Synthesis in ionic liquids: [[Bi.sub.2][Te.sub.2]Br](Al[Cl.sub.4]), a direct gap semiconductor with a cationic framework

The Lewis acidic liquid EMIMBr-Al[Cl.sub.3] (EMIM = 1-ethyl-3-methylimidazolium) has provided a synthetic route to the semiconducting layered metal chalcogenides halide [[Bi.sub.2][Te.sub.2]Br](Al[Cl.sub.4]) and its Sb analogue. [[Bi.sub.2][Te.sub.2]Br](Al[Cl.sub.4]) is shown to be a direct band gap, strongly anisotropic semiconductor and has cationic infinite layers of [[[Bi.sub.2][Te.sub.2]Br].sup.+] and [[Al[Cl.sub.4].sup.-] anions inserted between the layers.