Abstract
The electrocrystallization of transition metal coordination polymers MTCNQF(4) containing TCNQF(4)(2-) dianions and M2+ cations (TCNQF(4) = 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. TCNQF(4) is sequentially reduced to TCNQF(4)(center dot-) and then TCNQF(4)(2-). In the presence of M2+, the TCNQF(4)(2-) formation is accompanied by the electrocrystallization of the sparingly soluble MTCNQF(4) on the electrode surface. Cyclic voltammetry studies reveal that two phases of MTCNQF(4) are formed. One is kinetically favoured and rapidly converts to a second thermodynamically stable phase. The formation of MTCNQF(4) is possible because of the relatively high solubility of M(TCNQF(4))(2) derivatives. The solubilities of CoTCNQF(4) and NiTCNQF(4) are 8.6x10(-6) and 9.2x10(-6) M, respectively, in neat acetonitrile and 2.2x10(-5) and 2.4x10(-5) M, respectively, in an acetonitrile solution containing Bu4NPF6 (0.1 M). The presence of TCNQF(4)(2-) dianions rather than TCNQF(4)(center dot-) 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 MTCNQF(4) depends on the applied potential for CoTCNQF(4), but not for the NiTCNQF(4) complex.