Synthesis, characterization and electrochemistry of nickel(II) complexes of Schiff base ligands containing a disulphide group. Crystal structure of [Ni{(o-OC6H4CHNC6H4)2S2}(MeOH)] · MeOH

The Schiff base disulphide ligands N,N′-[1,1′-dithiobis(phenylene)]bis(salicylideneimine), designated hereunder as H2salps, and N,N′-[1,1′-dithiobis(ethylene)]bis(salicydeneimine), designated hereunder as H2sales, react with nickel(II) acetate tetrahydrate in methanol giving two mononuclear complexes: [Ni(salps)(MeOH)] · MeOH and [Ni(sales)], respectively. These complexes have been characterized by spectral, magnetic and electrochemical methods. The structure of [Ni(salps)(MeOH)] · MeOH has been determined by X-ray diffraction analysis. This complex crystallizes in the triclinic crystal system, space group P1, Z = 2, a = 9.476(1), b = 11.297(3) and c = 13.215(3) A, α = 106.66(1), β = 97.10(1), and γ = 99.94(1)° and V = 1312.3(3) A3. The refinement converged to R = 0.034 and Rw = 0.045 based on 2599 reflections with I ⪢ 3σ(I). The salps functions as a quinquedentate ligand coordinating through the two phenolate oxygen atoms the two imine nitrogen atoms and only one of the disulphide sulphur atoms. The sixth coordination site is occupied by the oxygen atom from a methanol molecule. The octahedron core, NiN2O3S, is highly distorted as indicated by the range in bond distances (from 2.063(3) to 2.531(1) A) and angles (from 79.47(8) to 100.4(1)°). The Ni bond distance is 2.531(1) A, while the SS bond distance is 2.066(1) A. On the other hand, the spectral and magnetic properties of [Ni(sales)] suggest a square-pyramidal structure with a NiS bond. The complexes show non-conjugated and irreversible redox processes in cyclic voltammetry, in DMF. The processes at − 1.30 and − 1.43 V have been attributed to the reduction of the disulphide group, whereas the oxidation process at ca + 0.74 V has been attributed to the nickel(II) oxidation.