Metals - complexes and their structures

Question 1

Give the equation for the Gibbs energy

Answer 1

Question 2

Define the enthalpy of hydration

Answer 2

This is a measure of how much energy is released as you surround a gas phase ion with water molecules. It is an exothermic process.

Question 3

Describe two factors affecting hydration enthalpy

Answer 3

1. The bigger the charge on the metal, the larger the hydration enthalpy will be.
2. The smaller the ion for a given charge, the bigger the enthalpy will be, as the water can get closer

note: the key factor is the charge to radius ratio, ie z/r

Question 4

Describe how water molecules arrange themselves around metal ions in solution

Answer 4

Water molecules slot around the centre of the metal ion in order to minimise the attraction between them and the centre and their mutual repulsion as they come closer.

Question 5

Define and describe a ligand

Answer 5

A ligand is an ion or molecule that binds to a central metal ion to form a coordination complex.

They ‘push’ some electron density onto the centre.

Question 6

Define a complex ion

Answer 6

A complex ion has a central metal ion and ligands surrounding it. Note that the ligands serve to stabilise the metal ion

Question 7

Describe an X - type ligand

Answer 7

Cl and other halogens are classified as X type ligands that bring a single electron to the metal.

If you pull O off neutral, it can form two bonds. This is classified as an X₂ type ligand

Question 8

Describe an L - type ligand

Answer 8

These are molecules which come off neutral without unpaired electrons, eg ammonia which has a lone pair. As ammonia can donate the 2 electrons in the lone pair, this is an L-type ligand. They are denoted as M <– L

Question 9

Describe a Z - type ligand

Answer 9

Z class ligands are lewis acids which bind by grabbing a pair of electrons from the metal

These ligands are written as M –> Z

Question 10

Define a lewis acid

Answer 10

A lewis acid is one which can accept a pair of electrons

Question 11

Describe the oxidation state of a metal complex

Answer 11

The oxidation state is the same as the number of X ligands

Question 12

Describe the number of d electrons in a transition metal

Answer 12

no of d electrons = group number - oxidation state

This is important because the number of d electrons determines the structure, geometry, magnetic behaviour and reactivity.

Question 13

Define the ligand denoted by ‘en’

Answer 13

en = 1,2-diaminoethane

Question 14

Describe three ways in which ligands bind

Answer 14

1. Ligands can bind in a terminal fashion, ie end on. eg M - Cl
2. Ligands can bind in what’s called a bridging mode. Ligands can sit between two or more metal centres and hold them together. Note that this bridging behaviour leads to arrays called clusters, and μⁿ denotes this, n = the number of metal centres are being linked.

Question 15

Describe how isomerism appears in complexes

Answer 15

• Linkage isomers
• Ionisation isomers
• Geometrical isomers
• Structural isomers

Question 16

Describe linkage isomers in metal complexes

Answer 16

Linkage isomers differ in connectivity

Question 17

Describe ionisation isomers in metal complexes

Answer 17

These isomers differ in which group/groups are in the first coordination sphere, ie which are directly attached to the metal

Question 18

Describe geometrical isomers in metal complexes

Answer 18

A set of ligands can have multiple arrangements around a metal centre

Question 19

Describe the LFSE, the ligand field stabilisation energy