structural:expansion, information:filtering
Compounds

Terbium combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming various binary compounds such as TbH, TbH, TbB, Tb S, TbSe, TbTe and TbN. In these compounds, Tb mainly exhibits the oxidation state +3, with the +2 state appearing rarely. Terbium(II) halides are obtained by annealing Tb(III) halides in presence of metallic Tb in tantalum containers. Terbium also forms the sesquichloride Tb Cl, which can be further reduced to TbCl by annealing at 800 °C; this compound, terbium(I) chloride, forms platelets with layered graphite-like structure.

Terbium(IV) fluoride is the only halide that tetravalent terbium can form. It has strong oxidizing properties and is a strong fluorinating agent, emitting relatively pure atomic fluorine when heated, rather than the mixture of fluoride vapors emitted from cobalt(III) fluoride or cerium(IV) fluoride. It can be obtained by reacting terbium(III) chloride or terbium(III) fluoride with fluorine gas at 320 °C:

When TbF and CsF is mixed in a stoichiometric ratio in a fluorine gas atmosphere, CsTbF is obtained. It is an orthorhombic crystal with space group Cmca and a layered structure composed of and 11-coordinated Cs. The compound BaTbF, an orthorhombic crystal with space group Cmma, can be prepared in a similar method. The compound also exists.

Terbium(III) oxide or terbia is the main oxide of terbium, and appears as a dark brown water-insoluble solid. It is slightly hygroscopic and is the main terbium compound found in rare earth-containing minerals and clays.

Other compounds include: