Stabilization of the tervalent nickel complex with meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane by axial coordination of anions in aqueous solution (original) (raw)

1982, Inorganic Chemistry

The electrochemical oxidation of NiL2+ (where L = meso-5,7,7,12,14,14-hexamethyl-1,4,8,1l-tetraazacyclotetradecane) in aqueous solutions in the presence of sulfate, phosphate, chloride, and phthalate yields Ni111LX2. The stability constants for the axial coordination of the anions X are estimated from the observed redox potentials and from kinetic measurements. The complexes [Ni111L(S04)H20]C104 and [Ni111L(H2P04)2]C104 were precipitated. The crystal structure of the latter complex was determined. The complex crystallizes in the triclinic space group Pi with a = 11.074 (3) A, b = 9.386 (2) A, c = 14.299 (2) A, a = 88.55 (1)O, @ = 106.33 (2)O, y = 1 1 1.46 (2)O, and two molecules in the unit cell; least-squares refinement based on 4282 reflections led to a conventional R of 0.046. The nickel is located in the plane determined by the four ligating nitrogen atoms, and the configuration of the remainder of the macrocyclic ligand is essentially identical with that reported for the divalent nickel complex with this ligand. The kinetics of decomposition of the complexes were studied and found to be complicated. The results indicate that the complexes Ni111L(S04)2-and Ni11'L(H2P04-)2+ decompose via Nim1L3+ and perhaps also partially via Ni111LS04+ and Ni"'LH2P0:+.