51205-54-0Relevant academic research and scientific papers
Voltammetric, EPR and UV-VIS-NIR spectroscopic studies associated with the characterisation of electrochemically generated tris(dithiocarbamato)cobalt(IV) complexes in dichloromethane
Webster,Heath,Bond
, p. 3189 - 3195 (2007/10/03)
CoIII(S2CNR2)3 (R = Et, cyclohexyl) complexes were electrochemically oxidised by one-electron in CH2Cl2 containing Bu4NPF6 as the supporting electrolyte. Voltammetric, EPR and UV-VIS-NIR spectroscopic data indicated that the cation complexes, [CoIV(S2CNR2)3]+, formed by oxidation of the parent CoIII compounds were stable for at least several hours at low temperatures (T = 233 K), although instability was evident at higher temperatures and/or longer times. EPR spectroscopic data obtained byin situ electrogeneration of the oxidised species at low temperatures indicated that the unpaired electron largely resided on the metal centre, thereby confirming a formally CoIV state. The UV-VIS-NIR spectra of the [CoIV(S2CNR2)3]+ complexes showed a new set of low energy and moderate intensity series of bands at ν = 9600, 13300 and 15500 cm-1 (ε = 700-1500 L cm-1 mol-1) which were interpreted as ligand-to-metal charge transfer excitations to the unfilled t2g orbital. The EPR spectra of [CoIV(S2CNR2)3]+ (g// ≈ 2.65 and g⊥ ≈ 1.90) required low temperatures to be detected (T > ca. 50 K) and displayed a high degree of anisotropy consistent with a distorted octahedral structure.
Investigations of mixed-ligand cobalt dithiocarbamate complexes by cobalt-59 nuclear magnetic resonance spectroscopy, mass spectrometry, and electrochemistry
Bond,Colton,Moir,Page
, p. 1298 - 1302 (2008/10/08)
Tris(dithiocarbamate) complexes of cobalt(III), CoL3 and CoL′3 (where L and L′ are different dithiocarbamato ligands), undergo ligand exchange at elevated temperatures both in an inert organic solvent and in the solid state to give CoL2L′ and CoLL′2. The mixed-ligand complexes may also be prepared by methods based on controlled-potential electrochemical oxidation or reduction of cobalt(III) dithiocarbamate complexes. In contrast to these preparative-scale electrolyses, short-time-scale voltammetric and polarographic data for oxidation and reduction exhibit independent responses for the mixed-ligand complexes, implying that the formally cobalt(IV) and cobalt(II) mixed-ligand species undergo slow rather than rapid ligand exchange. Cobalt-59 NMR spectroscopy and electrochemistry in CH2Cl2 solution and mass spectrometry are useful techniques to illustrate ligand exchange. Cobalt-59 chemical shifts of the dithiocarbamate complexes cover a wide range and allow identification of the mixed-ligand species in many reaction mixtures as the ligand exchange for the oxidation state III complexes is slow on the NMR (and synthetic) time scales at ambient temperatures. Generally, 59Co NMR chemical shifts do not correlate in a simple linear fashion with electrochemical E° data (or with 13C NMR data), implying that steric effects influence the two techniques in different ways. However, for the mixed-ligand series CoL3, CoL2L′, CoLL′2, and CoL′3, the E° and 59Co chemical shifts do correlate exceedingly well. Positive and negative ion mass spectra of CoL3 species, generally show the molecular ions [CoL3]+. and [CoL3]-., respectively, but the most abundant ions are [CoL2]+. and [CoL2]-.. Mass spectrometric examination of mixtures of CoL3 and CoL′3 show evidence of ligand exchange. Mass spectrometry in the gas phase and electrochemical data show interesting correlations.
Electrochemical reduction and oxidation of cobalt(III) dithiocarbamates
Bond,Hendrickson,Martin,Moir,Page
, p. 3440 - 3446 (2008/10/08)
The literature describing the oxidation and reduction of cobalt(III) dithiocarbamate complexes, Co(R2dtc)3, and the chemistry of formally cobalt(II) and cobalt(IV) dithiocarbamate complexes contains substantially conflicting data. An extensive investigation of the electrochemical reduction and oxidation of Co(R2dtc)3 leads to the following conclusions: (i) In CH2Cl2 and for R = cyclohexyl, controlled-potential oxidative electrolysis at platinum electrodes produces a complex that appears to be the elusive cobalt(IV) complex [Co(R2dtc)3]+ (or possibly [Co2(R2dtc)6]2+ or related species). In acetone, electrolysis of the cyclohexyl derivative at platinum electrodes produces the cobalt(III) dimer [Co2(R2dtc)5]+. At mercury electrodes, the oxidation process proceeds via a pathway different from that at platinum electrodes and [Co2(R2dtc)5]+ and mercury dithiocarbamate complexes are obtained as products. (ii) On the electrochemical time scale, oxidation of most Co(R2dtc)3 complexes is chemically reversible in CH2Cl2 but not always in acetone or acetonitrile, implying that [Co(R2dtc)3]+ has a finite stability for many complexes, at least in CH2Cl2. However, with the exception of R = cyclohexyl, noted above, this complex is not obtained from electrolysis experiments. While [Co2(R2dtc)5]+ rather than [Co(R2dtc)3]+ may be isolated from the oxidized solution in CH2Cl2, it is not formed at the electrode surface and results from a series of chemical reactions subsequent to electron transfer. (iii) Electrochemical reduction of Co(R2dtc)3 is extremely complex and depends markedly on the nature of the R group, solvent, and electrode. Formation of [Co(R2dtc)3]- is favored by solvents such as acetone or acetonitrile and is stabilized by adsorption on mercury electrodes. Thus, chemically reversible one-electron reduction steps are observed in some circumstances. By contrast, Co(R2dtc)2 appears to be significantly more stable in CH2Cl2 than [Co(R2dtc)3]-, and chemically irreversible reduction is generally associated with this solvent at platinum electrodes. The nature of further electrochemical reduction steps, which ultimately produce cobalt metal and dissociated ligands, also depends on numerous variables.
