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Electrochemically Directed Synthesis of Cu2I(TCNQF4II–)(MeCN)2 (TCNQF4 = 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane): Voltammetry, Simulations, Bulk Electrolysis, Spectroscopy, Photoactivity, and X‑ray Crystal Structure of the Cu2I(TCNQF4II–)(EtCN)2 Analogue

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posted on 17.03.2014 by Thanh H. Le, Ayman Nafady, Nguyen T. Vo, Robert W. Elliott, Timothy A. Hudson, Richard Robson, Brendan F. Abrahams, Lisandra L. Martin, Alan M. Bond
The new compound Cu2I(TCNQF4II–)­(MeCN)2 (TCNQF42– = dianion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been synthesized by electrochemically directed synthesis involving reduction of TCNQF4 to TCNQF42– in acetonitrile containing [Cu­(MeCN)4]+(MeCN) and 0.1 M Bu4NPF6. In one scenario, TCNQF42– is quantitatively formed by reductive electrolysis of TCNQF4 followed by addition of [Cu­(MeCN)4]+ to form the Cu2I(TCNQF4II–)­(MeCN)2 coordination polymer. In a second scenario, TCNQF4 is reduced in situ at the electrode surface to TCNQF42–, followed by reaction with the [Cu­(MeCN)4]+ present in the solution, to electrocrystallize Cu2I(TCNQF4II–)­(MeCN)2. Two distinct phases of Cu2I(TCNQF4II–)­(MeCN)2 are formed in this scenario; the kinetically favored form being rapidly converted to the thermodynamically favored Cu2I(TCNQF4II–)­(MeCN)2. The postulated mechanism is supported by simulations. The known compound CuITCNQF4I– also has been isolated by one electron reduction of TCNQF4 and reaction with [Cu­(MeCN)4]+. The solubility of both TCNQF42–- and TCNQF4•–-derived solids indicates that the higher solubility of CuITCNQF4I– prevents its precipitation, and thus Cu2I(TCNQF4II–)­(MeCN)2 is formed. UV–visible and vibrational spectroscopies were used to characterize the materials. Cu2I(TCNQF4II–)­(MeCN)2 can be photochemically transformed to CuITCNQF4I– and Cu0. Scanning electron microscopy images reveal that CuITCNQF4I– and Cu2I(TCNQF4II–)­(MeCN)2 are electrocrystallized with distinctly different morphologies. Thermogravimetric and elemental analysis data confirm the presence of CH3CN, and single-crystal X-ray diffraction data for the Cu2I(TCNQF4II−)­(EtCN)2 analogue shows that this compound is structurally related to Cu2I(TCNQF4II–)­(MeCN)2.