ELECTROCHEMICAL AND STRUCTURAL STUDIES OF NICKEL(II) COMPLEXES WITH N2O2 SCHIFF-BASE LIGANDS .2. CRYSTAL AND MOLECULAR-STRUCTURE OF BIS(2-HYDROXYACETOPHENONYLIDENEIMINATE)NICKEL(II), BIS(2-HYDROXYACETOPHENONYLIDENEIMINATE)-NICKEL(II) AND IYL-BIS(3,5-DICHLOROSALICYLIDENEIMINATE)NICKEL(II)

Reductive and oxidative chemistry of three complexes of formula [Ni(L) ], where L represents a N2O2 Schiff base pseudomacrocyclic ligand base d on salicylaldehyde derivatives and three different diamines, was stu died in (CH3)2SO: -bis(2-hydroxyacetophenonylideneiminate)nicke](II) ( 1); -bis(2-hydroxyacetophenonylideneiminate)nickel(II) (2); l-(bis(3,5 -dichlo-rosalicylideneiminate)nickel(II) (3). Electrochemical behavior of the complexes was determined by cyclic voltammetry, and EPR spectr oscopy was used to characterize the one-electron reduced/oxidized spec ies. Reduction of the complexes 1 and 2 yielded Ni(I) complexes with a d(xy) ground state (g(z)>g(x),g(y)), 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 N i(III) species with two solvent molecules coordinated axially, with a d(z2) ground state (g(x),g(y)>g(z)). The crystal structures of the thr ee Ni(II) complexes were determined from single crystal X-ray diffract ion data collected with the use of Mo Kalpha radiation. 1: space group C2/c with a=25.963(3), b=7.2973(4), c=17.357(2) angstrom, beta = 107. 085(5)-degrees, Z=8 (R=0.061); 2: space group P2(1)/a with a=9.645 (6) , b=19.149(16), c=10.743(5) angstrom, beta=94.66(2)-degrees, Z=4 (R=0. 085); 3: space group P2(1)/n with a=13.372(5), b=8.785(2), c=16.534(5) angstrom, beta=101.60(3)-degrees, 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 ratio nale for the E1/2 values obtained for the reduction and oxidation proc esses.