Charge distribution in transition-metal complexes of a Schiff base biquinone ligand. Structural and electrochemical properties of the MII(Cat-N-BQ)2MIII(Cat-N-BQ)(Cat-N-SQ)MIV(Cat-N-SQ)2 tautomeric series

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

“…Complexes 2-6 were synthesized as previously described. [20,21] Physical measurements: Electronic absorption spectra were recorded by using a Varian Cary05e spectrophotometer equipped with a thermostated cell holder that can operate between 280 and 370 K. Temperature stability was better than AE 5 K. Spectra were collected after the sample had been allowed to thermally equilibrate at each temperature for 10 min. T c , the temperature at which the isomer ratio is 1:1, was deduced from the temperature at which the peaks of the low spin and the high spin exhibit similar intensities.…”

“…[21] The tridentate Schiff-base ligand 3,5-ditert-butyl-1,2-quinone-1-(2-hydroxy-3,5-di-tert-butylphenyl)-A C H T U N G T R E N N U N G imine [22] leads to stable coordination complexes with several metal ions, and exhibit different oxidation states ranging from 0 to À3 (see Scheme 1). Nevertheless, it usually coordinates in the mononegative Cat-N-BQ À or dinegative Cat-N-SQ 2À radical forms [23] generating mixed-valence species.…”

Transition metal complexes with bulky 4,6-di-tert-butyl-N-aryl(alkyl)-o-iminobenzoquinonato ligands: Structure, EPR and magnetism

“…[106,107,109,111,112]. Evidently, this cobalt(III) complex is in an equilibrium with a form of cobalt(II) (valence tautomerism) [111] in non-polar solvents (toluene, sim-dichloroethane): Co III (AP-IBQ L9 )(AP-ISQ L9 ) ↔ Co II (AP-IBQ L9 ) 2 .…”

“…It can be due to differences in geometry of ML 3 fragments and the ML 3 -ML 3 units -the different dihedral angles between the planes containing the next-neighbor rings (the iminosemiquinonato rings with Scheme 21. Complexes 75, 77 [104], 78-83 [105][106][107][108][109][110]. The dinuclear and spin triplet ruthenium(II) complex [(bipy) 2 Ru(ISQ-ISQ L11 )Ru(bipy) 2 ](PF 6 ) 2 (93), Scheme 22, contains iminobenzosemiquinonato fragments [L 2 Ru(ISQ)] + which are intramolecularly ferromagnetically coupled (J = 85 cm −1 ) as established by EPR and variable-temperature magnetic susceptibility measurements [37].…”

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox‐Active Ligands

“…We selected the redox O,N,O ligand Cat‐N‐SQ (Cat=catechol, Scheme ) and the reasons for this choice are three‐fold: i) structural proximity with the original SQ ligand, ii) distinct tridentate coordination sphere, and iii) only one oxidized state available. The nickel complex bearing one Cat‐N‐SQ ligand cannot be isolated as only the (Cat‐N‐SQ) 2 Ni complex is recovered . However, [Cu II (Cat‐N‐SQ)(Py) 2 ] complex 8 is readily available and, considering our previous results on SET performed by copper complex Cu(L SQ ) 2 1 , its reactivity was investigated.…”