A New Valence Tautomerism Example in an Electroactive Ferrocene Substituted Triphenylmethyl Radical

Abstract

A new molecular system combining an open-shell organic radical that acts as an acceptor group, different from an o-quinone moiety, covalently linked to a ferrocene moiety, acting as the donor group, is shown to exhibit valence tautomerism.

Electronic Structural Changes between Nickel(II)–Semiquinonato and Nickel(III)–Catecholato States Driven by Chemical and Physical Perturbation

“…The twoline isotropic signal is ascribed to the hyperfine coupling (a H = 0.38 mT) of an unpaired electron with the proton in the 4-position of the dioxolene ligand. [27] The observed sharp isotropic signal with the g value of 2.0061 is close to free-spin value (g = 2.0023) and can be assigned to the ligand-centered radical species consisted of the squareplanar low-spin d 8 Ni II (S = 0) and semiquinone radical (S = 1/2) frameworks.…”

“…Much information about metal complexes with dioxolene [2][3][4] and other redox-active ligands [5][6][7][8] exhibiting valence tautomeric behavior has been accumulated and this phenomenon has been explored in order to develop molecular switching devices.…”

Valence Tautomerism: New Challenges for Electroactive Ligands

“…Nevertheless, the same authors did report valence tautomerism on a new family of molecular systems comprising PTM radicals and ferrocene units (see Scheme 7). [74] Ferrocene chromophores are interesting not only because of their electron donor capacities and rich electrochemistry but also because they are electroactive species whose oxidation state can be controlled by means of a chemical or electrochemical stimulus, with their oxidized states being of open-shell character.…”

Polychlorotriphenylmethyl Radicals: Towards Multifunctional Molecular Materials

“…Indeed 17 was shown to exist in the solid state in two distinct electronic isomeric forms -one neutral form and another zwitterionic form with separated charges (Scheme 2.5) that may be reversibly interconverted. 79 Variable temperature Mössbauer spectra (Figure 2.21) show that the Fc-PTM dyad exists in a neutral form at low temperature, while the zwiterionic form is favored at higher temperatures, meaning this thermal conversion is completely reversible. Very recently, it has been found out that the coexistence in a crystalline sample of both the neutral and zwitterionic forms of Fc-PTM is a result of the bistability of crystals, induced by stabilizing electrostatic intermolecular interactions developed in the charge separated state.…”