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Electrochemical and structural studies of nickel(II) complexes with N2O2 Schiff base ligands 2. Crystal and molecular structure of N,N′-l,2-ethane-1,2-diyl-bis(2- hydroxyacetophenonylideneiminate)nickel(II), N, N′-1,2-cis cyclohexane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)- nickel(II) and N,N′-1,2-benzene-1,2-diyl-bis(3,5-dichlorosalicylideneiminate)nickel(II)

1994; Elsevier BV; Volume: 219; Issue: 1-2 Linguagem: Inglês

10.1016/0020-1693(94)03821-x

1873-3255

Fernando Azevedo, M.A. Carrondo, Baltazar de Castro, M.A. Convery, Deolinda Domingues, Cristina Freire, M. Teresa Duarte, K.T. Nielsen, Isabel C. Santos,

Free Radicals and Antioxidants

Reductive and oxidative chemistry of three complexes of formula [Ni(L)], where L represents a N2O2 Schiff base pseudomacrocyclic ligand based on salicylaldehyde derivatives and three different diamines, was studied in (CH3)2SO: N,N′-1,2-ethane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)nickel(II) (1); N,N′-1,2-cis-cyclohexane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)nickel(II) (2); N,N′-1,2-benzene-1,2-diyl-(bis(3,5-dichlorosalicylideneiminate)nickel(II) (3). Electrochemical behavior of the complexes was determined by cyclic voltametry, and EPR spectroscopy was used to characterize the one-electron reduced/oxidized species. Reduction of the complexes 1 and 2 yielded Ni(I) complexes with a dxy ground state (gz>gx, gy), but the reduction of 3 is ligand-centered as suggested from the pseudo-isotropic radicalar EPR signal of frozen electrolyzed solutions. Oxidation of all three complexes is metal-centered and the oxidized products are low spin hexacoordinate Ni(III) species with two solvent molecules coordinated axially, with a dz2 ground state (gx, gy>gz). The crystal structures of the three Ni(II) complexes were determined from single crystal X-ray diffraction data collected with the use of Mo Kα radiation. 1: space group C2/c with a = 25.963(3), b = 7.2973(4), c = 17.357(2) Å, β = 107.085(5)°, Z = 8 (R = 0.061); 2: space group P21/a with a = 9.645(6), b = 19.149(16), c = 10.743(5) Å, β = 94.66(2)°, Z = 4 (R = 0.085); 3: space group P21/n with a = 13.372(5), b = 8.785(2), c = 16.534(5) Å, β = 101.60(3)°, Z = 4 (R = 0.054). Crystal packing of 1 and 3 involves the pairing of two centrosymmetrical related molecules in dimers, but that of 2 shows no systematic parallel orientation of any part of the molecules. X-ray structural data have provided a rationale for the E12 values obtained for the reduction and oxidation processes.