Cobaltocenium Hexafluorophosphate Research Articles

Conductivity and Voltammetry in Liquid and Supercritical Halogenated Solvents

A previous study of the voltammetry of ferrocene in liquid and supercritical chlorodifluoromethane revealed electrochemically reversible behavior. However, shifts in the half-wave potential as a function of fluid conditions were observed which were tentatively attributed to ohmic distortion due to changes in fluid resistance. To more completely understand the voltammetry in this fluid, conductivity measurements have been made for a range of fluid conditions. Additionally, a second reference couple, cobaltocenium hexafluorophosphate, has been introduced, and the difference in half-wave potentials between the two redox couples has been examined as a function of fluid conditions. In the liquid, the difference in the half-wave potentials of the two couples corrected for ohmic distortion decreases as the fluid temperature increases (25-85 °C) at constant pressure (5.2 MPa). In the supercritical fluid at constant temperature (115 °C), the difference in the half-wave potentials corrected for ohmic distortion is constant at 1.276 ± 0.005 V over a considerable range of fluid pressure (10-30 MPa). Ion aggregation in the supercritical fluid is indicated both by the conductivity measurements and by the rather large hydrodynamic radius of cobaltocenium computed from the voltammograms. Preliminary voltammetry in supercritical trifluoromethane is also presented.

Synthesis, structure and anion co-ordination chemistry of a novel macrocyclic cobaltocenium receptor

A new macrocyclic amide-substituted cobaltocenium receptor, 1,1′-[(ethylenedioxy)bis(ethyleneaminocarbonyl)]cobaltocenium hexafluorophosphate 2 has been prepared and its single-crystal X-ray structure determined. Proton NMR anion co-ordination studies revealed that 2 and other new acyclic cobaltocenium derivatives complex chloride and bromide anions with 1:1 stoichiometry. Comparative stability constant evaluations imply that the macrocyclic receptor 2 forms halide complexes of greatest thermodynamic stability, suggestive of a ‘macrocyclic anion effect’. Cyclic voltammetric investigations showed the cobaltocenium receptors to electrochemically recognise halide anions.

Microelectrode studies in the absence of deliberately added supporting electrolyte: solvent dependence for a neutral and singly charged species

Steady state voltammetric studies utilizing a 5.6 μm radius platinum inlaid disk microelectrode have been carried out in a series of solvents containing ferrocene (FeCp 2) and/or cobaltocenium hexafluorophosphate ([CoCp 2] + [PF 6] −) in both the presence and absence of intentionally added supporting electrolyte. The very low dependence of the ferrocene oxidation process (FeCp 2 ⇋ [FeCp 2] + + e −) on the concentration of electrolyte enables this compound to be used as a convenient internal reference standard for charged compounds. For reduction of the charged [CoCp 2] + ion, ([CoCp 2] + + e − ⇋ CoCp 2), changes in the migration current as a function of solvent in the absence of electrolyte can be related to the dependence of ionic mobility on solvent viscosity. The ohmic IR drop effects observed in solvents with lower dielectrics are related to the degree of ionic association. Possible reasons for the lack of a simple relation for either migration or IR drop trends with solvent properties are discussed. A steady state analytical solution for mass transport for the charged system is compared to the experimental data. In practical terms, it has been shown that in the absence of deliberately added electrolyte, steady state voltammograms can be obtained for both neutral and singly charged species in solvents as non-polar as tetrahydrofuran with little distortion, whereas with toluene, which has only a slightly lower dielectric constant, the IR drop distortion is extremely large. As expected, the IR distortion for an ionic sample is less than that for a neutral sample. However, whether the IR drop is important or not in non-polar solvents is very dependent on the exact nature of the experimental conditions.

Pressure tuning of the electronic energy levels of ferrocene, cobaltocenium hexafluorophosphate, and nickelocene

The effects of pressure on various d-d transitions for ferrocene, cobaltocenium hexafluorophosphate, and nickelocene in the solid state are presented here. The bands are found to shift in a manner such as to increase the symmetry-imposed splittings between the d orbitals, which is consistent with a qualitative molecular orbital picture. These splittings are found to increase between 2 and 8% in 100 kbar, as compared with 7-15% for simple ionic compounds. The Racah parameter B is almost independent of pressure, in contrast to the results seen for simple ionic compounds. These results are discussed in terms of the large degree of covalency for these compounds.

1,1′-Bis( N,N-dimethylamino)ferrocene,1,1′-bis( N,N-dimethylamino) cobaltocenium hexafluorophosphate and 1,1′-bis( N,N-dimethylamino)titanocene dichloride. Crystal structure of 1,1′-bis( N,N-dimethylamino)titanocene dichloride

A general method for the preparation of 1,1′-bis( N,N-dimethylamino)metallocenes is described, involving the reaction of N,N-dimethylamino-cyclopentadienyllithium ( 1-Li) with metal chlorides. 1,1′-Bis( N,N-dimethylamino)ferrocene ( 2), 1,1′-bis( N,N-dimethylamino)cobaltocenium hexafluorophosphate ( 3 + PF 6 −) and 1,1′-bis( N,N-dimethylamino)titanocene dichloride ( 4) have been synthesized in this way. The influence of the dimethylamino donor substituent has been studied by means of cyclic voltammetry. 1,1′-Bis( N,N-dimethylamino)ferrocene ( 2), e.g., has the most negative redox potential ( E o −0.23 V (SCE)) so far reported for a ferrocene derivative. The structure of 1,1-bis( N,N-dimethylamino)titanocene dichloride ( 4) has been determined by X-ray crystallography. It crystallizes in hexagonal plates with the space group C2/c ( Z = 4, a 1301.4, b 647.2, c 1828.5 pm, β 98.81°). The titanium atom does not lie exactly above the centres of the cyclopentadienyl rings, and the CN bond from the cyclopentadienyl ring carbon atom C(1) to the nitrogen atom of the dimethylamino group is very short (134.7 pm).