Ionic compounds are non-molecular species. During melting they require a lot of energy input so that the strong ionic bonds that constitute the electrostatic lattice be disrupted. It thus requires very high temperatures. This is indicative of a very strong ion-ion electrostatic interaction which is typical of ionic bonds and results in high melting points of ionic solids.
Hence, the process of melting an ionic solid needs the addition of a large amount of energy in order to break all of the ionic bonds in the crystal.
On the other hand, Br2 is a covalent molecular specie. Most covalent compound have low melting points since their molecules are mostly held together only by weak van der waals forces.
