Redox-induced solid-solid phase transformation of TCNQ microcrystals into semiconducting Ni[TCNQ]2(H2O)2 nanowire...

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 Ni2+(aq)-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, Ni2+(aq) 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 Ni2+(aq) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ|electrode|electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ]2(H2O)2 back to TCNQ0 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: TCNQ0(S) + 2e- + Ni2+(aq)+ 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.