Bis-o-semiquinonato nickel complexes with pyridine and pyridine modified by nitronyl-nitroxide moiety

Redox Ladder of Ni3 Complexes with Closed‐Shell, Mono‐, and Diradical Triphenylene Units: Molecular Models for Conductive 2D MOFs

“…Expectedly, the strongest exchange interaction takes place within the HOTP moiety, where the geometric distortion away from planarity likely determines the antiferromagnetic coupling of the two radicals. The ferromagnetic Ni 2+ ‐radical interactions are in line with previous observations in Ni 2+ ‐semiquinonate complexes, and can be explained by the orthogonality of the Ni 2+ and HOTP 4− magnetic orbitals [18, 31] …”

“…HOTP serves as a particularly attractive target because its three catechol units are, in principle, each capable of engaging in two consecutive one‐electron reversible redox couples in the catecholate‐semiquinonate‐quinonate (cat‐sq‐q) sequence (Scheme 1 a), affording up to six different oxidation states for a Ni 3 HOTP complex. Ni 2+ is also a rational choice because it exhibits an open‐shell electronic structure under octahedral coordination, important for studying spin exchange interactions, but otherwise exhibits redox inert behavior in catecholate complexes [1, 16–20] …”

Redox Ladder of Ni3 Complexes with Closed‐Shell, Mono‐, and Diradical Triphenylene Units: Molecular Models for Conductive 2D MOFs

“…Expectedly,t he strongest exchange interaction takes place within the HOTP moiety,w here the geometric distortion away from planarity likely determines the antiferromagnetic coupling of the two radicals.T he ferromagnetic Ni 2+ -radical interactions are in line with previous observations in Ni 2+ -semiquinonate complexes,and can be explained by the orthogonality of the Ni 2+ and HOTP 4À magnetic orbitals. [18,31] Parallel and perpendicular X-band electron paramagnetic resonance (EPR) spectroscopy provided further validation for the electronic structure of the complexes.At4.5 K, frozen glasses of DCM solutions of 2 gave an intense signal with g = 15.14 and aw eaker signal with g = 2.31, both only observed under parallel mode (Figure 4). These features are assigned to the transition within the m s =AE 3and m s =AE 1doublets of the S = 3ground state upon further introducing rhombicity to the Ni 2+ -centered spins.Indeed, the two main EPR features were reproduced by asimulation with the above fitting parameters and an E/D = 0.12 (Figure 4a,black trace), without losing the quality of fit of the magnetometry data (Figure S11).…”

“…Ni 2+ is also ar ational choice because it exhibits an open-shell electronic structure under octahedral coordination, important for studying spin exchange interactions,b ut otherwise exhibits redox inert behavior in catecholate complexes. [1,[16][17][18][19][20] Scheme 1. a) Lewis structures of HOTP 6À and the redox sequence on acatecholate sub-unit;b )selected resonancestructures of 1, 2,and 3, illustratingthe charge states and spin structures of HOTP nÀ .M e 3 TPA capping ligands are omitted for clarity.…”