title: Proton-mediated redox control in a nickel(II)-bisimidazolate complex: spectroscopic characterisation and density functional analysis.
abstract: The synthesis and characterisation of the pro-ligand LH4, in which L is the o-phenylenebisamide-2-imidazole and its nickel(II) complexes are reported. The X-ray structures of the fully protonated [NiLH2] and deprotonated [NiL] complexes are presented. The effects of the deprotonation of the imidazole functions on the electronic structure of the complexes are analysed by (1)H NMR, UV/Vis and IR spectroscopy and cyclic voltammetry. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations support the analysis based on experimental data. The singly oxidised form of the deprotonated complex [NiL] was generated by preparative electrolysis and its electronic structure was investigated. Spectroelectrochemistry shows the appearance of intense transitions in the region lambda = 600-900 nm with several isosbestic points. X-band EPR spectroscopy presents an isotropic signal at g = 2.03, whereas the Q-band EPR reveals a weak anisotropic signal characteristic of a metalloradical species. DFT and TDDFT data support the description of the species as a nickel(II)-radical form, with a major contribution of the spin density on the phenylene ring and the amidate functions with a negligible participation of the imidazolate groups. This finding is in sharp contrast with those obtained from the one-electron-oxidised form of nickel(II) complexes containing phenolate groups.
authors: Institut de Chimie Moléculaire et des Matériaux d'Orsay, UMR-CNRS 8182, Université de Paris-Sud, F-91405 Orsay, France.
authors: Benedikt
authors: B
authors: Lassalle-Kaiser
authors: Régis
authors: R
authors: Guillot
authors: Joëlle
authors: J
authors: Sainton
authors: Marie-France
authors: MF
authors: Charlot
authors: Ally
authors: A
authors: Aukauloo
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011522:Protons; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D007093:Imidazoles; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; D009532:Nickel