Determination of the state of charge of TCNQ0/− mixed-valence complexes based on a spectroscopic model. Application to thin films of electrocrystallised tetraethylammonium complexes

A simple and inexpensive method is proposed as a powerful and rapid tool for the determination of the state of charge of mixed-valence compounds. Based on UV-spectrometry and integration of voltammetric peaks, the stoichiometric ratio between both oxidation states of TCNQ (that is TCNQ0/−) has been determined for thin films obtained by electrocrystallisation on a glassy carbon electrode. This method permits such determination, regardless of the experimental conditions and, thus, it can be used to establish the reproducibility of the methods of synthesis of mixed-valence compounds by using simple spectroscopic measurements. The method has been validated with the well-known Cs2TCNQ3 system and applied to ethylammonium salts of unknown structure.