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

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The electrochemical oxidation of NiL2+ (where L = meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) in aqueous solutions in the presence of sulfate, phosphate, chloride, and phthalate yields NiIIILX2. The stability constants for the axial coordination of the anions X are estimated from the observed redox potentials and from kinetic measurements. The complexes [NiIIIL(SO4)H2O]ClO4 and [NiIIIL(H2PO4)2]ClO4 were precipitated. The crystal structure of the latter complex was determined. The complex crystallizes in the triclinic space group P1̅ with a = 11.074 (3) Å, b = 9.386 (2) Å, c = 14.299 (2) Å, α = 88.55 (1)°, β = 106.33 (2)°, γ = 111.46 (2)°, 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 NiIIIL(SO4)2− and NiIIIL(H2PO4−)2+ decompose via NiIIIL3+ and perhaps also partially via NiIIILSO4+ and NiIIILH2PO42+. On the other hand decomposition of the complex NiIIILCl2+ is predominantly via NiIIILCl2+ with partial decomposition via NiIIILCl2+. © 1982, American Chemical Society. All rights reserved.

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Inorganic Chemistry