Complex Ions

Question 1

Ligand

Answer 1

Molecule or ion which donates a LONE PAIR of electrons to a central metal ion to form a COORDINATE bond

Question 2

Complex ion

Answer 2

A metal ion bonded to one or more ligands by coordinate bonds

Question 3

Coordination Number

Answer 3

The TOTAL NUMBER of coordinate bonds formed between the central metal ion & its ligands

Question 4

Monodentate Ligands

Examples

Answer 4

A ligand which donates one lone pair of electrons to a central metal ion to form a coordinate bond

Water,OH2 = neutral

Ammonia, NH3 = neutral

Thiocyanate, SCN- = -1

Cyanide, CN- = -1

Chloride, Cl- = -1

Hydroxide, OH- = -1

Question 5

Naming Complex Ions

Answer 5

State number of coordinate ligands for each type of ligand:
2 = di
4 = tetra
6= hexa

Identify the names of the ligands:
Water = aqua
Ammonia = ammine
Cyanide = cyano
Chloride = chloro
Hydroxide = hydroxo

Name the transition metal:
- Positively charged ~ English name
- Negatively charged ~ Latin name
- Iron (ferrate) & Copper (cuprate)

Indicate the oxidation number of the transition metal using roman numerals

Question 6

Splitting of d-orbitals

Answer 6

• in an isolated transition metal ion the d-orbitals are DEGENERATE (identical in energy)
• in a complex ion, ligands form coordinate bonds with the metal ion using their lone pair of electrons
• if a d-orbital lies on the SAME AXIS as the incoming lone pair it will cause some REPULSION & raise the energy of the orbital
• The other orbitals lying between the axes will be LOWERED in energy

Question 7

What occurs due to splitting of d-orbitals?

Answer 7

• There are now two energy levels within the d sub-shell
• the energy gap is small & so it is possible for an electron to move from the lower to the higher energy level
• The energy difference is EQUIVALENT to a particular frequency of light in the visible range of the electromagnetic spectrum

Question 8

The extent of splitting, energy difference & colour depends on …

Answer 8

• The central transition metal ion
• Its oxidation state
• The ligands

Question 9

Coloured compounds

Answer 9

• Colour arises when electrons move between energy levels
• OBSERVED colour of a solution depends on the wavelengths ABSORBED & REFLECTED

Examples:

Copper(II) sulfate:
- Reflects & appears BLUE
- absorbs RED & YELLOW wavelengths

Nickel(II) sulfate:
- Reflects & appears GREEN
- absorbs VIOLET, BLUE & RED wavelengths

Question 10

Cis-trans isomerism:

Octahedral complexes

Answer 10

Six monodentate ligands ~ four of one type & two of a different type

Example ~ [Cr9NH3)4Cl2]+

CIS:
- violet
- two Cl- ligands are at adjacent corners of the octahedron
- 90 degrees to one another

TRANS:
- green
- two Cl- ligands are at opposite corners of the octahedron
- 180 degrees to one another

Question 11

Cis-trans isomerism:

Four coordinate square planar complexes

Answer 11

Two monodentate ligands & two different monodentate ligands.

[Pt(NH3)2Cl2]

CIS:
- two Cl- ligands are at adjacent corners of the square
- 90 degrees to one another

TRANS:
- two Cl- ligands are at opposite corners of the square
- 180 degrees to one another

Question 12

Bidentate Ligands

• definition
• what do they produce
• type of isomerism

Answer 12

Form TWO coordinate bonds by donating two lone pairs of electrons to a central metal ion

• produce OCTAHEDRAL complexes

CIS-TRANS isomerism in octahedral complexes arises when the following are present:

• two identical bidentate ligands
• two identical monodentate ligands

Question 13

Hexadentate Ligand

Answer 13

Forms SIX coordinate bonds through the donation of six lone pairs of electrons to a central metal ion

Ethylenediaminetetraacetic acid, EDTA:

• dissociates to form EDTA4-
• the ligand acts as a chelating agent ~ forms complexes with metal ions & reduces their concentration in solution

Question 14

Ethylenediaminetetraacetic acid, EDTA:

Answer 14

• A hexadentate ligand
• dissociates to form EDTA4-

The ligand acts as a CHELATING AGENT~ forms complexes with metal ions & reduces their concentration in solution

Uses of EDTA4-:

• Detergents to reduce hardness of water by binding Ca2+ & Mg2+ ions
• Prevents blood from clotting

Question 15

Optical Isomerism in Complex Ions

Answer 15

Optical isomerism arises in OCTAHEDRAL complexes when the following are present:

• 3 identical bidentate ligands
• 2 identical bidentate ligands & 2 identical monodentate ligands (the monodentate ligands must be in the cis arrangement)
• a single hexadentate ligand such as EDTA4-

Question 16

When answering exam questions

Answer 16

• a curved line can sometimes be used to represent a BIDENTATE ligand
• the coordinating atoms should be included in the simplified drawing