1.3 V Inorganic Sequential Redox Chain with an All-Anionic Couple 1-/2- in a Single Framework

Abstract

The relatively low symmetry of [3,3'-Co(1,2-C2B9H11)2]- ([1]-), along with the high number of available substitution sites, 18 on the boron atoms and 4 on the carbon atoms, allows a fairly regioselective and stepwise chlorination of the platform and therefore a very controlled tuning of the electrochemical potential tuning. This is not so easily found in other systems, e.g., ferrocene. In this work, we show how a single platform with boron and carbon in the ligand, and only cobalt can produce a tuning of potentials in a stepwise manner in the 1.3 V range. The platform used is made of two icosahedra sharing one vertex. The E1/2 tuning has been achieved from [1]- by sequential chlorination, which has given potentials whose values increase sequentially and linearly with the number of chloro groups in the platform. [Cl8-1]-, [Cl10-1]-, and [Cl12-1]- have been obtained, which are added to the existing [Cl-1]-, [Cl2-1]-, [Cl4-1]-, and [Cl6-1]- described earlier to give the 1.3 V range. It is envisaged to extend this range also sequentially by changing the metal from cobalt to iron. The last successful synthesis of the highest chlorinated derivatives of cobaltabis(dicarbollide) dates back to 1982, and since then, no more advances have occurred toward more substituted metallacarborane chlorinated compounds. [Cl8-1]-, [Cl10-1]-, and [Cl12-1]- are made with an easy and fast method. The key point of the reaction is the use of the protonated form of [Co(C2B9H11)2]-, as a starting material, and the use of sulfuryl chloride, a less hazardous and easier to use chlorinating agent. In addition, we present a complete, spectroscopic, crystallographic, and electrochemical characterization, together with a study of the influence of the chlorination position in the electrochemical properties.