Homo-dinuclear hexadentate copper(II) and nickel(II) cryptates: synthesis, spectroscopic and electrochemical characterization of the perchlorate salts

Ragunathan, K. ; Bharadwaj, Parimal K. (1995) Homo-dinuclear hexadentate copper(II) and nickel(II) cryptates: synthesis, spectroscopic and electrochemical characterization of the perchlorate salts Polyhedron, 14 (5). pp. 693-698. ISSN 0277-5387

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/027753...

Related URL: http://dx.doi.org/10.1016/0277-5387(94)00286-N

Abstract

Two homo-dinuclear cryptates of CuII and NiII with a ditopic cryptand incorporating both hard and soft donors are described. The electronic and EPR spectral data for the dicopper cryptate are consistent with a distorted octahedral coordination geometry. The EPR spectra of this complex is axial in nature at 77 K corresponding to the dx2-y2 ground state. A room temperature magnetic moment number (µeffB) of 1.98 per copper indicate that the two CuII centres are not magnetically coupled. Cyclic voltametric experiments show a quasi-reversible (ΔEp = 115 mV) reductive response at Ef = -0.17 V (vs SCE) corresponding to the CuII/CuI couple. Exhaustive controlled potential coulometry on this cryptate at 295 K gives n = 1.96 e-, signifying that the cyclic response is a two-electron process involving two independent CuII centres. The dinickel cryptate, on the other hand, does not show any cyclic response in the range +1.0 to -1.0 V. However, the electronic spectral and magnetic susceptibility data obtained on this cryptate are consistent with a distorted octahedral geometry around each NiII. The Schiff base precursor of the cryptand also readily forms a dicopper cryptate having similar electronic spectral, EPR and magnetic properties as the dicopper cryptate described above. However, the CuII/CuI couple for this cryptate appears at Ef = +0.14 with ΔEp = 95 mV. The difference in Ef values for the two cryptates are attributable to the greater σ-donor ability of the amino nitrogens compared to the imino nitrogens.

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