Lewis acids/bronsted acidity of LA complexes Flashcards
What is a lewis acid?
Electron deficient
What is a lewis base?
Electron rich
What are acids?
Co-ordinatively unsaturated
They need to be able to accept electrons
What do bases have?
Excess electrons in the form of a lone pair or an anion
Where are electrons transferred from and to in acids and bases?
From a filled orbital to a vacant orbital
Show the general equation for LB and LA reaction?
M+ (LA) + X- (LB) M-X
electrons transferred from X- to the metal
What is the mesomeric effect in determining the strength of lewis acids?
Orbital overlab
In the mesomeric effect, the heavier the halogen…
The more acidic
How do the ligands relate to the acidity?
Small ligands are able to give a better orbital overlap as they have a shorter B-X bond.
Weaker lewis acids
What is the trend in acidity from BF3 - BCl3 - BBr3 - BI3 for the mesomeric effect?
Increasing lewis acidity
What is the inductive effect?
The electronegative atoms surrounding the central atom withdraw the electrons, meaning the central atom is more electron deficient and this means that it is a stronger lewis acid
What is the trend in acidity from SiF4 - SiCl4 - SiBr4 - SiI4 for the inductive effect?
Decreasing lewis acidity
In the electronegative effect, the lighter the halogen…
the more acidic
What is an aqua complex?
Metal with H2O ligands
In an aqua complex, what happens to the likelihood of releasing a proton by having the metal present?
Increases
What does acidity depend on in aqua complexes?
oxidation state and ionic radius
What is acidity governed by in aqua complexes?
Electrostatic interactions
What is the acidity like of a small ion aqua complex with a high oxidation state?
Strong acid
Stable conjugate base
What is the acidity like of a large ion aqua complex with a low oxidation state?
Weaker acid
Less stable conjugate base
How are polymers of aqua acid formed?
Condensation reaction - removal of water
This is facilitated by a bronsted base
What condition does the polymerisation of aqua acids happen?
Basic conditions
What does the loss of H2O in the condensation of aqua acids result in?
Bridging oxygen
What would most metal hydroxides be classed as?
Basic
What does acidity depend on for hydroxo acids?
Ionic radius and charge
What can oxoion be stabilised by?
A strong enough acid
How does the acidity of a hydroxo acid compare to an aqua acid?
They are much less acidic
What happens to the hydroxo acids?
Complex is deprotonated to form the conjugate base which is then stabilised
How does charge of hydroxo acid complexes relate to acidity?
The higher the charge, the more ionic interactions to stabilise the conjugate base
What is the oxo group in a metal oxo acids?
M=O double bonds
Which block of oxoacids does Pauling’s rule apply to?
P-block
What does the oxyanion resonate with?
The oxogroup
What are the relative acidities of oxoacids, aqua acids and hydroacids?
Oxoacids>aqua acids>hydroacids
How are polyoxo anions formed?
Condensation reaction - removal of water
What is acidic polymerisation?
Start with a base and add protons
