Structural Expansion and Enhanced Photocurrent Conversion of Selenido Stannates with Cu Ions.

As a means of tuning the electronic properties of tin-chalcogenide-based compounds, we present a strategy for the compositional and structural expansion of selenido stannate frameworks under mild conditions by introducing Cu ions into binary anionic Sn/Se aggregates in ionothermal reactions. The variable coordination modes of Cu-contrasting with tetrahedral {SnSe} or trigonal bipyramidal {SnSe} units-and corresponding expansion toward ternary Cu/Sn/Se substructures helped to add another degree of freedom to the nanoarchitectures. As desired, the variation of the structural features was accompanied by concomitant changes of the physical properties. Upon treatment of alkali metal salts of the [SnSe] anion at slightly elevated temperatures (120 or 150 °C) in ionic liquids, we isolated a series of compounds comprising ternary or quaternary cluster molecules or networks of cluster units, (CCIm)Li[CuSnSe] (), (CCIm)[CuSnSe] (), (CCIm)[CuSnSe] (), and (CCIm)[CuSnSeF]·(CCIm)[BF] (; CCIm = 1,3-diethyl-imidazolium, CCIm = 1-ethyl-3-methyl-imidazolium), which were investigated in terms of their optical gaps and photocurrent conversion properties. As illustrated by the synthesis and characterization of an additional salt that does not include Cu, {(CCIm)[SnSe]}·{(CCIm)[BF]} (), the significant role of Cu in this system was shown to be 3-fold: (a) structural expansion, (b) narrowing of the optical gap, and (c) photocurrent enhancement. By this three-in-one effect, the work offers an in-depth understanding of chalcogenido metalate chemistry with atomic precision.