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Lanthanides & Actinides
Lanthanide Binary Oxides

Hydrides
Binary Oxides

Ln2O3

  • The most common lanthanide oxide (notable exceptions; CeO2, Pr6O11, Tb4O7)
  • Sesquioxides, Ln2O3, adopt three structure types
  • Strongly Basic
  • Absorb water / CO2 from air Æ hydroxide / carbonate salts
  • Pale colours
  • Properties strongly resemble alkaline earth oxides
A-type
  • light Ln
  • unusual LnO7 capped-octahedra
B-type
  • middle Ln
  • LnO7 units of three types:
    • 2 x capped trigonal prisms
    • 1 x capped octahedron
  • B-M2O3 structure is very complex
  • Densest of M2O3 structure types Þ favoured by increased pressure
C-type
  • heavy Ln
  • LnO6 units, but not octahedra
  • (face & body - divacant cubic)
  • C-type M2O3 is related to Fluorite (MO2) 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 Ln2O3 under hydrothermal conditions
  • 9-coordinate Ln with tricapped trigonal prismatic (ttp) geometry
  • basicity increases with Z - correlates with decrease in r(Ln3+)

LnO2

  • CeO2 (most stable)
  • Fluorite (CaF2 ) structure
  • Pr6 O11 , Tb4 O7 (formed at high PO2 and high temperature)
  • Range of non-stoichiometric phases between Fluorite LnO2 and C-type LnO1.5
    ~ 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 + Ln2O3 Æ 3LnO
  • NaCl structure
  • NdO, SmO lustrous golden yellow, conducting formulated as Ln3+(O2-)(e-)
  • EuO (dark red), YbO (greyish-white) insulating genuine Ln2+O2-
  • 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]


--Info & DownloadsBibliography  [textbook & online resources]

Source: Dr. S.J. Heyes; University of Oxford
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