Nickel(II) derivatives based on o-iminobenzoquinone-type ligands: Structural modifications, magnetism and electrochemical peculiarities

New bis- o -iminobenzosemiquinonato derivatives of nickel ligated by functionalized o -aminophenols were synthesized. The electrochemical behavior of new compounds is represented by four ligand-centered redox transitions. Ni II derivative with two o -iminobenzoquinones as well as species including radical anion and o -amidophenolate forms of redox-active ligand were prepared as products of oxidation and reduction of the initial complex. • Synthesis of tetracoordinated Ni II bis-o-iminosemiquinonates. • Redox chemistry of Ni II bis-o-iminosemiquinonate. • Molecular structure and magnetic properties. New bis- o -iminobenzosemiquinonato derivatives of nickel (imSQ C(O)Ph ) 2 Ni ( 1 ) and (imSQ Ph ) 2 Ni ( 2 ) that are ligated by functionalized o -aminophenols H 2 L C(O)Ph and H 2 L Ph , respectively, were synthesized. Complex 1 is distinguished by a square-planar geometry of N 2 O 2 coordination core while the bis- o -iminobenzosemiquinonate 2 demonstrates a slight deviation from planarity. Both complexes 1 and 2 show the strong antiferromagnetic interactions between radical anion ligands as established by variable-temperature magnetic susceptibility measurements. Electrochemical behavior of 1 and 2 is represented by ligand-centered redox transitions: two quasi-reversible one-electron reduction processes and two-electron oxidation one. The salient peculiarity of cyclic voltammogram for 1 is an increase in number of redox waves owing to the quasi-reversible reduction of benzophenone fragments in ligands. Six-coordinated Ni II derivative [(imQ C(O)Ph ) 2 Ni(H 2 O) 2 ](OSO 2 CF 3 ) 2 ( 3 ) with two o -iminobenzoquinones as well as four-coordinated Ni II species [(imSQ C(O)Ph )Ni(AP C(O)Ph )]CoCp 2 ∙2.1toluene ( 4∙2.1toluene ) including radical-anion and o -amidophenolate forms of redox-active ligand were prepared as products of oxidation and reduction of the initial 1 , respectively, in accordance with the CV data. The value of effective magnetic moment (μ eff ) unambiguously indicates the high-spin state for nodal Ni II ion in 3 . Low-temperature EPR signal demonstrates rather the ligand-centered nature of unpaired electron in 4 that corresponds to the total doublet ground spin state (S = 1/2) for compound and diamagnetic low-spin (S Ni = 0) configuration of the metal center.