Role of Water in the Dynamic Disproportionation of Zn-Based TCNQ(F4) Coordination Polymers (TCNQ = Tetracyanoquinodimethane)

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• 作者：Ayman Nafady ; Thanh Hai Le ; Nguyen Vo ; Naomi L. Haworth ; Alan M. Bond ; Lisandra L. Martin
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：February 17, 2014
• 年：2014
• 卷：53
• 期：4
• 页码：2268-2275
• 全文大小：426K
• ISSN：1520-510X

文摘

Intriguingly, coordination polymers containing TCNQ^{2鈥?/sup> and TCNQF₄2鈥?/sup> (TCNQ = 7,7,8,8-tetracyanoquinodimethane, TCNQF₄ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, both designated as TCNQ(F₄)2鈥?/sup>) may be generated from reaction of metal ions with TCNQ(F₄)鈥⑩€?/sup>. An explanation is now provided in terms of a solvent-dependent dynamic disproportionation reaction. A systematic study of reactions associated with TCNQ(F₄) and electrochemically generated TCNQ(F₄)_MeCN鈥⑩€?/sup> and TCNQ(F₄)_MeCN2鈥?/sup> revealed that disproportionation of TCNQ(F₄)_MeCN鈥⑩€?/sup> radical anions in acetonitrile containing a low concentration of water is facilitated by the presence of Zn_MeCN2+. Thus, while the disproportionation reaction 2TCNQ(F₄)_MeCN鈥⑩€?/sup> TCNQ(F₄)_MeCN + TCNQ(F₄)_MeCN2鈥?/sup> is thermodynamically very unfavorable in this medium (K_eq 鈮?9 脳 10鈥?0; TCNQF₄), the preferential precipitation of ZnTCNQ(F₄)_(s) drives the reaction: Zn_MeCN2+ + 2 TCNQ(F₄)_MeCN鈥⑩€?/sup> ZnTCNQ(F₄)_(s) + TCNQ(F₄)_MeCN. The concomitant formation of soluble TCNQ(F₄)_MeCN and insoluble ZnTCNQ(F₄)_(s) and the loss of TCNQ(F₄)_MeCN鈥⑩€?/sup> were verified by UV鈥搗isible and infrared spectroscopy and steady-state voltammetry. Importantly, the reverse reaction of comproportionation rather than disproportionation becomes the favored process in the presence of 鈮?% (v/v) water, due to the increased solubility of solid ZnTCNQ(F₄)_(s). Thus, in this 鈥渨et鈥?environment, Zn_MeCN2+ and TCNQ(F₄)_MeCN鈥⑩€?/sup> are produced from a mixture of ZnTCNQ(F₄)_(s) and TCNQ(F₄)_MeCN and with the addition of water provides a medium for synthesis of [Zn(TCNQ(F₄))₂(H₂O)₂]. An important conclusion from this work is that the redox level of TCNQ(F₄)-based materials, synthesized from a mixture of metal cations and TCNQ(F₄)鈥⑩€?/sup>, is controlled by a solvent-dependent disproportionation/comproportionation reaction that may be tuned to favor formation of solids containing the monoanion radical, the dianion, or even a mixture of both.}