Lanthanide trichlorides are a family of

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Ln Cl₃, where Ln stands for a lanthanide metal. The trichlorides are standard reagents in applied and academic chemistry of the lanthanides. They exist as anhydrous solids and as hydrates.

Properties

The anhydrous solids have melting points range from ca. 582 (Tb) - 925 °C (Lu). They are generally pale colored, often white. As coordination polymers, they only dissolve in donor solvents, including water.

Preparation

The lanthanide oxides and carbonates dissolve in

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

to give chloride salt of the hydrated cations: :M₂O₃ + 6HCl + n H₂O → 2 n(H₂O)_nl₃

Industrial routes

Anhydrous trichlorides are produced commercially by

carbothermic reaction Carbothermic reactions involve the reduction of substances, often metal oxides (O2-), using carbon (C) as the reducing agent. The reduction is usually conducted in the electric arc furnace or reverberatory furnace, depending on the metal ore. The ...

of the oxide: :M₂O₃ + 3Cl₂ + 3C → 2MCl₃ + 3CO

Ammonium chloride route

The ammonium chloride route refers to a general procedure to produce

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

lanthanide chlorides. The method has the advantages of being general for the 14 lanthanides and it produces air-stable intermediates that resist hydrolysis. The use of ammonium chloride as a reagent is convenient because the salt is anhydrous, even when handled in air. Ammonium chloride is also attractive because it thermally decomposes to volatile products at temperatures compatible with the stability of the trichloride targets. ;Step 1: preparation of ammonium lanthanide chlorides The reaction of an intimate mixture of lanthanide oxides with excess ammonium chloride produces anhydrous ammonium salts of the penta- and hexachlorides. Typical reaction conditions are hours at 230-250 °C. Some lanthanides (as well as

scandium Scandium is a chemical element; it has Symbol (chemistry), symbol Sc and atomic number 21. It is a silvery-white metallic d-block, d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lantha ...

and

yttrium Yttrium is a chemical element; it has Symbol (chemistry), symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost a ...

) form ''penta''chlorides: :M₂O₃ + 10NH₄Cl → 2(NH₄)₂MCl₅ + 3H₂O + 6NH₃ (M = Dy, Ho, Er, Tm, Lu, Yb, Y, Sc) :Tb₄O₇ + 22NH₄Cl → 4(NH₄)₂TbCl₅ + 7H₂O + 14NH₃ Other lanthanides for ''hexa''chlorides: :M₂O₃ + 12NH₄Cl → 2(NH₄)₃MCl₆ + 3H₂O + 6NH₃ (M = La, Ce, Nd, Pm, Sm, Eu, Gd) :Pr₆O₁₁ + 40NH₄Cl → 6(NH₄)₃PrCl₆ + 11H₂O + 22NH₃ These reactions can also start with the metals, e.g.: :Y + 5NH₄Cl → (NH₄)₂YCl₅ + 1.5H₂ + 3NH₃ ;Step 2: thermolysis of ammonium lanthanide chlorides The ammonium lanthanum chlorides are converted to the trichlorides by heating in a vacuum. Typical reaction temperatures are 350–400 °C: :(NH₄)₂MCl₅ → MCl₃ + 2HCl + 2NH₃ :(NH₄)₃MCl₆ → MCl₃ + 3HCl + 3NH₃

Other methods

Hydrated lanthanide trichlorides dehydrate under a hot stream of

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

Structures

As indicated in the table, the anhydrous trichlorides follow two main motifs, UCl₃ and YCl₃. The UCl₃ structure features 9-coordinate metal centers. The PuBr3 structure, adopted uniquely by TbCl₃, features 8-coordinated metals. The remaining later metals are 6-coordinate as is

aluminium trichloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms a hexahydrate with the formula , containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are col ...

Reactions

Lanthanide trichlorides are commercial precursors to the metals by reduction, e.g. with

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

: :LnCl₃ + Al → Ln + AlCl₃ In some cases, the trifluoride is preferred. They react with humid air to give

oxychloride In chemistry, oxohalides or oxyhalides are a group of chemical compounds with the chemical formula , where X is a halogen, and A is an element different than O and X. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine ( ...

s: :LnCl₃ + H₂O → LnOCl + 2 HCl For synthetic chemists, this reaction is a problematic since the oxychlorides are less reactive.

References

{{Chlorides Chlorides Lanthanum compounds Lanthanide halides