Redox-induced solid-solid phase transformation of TCNQ microcrystals into semiconducting Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures:: A combined voltammetric, spectroscopic, and microscopic study

The facile solid-solid phase transformation of TCNQ microcrystals into semiconducting and magnetic Ni[TCNQ](2)(H2O)(2) nanowire (flowerlike) architectures is achieved by reduction of TCNQ-modified electrodes in the presence of Ni-(aq)(2+)-containing electrolytes. Voltammetric probing revealed that the chemically reversible TCNQ/Ni[TCNQ](2)(H2O)(2) conversion process is essentially independent of electrode material and the identity of nickel counteranion but is significantly dependent on scan rate, Ni-(aq)(2+) electrolyte concentration, and the method of solid TCNQ immobilization (drop casting or mechanical attachment). Data analyzed from cyclic voltammetric and double-potential step chronoamperometric experiments are consistent with formation of the Ni[TCNQ](2)(H2O)(2) complex via a rate-determining nucleation/growth process that involves incorporation of Ni-(aq)(2+) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ parallel to electrode parallel to electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ](2)(H2O)(2) back to TCNQ(0) crystals, is also controlled by nucleation/growth kinetics. The overall redox process associated with this chemically reversible solid-solid transformation, therefore, is described by the equation: TCNQ((S))(0) + 2e(-) + Ni-(aq)(2+)+ 2 H2O -><- {Ni[TCNQ](2)(H2O)(2)}((S)). SEM monitoring of the changes that accompany the TCNQ/Ni[TCNQ](2)(H2O)(2) transformation revealed that the morphology and crystal size of electrochemically generated Ni[TCNQ](2)(H2O)(2) are substantially different from those of parent TCNQ crystals. Importantly, the morphology of Ni[TCNQ](2)(H2O)(2) can be selectively manipulated to produce either 1-D/2-D nanowires or 3-D flowerlike architectures via careful control over the experimental parameters used to accomplish the solid-solid phase interconversion process.