Higham group 4 and 5 Flashcards
What is the lanthanide contraction
as we go from a 3d metal, to a 4d metal there is an increase in metallic atomic radii. But when we go from 4d elements to 5d elements the metallic atomic radii radii are almost the same
Why is the metallic atomic radii for 4d and 5d elements almost the same
the 5 d orbitals follow the lanthanides but they are into screened from the nucleus effectively by the f electrons, as f electrons are very poor at electron screening. This means we get very similar radii sizes for the 4d and 5d elements even though atomic number is much higher for 5d
Explain what the the lanthanide contraction means in terms of the chemistry down the group
means that the first element of the group has very different chemistry to the rest of the elements in the group
Describe group 3
group 3 has predominantly ionic character
Describe ScCl3
Sc +3 oxidation state, white ionic solid - high MP. Can buy it anhydrous or the hydrate. In ScCl3 the electropositive metal centre attracts electron pair donors
Describe YX3
Y found in +3 oxidation state, white crystalline solid.
YCl3 forms hydrates and reacts with KCl
What do the larger sizes of zirconium and hafnium give rise to
- higher coordination numbers
- higher oxidation state is more favourable
- metal-metal bonding ``
Describe titanium oxides
From a stoichometric point of view, titanium feels most energetically stable when it has 2 oxygens associated with it. And it achieves an oxidation state of +4
What are the 3 different forms of TiO2
rutile, anatase and brookite
Describe the rutile structure of TiO2
each oxygen binds to 3 titanium’s. Each titanium therefore gets 1/3 of each oxygen, there are 6 O per Ti so 6 x 1/3 =2 get TiO2
Describe titanium chlorides
TiCl 4 so Ti still in +4 oxidation state, tetrahedrally molecule. Covalent liquid
TiCl3 is also accessible but less common
[TiCl2] reacts violently with water liberating H2
Describe the bonding in TiCl4
Ti-Cl bond is shorter and therefore than expected from a purely sigma component.
Why is the Ti-Cl bond in TiCl4 shorter than expected
we have a highly electropositive metal centre we have sigma bonding and pi bonding. The lone pair on the chloride ligand is donated to the Ti metal empty d orbitals. Making a shorted and stronger bond
Describe the properties of TiCl4
lewis acid - if there is a donor around there will be an attraction to electropositive metal centre
Hydrolyses giving off HCl - as chloride is a good leaving group. The lone pairs on the oxygen of water will attack the Ti and will kick off the chlorine.
Describe acaH
3 electron type donor
Both X and L type ligand
Why is [TiCl3L3] used as reducing agents
it is a d1 system so it can be used as a reducing agent by donating that electron and itself gets oxidised
Describe the aqueous chemistry of titanium
we do not get [Ti(H2O)n] 4+
We do get [Ti(H2O)6]3+ and [Ti(H2O)6]2+
Describe [Ti(H2O)6]3+
violet compound d1-Ti3+
Can be prepared by reducing Ti4+
Describe [Ti(H2O)6]2+
d2 - Ti2+
Very reactive because Ti2+ reduces H2O
Describe Ti organometallic chemistry
dominated by [Cp2TiX2]
How is Cp2TiCl2
Start with TiCl4 and a source of Cp-
2NaCp + TiCl4 -> Cp2TiCl2 + 2NaCl
Describe the oxides for zirconium and hafnium and contrast this with Ti
Hafnium chemistry is less extensively studied
ZrO2 -withstands high temperatures although it has the same oxidation state, the structure is different
contains 7 coordinate Zr not the rutile structure in TiO2
Describes the chlorides for zirconium and hafnium and contrast this with titanium
ZrCl4
Similarity tetrachlorides are the most stable for group 4. But Zr has a larger radius than Ti so Zr has a coordination of 6 as opposed to 4 for Ti
Describe metal metal bonding
we need to think about which orbitals are used to make metal ligand bonds, then we will know which orbitals are used we will have for metal metal bonding
Which orbitals are used in M-L bonds
S, P, dYZ and dx^2-dy^2
Which orbitals are available for M-M bonding
dxy, dxz and dz^2
Describe the metal-metal bonding in [Zr2Cl6(Pr3)4]
[Zr2Cl6(PR3)4] - Zr(III) d1
2e- for Zr-Zr bonding ie single bond
Describe the oxidation states for vanadium
maximum oxidation state is 5, for vanadium we don’t always see it in it +5 oxidation state
Describe the +5 oxidation state for vanadium
The +5 oxidation state for vanadium is a very good oxidising agent. As it can be reduced into a lower oxidation state
Describe the halides for vanadium
VF5 is the only stable VX5. VCl5 decomposes to VCl4 and 1/2Cl2
VCl4 can be prepared but readily decomposes to VCl3 + 1/2Cl2
VCl3 can react with 3 L to give [VCl3L3]
describe vanadium oxohalides
VOCl3 - yellow liquid V(V) no d electrons: tetrahedral gives maximum ligand separation
Lewis acid: forms adducts with l donors to give VOCl3L and VOCl3L2
Electropositive centre - hydrolyses readily
How is VOCl3 prepared
V2O5 + 3SOCl2 -> 2VOCl3 + 3SO2
