Thulium perchlorate is an inorganic compound of thulium in the +3 oxidation state and the perchlorate ion, with the formula Tm(ClO4)3. It is known in hydrated and anhydrous forms. Anhydrous Tm(ClO4)3 is polymorphic, with a hexagonal low-temperature phase and a trigonal high-temperature phase.
Preparation Hydrated thulium perchlorate can be prepared by dissolving thulium(III) oxide in aqueous perchloric acid:
Tm2O3 + 6 HClO4 → 2 Tm(ClO4)3 + 3 H2O
A modern Raman study prepared aqueous Tm(ClO4)3 solutions by dissolving Tm2O3 in 6 mol/L perchloric acid.
Anhydrous Tm(ClO4)3 can be prepared by dehydrating hydrated thulium perchlorate with chlorine oxide dehydrating agents under reduced pressure.
Properties Anhydrous polymorphs Two polymorphs of anhydrous Tm(ClO4)3 have been characterized.
The low-temperature form crystallizes in the hexagonal crystal system, space group P63/m (No. 176), with lattice parameters a = 9.211(3) Å, c = 5.563(1) Å and two formula units per unit cell.
It belongs to the same structure family as the anhydrous perchlorates of La through Er. The Tm3+ ion is nine-coordinate, with oxygen atoms supplied by tridentate perchlorate groups that link the metal centres into a channel-containing three-dimensional framework.
The high-temperature form crystallizes in the trigonal crystal system, space group R3c (No. 161), with lattice parameters a = 8.13286(2) Å, c = 24.1586(1) Å and six formula units per unit cell.
This structure is closely related to that of anhydrous Lu(ClO4)3. In the trigonal phase, the Tm atoms form layers connected through bridging and chelating perchlorate groups.
Hydrates A hexahydrate, Tm(ClO4)3·6H2O, is a commonly reported hydrated form and has been described as forming green crystals.
The hydrate is readily soluble in water and can serve as a precursor to the anhydrous salt.
Aqueous solution In dilute aqueous thulium perchlorate, Tm3+ occurs predominantly as the octaaqua ion [Tm(H2O)8]3+.
Raman spectroscopy assigns a strongly polarized band near 391 cm−1 to the symmetric Tm–O breathing vibration of [Tm(H2O)8]3+.
Perchlorate behaves mainly as a weakly coordinating counterion in dilute solution, although ion pairing becomes more important at higher concentrations.
Safety Thulium(III) perchlorate is an oxidizing perchlorate salt and should be kept away from combustible and strongly reducing materials.
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