#### Hydrides Binary Oxides**Ln**_{2}**O**_{3}
- The most common lanthanide oxide (
*notable* *exceptions*; CeO_{2}, Pr_{6}O_{11}, Tb_{4}O_{7}) **Sesquioxides**, **Ln**_{2}**O**_{3}, adopt **three structure types**- Strongly
**Basic** - Absorb water / CO
_{2} from air Æ hydroxide / carbonate salts **Pale** colours- Properties strongly
**resemble alkaline earth oxides **
**A-type**
*l**ight Ln*- unusual LnO
_{7} **capped-octahedra**
**B-type**
*middle Ln***LnO**_{7}** units** of three types:- 2 x capped trigonal prisms
- 1 x capped octahedron
- B-M
_{2}O_{3} structure is very complex **Densest** of M_{2}O_{3} structure types Þ *favoured by increased pressure*
**C-type**
*heavy Ln*- LnO
_{6} units, but **not octahedra** - (
**face ****&**** body - divacant cubic**)
**C-type M**_{2}**O**_{3} is related to **Fluorite (MO**_{2}**) with **^{1}**/**_{4}** of anions removed**
##### Polymorphism**A** (high T)
**B** (medium T)
**C** (low T)
See: Wells, *Structural Inorganic Chemistry*, p. 543-547 for structural details #### Ln(OH)_{3}- obtained by action of
**conc. NaOH** on Ln_{2}O_{3} under **hydrothermal conditions** - 9-coordinate Ln with
*tricapped trigonal prismatic* (ttp) geometry **basicity increases with Z** - correlates with decrease in r(Ln^{3+})
#### LnO_{2}**CeO**_{2 }**(***most stable*)*Fluorite* (CaF_{2 }) structure**Pr**_{6 }**O**_{11 }**, Tb**_{4 }**O**_{7}_{ } (*formed at high P*_{O}_{2}* and high temperature*)- Range of
**non-stoichiometric phases** between Fluorite LnO_{2} and *C-type* LnO_{1.5}~ intermediate phases were the first known examples of **shear structures**See: Wells, *Structural Inorganic Chemistry*, p. 226-228 for an introduction to shear structures
#### LnO- known for some Ln
*Preparation**:* *Comproportionation* Ln + Ln_{2}O_{3} Æ 3LnO- NaCl structure
**NdO, SmO** *lustrous golden yellow, **conducting* formulated as **Ln**^{3+}**(O**^{2-}**)(e**^{-}**)****EuO** (dark red), **YbO** (greyish-white) *insulating* **genuine Ln**^{2+}**O**^{2-}**EuO** is *ferromagnetic* and an insulator when pure[C.N.R. Rao & J. Gopalkrishnan, *New Directions in Solid State Chemistry*, 2nd ed, CUP, 1996 p. 302-3]
*Bibliography* [textbook & online resources] |