Coexistence of Two Thermally Induced Intramolecular Electron Transfer Processes in a Series of Metal Complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)₂] (M=Co, Fe, and Ni) bearing Non‐Innocent Catechol‐Based Ligands: A Combined Experimental and Theoretical Study

Abstract

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)2], for which M=Co (2), Fe (3) and Ni(4), and Cat‐N‐BQ and Cat‐N‐SQ denote the mononegative (Cat‐N‐BQ−) or dinegative (Cat‐N‐SQ2−) radical forms of the tridentate Schiff‐base ligand 3,5‐di‐tert‐butyl‐1,2‐quinone‐1‐(2‐hydroxy‐3,5‐di‐tert‐butylphenyl)imine, have been studied by variable‐temperature UV/Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2 has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand‐to‐metal (IETLM) and ligand‐to‐ligand (IETLL). IETLL was only found to take place in complex 3, and no IET was observed for complex 4. Such experimental studies have been combined with ab initio wavefunction‐based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitals and to access the ground states and excited‐spin states, as well as charge‐transfer states giving additional information on the different IET processes.

Orientation-Induced Redox Isomerism in Planar Supramolecular Systems

“…Furthermore, the action of these driving forces are investigated mainly in the case of dispersed molecular systems (solu tions) 2−4,12 and crystals. 3,4 Only a few works are devoted to the study of IET in aggregated molecules (including liquid crystals). 5,6,13 In systems characterized by the coexistence of two redox isomers of the same compound, we can suppose that not only driving forces listed above (light, temperature, microenviron ment), but any physical effect that even slightly affects the internal energy of the system can shift the dynamic equilibrium toward the predominance of one of the isomers.…”

Conjugated compounds in supramolecular informational systems: A review

“…Since then, molecular systems that exhibit bista bility-the ability to exist in two different electronic states and change their electronic state upon the effect of external actions-have attracted especial attention of researchers. The continuing interest in processes of reversible intramolecular electron transfer exists because these processes appear promising as a basis for develop ment of molecular sensors and nanosized devices for recording and storage of information [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”

“…Presently, such effects as changes in the microenvi ronment (solvent replacement) [23,24,31,43] and thermal [27,28,33,[43][44][45] and magnetic and photo physical [26,30,32,38,39,[46][47][48] effects are used most widely as external controlling signals. Some separate works that describe the processes of redox isomerization in a 3D system under the influ ence of external pressure [49,50] deserve special atten tion.…”

Catechol‐Based Biomimetic Functional Materials and their Applications

“…Importantly, valence tautomerism can be induced not only by temperature variations but also by irradiation, both in solution and in the solid state [163]. A further step in this sense is the catechol-based O,N,Ocoordinated type ligands such as ligand BQ-N-SQ, because this family of complexes may exist at least in four different oxidation states [166,167]. Other new redox-active catechol-based ligands have been described to show VT phenomena [165].…”