3.5.5 Reactions of Inorganic Compounds in Aqueous Solution - Metal-aqua ions
Metal salt solutions
In aqueous solution transition metals tend to form octahedral complexes in which the ligands are water molecules. These complexes have six water molecules and are called hexaaqua or hexaaquo complexes.
As transition metals have variable oxidation states, the hexaaqua complexes may be with metals in the 2+ or 3+ oxidation states. However, not all oxidation states are stable in aqueous solution.
Apart from the transition metals, aluminium is also known to form hexaaquaaluminium complex ions: