The relationship between the electrochemistry and the crystallography of microcrystals. The case of TCNQ (7,7,8,8-tetracyanoquinodimethane)†‡
The relationship between the electrochemistry and the crystallography of microcrystals. The case of TCNQ (7,7,8,8-tetracyanoquinodimethane)†‡
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DOI：
10.1039/a805860a
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发表时间：
1998
期刊：
影响因子：
4.2
通讯作者：
A. Bond;P. Symons;S. Fletcher
中科院分区：
文献类型：
--
作者：
A. Bond;P. Symons;S. Fletcher
尺寸范围为100-2000 nm的TCNQ微晶可以通过干磨工艺附着到石墨、玻璃碳、金、铂和RAMTM电极的表面。当所得的表面被放置在第I族阳离子，如Na+，K+，Rb+和Cs+的水溶液中，并且电极电位循环时，TCNQ和其相应的阳离子盐之间发生可逆的相变。这些可逆相变的电化学响应表明，在所有情况下，成核-生长动力学是速率决定的。辅助技术，如光学显微镜，扫描电子显微镜和X射线衍射，阐明相应的晶体结构的变化。结合这些技术，提供了深入了解之间的关系电化学和微晶结晶学。光学显微镜揭示了颜色从黄色到蓝绿色的TCNQ微晶电化学还原后的变化，也揭示了小晶体反应速度比大晶体。遗憾的是，光学技术的有限分辨率（500 nm）阻止了在真实的时间内原位分析形态变化。然而，扫描电子显微镜是能够提供非原位的“快照”的微晶形态之前和之后的相变与1 nm的分辨率，这些可以用来重建的反应途径。最后，X射线衍射法允许在相变之前和之后确定TCNQ分子的空间坐标，精度为± 0.001 nm。这样的数据揭示，第一次，在电化学诱导的固-固相转化过程中发生在π堆叠的有机导体的分子取向的变化。
Microcrystals of TCNQ, in the size range 100–2000 nm, may be attached to the surfaces of graphite, glassy carbon, gold, platinum and RAMTM electrodes by a process of dry abrasion. When the resulting surfaces are placed in aqueous solutions of Group I cations, such as Na+, K+, Rb+ and Cs+, and the electrode potential is cycled, reversible phase transformations take place between the TCNQ and its corresponding cation salts. The electrochemical responses of these reversible phase transformations show that, in all cases, nucleation–growth kinetics are rate-determining. Ancillary techniques, such as optical microscopy, scanning electron microscopy and X-ray diffractometry, elucidate the corresponding crystal structure changes. In combination, these techniques provide deep insights into the relationship between the electrochemistry and crystallography of microcrystals.Optical microscopy reveals a colour change from yellow to blue–green upon electrochemical reduction of TCNQ microcrystals, and also reveals that small crystals react faster than large crystals. Unfortunately, analysis of morphological changes in situ in real time is prevented by the limited resolution of optical techniques (500 nm). However, scanning electron microscopy is able to provide ex situ ‘snapshots’ of the microcrystal morphologies before and after the phase transformations with a resolution of 1 nm, and these can be used to reconstitute the reaction pathway. Finally, X-ray diffractometry allows the spatial coordinates of the TCNQ molecules to be determined both before and after the phase transformations with accuracies of ± 0.001 nm. Such data reveal, for the first time, the changes that occur in molecular orientation during electrochemically induced solid–solid phase transformations in pi-stacked organic conductors.