Tunable Charge Delocalization in Dinickel Quinonoid Complexes

Abstract

When a 2,5-diamino-1,4-benzoquinonediimine C6H2(=NR)2(NHR)2 (2) is used as a bridging ligand, new dinickel(II) complexes [(acac)Ni[mu-C6H2(=NPh)4]Ni(acac)] (3a: R=Ph) and [(acac)Ni[mu-C6H2(=NCH2tBu)4]Ni(acac)] (3b: R=CH2tBu) are obtained; upon one-electron oxidation of these complexes delocalized mixed-valence compounds are formed. An X-ray diffraction study on 3b reveals equalization of the bond lengths within each of the ligand 6 systems and a lack of conjugation between them. The oxidized state in 3b+ involves both the bridging quinonoid ligand and the metal centers, with a major contribution coming from the bridging ligand. Electrochemical and spectroscopic methods were used to study the influence of the N-substituents of the tetranitrogen donor ligands 2. In this combined experimental and theoretical (DFT) study, it is also shown that the electronic structure within the dinickel system can be altered by addition of a coordinating ligand such as pyridine. The latter favors the high-spin configuration with semi-occupied metal-centered orbitals, leading to a metal-metal interaction in the mixed-valence Ni(II)-Ni(III) 3b+ system.

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].…”

Oxidation Leading to Reduction: Redox‐Induced Electron Transfer (RIET)

“…[19] The 4 K EPR spectrum of the one-electron oxidation species (15 + ) has two broad signals corresponding to g k = 2.13 and g ? = 4.16 in the presence of a drop of anhydrous pyridine.…”

Extendable nickel complex tapes that reach NIR absorptions

“…This shortcoming can be explained by the strongly limited access to 2 owing to its in situ preparation in solution, 16,17 or deposit by sublimation on a CsI plate cooled by closed-cycle refrigeration at 15 K. 18 In contrast, N-substituted analogues of type 4 (R = alkyl or aryl) have attracted much more interest as their easy access paved the way to their use as ligand for the preparation of dinuclear complexes 5 with a high degree of electronic delocalization. [19][20][21] Importantly, no metal complex oligomers based on 4 could be attained presumably due to the steric hindrance of the N-substituents. Consequently, we decided to reinvestigate the isolation of 2 to study in detail its coordination chemistry (metal-ligand assembling) since the absence of N-substituents should favour the formation of monodisperse nickel complex tapes with extension of the -delocalization.…”