Thermally and Light‐Induced Valence Tautomeric Transition in a Dinuclear Cobalt–Tetraoxolene Complex

Abstract

A photoswitchable system that undergoes entropy-driven valence tautomerism has been obtained by successfully tuning the electronic properties of a dinuclear cobalt-polyoxolene complex by molecular techniques. For more information see the Communication by A. Dei, J.-F. Létard, and co-workers on the following pages.

Valence Tautomerism: New Challenges for Electroactive Ligands

“…[20] Similar interconversion in the solid state has been reported by Dei et al for the new dinuclear complex [{Co(cth)} 2 (dhbq)](PF 6 ) 3 (3), both by irradi-ation with a laser connected to the SQUID magnetometer and by reflectivity spectra. [21] Their results showed that the light-induced phenomenon is perfectly reversible although the photoinduced population rate corresponds to only 43 % of the sample, most likely due to opacity phenomena. Finally, additional femtosecond spectroscopic experiments by Neuwahl et al in a simple cobalt-dioxolene derivative in solution demonstrated the involvement of not two but at least three states in a two-step process for a valence tautomeric interconversion in solution.…”

Radical ligand-containing single-molecule magnets

“…Efforts to generate benzosemiquinonoid-containing transition metal complexes with a nuclearity of greater than one have resulted in numerous dinuclear compounds, including those containing metal centers bridged by derivatives of 2,5-dihydroxy-1,4-benzoquinonoids [172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][188][189], bis(pyrazolyl)benzoquinonoids [190][191][192][193], bis(phosphine)benzoquinonoids [194,195], bis(amino) benzoquinonoids [196][197][198][199][200][201][202], and bis(amino)diiminobenzoquinonoids [86,[203][204][205][206]. Indeed, the radical form of these ligands has shown enhanced magnetic coupling compared to their non-radical redox isomers [174,180,182].…”

Photomagnetic Effects in Polycyanometallate Compounds: An Intriguing Future Chemically Based Technology?

“…[6,7] The number of coordination compounds showing photoinduced magnetic properties in the solid state is still limited to some dithienylethylene derivatives, [8,9] tetracyanoethylene organometallic compounds, [10] spin-crossover, [11,12] and valence-tautomeric complexes. [13,14] [15,16] Few years ago Hashimoto and coworkers discovered that long-range magnetic ordering in the compound K 0.2 Co 1. 4 [Fe(CN) 6 ]·6.9 H 2 O can be achieved by irradiation with red light at low temperature, the original material being restored by blue light irradiation or by heating.…”