Lanthanide Complexes Flashcards
1
Q
What are formula of lanthanide halides
A
- LnX3
- All LnX3 are known except for Pm which hasn’t been attempted and possibly EuI3
2
Q
What are properties of LnX3
A
- Ionic
- Crystalline
- High melting point
- Apart from trifluorides are highly deliquescent (tendency to dissolve?)
3
Q
What are the LnX3 structures indicative of
A
- Lanthanide contraction
4
Q
What size are lanthanides
A
- Very big
5
Q
What are the fluorides of larger lanthanides like
A
- 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.
6
Q
What are the structures of smaller lanthanide fluorides
A
- 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.
7
Q
What happens to atomic radius across a period
A
- In general it decreases
8
Q
What happens to the coordination number of halides to lanthanides as you move acorss the table
A
- Lower coordinate number due to lanthanide contraction
9
Q
Describe the chlorides of La to Gd
A
- 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.
10
Q
Describe TbCl3 structure
A
- TbCl3 has the eight coordinate PuBr3 structure (like the UCl3 structure but with one of the capping Cl- removed.
11
Q
Describe the LnCl3 compounds following Tb
A
- The LnCl3 compounds of the lanthanides following Tb all have a six-coordinate AlCl3 structure.
12
Q
What impact does the size of an anion have on the coordination number to a given Ln3+ ion
A
- 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.
13
Q
Describe structure of LaBr3, CeBr3 and PrBr3
A
- LaBr3, CeBr3 and PrBr3 all have the (nine coordinate) UCl3 structure,
14
Q
Describe the structure of tribromides of Nd to Eu
A
- the tribromides of Nd to Eu adopt the (eight coordinate) PuBr3 structure.
15
Q
Describe structure of LnBr3 structures after Eu
A
- The remaining LnBr3 have the six coordinate FeCl3 structure.
16
Q
What is a common Ln oxide
A
- Ln2O3
- Sesquioxides
17
Q
How can common sesquioxide Ln2O3 be made
A
- By heating lanthanide metals in air
- Or heating oxy-compounds such as nitrates or carbonate
18
Q
Give equation to show formation of Ln2O3 from nitrate
A
- 4Ln(NO3)3 –> 2Ln2O3 + 12 NO2 + 3O2
19
Q
What elements need an extra step in formation of Ln2O3 and what is it
A
- Ce, Pr, And Tb
- Form LnO2 (Ln4+) under heating of oxy-compounds
- Can be reduced to Ln2O3 with H2
20
Q
What structures can Ln2O3 be divided into
A
- 3 structural types
- A-type
- B-type
- C-type
21
Q
Describe A-type structure of Ln2O3
A
- Light Ln
- Unusual LnO7 capped-octahedra
22
Q
Describe B-type structure of Ln2O3
A
- Middle Ln
- LnO7 units - but smaller arrangement of them as smaller lanthanides
- 2 capped trigonal prisms
- 1 capped octahedron
23
Q
Describe C-type structure of Ln2O3
A
- Heavy Ln
- LnO6 units but not octahedra- reflection of lanthanide contraction
- Face and body - divacant cubic
24
Q
Which elements form LnO2
A
- Ce, Pr, Tb when burnt
- Ln4+
25
Can you get tetravalent halides
1. These are confined to the fluorides of Ce(IV), Pr(IV) and Tb(IV),
2. however only CeF4 is thermally stable.
26
Describe CeO2 colours
1. CeO2 (Ceria) is white when pure but is usually pale yellow due to some sub-stoichiometry.
27
What are uses of CeO2
1. This is exploited in catalytic converters catalysing the oxidation of unburnt hydrocarbons and converting CO to CO2.
2. 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.
28
What does the occurrence of dihalides relate to
1. The Occurrence of dihalides parallels the high values for the third ionisation energy
2. Depends upon the oxidizing power of the halogen (iodides most numerous!)
3. They are subdivided into 2 classes
29
What are the 2 classes of LnX2
1. Metallic compounds
2. Insulating salt-like dihalides
30
Describe the metallic compounds subclass of LnX2
1. La, Ce, Pr, Gd
2. Metallic lustre and high conductivity
3. very good reducing agents
31
What is actual structure of metallic compounds
1. Actually Ln3+ system
2. Ln3+(X-)2(e-) with the odd electron in a conduction band - due to how reducing system is
3. Overlap of 4f orbitals too inefficient to produce a conduction band - so it isn't produced from them
32
Describe Insulating salt-like dihalides LnX2
1. Eu, Sm Yb (ones that have Ln2+ systems)
2. [Xe]4fn+1 config is more stable consistent with Ln2+(X-)2 structures
3. Not as reducing as metallic compounds
4. All LnX2 are easily oxidized and liberate H2 from H2O (Except for EuX2 which is stable in aqueous solution.)
33
How are the synthetically useful iodides of the ‘divalent’ lanthanides obtained
1. (Sm,Eu,Yb)I2 are obtained from thermal decomposition of LnX3
2. or by reaction of NH4I and the Ln metal in liquid NH3.
34
How are the metallic dihalides prepared
1. The metallic dihalides are typically prepared by comproportionation:
2. Ln + 2LnX3 --> 3LnX2
35
Describe divalent oxides of Lanthanides
1. LnO of Nd, Sm, Eu and Yb may be prepared by reduction of Ln2O3 with the elemental lanthanide at high temperature (800-2000 oC).
2. All four oxides have the NaCl structure.
3. However, while EuO and YbO are insulating (i.e. genuine Ln2+ O2-),
4. the lustrous golden yellow NdO and SmO are electrically conducting (have free e- in conduction band as actually Ln3+
