Electrochemically-Induced TCNQ/Mn[TCNQ]₂(H₂O)₂(TCNQ = 7,7,8,8-Tetracyanoquinodimethane) Solid−Solid Interconversion: Two Voltammetrically Distinct Processes That Allow Selective Generation of Nanofiber or Nanorod Network Morphologies

Abstract

Unlike the case with other divalent transition metal M[TCNQ](2)(H(2)O)(2) (M = Fe, Co, Ni) analogues, the electrochemically induced solid-solid phase interconversion of TCNQ microcrystals (TCNQ = 7,7,8,8-tetracyanoquinodimethane) to Mn[TCNQ](2)(H(2)O)(2) occurs via two voltammetrically distinct, time dependent processes that generate the coordination polymer in nanofiber or rod-like morphologies. Careful manipulation of the voltammetric scan rate, electrolysis time, Mn(2+)((aq)) concentration, and the method of electrode modification with solid TCNQ allows selective generation of either morphology. Detailed ex situ spectroscopic (IR, Raman), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) characterization clearly establish that differences in the electrochemically synthesized Mn-TCNQ material are confined to morphology. Generation of the nanofiber form is proposed to take place rapidly via formation and reduction of a Mn-stabilized anionic dimer intermediate, [(Mn(2+))(TCNQ-TCNQ)(2)(*-)], formed as a result of radical-substrate coupling between TCNQ(*-) and neutral TCNQ, accompanied by ingress of Mn(2+) ions from the aqueous solution at the triple phase TCNQ/electrode/electrolyte boundary. In contrast, formation of the nanorod form is much slower and is postulated to arise from disproportionation of the [(Mn(2+))(TCNQ-TCNQ)(*-)(2)] intermediate. Thus, identification of the time dependent pathways via the solid-solid state electrochemical approach allows the crystal size of the Mn[TCNQ](2)(H(2)O)(2) material to be tuned and provides new mechanistic insights into the formation of different morphologies.

Synthesis of CuTCNQ/Au Microrods by Galvanic Replacement of Semiconducting Phase I CuTCNQ with KAuBr4 in Aqueous Medium

“…Over the past few decades, significant attention has been directed toward metal–organic semiconducting materials based on charge-transfer complexes of metal-7,7,8,8-tetracyanoquinodimethane (TCNQ), principally investigated by Dunbar, Miller, and Bond. − In particular, CuTCNQ has been the subject of intensive research, based on the observation of switching effects from a high to low impedance state upon application of an external electric field or optical excitation. − There exists two phases of CuTCNQ, namely phase I, which possesses a higher room-temperature conductivity (0.2 S cm –2 ), with respect to phase II (1 × 10 –5 S cm –2 ). The two phases also differ in morphology: phase I tends to form rodlike structures and phase II typically leads to platelike structures.…”

Galvanic Replacement of Semiconductor Phase I CuTCNQ Microrods with KAuBr4 to Fabricate CuTCNQ/Au Nanocomposites with Photocatalytic Properties

“…Metal−organic semiconducting materials based on charge transfer complexes of metal-7,7,8,8-tetracyanoquinodimethane (TCNQ) have received considerable attention over the past 40 years, with a particular resurgence in interest in the past few years through the work of Dunbar et al, Miller et al, and Bond et al − In particular, CuTCNQ has been the subject of intensive research given the observation of a switching effect from a high to low impedance state upon the application of an electric field or optical excitation. − It has also been demonstrated that CuTCNQ can exist in two phases, namely, phase I that has a room temperature conductivity of 0.2 S cm −1 and phase II with a conductivity of 10 −5 S cm −1 . There have been many attempts to synthesize CuTCNQ in various morphologies using chemical, electrochemical, and photochemical techniques; however, to date there has been little or no attempt to modify the surface of CuTCNQ once it has been formed .…”

Structural, Spectroscopic, and Electrochemical Characterization of Semi-Conducting, Solvated [Pt(NH3)4](TCNQ)2·(DMF)2 and Non-Solvated [Pt(NH3)4](TCNQ)2

“…As found for TCNQ/M nþ (TCNQ) n solid-solid interconversion reactions (M nþ ¼ Mn 2þ , Fe 2þ , Co 2þ , Ni 2þ , Cu þ or alkali metal cations), [36,[38][39][40][43][44][45]49] (aq) , presumably owing to increasing ohmic drop effects (iR u ). [36,[38][39][40][43][44][45] This effect is also apparent when the scan rate is increased from 5 to 50 mVs À1 (Fig. S6a, (aq) electrolyte concentration over the range of 5 mM to 0.50 M using TCNQmodified GC electrode (mechanical attachment) and a scan rate of 20 mV s À1 is relatively small, ,8 mV shift per decade change in concentration as shown in Fig.…”

“…and other related parameters are similar to those reported for electrochemically driven TCNQ/M-TCNQ solid-solid interconversion, where M is a group I (alkali metal), [39,40] group II (alkaline earth) [41,42] cation or first-row transition metal cation. [36,38,[43][44][45] On this basis, the observed voltammetry is attributed to the one-electron reduction of solid TCNQ 0 to TCNQ 1accompanied by rapid interaction with the [Pt(NH 3 ) 4 ] 2þ cation from the aqueous electrolyte at the TCNQ/TCNQ 1-(s) tGC (s) t[Pt(NH 3 ) 4 ](NO 3 ) 2(aq) triple-phase junction.…”