Lanthanum perchlorate is an inorganic compound of lanthanum and the perchlorate ion, with the chemical formula La(ClO4)3. It is known in anhydrous form and as hydrated salts, including the octahydrate. The anhydrous compound crystallizes in the hexagonal structure adopted by many of the lighter rare-earth perchlorates.
Preparation Hydrated lanthanum perchlorate can be prepared by dissolving lanthanum(III) oxide, lanthanum hydroxide or lanthanum carbonate in perchloric acid:
La2O3 + 6 HClO4 → 2 La(ClO4)3 + 3 H2O
Anhydrous La(ClO4)3 has been obtained by dehydrating the products formed by evaporation of solutions of La2O3 in approximately 70% perchloric acid.
Properties Anhydrous structure Anhydrous La(ClO4)3 crystallizes in the hexagonal crystal system, space group P63/m (No. 176), with two formula units per unit cell.
It is the largest-cell member of the hexagonal lanthanide-perchlorate series. Across the series from La to the later lanthanides, the lattice parameters decrease progressively as a result of the lanthanide contraction.
Lanthanum is nine-coordinate in the anhydrous structure. The LaO9 coordination environment is formed by oxygen atoms from perchlorate groups, which act as tridentate ligands and connect the metal centres into a three-dimensional framework containing channels.
The structure is related to the UCl3 structure type.
Hydrates Lanthanum perchlorate readily forms hydrates on crystallization from aqueous solution. The octahydrate, La(ClO4)3·8H2O, is a commonly reported form.
More highly and less highly hydrated rare-earth perchlorates can form depending on temperature, concentration and drying conditions.
Aqueous solution In dilute aqueous lanthanum perchlorate, La3+ is present predominantly as the nona-aqua ion [La(H2O)9]3+.
The first hydration shell has a tricapped trigonal-prismatic arrangement of nine water molecules. Perchlorate behaves mainly as a weakly coordinating counterion in dilute solution.
At higher La(ClO4)3 concentrations, outer-sphere and contact ion pairs increasingly form between La3+ and ClO4−.
Coordination chemistry Lanthanum perchlorate is used as a soluble source of La3+ in coordination chemistry, particularly when a weakly coordinating counterion is desirable.
The salt is used in the preparation of lanthanum complexes with crown ethers, macrocycles and other oxygen- or nitrogen-donor ligands.
Safety Lanthanum perchlorate is an oxidizing perchlorate salt and should be kept away from combustible and strongly reducing materials.
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