Aluminium chloride exists as dimer ${\mathrm{Al}}_2{\mathrm{Cl}}_6$  in solid state as well as in solution of non-polar solvents such as benzene. When dissolved in water, it gives 

AlCl₃ is a covalent compound and exists as dimer (Al₂Cl₆) in solid state and in non-polar solvents (benzene). In the presence of water, AlCl₃ shows hydrolysis due to high hydration energy of Al³⁺.

${\mathrm{AlCl}}_3+6{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}+3{\mathrm{Cl}}^{-}$