title: Nickel(II) Complex of a Hexadentate Ligand with Two o-Iminosemiquinonato(1-) π-Radical Units and Its Monocation and Dication.
abstract: Aerobic reaction of a hexadentate redox-active o-aminophenol-based ligand, H4L(3) = N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'-diamino(diphenyldithio)-ethane, in CH3OH with Ni(II)(O2CCH3)2·4H2O and Et3N afforded isolation of a reddish-brown crystalline solid [Ni(L(3))] 1. Cyclic voltammetry (CV) experiment exhibits two oxidative responses at E1/2 = 0.09 and 0.53 V vs SCE (saturated calomel electrode). Chemical oxidation of 1 in air by [Fe(III)(η(5)-C5H5)2][PF6] and AgBF4 in CH2Cl2 led to the isolation of one-electron oxidized species [1](1+) as purple [1][PF6]·CH2Cl2 and two-electron oxidized species [1](2+) as dark purple [1][BF4]2·CH2Cl2, respectively. X-ray crystallographic analysis at 100(2) K unambiguously established that the ligand is present in [Ni(II){(L(ISQ)O,N)(•-)}{(L(ISQ)O,N)(•-)}{(LS,S)(0)}] 1, [Ni(II){(L(IBQ)O,N)(0)}{(L(ISQ)O,N)(•-)}{(LS,S)(0)}][PF6]·CH2Cl2, and [Ni(II){(L(IBQ)O,N)(0)}{(L(IBQ)O,N)(0)}{(LS,S)(0)}][BF4]2·CH2Cl2, as monoanionic o-iminosemiquinonate(1-) π-radical (Srad = 1/2) (L(ISQ))(•-) and neutral o-iminoquinone (L(IBQ))(0) redox-levels. Complexes 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 possess an S = 2, 3/2, and 1 ground-state, respectively, established by temperature-dependent (2-300 K) magnetic behavior of 1 and [1][PF6]·CH2Cl2, and a μeff value of [1][BF4]2·CH2Cl2 at 300 K. Both 1 and [1][PF6]·CH2Cl2 exhibit ferromagnetic exchange-coupling between the two electrons of Ni(II) and two/one ligand π-radicals, respectively. The redox processes are shown to be ligand-based. Spectroscopic and redox properties, and density functional theory (DFT) calculations at the CAM-B3LYP-level of theory adequately describe the electronic structure of 1, [1](1+), and [1](2+). The observed UV-vis-NIR absorptions for 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 have been assigned, based on time-dependent (TD)-DFT calculations.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Akram
authors.initials: A
authors.lastname: Ali
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Debanjan
authors.initials: D
authors.lastname: Dhar
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.|Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741 246, India.
authors.forename: Suman K
authors.initials: SK
authors.lastname: Barman
authors.affiliation: Departament de Quımíca, Inorgànica/Instituto de Ciencia Molecular (ICMOL), Universitat de Valeńcia , Polígono de la Coma, s/n, 46980-Paterna, València, Spain.
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.|Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741 246, India.
authors.forename: Rabindranath
authors.initials: R
authors.lastname: Mukherjee