1980 reporting on valence tautomerization of the cobalt complex with semiquinone and dioxolene ligands, , numerous examples of redox-isomeric d-metal complexes were described and comprehensively reviewed. − …”

Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals

“…Indeed, the emergent electron-based polarization properties can be realized by designing compounds whose electronic structure lies at the boundary of multiple states. A number of processes in dynamic molecular crystals, such as spin transition and intramolecular electron transfer, are accompanied by redistribution of electronic density 23 . Therefore, such compounds can be potentially used to induce polarization change and hence, the pyroelectric effect 24 .…”