Electrochemically directed synthesis of Co2+ and Ni2+ complexes with TCNQF(4)(2-) (TCNQF(4)=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane)

The electrocrystallization of transition metal coordination polymers MTCNQF₄ containing TCNQF4^2– dianions and M²⁺ cations (TCNQF₄ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, M = Co or Ni) has been achieved in acetonitrile (0.1 M Bu₄NPF₆) at glassy carbon and indium tin oxide electrodes and the reaction pathway monitored by cyclic voltammetry and surface plasmon resonance. TCNQF₄ is sequentially reduced to TCNQF₄·– and then TCNQF₄^2–. In the presence of M²⁺, the TCNQF₄^2– formation is accompanied by the electrocrystallization of the sparingly soluble MTCNQF₄ on the electrode surface. Cyclic voltammetry studies reveal that two phases of MTCNQF₄ are formed. One is kinetically favoured and rapidly converts to a second thermodynamically stable phase. The formation of MTCNQF₄ is possible because of the relatively high solubility of M(TCNQF₄)₂ derivatives. The solubilities of CoTCNQF₄ and NiTCNQF₄ are 8.6 × 10^–6 and 9.2 × 10^–6 M, respectively, in neat acetonitrile and 2.2 × 10^–5 and 2.4 × 10^–5 M, respectively, in an acetonitrile solution containing Bu₄NPF₆ (0.1 M). The presence of TCNQF₄^2– dianions rather than TCNQF₄^·– monoanions in the coordination polymers was confirmed by UV/Vis, IR and Raman spectroscopy. Scanning electron microscopy images show that the morphology of the electrocrystallized MTCNQF₄ depends on the applied potential for CoTCNQF₄, but not for the NiTCNQF₄ complex.