What is the structure of BeCl₂ molecule in gaseous and solid state?

Beryllium chloride is covalent in nature.

The structure of BeCl₂ in solid state is a polymeric chain structure and each Be atom is surrounded by four Cl atoms. Two Cl atoms are covalently bonded and two are bonded by coordinate bonds. The gaseous/vapour state is different than the solid state. BeCl₂ tends to form a chloro-bridged dimer at temperatures below 1200K and dissociates into a linear monomer at high temperatures of the order of 1200 K.