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

The relatively low symmetry of [3,3′-Co­(1,2-C₂B₉H₁₁)₂]⁻ ([<b>1</b>]⁻), 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 <i>E</i>_1/2 tuning has been achieved from [<b>1</b>]⁻ by sequential chlorination, which has given potentials whose values increase sequentially and linearly with the number of chloro groups in the platform. [<b>Cl</b>_<b>8</b><b>-1</b>]⁻, [<b>Cl</b>_<b>10</b><b>-1</b>]⁻, and [<b>Cl</b>_<b>12</b><b>-1</b>]⁻ have been obtained, which are added to the existing [<b>Cl-1</b>]⁻, [<b>Cl</b>_<b>2</b><b>-1</b>]⁻, [<b>Cl</b>_<b>4</b><b>-1</b>]⁻, and [<b>Cl</b>_<b>6</b><b>-1</b>]⁻ 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. [<b>Cl</b>_<b>8</b><b>-1</b>]⁻, [<b>Cl</b>_<b>10</b><b>-1</b>]⁻, and [<b>Cl</b>_<b>12</b><b>-1</b>]⁻ 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.