Magnetic and Spectroscopic Investigation of Thermally and Optically Driven Valence Tautomerism in Thioether-Bridged Dinuclear Cobalt–Dioxolene Complexes

Abstract

A series of dinuclear cobalt complexes of general formula [Co(Mentpa)(diox-S-diox)Co(Mentpa)](PF6)2·MeOH (n = 0, 2, 3) was prepared through the synthesis of the bis-bidentate ligand 6,6'-((1,4-phenylenebis(methylene))bis(sulfanediyl))bis(3,5-di-tert-butyl-benzene-1,2-diol) (diox-S-diox). The ancillary ligands Mentpa are obtained by the tripodal tris(2-pyridylmethyl)amine (tpa) ligand through successive introduction of methyl groups into the 6 position of the pyridine moieties. As expected, the steric hindrance induced by this substitution modulates the redox properties of the metal acceptor, determining the charge distribution of the metal-dioxolene adduct at room temperature. Magnetic measurements and X-ray photoelectron and X-ray absorption spectroscopies indicate that the charge distributions low-spin-Co(III)-catecholate and high-spin-Co(II)-semiquinonate characterize the complexes formed by the tpa and Me3tpa tetradentate ligands, respectively. The complex formed by the Me2tpa ligand undergoes a thermal- and light-induced interconversion of the two states, in agreement with the existence of a valence tautomeric equilibrium. All complexes were stable and behaved reproducibly under X-ray irradiation. This work points out a fast and simple chemical approach to structurally and electronically modify the catechol ring while leaving its coordination capabilities unaffected. These findings afford a robust chemical method to prepare sulfur-functionalized dioxolene ligands as new molecular bricks for chemical functionalization of noble metal surfaces with this class of molecular switches.

Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols

“…However, there are only few model systems which follow this pathway [138][139][140][141]. Most designed complexes that catalytically perform catechol oxidation are known to perform the oxidation through alternate pathway which involves production of quinone along with H 2 O 2 rather than water [24,[34][35][36]52,53,76,140,[142][143][144][145]. Presence or absence of hydrogen peroxide as end product in our cases were tested by using KI solution and Horse Radish Peroxidase [53,140] and also using potassium titanium(IV) oxalate [97,98].…”

Covalent Grafting of Coordination Polymers on Surfaces: The Case of Hybrid Valence Tautomeric Interphases

“…The Co2p 1/2 spectrums were then fitted to four components (along with the corresponding Co2p 1/2 spin-orbit coupled contributions) following a previously reported procedure. [20] At 80 K, a main peak at 782.8 eV and minor satellites at 786.0, 789.2 and 793.07 eV, with a ΔE SO contribution of 15.2 eV are obtained. These values are within the range of those previously described for a mixture of lsCo(III) and hs-Co(II).…”

“…These values are within the range of those previously described for a mixture of lsCo(III) and hs-Co(II). [20] [20] reveal that over the whole temperature range studied no pure electronic states are found but rather the coexistence of both charge distributions, being the ls-Co(III) predominant at low temperatures and the hs-Co(II) electronic isomer at high temperature.…”

“…This technique has already allowed the determination of charge distribution in different bulk VT complexes, both at fixed [19] and variable temperatures, [20] in addition to have sufficient sensitivity. Spectra were taken at three different temperatures: 80 K, 293 K and 373 K. Best-fits and spin-orbit (SO) couplings within the Co2p region at the three different temperatures are shown in Figure 3.…”

Valence tautomeric dinuclear adducts of Co(ii) diketonates with redox-active diquinones for the design of spin qubits: computational modeling

“…8 The known dinuclear cobalt complexes with VT properties include the compounds with tethered dioxolene ligands, 9 biscatecholate ligands containing an acetylene linker, 10 spiroconjugated bis-o-quinone and trispyridine ligands 11 and thioether-bridged tetraoxolene ligands. 12 These complexes possess promising switchable magnetic properties, but their possible employment as spin qubit carriers may be complicated because of their ionic character that affects electron transfer and moving charges processes in a solid material with the resulting increase in decoherence of the system. 4b,d Therefore, the search for 2-qubit gate systems within the families of dinuclear VT complexes must be confined within electrically neutral compounds of this type.…”