Effects of sulfur site modification on the redox potentials of derivatives of [N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctanato]nickel(II) Academic Article uri icon

abstract

  • Cyclic voltammetry has been used to examine NiII/I and NiII/III redox potential data for a structurally characterized homologous series of six NiN2S2 complexes, in which the sulfur sites are systematically varied in donor ability: thiolate (RS−), thioether (RSR), sulfinate (RSO2−), and mixtures of these. These include [N,N′-bis(mercaptoethyl)-1,5-diazacyclooctanato]nickel(II) ((bme-daco)NiII,1), [N-(mercaptoethyl)-A-(sulfinoethyl)-1,5-diazacyclooctanato]nickel(II) ((mese-daco)NiII, 2), [N,N′-bis(sulfinoethyl)-1,5-diazacyclooctanato] nickel(II) ((bse-daco)NiII, 3), [N-(mercaptoethyl)-N′-(3-thiabutyl)-1,5-diazacyclooctanato]nickel(II)iodide([(metb-daco)Ni][I], 4), [N-(sulfinoethyl)-N′-(3-thiabutyl)-1,5-diazacyclooctanato]nickel(II) iodide ([(setb–daco)Ni][I], 5), and [N,N′-bis(3-thiabutyl)-1,5-diazacyclooctane]nickel(II) diiodide ([(btb-daco)Ni][I]2, 6). X-ray crystallography has established that all complexes are largely square planar with distortions toward tetrahedral ranging from 1° (strictly square planar) to 18.3°. Throughout the series, the differences in Ni-S bond distances vary <0.08 Å, with the shortest distance at 2.133(3) Å for Ni-SO2R in 3 and the longest distance at 2.211(3) Å for Ni-SR2 in 6. All complexes show reversible reduction waves in CH3CN, assigned to the NiII/I couple in complexes 2–6 by EPR of chemically reduced solutions. The NiII/I potentials vary over a ca. 1.5-V range. Within the series the Ni1 state is most accessible (−482 mV vs NHE in CH3CN) for the dithioether complex (6) and least for the dithiolate (1). Changes in the donor character of the sulfur ligands have a consistent and additive effect on the redox potentials: in CH3CN each methylation of the nickel-bound thiolates results in stabilization of Ni1 by ca. 700 mV whereas each oxygenation stabilizes the NiII/I couple ca. 300 mV. Potential measurements in water demonstrate large hydrogen-bonding effects for the complexes with thiolate and sulfinate donor sites. Reversible NiII/III couples are observed only for complexes 3 and 6. For all complexes the separation between reduction and oxidation events is ca. 2 V. The crystal structure is given of previously reported (bse–daco)NiII (3), which crystallizes in the orthorhombic P21212 (No. 18) space group with a = 8.696(4) Å, b = 9.993(5) Å, c = 8.015(4) Å, V = 696.5(5) Å3, and Z = 2. The synthesis and structure of two new compounds are given: [(metb–daco)NiII] [I] (4) crystallizes in the triclinic [formula omitted] (No. 2) space group with a = 7.558(5) Å, b = 8.922(7) Å, c = 12.559(9) Å, α = 102.79(6)°, β = 95.05(6)°, γ = 107.23(6)°, V= 778.0(10) Å3, and Z = 2; and [(setb-daco)NiII][I] (5) crystallizes in the monoclinic P21/n (No. 14) space group with a = 9.012(2) Å, b = 12.891(3) Å, c = 14.055(3) Å, β = 99.42(2)°, V= 1610.8(6) Å3, and Z = 4. © 1993, American Chemical Society. All rights reserved.

published proceedings

  • Journal of the American Chemical Society

author list (cited authors)

  • Farmer, P. J., Reibenspies, J. H., Lindahl, P. A., & Darensbourg, M. Y

citation count

  • 101

complete list of authors

  • Farmer, Patrick J||Reibenspies, Joseph H||Lindahl, Paul A||Darensbourg, Marcetta Y

publication date

  • June 1993