What is the structure of `BeCI_(2)` molecule in gaseous and solid state?

Explanation

Beryllium chloride has different structures in solid and vapour state. In solid state, it exists in the form of polymeric chain structure in which each Be-atom is surrounded by four chlorine atoms having two of the chloride atoms covalently bonded while the other two by coordinate bonds. The resulting bridge structure contains infinite chains.
ltbr. In vapour state, above 1200K, it exists as a monomer having linear structure and zero dipole moment. But below 1200K, it exists as dimer structure even in vapour state.