Electroregulated metal-binding with a crown ether tetrathiafulvalene derivative: Toward electrochemically addressed metal cation sponges

A redox responsive ligand incorporating the tetrathiafulvalene unit has bee n synthesized. The crystal structure of the free ligand (Z)-1 (C20H30O5S8, triclinic P (1) over bar, Z = 2, a = 9.087(6) Angstrom, b = 11.637(7) Angst rom, c = 14.370(8) Angstrom, alpha = 65.54(3)degrees, beta = 82.32(5)degree s, gamma = 84.18(6)degrees, V = 1368 Angstrom(3)) shows the redox-active te trathiafulvalene core to be essentially planar, which allows observation of two reversible one-electron processes upon electrochemical oxidation. The efficiency of this system in the control of the reversible complexation/exp ulsion sequence of a metallic cation (i.e., Ba2+) has been made possible th anks to a combination of (a) an unprecedented high coordination ability amo ng tetrathiafulvalene-based macrocycles as determined by LSI mass spectrome try (log K degrees = 3.5, NBA-matrix) as well as by solution investigations (H-1 NMR and cyclic voltammetry titration studies), which remarkably conve rge to similar binding constant values (i.e., log K degrees = 4.2-4.3), and (b) reversible metal cation expulsion upon electrochemical oxidation to th e dicationic state. A channel-like solid-state structure is observed for th e Ba2+ complex (C20H30O5S8, Ba2+(CF3SO3)(2)(2-), (H2O)(2), CD3CN, monoclini c C2/c, Z= 8, a = 45.66(1) Angstrom, b = 8.897(5) Angstrom, c 23.124(8) Ang strom, beta = 105.54(4)degrees, V = 9050 Angstrom(3)). which results from t he segregated stacking mode of the crown ether and the redox-active tetrath iafulvalene subunits, respectively.