Lanthanide Complexes Flashcards
What are formula of lanthanide halides
- LnX3
- All LnX3 are known except for Pm which hasn’t been attempted and possibly EuI3
What are properties of LnX3
- Ionic
- Crystalline
- High melting point
- Apart from trifluorides are highly deliquescent (tendency to dissolve?)
What are the LnX3 structures indicative of
- Lanthanide contraction
What size are lanthanides
- Very big
What are the fluorides of larger lanthanides like
- The fluorides of the larger lanthanides LnF3 (Ln = La–Pm) adopt the ‘tysonite’ (LaF3) structure
- in which the Ln3+ is coordinated by nine F- (massive ions) in a tricapped trigonal prismatic arrangement, with a further two F- at a slightly longer distance.
What are the structures of smaller lanthanide fluorides
- Beyond promethium, all of the LnF3 have the YF3 structure which features eight close contacts and one longer Ln-F distance.
- This is a result of the decreasing size of Ln.
What happens to atomic radius across a period
- In general it decreases
What happens to the coordination number of halides to lanthanides as you move acorss the table
- Lower coordinate number due to lanthanide contraction
Describe the chlorides of La to Gd
- The halides from La to Gd adopt the nine coordinate UCl3 structure a tricapped trigonal prismatic arrangement
- which is like the structure of LaF3 but with the two more distant F- removed.
Describe TbCl3 structure
- TbCl3 has the eight coordinate PuBr3 structure (like the UCl3 structure but with one of the capping Cl- removed.
Describe the LnCl3 compounds following Tb
- The LnCl3 compounds of the lanthanides following Tb all have a six-coordinate AlCl3 structure.
What impact does the size of an anion have on the coordination number to a given Ln3+ ion
- The size of the anion is also important in determining the coordination number to a given Ln3+ ion,
- with decreasing coordination number seen for increasing ion radius.
Describe structure of LaBr3, CeBr3 and PrBr3
- LaBr3, CeBr3 and PrBr3 all have the (nine coordinate) UCl3 structure,
Describe the structure of tribromides of Nd to Eu
- the tribromides of Nd to Eu adopt the (eight coordinate) PuBr3 structure.
Describe structure of LnBr3 structures after Eu
- The remaining LnBr3 have the six coordinate FeCl3 structure.
What is a common Ln oxide
- Ln2O3
- Sesquioxides
How can common sesquioxide Ln2O3 be made
- By heating lanthanide metals in air
- Or heating oxy-compounds such as nitrates or carbonate
Give equation to show formation of Ln2O3 from nitrate
- 4Ln(NO3)3 –> 2Ln2O3 + 12 NO2 + 3O2
What elements need an extra step in formation of Ln2O3 and what is it
- Ce, Pr, And Tb
- Form LnO2 (Ln4+) under heating of oxy-compounds
- Can be reduced to Ln2O3 with H2
What structures can Ln2O3 be divided into
- 3 structural types
- A-type
- B-type
- C-type
Describe A-type structure of Ln2O3
- Light Ln
- Unusual LnO7 capped-octahedra
Describe B-type structure of Ln2O3
- Middle Ln
- LnO7 units - but smaller arrangement of them as smaller lanthanides
- 2 capped trigonal prisms
- 1 capped octahedron
Describe C-type structure of Ln2O3
- Heavy Ln
- LnO6 units but not octahedra- reflection of lanthanide contraction
- Face and body - divacant cubic
Which elements form LnO2
- Ce, Pr, Tb when burnt
- Ln4+
Can you get tetravalent halides
- These are confined to the fluorides of Ce(IV), Pr(IV) and Tb(IV),
- however only CeF4 is thermally stable.
Describe CeO2 colours
- CeO2 (Ceria) is white when pure but is usually pale yellow due to some sub-stoichiometry.
What are uses of CeO2
- This is exploited in catalytic converters catalysing the oxidation of unburnt hydrocarbons and converting CO to CO2.
- A further application is as a thin film on the walls of ‘self-cleaning’ ovens in which it can prevent the build up of tarry deposits.
What does the occurrence of dihalides relate to
- The Occurrence of dihalides parallels the high values for the third ionisation energy
- Depends upon the oxidizing power of the halogen (iodides most numerous!)
- They are subdivided into 2 classes
What are the 2 classes of LnX2
- Metallic compounds
- Insulating salt-like dihalides
Describe the metallic compounds subclass of LnX2
- La, Ce, Pr, Gd
- Metallic lustre and high conductivity
- very good reducing agents
What is actual structure of metallic compounds
- Actually Ln3+ system
- Ln3+(X-)2(e-) with the odd electron in a conduction band - due to how reducing system is
- Overlap of 4f orbitals too inefficient to produce a conduction band - so it isn’t produced from them
Describe Insulating salt-like dihalides LnX2
- Eu, Sm Yb (ones that have Ln2+ systems)
- [Xe]4fn+1 config is more stable consistent with Ln2+(X-)2 structures
- Not as reducing as metallic compounds
- All LnX2 are easily oxidized and liberate H2 from H2O (Except for EuX2 which is stable in aqueous solution.)
How are the synthetically useful iodides of the ‘divalent’ lanthanides obtained
- (Sm,Eu,Yb)I2 are obtained from thermal decomposition of LnX3
- or by reaction of NH4I and the Ln metal in liquid NH3.
How are the metallic dihalides prepared
- The metallic dihalides are typically prepared by comproportionation:
- Ln + 2LnX3 –> 3LnX2
Describe divalent oxides of Lanthanides
- LnO of Nd, Sm, Eu and Yb may be prepared by reduction of Ln2O3 with the elemental lanthanide at high temperature (800-2000 oC).
- All four oxides have the NaCl structure.
- However, while EuO and YbO are insulating (i.e. genuine Ln2+ O2-),
- the lustrous golden yellow NdO and SmO are electrically conducting (have free e- in conduction band as actually Ln3+
