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 UF₈^2-, Th(S₂CNEt₂)₄, Th(trop)₄(H₂O)
- Distortions from idealised stereochemistries
  e.g. PuF₆^2- 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: CO₃^2- > C₂O₄^2- > SO₄^2-
- geometry may be strongly influenced by covalent bonding effects
  e.g. MO₂²⁺ unit is always linear Þ 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 Æ even greater diversity of structure
Wide variety of oxidation states of ligands & number of oxidation states
Þ Extraordinary range of stereochemistry in actinide complexes and compounds

C.N.	Geometry	O.N.	*e.g.*
4	distorted	+4	U(NPh₂)₄

5	distorted tbp	+4	U₂(NEt₂)₈

6	octahedral	+3	An(H₂O)₆³⁺, An(acac)₃
		+4	UCl₆^2-
		+5	UF₆&endash, a-UF₅
		+6	AnF₆
		+7	Li₅[AnO₆] (An = Np, Pu)
	distorted octahedral	+6	Li₄UO₅ , UO₃

		+5/+6	U₅O₈
		+6	UO₂(S₂CNEt₂)₂(ONMe₃)

8	cubic	+4	(Et₄N)₄[U(NCS)₈], ThO₂, UO₂
		+5	AnF₈^3-
	square antiprismatic	+4	ThI₄, U(acac)₄, Cs₄[U(NCS)₈],
		+5	b-UF₅
	dodecahedral	+4	Th(ox)₄^4-, Th(S₂CNEt₂)₄
	bicapped trigonal prismatic	+3	PuBr₃
	hexagonal bipyramidal	+6	UO₂(h²-NO₃)₂(H₂O)₂
	?	+6	UF₈^2-

9	tricapped trigonal prismatic	+3	UCl₃
	capped square antiprismatic	+4	Th(trop)₄(H₂O)

10	bicapped square antiprismatic	+4	KTh(ox)₄.4H₂O

11?	fully capped trigonal prismatic?	+3	UF₃

12	irregular icosahedral	+4	Th(NO₃)₆^2-
	distorted cuboctahedral	+4	An(h³-BH₄)₄, (Np, Pu)

14?	complex	+4	An(h³-BH₄)₄, (Th, Pa, U)

If you have any comments please contact stephen.heyes@chem.ox.ac.uk