An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5]− to [Br11]− in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11]− units, forming a previously unknown polymeric [Br24]2− dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.