The substitution of hydrogen with chlorine in the metallacarborane [3,3-Fe(1,2-closo-C₂B₉H₁₁)₂]⁻ cluster modulates the formal potential of the Fe³⁺/Fe²⁺ redox couple, shifting it to a more positive value. Hence, very similar redox probes with a wide range of formal potentials, ranging from negative to positive values, are available. Thus, we have achieved the synthesis and studied the electrochemical behaviour of the sodium salt of [3,3-Fe(8,9,12-Cl₃-1,2-closo-C₂B₉H₈)₂]⁻ in aqueous media. This strategy allows tuning of the redox potential of the [3,3-Fe(1,2-closo-C₂B₉H₁₁)₂]⁻ framework with a minor change in its shape and dimensions. We also describe the interaction of the prepared [3,3-Fe(8,9,12-Cl₃-1,2-closo-C₂B₉H₈)₂]⁻ and the pristine [3,3-Fe(1,2-closo-C₂B₉H₁₁)₂]⁻ with DNA. These studies have been carried out not only with DNA in solution but also with DNA immobilized on screen-printed gold electrodes. The results obtained point to a strong interaction between the metallacarboranes and DNA, to a different extent with single stranded DNA (ssDNA) compared to double stranded DNA (dsDNA). This property makes them selective and wide-ranging potential electrochemical indicators of hybridization. The suitability of these new redox indicators for selective DNA biosensor development has been probed by the direct detection of two different mutations associated with cystic fibrosis in PCR amplicons extracted from blood cells.

The development of new types of ion conducting materials is one of the most important challenges in the field of energy. Lithium salt polymer electrolytes have been the most convenient, and thus the most widely used in the design of the new generation of batteries. However, in this work, we have observed that Na⁺ ions provide a higher conductivity, or at least a comparable conductivity to that of Li⁺ ions in the same basic material. This provides an excellent possibility to use Na⁺ ions in the design of a new generation of batteries, instead of lithium, to enhance conductivity and ensure wide supply. Our results indicate that the dc-conductivity is larger when the anion is [Co(C₂B₉H₁₁)₂]⁻, [COSANE]⁻, compared to tetraphenylborate, [TPB]⁻. Our data also prove that the dc-conductivity behavior of Li⁺ and Na⁺ salts is opposite with the two anions. At 40 °C, the conductivity values change from 1.05 × 10⁻² S cm⁻¹ (Li[COSANE]) and 1.75 × 10⁻² S cm⁻¹ (Na[COSANE]) to 2.8 × 10⁻³ S cm⁻¹ (Li[TPB]) and 1.5 × 10⁻³ S cm⁻¹ (Na[TPB]). These findings indicate that metallacarboranes can be useful components of mixed matrix membranes (MMMs), providing excellent conductivity when the medium contains sufficient amounts of ionic components and a certain degree of humidity.

The conductivity of a series of composite membranes, based on polybenzimidazole (PBI) containing the metallacarborane salt M[Co(C₂B₉H₁₁)₂], M[COSANE] and tetraphenylborate, M[B(C₆H₅)₄], M[TPB] both anions having the same number of atoms and the same negative charge, has been investigated. Different cations (M = H⁺, Li⁺ and Na⁺) have been studied and the composite membranes have been characterized by water uptake, swelling ratios, ATR FT-IR, thermogravimetric analysis and electrochemical impedance spectroscopy to explore the dielectric response and ion dynamics in composite membranes. Our results show that conductivity increases with increasing temperature and it is higher for H⁺ than for Li⁺ and Na⁺ for all temperatures under study. The mobility of Li⁺ is greater in [COSANE]⁻ than in [TPB]⁻ composite PBI@membranes while for Na⁺ it is the opposite. The temperature dependence of the conductivity of the composite was followed by a typical Arrhenius behaviour with two different regions: (1) between 20 and 100 °C, and (2) between 100 and 150 °C. Using the analysis of electrode polarization (EP) based on the Thrukhan theory we have calculated the ionic diffusion coefficients and the density of carriers. From the double logarithmic plot of the imaginary part of the conductivity (σ′′) versus frequency in the entire range of temperatures studied we have determined for each sample at each temperature, the frequency values of the onset (f_ON) and full development of electrode polarization (f_MAX), respectively, which permit us to calculate static permittivity.

The addition of a tailored metallacarborane to a commercial AC allows using supercapacitors (in 0.5 M Na₂SO₄ electrolyte) at 2.2 V.