Paul R. Murray

Electrochemistry of Sulfur and Polysulfides in Ionic Liquids

The electrochemistry of elemental sulfur (S(8)) and the polysulfides Na(2)S(4) and Na(2)S(6) has been studied for the first time in nonchloroaluminate ionic liquids. The cyclic voltammetry of S(8) in the ionic liquids is different to the behavior reported in some organic solvents, with two reductions and one oxidation peak observed. Supported by in situ UV-vis spectro-electrochemical experiments, the main reduction products of S(8) in [C(4)mim][DCA] ([C(4)mim] = 1-butyl-3-methylimidazolium; DCA = dicyanamide) have been identified as S(6)(2-) and S(4)(2-), and plausible pathways for the formation of these species are proposed. Dissociation and/or disproportionation of the polyanions S(6)(2-) and S(4)(2-) appears to be slow in the ionic liquid, with only small amounts of the blue radical species S(3)(•-) formed in the solutions at r.t., in contrast with that observed in most molecular solvents.

An in situ electrochemical cell for Q- and W-band EPR spectroscopy

A simple design for an in situ, three-electrode spectroelectrochemical cell is reported that can be used in commercial Q- and W-band (ca. 34 and 94 GHz, respectively) electron paramagnetic resonance (EPR) spectrometers, using standard sample tubing (1.0 and 0.5 mm inner diameter, respectively) and within variable temperature cryostat systems. The use of the cell is demonstrated by the in situ generation of organic free radicals (quinones and diimines) in fluid and frozen media, transition metal ion radical anions, and on the enzyme nitric oxide synthase reductase domain (NOSrd), in which a pair of flavin radicals are generated.

Determining the site of reduction of 4-NO2-2,2′-bipyridine and [Pt(4-NO2-2,2′-bipyridine)Cl2]

In situ UV/Vis and EPR spectroelectrochemistry experiments show that the unpaired electron in [4-NO(2)-bpy](1-) sits in an orbital which is based on the 4-NO(2)-py moiety and not spread over both py rings. The unpaired electron in [Pt(4-NO(2)-bpy)Cl(2)](1-) is based on the 4-NO(2)-bpy ligand with some [bpy](1-) character. Labelling the NO(2) group of 4-NO(2)-bpy with (15)N revealed that the larger coupling constant in the EPR spectrum of [4-NO(2)-bpy](1-) can be assigned to the N atom of the NO(2) group. This coupling constant is significantly smaller in the EPR spectrum of [Pt(4-NO(2)-bpy)Cl(2)](1-).