In a eutectic mixture of two ionic liquids, we have synthesized and crystallized the new polychloride compound [Et₄N]₂ [(Cl₃)₂⋅Cl₂] that exhibits a periodic 2D polychloride network acting as an anionic layer. Based on its low melting point and vapor pressure, this compound can be described as a room‐temperature ionic liquid. The compound was fully characterized by IR and Raman spectroscopy as well as single‐crystal X‐ray structure determination. The characterization was complemented by solid‐state quantum‐chemical calculations confirming the results of the experimental work.