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Lanthanides & Actinides
Actinide Stereochemistries
  • Actinide Stereochemistries show similarities with the Lanthanides
    • High coordination numbers

      e.g. [Th(NO3)6]2- has distorted icosahedral (C.N. = 12) geometry

      e.g. C.N. = 8, 9 are very common UF82-, Th(S2CNEt2)4, Th(trop)4(H2O)

    • Distortions from idealised stereochemistries

      e.g. PuF62- is not octahedral

    • but widest range of stereochemistries is for An(IV) rather than An(III)

      {possibly because chemistry of early actinides has received most attention!}

  • Complexes
    • a wide range of complexes with monodentate and chelating ligands
    • complexing ability:- [M5+] > M4+ > MO22+ > M3+ > MO2+

      uni-negative: F- > NO3- > Cl- > ClO4-

      bi-negative: CO32- > C2O42- > SO42-

    • geometry may be strongly influenced by covalent bonding effects

      e.g. MO22+ unit is always linear UO2(h2-NO3)2(H2O)2 is hexagonal bipyramidal

  • Compounds Actinide Hydrides, Halides, Oxides, Oxyhalides,...
    • for a given oxidation state show similarly diverse C.N. to Lanthanides
    • different accessible oxidation states even greater diversity of structure
  • Wide variety of oxidation states of ligands & number of oxidation states

    Extraordinary range of stereochemistry in actinide complexes and compounds

Stereochemistry of Actinides in Well-Defined Complexes and Crystalline Solids
C.N.GeometryO.N.e.g.
4distorted+4U(NPh2)4
    
5distorted tbp+4U2(NEt2)8
    
6octahedral+3An(H2O)63+, An(acac)3
  +4UCl62-
  +5UF6&endash, a-UF5
  +6AnF6
  +7Li5[AnO6] (An = Np, Pu)
 distorted octahedral+6Li4UO5 , UO3
    
  +5/+6U5O8
  +6UO2(S2CNEt2)2(ONMe3)
    
8cubic+4(Et4N)4[U(NCS)8], ThO2, UO2
  +5AnF83-
 square antiprismatic+4ThI4, U(acac)4, Cs4[U(NCS)8],
  +5b-UF5
 dodecahedral+4Th(ox)44-, Th(S2CNEt2)4
 bicapped trigonal prismatic+3PuBr3
 hexagonal bipyramidal+6UO2(h2-NO3)2(H2O)2
 ?+6UF82-
    
9tricapped trigonal prismatic+3UCl3
 capped square antiprismatic+4Th(trop)4(H2O)
    
10bicapped square antiprismatic+4KTh(ox)4.4H2O
    
11?fully capped trigonal prismatic?+3UF3
    
12irregular icosahedral+4Th(NO3)62-
 distorted cuboctahedral+4An(h3-BH4)4, (Np, Pu)
    
14?complex+4An(h3-BH4)4, (Th, Pa, U)

--Info & DownloadsBibliography  [textbook & online resources]

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