Aluminium chloride (A_lC_l3) is an interesting compound as it exhibits both ionic and covalent properties. The compound demonstrates the complexity and nuances of chemical bonding.

• The bonding triangle is a graphical representation of how different elements interact based on their electronegativity (χ) difference (∆χ).
• In the bonding triangle, A_lC_l3 is right at the boundary between ionic and polar covalent, with ∆χ = 1.6 and χ = 2.4.
• However, AlCl3 has an unusually low melting point for an ionic compound, indicating that it has a mixed character and cannot be strictly classified as ionic.
• This shows that the bonding triangle isn't a foolproof method to predict the properties of a compound, especially if the compound has mixed bonding characteristics.

• Ionic Property: AlCl3 forms ionic lattices when it is in the solid state.
• Covalent Property: At high pressure and a temperature of 190°C, AlCl3 melts into Al2Cl6 dimers, which is very unusual for an ionic compound.
• Solubility: Unlike a typical ionic compound, AlCl3 is soluble in non-polar solvents like trichloromethane.

• AlCl3 as a Catalyst: A_lC_l3 is used as a catalyst in the Friedel-Crafts alkylation and acylation reactions, which are used in the synthesis of organic compounds like drugs and dyes.
• Water Purification: A_lC_l3 is also used as a coagulant in water treatment processes to remove impurities.