8b: New oxidation states

Question 1

Oxidation state of lanthanides/actinides 

Answer 1

Lanthanides exist at the +3 oxidation state

Actinides: U+3 to +6 and Th +3 and +4

Question 2

Normal Lanthanide halides

Answer 2

Metallic dihalides can be prepared by comproportionation

Ln +2LnX3 <=> 3 LnX2 with LN in dihalides
-occurrence parallels the high values for the ionization energies.
iodides are the most numerous.
All LnX2 are easily oxidised and liberate H2 from H2O
Nd, Tm and Tb ether-stabilised diiodides have become available allowing them to be studied

Question 3

Divalent lanthanide halides

Answer 3

divalent lanthanides (Sm, Eu, Yb)I2 are obtained from thermal composition of LnX3

OR

PIcture of slide

Question 4

Two structural types of lanthanide dihalides

Answer 4

1) Metallic
LnX2 Ln= La, Ce, Pr and Gd
high conductivity and metallic lustre
good reducing agents
-overlap of 4f orbitals too inefficient to produce a conduction band
[Xe]4fn5d1 configuration more stable
producing a 5d conduction band occupied by a single electron per lanthanide atom
formed by elemets that dont readily accomodate the +2 OS
2) Insulating
Ln= Eu, Sm and Yb
[Xe]4fn+1 configuration more stable
formed from elements that readily accomodate the +2 OS, aka ones w high I3 ionisation energies

Question 5

LnO 

Answer 5

Nb, Sm, Eu and Yb prepared by reduction of Ln2O3 with the corresponding lanthanide at high temperatures (800-2000)
The oxides have an NaCl primitive cubic structure eg, ionic
EuO and YbO are insulating
NdO SmO are conducting and golden in colour

Question 6

Ln(II) organometallics

Answer 6

The entire Ln2+ series can be accessed
Simple ethers for Nb, Tm and Tb
Y, La, Ce, Ho, Er
reduction of tris(Cp’) with potassium, transferring a single electron to reduce the lanthanide to the +2 oxidation state
The product is a salt with the macrocyclic 18-crown-6 used to trap the K
Pr, Gd, Tb, Lu
reduction of tris(Cp’) with potassium (KC8)
trap K with a 2,2,2-cryptand 

if product must be isolated, under inert atmosphere at low temperatures

Question 7

what does Cp’ mean?

Answer 7

substituted

Question 8

Can Actinides have II states

Answer 8

yes U and Th with the KC8 and cryptand

(mius graphite in process) expand oxidation state to +2