Gadolinium perchlorate is an inorganic compound of gadolinium and the perchlorate ion, with the chemical formula Gd(ClO4)3. It is known in anhydrous form and as several hydrates, including the octahydrate. Anhydrous gadolinium perchlorate belongs to the hexagonal structural family adopted by many rare-earth perchlorates.
Preparation Hydrated gadolinium perchlorate can be prepared by dissolving gadolinium(III) oxide in concentrated perchloric acid:
Gd2O3 + 6 HClO4 → 2 Gd(ClO4)3 + 3 H2O
Aqueous solutions used in modern spectroscopic studies have been prepared by dissolving Gd2O3 in 70% perchloric acid.
Anhydrous Gd(ClO4)3 can be obtained by controlled dehydration of hydrated gadolinium perchlorate.
Properties Anhydrous structure Anhydrous Gd(ClO4)3 crystallizes in the hexagonal crystal system, space group P63/m (No. 176), with two formula units per unit cell. It belongs to the isostructural rare-earth perchlorate series extending from La through Er and Y. The Gd3+ centres are nine-coordinate, with oxygen atoms from perchlorate groups forming a three-dimensional framework related to the UCl3 structure type. The lattice dimensions decrease progressively across the rare-earth series as a consequence of the lanthanide contraction.
Hydrates Several hydrated forms of gadolinium perchlorate are known. The octahydrate, Gd(ClO4)3·8H2O, is a commonly cited crystalline hydrate. A nonahydrate has also been identified in aqueous phase-equilibrium studies. In the LiClO4–Gd(ClO4)3–H2O system, Gd(ClO4)3·9H2O occurs as an equilibrium solid phase.
Aqueous solution Gd3+ is strongly hydrated in aqueous gadolinium perchlorate solutions. Unlike the light rare-earth ions, which predominantly form nona-aqua complexes, and the heavy rare-earth ions, which predominantly form octaaqua complexes, gadolinium lies close to the crossover between these two hydration regimes. Raman spectroscopy of dilute Gd(ClO4)3 solutions therefore indicates an average first-shell hydration number between eight and nine rather than a single sharply defined coordination number. Perchlorate remains mainly outside the first hydration shell in dilute solutions, while contact ion pairing becomes increasingly important at high perchlorate concentration.
Coordination chemistry Gadolinium perchlorate is commonly used as a soluble source of Gd3+ in coordination chemistry. For example, reaction with myo-inositol, sodium acetate and sodium hydroxide has been used to prepare a giant wheel-shaped cluster containing 140 gadolinium ions. Gadolinium perchlorate hydrates also form solvates with oxygen-donor solvents; a dioxane-containing crystalline adduct of composition Gd(ClO4)3·9H2O·4C4H8O2 has been reported.
Safety Gadolinium perchlorate is an oxidizing perchlorate salt and should be kept away from combustible and strongly reducing materials.
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