Synthesis and crystal structure of rare-earth biuret complexes with linear pentaiodide ions: Infinite polyiodide chains in a cationic framework

•Linear pentaiodide ion can be described as two I2 molecules attached to the central I–.•Pentaiodide-ions fill channels of 3-D framework of complex cations and iodide ions.•The structure resembles iodine–starch complex.•The polarizability is maximal along polyiodide chain.•Electronic conductivity along polyiodide chain can be assumed.