STRUCTURE AND O-2 UPTAKE PROPERTIES OF A NOVEL NICKEL(II) COMPLEX OF PYRIDYL-PENDANT DIOXOCYCLAM ETHYL-5,7-DIOXO-1,4,8,11-TETRAAZACYCLOTETRADECANE]

Novel potentially five-coordinate pyridyl-pendant dioxocyclam methyl-5 ,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H(2)L) and its homologs (6 -methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nicker(II) complex with a deprotonat ed amide (NiHL) was isolated from aqueous equimolar solution of H(2)L and Ni(ClO4)(2). A yellow nicker(II) complex with two deprotonated ami des (Nit) was crystallized from an H2O/CH3CN solution of H(2)L and Ni( OH)(2). The X-ray crystal study of Nit showed a square-planar nickel(I I) complex with the pyridyl-pendant remaining uncoordinated. It is con cluded from the visible absorption and NMR study of Nit in aqueous sol ution that the four-coordinate Nit is in equilibrium with a five-coord inate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl-pendant. A voltammetric study disclosed a low nickel(I I/III) redox potential of + 0.29 V vs SCE for NiL at pH 9.5 and 25 deg rees C with 0.10 M Na2SO4. The nickel(II) complex Nit absorbed an equi molar amount of O-2 at pH 9.5 and 25 degrees C, and the O-2 was activa ted to cleave plasmid DNA.