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
By Le, Thanh H.; Nafady, Ayman; Vo, Nguyen T.; Elliott, Robert W.; Hudson, Timothy A.; Robson, Richard; Abrahams, Brendan F.; Martin, Lisandra L. & Bond, Alan M.
Published in Inorganic Chemistry
2014
Abstract
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.