Tuning the Electrocrystallization Parameters of Semiconducting Co[TCNQ]₂-Based Materials To Yield either Single Nanowires or Crystalline Thin Films

Abstract

Electrocrystallization of single nanowires and/or crystalline thin films of the semiconducting and magnetic Co[TCNQ]2(H2O)2 (TCNQ=tetracyanoquinodimethane) charge-transfer complex onto glassy carbon, indium tin oxide, or metallic electrodes occurs when TCNQ is reduced in acetonitrile (0.1 M [NBu4][ClO4]) in the presence of hydrated cobalt(II) salts. The morphology of the deposited solid is potential dependent. Other factors influencing the electrocrystallization process include deposition time, concentration, and identity of the Co2+(MeCN) counteranion. Mechanistic details have been elucidated by use of cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance, and galvanostatic methods together with spectroscopic and microscopic techniques. The results provide direct evidence that electrocrystallization takes place through two distinctly different, potential-dependent mechanisms, with progressive nucleation and 3-D growth being controlled by the generation of [TCNQ]*- at the electrode and the diffusion of Co2+(MeCN) from the bulk solution. Images obtained by scanning electron microscopy reveal that electrocrystallization of Co[TCNQ]2(H2O)2 at potentials in the range of 0.1-0 V vs Ag/AgCl, corresponding to the [TCNQ]0/*- diffusion-controlled regime, gives rise to arrays of well-separated, needle-shaped nanowires via the overall reaction 2[TCNQ]*-(MeCN)+Co2+(MeCN)+2H2O right harpoon over left harpoon {Co[TCNQ]2(H2O)2}(s). In this potential region, nucleation and growth occur at randomly separated defect sites on the electrode surface. In contrast, at more negative potentials, a compact film of densely packed, uniformly oriented, hexagonal-shaped nanorods is formed. This is achieved at a substantially increased number of nucleation sites created by direct reduction of a thin film of what is proposed to be cobalt-stabilized {(Co2+)([TCNQ2]*-)2} dimeric anion. Despite the potential-dependent morphology of the electrocrystallized Co[TCNQ]2(H2O)2 and the markedly different nucleation-growth mechanisms, IR, Raman, elemental, and thermogravimetric analyses, together with X-ray diffraction, all confirmed the formation of a highly pure and crystalline phase of Co[TCNQ]2(H2O)2 on the electrode surface. Thus, differences in the electrodeposited material are confined to morphology and not to phase or composition differences. This study highlights the importance of the electrocrystallization approach in constructing and precisely controlling the morphology and stoichiometry of Co[TCNQ]2-based materials.

A General Electrochemical Strategy for Synthesizing Charge‐Transfer Complex Micro/Nanowires

“…In a recent publication, Nafady et al studied the electrocrystallization progress of Co[TCNQ] 2 (H 2 O) 2 on various macroscopic electrodes such as glassy carbon, ITO and metal. [19] They claimed that two distinctly different mechanisms lead to the formation of different morphologies, including thin films and nanowires, depending on the potential. The nanowires obtained in their work were hollow, at least near the tips, and had a polygonal/cone shape, which is obviously different to the Co[TCNQ] 2 (H 2 O) 2 nanowires obtained on CNT electrodes.…”

“…[10,11] A number of methods have been developed to fabricate 1D CT nanostructures, including spontaneous electrolysis, [12] organic vapor-solid-phase reaction, [10,13] thermal co-deposition, [14] the two-phase solution method, [15] photocrystallization, [16] and electrocrystallization. [17][18][19][20][21][22][23][24] In general, these methods can be categorized into two different reaction types. One is based on a spontaneous charge transfer reaction, wherein neutral organic conjugated molecules either in vapor or solution react with counter molecules or metal, such as Ag and Cu, as occurs during spontaneous electrolysis, vapor-solid chemical reaction, thermal co-deposition and the two-phase solution method.…”

“…For instance, the initial oxidation potential for organic donors containing sulfur atoms (e.g., TTF and ET) or selenium atoms (e.g., TMTSF) does not exceed 0.6 V (vs. SCE) whereas the reduction potential for commonly employed organic acceptor such as TCNQ and its derivatives is in the range of À0.02 to 0.65 V (vs. SCE), which suggests that they could be changed to suitable states by electrochemical reaction for the purpose of forming CT complexes. Although there have been several studies on the electrochemical synthesis of CT complex nanostructures on either macroscopic electrodes or microelectrodes, [17][18][19][20][21][22][23][24][25] lowdimensional structures with large aspect ratios cannot easily be obtained due to the severe competition between densely packed crystal nuclei on such electrode surfaces. It has been found that electrocrystallization on macroscopic electrodes could only generate short bundles instead of isolated micro/nanowires.…”

Water-controlled synthesis of low-dimensional molecular crystals and the fabrication of a new water and moisture indicator

“…3(a). The band at 2196 cm 1 occurs at lower energy than that of the [19,24]. The distinct difference in the TGA traces of the columns and lamellae possibly indicates that they are different phases.…”

Fabrication and Field‐Emission Properties of Large‐Area Nanostructures of the Organic Charge‐Transfer Complex Cu‐TCNAQ

“…[1][2][3][4][5] Metal-organic charge-transfer (CT) complexes are of growing interest because of their unique solid-state physical properties. [6][7][8] In particular, with well-defined architecture,CT complexes are showing prominent merits over their bulk counterparts for applications in electrical and optical memory devices, sensors, and magnetic devices. [9][10][11] Many researchers therefore launched studies on the controllable synthesis of CT complexes.…”