The behaviour of copper and thallium hexafluoromolybdates(V) in acetonitrile

Abstract

Copper(I), copper(II), and thallium(III) hexafluoromolybdates(V), prepared by the oxidation of the metals in acetonitrile with molybdenum hexafluoride (A. Prescott, D.W.A.Sharp, and J.M. Winfield, J. Chem. Soc., Dalton Trans. , 1975, 963) have been investigated by cyclic voltametry. Half wave potentials, E 1 2 V vs. Ag p+/Ag were obtained using a evacuable cell equipped with anexternal Ag p+/Ag electrode, enabling strict anerobic conditions to be maintained. A number of reversible or quasi-reversible electron transfer processes have been observed, enabling comparison with synthetic work to be made. Results for Cu I and Cu II hexafluoromolybdates(V) are in accord with preparative experience. MoF 6. Mo VI/Mo VE 1 2 +1.600V, oxidises Cu metal to Cu II in MeCN, and Cu II is reduced by Cu O to Cu I , Cu lI/Cu IE 1 2 = +0.750 or +0.710V for Cu I and Cu II solutes respectively, Cu I/Cu OE 1 2 = −0.720V not reversible. A wave at E 1 2 = −0.350V is assigned to Mo V/Mo IV by analogy with Ag I hexafluoromolybdate (D.W.A. Sharp, unpublished work). E 1 2 data for I 2 in MeCN, I 2/I 3 - = 0.280, I 3 −/I − = -0.116V, suggest that reduction of MoF 6 − by I is not likely, in contrast to the situation in SO 2 (A.J. Edwards and R.D. Peacock, Chem. Ind. , 1960, 1441). Reduction of MoF 6 − by Cu o in MeCN should be feasible, but appears to be very slow. Pure Tλ III hexafluoromolybdate(V) is obtained from Tλ o and MoF 6 only when the mole ratio MoF 6:Tλ>5:1. Smaller ratios produce yellow solids in which Mo:Tλ is ca . 2:1. Tλ III is a stronger oxidising agent than Cu II in MeCN, as oxidation of Cu I by Tλ III is rapid and quantitative. However a reversible electron transfer wave assignable to Tλ III/Tλ I is not observed in the expected fange +1.600 to +0.710V possibly because of solute-electrode interactions.