Abstract
Microstructured sheets of semiconducting Ca[TCNQ](2) (TCNQ = 7,7,8,8-tetracyanoquinodimethane) have been synthesized via electrochemically driven (TCNQ)/Ca[TCNQ](2) solid-solid phase transformation that occurs upon one-electron reduction of solid TCNQ, mechanically attached to an electrode surface, in the presence of an aqueous Ca2+ ((aq)) electrolyte solution. Voltammetric probing of the electrochemically irreversible TCNQ/Ca[TCNQ](2) interconversion revealed that it is highly dependent on scan rate and Ca2+ ((aq)) electrolyte concentration. This voltammetric behavior, supported by double potential-step chronoamperometric evidence, clearly attests that formation of Ca[TCNQ](2) takes place via a rate-determining nucleation/growth process, which involves ingress of Ca2+ ((aq)) cations into the TCNQ(center dot-) crystal lattice at the triple phase TCNQ/TCNQ(center dot-) ((s))a",GC((s))a",Ca2+ ((aq)) electrolyte junction. The overall redox process associated with this chemically reversible solid-solid transformation can be described by the equation: TCNQ(0) ((S)) + 2e(-) + Ca2+ ((aq)) a double dagger" {Ca[TCNQ](2)}((S)). SEM characterization of the morphology of the generated Ca[TCNQ](2) material showed the formation of microstructured sheets, which are substantially different from those of parent TCNQ crystals and the needle-shaped crystals of group I cations (M+ = Li, Na, K, Rb, and Cs). The kinetic and thermodynamic implications of the Delta E (p) and E (m) values as a function of scan rate are discussed in terms of nucleation-growth and their relevance to those reported for the conceptually related group I cations and binary M[TCNQ](2) (M2+ = Mn, Fe, Co, and Ni)-based coordination polymers.