Electrochemical Synthesis and Characterization of Semiconducting Ni(TCNQF4)2(H2O)2 (TCNQF4=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane)

An electrochemical technique has been used to synthesize Ni(TCNQF4)2(H2O)2 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane). The method involves the reduction of solid TCNQF4 immobilized on an electrode surface in contact with Ni2+?(aq.)-containing electrolyte. The electrochemically irreversible, but chemically reversiblesolidsolid TCNQF4/Ni(TCNQF4)2(H2O)2 interconversion process is governed by nucleation and growth kinetics and is represented by the overall reaction: 2TCNQF4?(s, electrode) + Ni2+?(aq.) + 2H2O + 2e [rlhar2] Ni(TCNQF4)2(H2O)2?(s, electrode). Thus, the formation of Ni(TCNQF4)2(H2O)2 involves the one-electron reduction of TCNQF4 to [TCNQF4]center dot coupled with an ingress of Ni2+?(aq.) from the aqueous electrolyte, while the reverse scan represents the oxidation of [TCNQF4]center dot to TCNQF4 coupled with the egress of Ni2+?(aq.). Cyclic voltammograms for the TCNQF4/Ni(TCNQF4)2(H2O)2 solidsolid phase transformation are independent of the electrode material and the identity of the Ni2+?(aq.) counteranion but are strongly dependent on the concentration of Ni2+?(aq.) and the scan rate. UV/Vis, infrared, and Raman spectra confirm the presence of [TCNQF4]center dot in the newly synthesized material. The composition of Ni(TCNQF4)2(H2O)2 was deduced from thermogravimetric and elemental analyses. Scanning electron microscopic images of Ni(TCNQF4)2(H2O)2 electrocrystallized onto the surface of an indium tin oxide electrode show a thin film morphology. Magnetic and conductivity data demonstrate that the complex behaves as a classical paramagnet and is a typical semiconductor with a band gap close to that of an insulator.