Chapter 21. Transition Metals and

Coordination Chemistry

The Transition Metals: A Survey

Main Group Elements Main Group Elements

changing

properties

similar

properties

similar

properties

Transition Metals

d-block transtion elecments

f-block transtion elecments

Key reason: Last electrons added are inner electrons (d’s, f’s). These electrons d and f electrons

cannot participate as easily in bonding as can the valence s and p electrons.

But despite their many similarities, the transition metals do vary considerably in many ways.

Ex) mp of W = 3422 oC , mp of Hg = -38.83 oC

General Properties

The Transition Metals: A SurveyGeneral Properties (Transition Metal Ions)

• More than one oxidation state is often found.

O+7

ooO+6

o△ooO+5

oooOooO+4

ooOOoOooO+3

OOOOOOoOo+2

Ooooooo+1

ooooooo≤0

ZnCuNiCoFeMnCrVTiSc

O : most common

Ex) Ionic compounds : FeCl2, FeCl3

+2 +3

• Forming complex ions, species where the transition metal ion is surrounded by a certain number of ligands (Lewis

bases).

• Several coordination numbers, number of ligands attached to a metal ion, and geometries exist.

Complex ions: Co(H2O)62+

L1

L2

L4

L3

Co(NH3)63+

+2 +3

Cu

H2O

H2O OH2

OH2

OH2

OH2

+2

Cu

NH3

NH3

NH3H3N

+2

• Many compounds containing transition metal ions are paramagnetic (they contain unpaired electrons)

EPR Cu2+ Mn2+

The Transition Metals: A SurveyGeneral Properties (Transition Metal Ions)

• Most compounds containing transition metal ions are colored because the ions can absorb visible light of

specific wavelength is often found.

Wulfenite (PbMoO4) Rhodochrosite (MnCO3)

Ruby

Pure (Al2O3 : colorless)

Impurity (Cr3+, < 1%)

absorption : violet and green

emission : red

Co(H2O)62+

Mn(H2O)62+

Cr(H2O)63+

Fe(H2O)63+

Ni(H2O)62+

The Transition Metals: A SurveyElectron Configuration

[Ar] = 1s22s22p63s23p6

Mn2+ => [Ar]3d5 Cu2+ => [Ar]3d9Ti3+ => [Ar]3d1 Fe3+ => [Ar]3d5 Zn2+ => [Ar]3d10

4s 3d

4s 3d

4s 3d

4s 3d

The Transition Metals: A SurveyOxidation States, Ionization Energies

Ionization Energy

M(g) → M+(g) + e-

Increase of nuclear charge

→ Decrease of energy level of 3d

M2+(g) → M3+(g) + e-

More rapid decrease of energy level of 3d

Removing of d-electron

O+7

ooO+6

o△ooO+5

oooOooO+4

ooOOoOooO+3

OOOOOOoOo+2

Ooooooo+1

ooooooo≤0

ZnCuNiCoFeMnCrVTiSc

O : most common

Oxidation States

Removing of s or d-electron

The Transition Metals: A SurveyReduction Potentials

E0 (Mn+ + ne- → M)

-2.08

-1.63

-1.2

-1.18

-0.91

-0.76

-0.44

-0.28

-0.23

0.34

E0 (2H+ + 2e- → H2) = 0

In acidic solution,

M(s) + 2H+(aq) → H2(g) + M2+(aq)

except for Cu

3d

4d5d

The Transition Metals: A SurveyThe 4d and 5d Transition Series

Atomic radii

Nuclear charge ↑

Lanthanide contraction:

4f shielding effect is not big.

=> 5d contracts.

The First-Row Transition Metals

Scandium (Sc): Ion => only +3

Titanium (Ti):

The First-Row Transition Metals

Coordination Compounds

Coordination coumpounds typically consists of a complex ion and counter ions (anions or cations

as needed to produce a neutral compound).

Complex ions: species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases).

L1

L2

L4

L3

[Co(NH3)5Cl]Cl2(s) → Co(NH3)5Cl2+(aq) + 2Cl-(aq)

complex ion

Co3+, Cl- => []2+

counter ion (Cl-)

H2O

Two characteristics of coordination compounds (complex ions):

oxidation number of the transition metal and coordination number (and geometry)

Coordination Compounds

Coordination Number: number of ligands attached to a metal (typically 2 ~8)

Coordination Compounds

Ligand: A neutral molecule or ion having a lone electron pair that can be used to form a bond to a

metal ion (Lewis base).coordinate covalent bond: metal-ligand bond

• monodentate ligand: one bond to metal ion

• bidentate ligand: two bonds to metal ion

• polydentate ligand: can form more than two

bonds to a metal ion

• chelate ligand: bidentate, polydentate ligands

• ambidentate ligand: bonding through different

atoms of a same ligand

Coordination CompoundsNomenclatures

1. As with any ionic compound, the cation is named before the anion. 국어이름에서는 반대 [“Chloride” goes

last.]

2. In naming a complex ion, the ligands are named before the metal ion. ["NH3, Cl-" named before cobalt]

3. For ligand, an “o” is added to the root name of an anion (Table 21.14). For neutral ligands the name of the

molecule is used, with exceptions of Table 21.14. ["Cl- = chloro", "NH3 = ammine"]

4. The prefixes di-, tri-, tetra-, penta-, and hexa- are used to denote the number of simple ligands.The prefix bis-,

tris-, tetrakis-, and so on are used for the ligands that already contain di-, tri-, etc. [pentaammine]

5. The oxidation state of the central metal ion is designated by a Roman numeral in parenthesis. [cobalt(III)]

6. When more than one type of ligand is present, they are named alphabetically. [pentaamminechloro]

7. If the complex ion has a negative charge, the suffix “-ate (산)” is added to the name of the metal with

exceptions of Table 21.15 [pentaamminechlorocobalt (III) chloride]

[Co(NH3)5Cl]Cl2

철산구리산납산은산금산주석산

Ex) K3Fe(CN)6

[Fe(en)2(NO2)2]2SO4

triamminebromoplatinum(II) chloride

potassium hexafluorocobaltate(III)

potassium hexacyanoferrate(III)

bis(ethylenediamine)dinitroiron(III) sulfate

[Pt(NH3)3Br]Cl

K3[CoF6]

Isomerism

When two or more species have the same formula but different properties, they are said to be isomers.

Coordination isomerism:

The composition of the complex ion varies.

[Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4

Linkage isomerism:

Same complex ion structure but point of attachment

of at least one of the ligands differs.

[Co(NH3)4(NO2)Cl]Cl

tetraamminechloronitrocobalt(III) chloride

[Co(NH3)4(ONO)Cl]Cl

tetraamminechloronitritocobalt(III) chloride

Geometrical isomerism (cis-trans): Atoms or groups of

atoms can assume different positions around a rigid ring.

cis-Pt(NH3)2Cl2 trans-Pt(NH3)2Cl2 trans-Co(NH3)4Cl2+ cis-Co(NH3)4Cl2

+

early 19C

Isomerism

Optical isomerism: the isomers have opposite effects on plane-polarized light.

Louis Pateur (1822-95)

At his age of 26, he first realized that optical activity is exhibited by

molecules that have non-superimposable mirro images.

said to be chiral, called enantiomers

one of the isomers

dextrorotatory (d)

the other

levorotatory (l)

mixture of the two : racemic mixture , when mixed ratio is 1:1, no optical activity

Isomerism

Optical isomerism: the isomers have opposite effects on plane-polarized light.

Co(en)33+

Co(en)2Cl2+

trans cis

Co(NH3)Br(en)22+

Co

N

N N

N

NH3

Br

CoN N

NH3

N

Br

N

CoN N

NH3

N

Br

N

Co

H3N

N N

N

N

Br

geometrical

optical

trans cis

Bonding In Complex Ions: The Localized Electron Model

Review of Chapters 8 amd 9

Covalent Bond

Localized electron bonding models

Delocalized electron bonding model

•Lewis dot structure

•VSEPR (Valence shell electron pair repulsion)

•Valence bond theory (hybridization)

•Molecular orbital (MO) theory

Central idea: Formation of hybride atomic orbitals

that are used to share electron pairs to form s

bond between atoms

Bonding Theories of Complex Ions :

Valence bond theory (Localized electron bonding model)

Crystal field theory

Ligand field theory (Delocalized electron bonding model)

Bonding In Complex Ions: The Localized Electron Model

For complex ions

Covalent Bond

Localized electron bonding models

•Lewis dot structure

•VSEPR (Valence shell electron pair repulsion)

•Valence bond theory (hybridization)

1. VSEPR model sometimes works. But it

generally does not work

2. The interaction between a metal ion and a ligand

can be viewed as a Lewis acid-base reaction with

the ligand donating a lone pair of electrons to an

empty orbital of the metal ion to form a coordinate

covalent bond.

M L

empty metal ion

hybrid orbitallone pair on the ligand in a

hybrid atomic orbital

M L

coordinate covalent

bond

sp3 dsp2sp

Co(NH3)6+

d2sp3Though the localized electron bonding model improved our understanding of metal-ligand

bondings, it does not explain well many important properties of metal ions, such as

magnetism and colors. So usually thesedays we do not use it for the complex ions.

The Crystal Field Model

Crystal field model focuses on the energies of the d orbitals to explain the magnetic properties and

color of complex ions.

Assumption

1. Ligands are negative point charge.

2. Metal-ligand bonding is entirely ionic.

To derive the energy splittings of the d-orbital

in complex ions.

3d orbitals

Octahedral Complexes

d

Free metal ion

3d orbital energies

3d orbitals in octahedral field

eg (dz2, dx2-y2)

t2g (dxy, dyz, dxz)

3d orbital energy splittings

in octahedral field

E

The Crystal Field ModelOctahedral Complexes (magnetic properties)

= ligand

field

splitting

parameter

Co3+ (3d6)

(low-spin, S = 0, diamagnetic) (high-spin, S = 2, paramagnetic)

Spectrochemical Series for Ligands

CO > CN- > PPh3 > NO2- > phen > bipy > en > NH3 > py > CH3CN > NCS- > H2O > C2O4

2- >

OH- > RCO2- > F- > N3

- > NO3- > Cl- > SCN- > S2- > Br- > I-

π acceptor π donor

(strong field ligand) (weak field ligand)

Spectrochemical Series for Metal Ions

(ox # ↑,ᇫ↑), (down a group in periodic table, ᇫ↑)

Pt4+ > Ir3+ > Pd4+ > Ru3+ > Rh3+ > Mo3+ > Mn4+> Co3+ > Fe3+ > V2+ > Fe2+ > Co2+ > Ni2+ > Mn2+

The Crystal Field ModelOctahedral Complexes (magnetic properties)

Ex) Fe(CN)63- has one unpaired electron. CN- is strong-field or weak-field ligand ?

eg

t2g

eg

t2g

Fe3+ (3d5)

weak-field

(high-spin, S=5/2, paramagnetic)

strong-field

(low-spin, S=1/2, paramagnetic)

Ex) How many unpaired electrons in Cr(CN)64- ?

eg

t2g

eg

t2g

Cr2+ (3d4)

weak-field

(high-spin, S=2, paramagnetic)

strong-field

(low-spin, S=1, paramagnetic)

CN- : strong-field ligand

Ex) S of Cu(H2O)62+ ?

Cu2+ (3d9)

S = 1/2

The Crystal Field ModelOctahedral Complexes (colors)

The Crystal Field ModelOctahedral Complexes (colors)

E = hn = hc/l

E

The Crystal Field ModelOther Coordination Geometries

Tetrahedral complexes

d

Free metal ion

3d orbital energies

eg (dz2, dx2-y2)

t2g (dxy, dyz, dxz)

3d orbital energy splittings

in octahedral field

E

tet ≈ (4/9)oct

All tetrahedral complexes are

weak-field cases (high-spin).

e (dz2, dx2-y2)

t2 (dxy, dyz, dxz)

3d orbital energy splittings

in tetrahedral field

The Crystal Field ModelOther Coordination Geometries

Square-planar complexes Linear complexes

Octahedral (Oh)

dz2, dx2-y2

dxy, dyz, dzx

t2g

eg

Uniform Field

Tetrahedral (Td)

dz2, dx2-y2

dxy, dyz, dzxt2

e

t

dx2-y2

dxy

dz2

dyz, dzx

eg

a1g

b1g

b2g

Square-planar (D4h)

dx2-y2

dxy

dz2

dyz, dzx

eg

a1g

b1g

b2g

1

2

3

d

Tetragonal elongation (D4h)

o

Bonding In Complex Ions: The Localized Electron Model

Bonding Theories of Complex Ions :

Valence bond theory (Localized electron bonding model)

Crystal field theory

Ligand field theory (Delocalized electron bonding model)

L6M ML6

electrons from ligands

frontier orbitals

•electrons from d-orbitals

•same splitting pattern and d-orbital

configuration as in CFT

Higher Class

has not talked

about bonding

The Biological Importance of Coordination Complexes

Roles of metals in biology – electron transport, oxygen storage, oxygen transport,

oxidation-reduction catalysis, metal ion storage and transport .......

(Heme proteins)cytochromes

The Biological Importance of Coordination ComplexesHow to get energy in our body ?

O2 : source of energy - combustion (burning gasoline in automobiles)

- oxidation of carbohydrates, proteins, fats through respiratory chain (mammal)

O2 storage and transport

O2 transport

O2 + nutrients

Air

e- transfer

(oxidation of nutrients)

Myoglobin

←

protein

Hemoglobin

heme = Fe + porphyrin

Hb(aq) + 4O2(g) → Hb(O2)4 (aq)

Hemoglobin Oxyhemoglobin

The Biological Importance of Coordination ComplexesOthers

Chlorophyll

Cisplatin

Nitrogenase

Metallurgy and Iron and Steel Production

Metallalurgy

1. Mining

2. Pretreatment of the ore

3. Reduction to the free metal

4. Purification of the metal (refining)

5. Alloying

removing CO2

FeCO3(s) → FeO(s) +CO2(g)

4FeO(s) + O2(g) →2F2O3(s)

3Fe2O3(s) + C(s) →Fe3O4(s)+CO(g)

heat