A Systematic (Spectro‐) Electrochemical Approach to the Synthesis and Characterisation of Co(II) and Ni(II) Compounds Containing Reduced Forms of TCNQF

Abstract

The electrochemistry of TCNQF (2‐fluoro‐7,7,8,8‐tetracyanoquinodimethane) in acetonitrile (0.1 M Bu4NPF6) in the presence of either Co2+ or Ni2+ is reported. Cyclic voltammetry over an extensive range of potentials revealed that the reduction of TCNQF to either TCNQF1− or the TCNQF2− species provides a route for electrocrystallisation of the respective M(TCNQF)2(H2O)2 and M(TCNQF) materials on the electrode surface. These materials were independently prepared by addition of the corresponding metal salts to a solution of either TCNQF1− or TCNQF2− prepared by bulk electrolysis. Comprehensive characterisation of these solids by Infrared and Raman spectroscopy indicated that the M(TCNQF)2(H2O)2 complexes were similar to other transition metal complexes in the M(TCNQX)2(S)2 series where S=solvent (H2O or CH3OH) and X = H4 or F4. The M(TCNQF) materials containing the TCNQF2− anion were not stable in air, similar to the highly air‐sensitive TCNQ2− derivatives. Scanning Electron Microscopy (SEM) images of electrocrystallised samples of Ni(TCNQF)2(H2O)2 were rod‐like, whereas the Co(TCNQF)2(H2O)2 formed needles. Energy‐dispersive X‐ray spectroscopy (EDX) analysis of these samples together with elemental microanalysis and thermogravimetric analysis (TGA) supported the composition and stoichiometry. The solubility products (Ksp values) of M(TCNQF)2(H2O)2 materials were determined spectrophotometrically and voltammetrically in acetonitrile, where Ksp for Co(TCNQF)2(H2O)2 was 3.37×10−11 M3 (or 1.14×10−10 M3 in the presence of electrolyte, 0.1 M Bu4NPF6) and Ni(TCNQF)2(H2O)2 was 5.54×10−12 M3 (or 2.65×10−10 M3 in the presence of electrolyte, 0.1 M Bu4NPF6).