Bài soạn Chapter 24 Transition Metals and Coordination Compounds

and very different to the properties of the main group metalshigh melting points, high densities, moderate to very hard, and very good electrical conductors • in general, the transitio

Gemstones

• the colors of rubies and emeralds are both due

to the presence of Cr3+ ions – the difference lies

in the crystal hosting the ion

Cr 3+

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

and very different to the properties of the main group metals

high melting points, high densities, moderate to very hard, and very good electrical conductors

• in general, the transition metals have two valence

electrons – we are filling the d orbitals in the shell

below the valence

Group 1B and some others have 1 valence electron due to

“promotion” of an electron into the d sublevel to fill it

form ions by losing the ns electrons first, then the (n – 1)d

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Atomic Size

• the atomic radii of all

the transition metals

are very similar

small increase in size

down a column

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

main group elements

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Electronegativity

• the electronegativity of

the transition metals

slowly increases across

Oxidation States

• often exhibit multiple oxidation states

• vary by 1

• highest oxidation state is group number for 3B to 7B

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Coordination Compounds

• when a complex ion combines with counterions to

make a neutral compound it is called a coordination compound

• the primary valence is the oxidation number of the

Coordination Compound

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Complex Ion Formation

• complex ion formation is a type of Lewis base reaction

acid-• a bond that forms when the pair of electrons is donated by one atom is called a coordinate

covalent bond

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Ligands with Extra Teeth

• some ligands can form more than one

coordinate covalent bond with the metal atom

lone pairs on different atoms that are separate

enough so that both can reach the metal

• chelate is a complex ion containing a

multidentate ligand

ligand is called the chelating agent

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

12 Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Complex Ions with Polydentate Ligands

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Geometries in Complex Ions

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Common Ligands

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

• Fe is +3

• 3 moles of AgCl would form

Fe N

Common Metals found in

Anionic Complex Ions

Chemistry, Julia Burdge, 2 nd e., McGraw Hill.

Naming Coordination Compounds

1) List ligand names in alphabetical order

 name each ligand alphabetically, adding a prefix in

front of each ligand to indicate the number found in the complex ion

2) follow with the name of the metal cation, indicate the

oxidation number with Roman numerals

3) If the complex is an anion, the suffix “ate” is added to

the metal name

Ligands Names

• anions ending with ate or ide change to “o” as in nitrate to nitrato or cyanide to cyano

• anions with ite change to “e”

• molecules uses common name except for:

water changes to aqua

ammonia to ammine

CO to carbonyl

• multiple simple ligands are prefixed with di, tri,

tetra, penta, or hexa

• Complex ligands are prefixed with bis, tris, tetrakis, pentakis, or hexakis

Tro, Chemistry: A Molecular Approach 24

Isomers

• Structural isomers are molecules that have the same number and type of atoms, but they are

attached in a different order

• Stereoisomers are molecules that have the same

number and type of atoms, and that are attached

in the same order, but the atoms or groups of

atoms point in a different spatial direction

25

Tro, Chemistry: A Molecular Approach 26

Linkage Isomers

Tro, Chemistry: A Molecular Approach 27

Geometric Isomers

• geometric isomers are stereoisomers that differ

in the spatial orientation of ligands

• cis-trans isomerism in octahedral complexes MA4B2

• fac-mer isomerism in octahedral complexes MA3B3

• cis-trans isomerism in square-planar complexes MA2B2

Tro, Chemistry: A Molecular Approach 28

Ex 24.5 – Draw the structures and label the type

for all isomers of [Co(en)2Cl2]+

the ethylenediamine ligand (en = H2NCH2CH2NH2) is bidentate

each Cl ligand is monodentate

octahedral

MA4B2

Tro, Chemistry: A Molecular Approach 31

Bonding in Coordination Compounds

Valence Bond Theory

• bonding takes place when the filled atomic

orbital on the ligand overlaps an empty atomic orbital on the metal ion

• explain geometries well, but doesn’t explain

color or magnetic properties

Tro, Chemistry: A Molecular Approach 32

Tro, Chemistry: A Molecular Approach 33

Bonding in Coordination Compounds

Crystal Field Theory

• bonds form due to the attraction of the electrons on the ligand for the charge on the metal cation

• electrons on the ligands repel electrons in the

unhybridized d orbitals of the metal ion

• the result is the energies of orbitals the d sublevel are

split

• the difference in energy depends on the complex and kinds of ligands

crystal field splitting energy

strong field splitting and weak field splitting

Tro, Chemistry: A Molecular Approach 34

Splitting of d Orbital Energies due to

Ligands in a Octahedral Complex

Tro, Chemistry: A Molecular Approach 35

Strong and Weak Field Splitting

36

How we see color

If we see black, the material absorbs all

Tro, Chemistry: A Molecular Approach 38

Complex Ion Color

• Absorbs all colors-but- the one you see or

• Reflects most colors but absorbs the

the complimentary

Tro, Chemistry: A Molecular Approach 39

Complex Ion Color and Crystal Field Strength

• the colors of complex ions are due to electronic

transitions between the split d sublevel orbitals

• the wavelength of maximum absorbance can be used to determine the size of the energy gap

between the split d sublevel orbitals

Ephoton = h = hc/ = 

Tro, Chemistry: A Molecular Approach 40

Ligand and Crystal Field Strength

• the strength of the crystal field depends in large part on the ligands

strong field ligands include: CN─ > NO2─ > en > NH3

weak field ligands include:

H2O > OH─ > F─ > Cl─ > Br─ > I─

• crystal field strength increases as the charge on the metal cation increases

Tro, Chemistry: A Molecular Approach 41

Crystal Field Strength

orbitals depends on the strength of the crystal field

leading to unpaired electrons and a paramagnetic complex

– leading to paired electrons and a diamagnetic complex

Tro, Chemistry: A Molecular Approach 42

Low Spin & High Spin Complexes

paramagnetic high-spin complex

diamagnetic low-spin complex

only electron configurations d4, d5, d6, or d7 can have low or high spin

Tro, Chemistry: A Molecular Approach 43

Tetrahedral Geometry and Crystal Field Splitting

• because the ligand approach interacts more

strongly with the planar orbitals in the

tetrahedral geometry, their energies are raised

• most high-spin complexes

Tro, Chemistry: A Molecular Approach 44

Square Planar Geometry and

Crystal Field Splitting

• d8 metals

• the most complex splitting pattern

• most are low-spin complexes

Tro, Chemistry: A Molecular Approach 45

Applications of Coordination Compounds

silver and gold as cyanide complexes

EDTA for Pb poisoning

qualitative analysis for metal ions

Tro, Chemistry: A Molecular Approach 46

Applications of Coordination Compounds

• commercial coloring agents

prussian blue = mixture of hexacyanoFe(II) and Fe(III)

inks, blueprinting, cosmetics, paints

Tro, Chemistry: A Molecular Approach 47

Applications of Coordination Compounds

• carbonic anhydrase

catalyzes the reaction between water and CO2

contains tetrahedrally complexed Zn2+

Tro, Chemistry: A Molecular Approach 48

Applications of Coordination Compounds

• Drugs and Therapeutic Agents

cisplatin

anticancer drug