Lanthanide Complexes

Question 1

What are formula of lanthanide halides

Answer 1

1. LnX3
2. All LnX3 are known except for Pm which hasn’t been attempted and possibly EuI3

Question 2

What are properties of LnX3

Answer 2

1. Ionic
2. Crystalline
3. High melting point
4. Apart from trifluorides are highly deliquescent (tendency to dissolve?)

Question 3

What are the LnX3 structures indicative of

Answer 3

1. Lanthanide contraction

Question 4

What size are lanthanides

Answer 4

1. Very big

Question 5

What are the fluorides of larger lanthanides like

Answer 5

1. The fluorides of the larger lanthanides LnF3 (Ln = La–Pm) adopt the ‘tysonite’ (LaF3) structure
2. 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.

Question 6

What are the structures of smaller lanthanide fluorides

Answer 6

1. Beyond promethium, all of the LnF3 have the YF3 structure which features eight close contacts and one longer Ln-F distance.
2. This is a result of the decreasing size of Ln.

Question 7

What happens to atomic radius across a period

Answer 7

1. In general it decreases

Question 8

What happens to the coordination number of halides to lanthanides as you move acorss the table

Answer 8

1. Lower coordinate number due to lanthanide contraction

Question 9

Describe the chlorides of La to Gd

Answer 9

1. The halides from La to Gd adopt the nine coordinate UCl3 structure a tricapped trigonal prismatic arrangement
2. which is like the structure of LaF3 but with the two more distant F- removed.

Question 10

Describe TbCl3 structure

Answer 10

1. TbCl3 has the eight coordinate PuBr3 structure (like the UCl3 structure but with one of the capping Cl- removed.

Question 11

Describe the LnCl3 compounds following Tb

Answer 11

1. The LnCl3 compounds of the lanthanides following Tb all have a six-coordinate AlCl3 structure.

Question 12

What impact does the size of an anion have on the coordination number to a given Ln3+ ion

Answer 12

1. The size of the anion is also important in determining the coordination number to a given Ln3+ ion,
2. with decreasing coordination number seen for increasing ion radius.

Question 13

Describe structure of LaBr3, CeBr3 and PrBr3

Answer 13

1. LaBr3, CeBr3 and PrBr3 all have the (nine coordinate) UCl3 structure,

Question 14

Describe the structure of tribromides of Nd to Eu

Answer 14

1. the tribromides of Nd to Eu adopt the (eight coordinate) PuBr3 structure.

Question 15

Describe structure of LnBr3 structures after Eu

Answer 15

1. The remaining LnBr3 have the six coordinate FeCl3 structure.

Question 16

What is a common Ln oxide

Answer 16

1. Ln2O3
2. Sesquioxides

Question 17

How can common sesquioxide Ln2O3 be made

Answer 17

1. By heating lanthanide metals in air
2. Or heating oxy-compounds such as nitrates or carbonate

Question 18

Give equation to show formation of Ln2O3 from nitrate

Answer 18

1. 4Ln(NO3)3 –> 2Ln2O3 + 12 NO2 + 3O2

Question 19

What elements need an extra step in formation of Ln2O3 and what is it

Answer 19

1. Ce, Pr, And Tb
2. Form LnO2 (Ln4+) under heating of oxy-compounds
3. Can be reduced to Ln2O3 with H2

Question 20

What structures can Ln2O3 be divided into

Answer 20

1. 3 structural types
2. A-type
3. B-type
4. C-type

Question 21

Describe A-type structure of Ln2O3

Answer 21

1. Light Ln
2. Unusual LnO7 capped-octahedra

Question 22

Describe B-type structure of Ln2O3

Answer 22

1. Middle Ln
2. LnO7 units - but smaller arrangement of them as smaller lanthanides
3. 2 capped trigonal prisms
4. 1 capped octahedron

Question 23

Describe C-type structure of Ln2O3

Answer 23

1. Heavy Ln
2. LnO6 units but not octahedra- reflection of lanthanide contraction
3. Face and body - divacant cubic

Question 24

Which elements form LnO2

Answer 24

1. Ce, Pr, Tb when burnt
2. Ln4+

Question 25

Can you get tetravalent halides

Answer 25

1. These are confined to the fluorides of Ce(IV), Pr(IV) and Tb(IV), 2. however only CeF4 is thermally stable.

Question 26

Describe CeO2 colours

Answer 26

1. CeO2 (Ceria) is white when pure but is usually pale yellow due to some sub-stoichiometry.

Question 27

What are uses of CeO2

Answer 27

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.

Question 28

What does the occurrence of dihalides relate to

Answer 28

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

Question 29

What are the 2 classes of LnX2

Answer 29

1. Metallic compounds 2. Insulating salt-like dihalides

Question 30

Describe the metallic compounds subclass of LnX2

Answer 30

1. La, Ce, Pr, Gd 2. Metallic lustre and high conductivity 3. very good reducing agents

Question 31

What is actual structure of metallic compounds

Answer 31

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

Question 32

Describe Insulating salt-like dihalides LnX2

Answer 32

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.)

Question 33

How are the synthetically useful iodides of the ‘divalent’ lanthanides obtained

Answer 33

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.

Question 34

How are the metallic dihalides prepared

Answer 34

1. The metallic dihalides are typically prepared by comproportionation: 2. Ln + 2LnX3 --> 3LnX2

Question 35

Describe divalent oxides of Lanthanides

Answer 35

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+