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Synthesis and characterization of microstructured sheets of semiconducting Ca[TCNQ]2 via redox-driven solid-solid phase transformation of TCNQ microcrystals |
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| Authors: | Ayman Nafady Nasser J Al-Qahtani Khalid A Al-Farhan Suresh Bhargava Alan M Bond |
| Institution: | 1. Department of Chemistry, College of Science, King Saud University, PO Box: 2455, Riyadh, 11451, Saudi Arabia 2. Chemistry Department, Faculty of Science, Sohag University, Sohag, 82524, Egypt 3. King Abdulaziz City for Science and Technology, Petrochemical Research Institute, Riyadh, 11451, Saudi Arabia 4. Centre for Advanced Materials & Industrial Chemistry, College of Science, Engineering and Health, RMIT University, Melbourne, Victoria, 3000, Australia 5. School of Chemistry, Monash University, Clayton Campus, Victoria, 3800, Australia |
| Abstract: | Microstructured sheets of semiconducting CaTCNQ]2 (TCNQ = 7,7,8,8-tetracyanoquinodimethane) have been synthesized via electrochemically driven (TCNQ)/CaTCNQ]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/CaTCNQ]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 CaTCNQ]2 takes place via a rate-determining nucleation/growth process, which involves ingress of Ca2+ (aq) cations into the TCNQ·? crystal lattice at the triple phase TCNQ/TCNQ·? (s)│GC(s)│Ca2+ (aq) electrolyte junction. The overall redox process associated with this chemically reversible solid-solid transformation can be described by the equation: TCNQ0 (S)?+?2e??+?Ca2+ (aq) ? {CaTCNQ]2}(S). SEM characterization of the morphology of the generated CaTCNQ]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 ΔE 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 MTCNQ]2 (M2+?=?Mn, Fe, Co, and Ni)-based coordination polymers. |
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