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Lanthanides & Actinides
Comparisons & Contrasts
Yttrium - Why consider it with the Lanthanides?
  • Occurs with lanthanides in rare earth minerals, e.g. monazite
  • Y occurs effectively exclusively in +3 oxidation state
    combines with non-metals Æ YHal3 Y2O3 , Y3+(H-)2(e-), YH3, etc...
  • Y3+ has same radius as Ho3+ and is difficult to separate from it
  • Forms complexes of high coordination number with chelating O-donors, e.g. Y(acac)3(H2O)
  • Typical organometallics include: Y(C5H5)3 (polymeric in the solid state)
    dimeric Y(C5H5)2Cl, monomeric form is a thf adduct
Scandium too?

6 Reasons why Scandium could be considered with the Lanthanides

1. Sc occurs effectively exclusively in +3 oxidation state

combines with non-metals Æ ScHal3 Sc2O3, etc...
but coordination octahedral (small size)

2. Sc forms reduced halidese.g. Sc7Cl12 which is Sc3+(Sc6Cl12)3- with Sc6 clusters (but c.f. Nb)

3. Scandium Hydride ScH2 is highly conducting Sc3+(H-)2(e-)

4. Forms complexes of high coordination number with chelating O-donors

e.g. Na+[Sc(CF3COCHCOCF3)4-] with C.N. = 8
but forms octahedral complexes with monodentate ligandse.g. mer-ScCl3(thf)3

5. Nitrate & Sulphate are obtained as hydrated salts Sc(NO3)3•4H2O & Sc2(SO4)3•5H2O

6. Typical organometallics include: Sc(C5H5)3 (polymeric in the solid state)

dimeric Sc(C5H5)2Cl, monomeric form is a thf adduct

6 Reasons why Scandium could be considered as main group IIIA

1. Sc3+ (r = 74 pm) is appreciably smaller than any of the rare earths

Þ behaviour intermediate between the Lanthanides & Aluminium

2. Sc2O3 is more like Al2O3 than Ln2O3: amphoteric Æ Sc(OH)63- in excess OH-

3. ScF3 disssolves in excess F- Æ ScF63-(N.B. scarcity of halogeno complexes for Lanthanides)

4. Anhydrous ScCl3 is easily obtained by P2O5-dehydration of hydrated halide

but unlike AlCl3, ScCl3 is not a Friedel-Crafts catalyst

Scandium may with similarly few exceptions be viewed as a 1st Row Transition Metal

  • Six-coordinate complexes are typical
  • Aqua-ion is Sc(H2O)63+ and is susceptible to hydrolysis Æ O-H-bridged dimers...
.:: Some CONTRASTS between Lanthanides & Pre-Transition & Transition Metals ::.

Pre-Transition Metals
Transition Metals
Essentially Monovalent

- show Group (n+) oxidation state

Essentially Monovalent (+3)

+2/+4 for certain configurations

Show Variable Valence

(extensive redox chemistry)

control by environment ~ ligands, pH etc…

Periodic trends

- dominated by (effective nuclear) charge

at noble gas config.

(i.e. on group valence)

Lanthanide Contraction of Ln3+
Size changes of Mn+ less marked
Similar Properties for a given group

(differentiated by size)

Similar Properties

(differentiated by size)

Substantial Gradation in Properties
widespread on earth
common mineralogy
diverse mineralogy
No Ligand Field Effects
Insignificant Ligand Field Effects
Substantial Ligand Field Effects
Always 'hard' (O, Hal, N donors)

(preferably negatively charged)

Always 'hard' (O, Hal, N donors)

(preferably negatively charged)

Later (increasingly from Fe&endash;Cu)/heavier metals

may show a 'soft' side

'Ionic' Æ 'Covalent' Organometallics
'Ionic' Organometallics
'Covalent' Organometallics
No -Ligand Effects
Paucity of -Ligand Effects
-Acceptor Ligands Æ Extensive Chemistry
Poor Coordination Properties

(C.N. determined by size)

High Coordination Numbers

(C.N. determined by size)

Extensive Coordination

C.N. = 6 is typical maximum

(but many exceptions)

Flexibility in Geometry
Flexibility in Geometry
Fixed (by Ligand Field effects) Geometries
No Magnetism from the metal ions

- noble gas configurations of ions

Free Ion-like Magnetism

ground state magnetism

Orbital Magnetism 'Quenched' by Ligand Fields

excited J-states populated

'Ionic' compound formulations

Þ large HOMO-LUMO gaps

Þ UV CT spectra

Weak, Narrow Optical Spectra

forbidden, unfacilitated transitions

Stronger, Broader Optical Spectra

forbidden transitions vibronically-assisted

--Info & DownloadsBibliography  [textbook & online resources]

Source: Dr. S.J. Heyes; University of Oxford
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.::© - 2003 ::.