Group 4 Flashcards
What is the cheapest reducing agent?
Carbon - coal, oil or charcoal
What does a more electropositive metal result in for reduction?
More electropositive metal = more endothermic reaction
Why can Ti not be reduced using carbon?
Because Ti is very a electropositive metal, whilst also forming Titanium carbide - which is hard and inert
BAD
What process is used to obtain Ti?
The Kroll process
What’re the steps of the Kroll process?
TiO2 is converted to TiCl4 using 2C and 2Cl2
TiCl4 is distilled under vacuum
TiCl4 is then reduced using even more electro+ve metal (Na) to form Ti and 4NaCl. (Mg can also be used.)
- 800 degrees
- batch reactor
- Ar atmosphere
Metal halide is washed out - recycled - giving Ti ‘sponge’
- has to be melted into ingot
What’re the uses of Ti?
Ti alloys used in aerospace & hi-tech sports equipment - 60% density of steel
Very corrosion resistant
Very high heat resistance - alloys don’t ‘creep’
Twice as ductile with similar tensile strength as steel
What is yielded when TiCl4 is added to water?
TiO2 and 4HCl
Hydrolysis of TiCl4 is a violent reaction
What type of ligands does Ti(IV) prefer?
Hard ligands - as is a hard metal ion
Are Ti(IV) complexes stable under reduction?
Yes
What does dissolving TiF4 in aqueous HF yield?
Mainly [TiF6]2-
d0 - complex so is colourless
How do Ti(IV) and V(IV) oxo-complexes differ?
V complexes are monomers - 1005cm-1
Ti complexes are dimers - 880cm-1
What is the reaction of Ti(IV) halide complexes with neutral monodentate ligands in non-polar solvents?
1 eq gives [TiCl4L]2
2 eq gives [TiCl4L2] - cis and trans variations
Why does Ti(IV) have no stereochemical preferences?
Because it is a d0 metal ion, and so cannot be controlled through CFT
What is ‘das’?
It is a very good chelate ligand
Benzene ring provides a rigid backbone
TiCl4 + 1das gives what in toluene?
TiCl4 + 2das gives what in toluene?
Whats the difference between a-TiCl3 and ß-TiCl3?
The a form consists of sheets of TiCl6 octahedral.
The ß form consists of single chains of TiCl6, sharing edges
The ß form converts to alpha form at ≥ 300 degrees
What’s the use of ß-TiCl3?
The ß form is a catalyst for alkene polymerisation
What type of polymer is given by polypropylene?
Yields ‘isotactic’ polypropylene - all Me groups oriented same way.
Why must Ti(III) complexes be made in strict absence of oxygen?
So that Ti(III) is not oxidised by oxygen in air.
What does dissolving Ti in dilute HCl give?
[Ti(H2O)6]3+
What does dissolving Ti in conc HCl give?
Both [TiCl(H2O)5]2+ and [TiCl2(H2O)4]+ are formed
What does dissolving Ti in very conc HCl give?
Ti in very concentrated HCl gives Ti(IV) complexes
What are Ti(II) complexes rare?
Because Ti(II) is very strongly reducing
What’re the 2 reasons Ti(II) chemistry has interest?
Organic chemistry
- Ti(II) is active in the McMurray coupling reaction
Dinitrogen chemistry
- Ti(II) reduces N-N triple bond since Ti=NR is isoelectronic with Ti=O.
How are Zr and Hf separated, as they appear in nature together?
By solvent extraction or chromatography
Why is separating Zr and Hf difficult?
Due to their very similar chemical properties
How are Zr and Hf elements obtained?
Elements are obtained by the Kroll process - same as Ti
What’re the uses of Zr?
Used as fuel cladding for nuclear fuels - has low neutron capture cross-section
Widely used as alkene polymerisation catalysts
What use has Hf recently found?
As a high dielectric constant insulator layer for the gates of tiny transistors
Is Ti(IV) chemistry similar to Zr(IV) and Hf(IV) chemistry?
Yes
How can stereochemistry be dictated for group 4 M(IV) complexes?
Through sterics, since there is no CFSE in d0 metal ions
What is the difference between TiCl4 / TiBr4 complexes with the Zr/Hf equivalents?
TiCl4 / TiBr4 complexes are tetrahedral and monomeric
ZrCl4 / ZrBr4 (and Hf) complexes are polymeric and octahedral
What tendencies do Zr and Hf exhibit with M(II) and M(III) complexes?
Zr and Hf do not form M(II) complexes AT ALL
They have lower tendency to form M(III)
ALL M(III) complexes are polymeric
How can Zr(III) complexes be diamagnetic?
As they are polymeric, the 2 electrons are shared between the Zr-Zr bond, as though covalent, in the same bonding orbital
Hence is diamagnetic (not magnetic)
How are M-M bonds made more stable?
They are made more stable with strong field ligands
