Transition Metals and Coordination

Chemistry

Dr. K. Kalpanadevi

20.1 The Transition Metals: A Survey

20.2 The First-Row Transition Metals

20.3 Coordination Compounds

20.4 Isomerism

20.5 Bonding in Complex Ions:

The Localized Electron Model

20.6 The Crystal Field Model

20.7 The Molecular Orbital Model

20.8 The Biological Importance of

Coordination Complexes

Transition Metals and Coordination Chemistry

Vanadium metal (center) and in solution as

V2+(aq), V3+(aq), VO2+(aq), and VO2+(aq),

(left to right).

Figure 18.1: The periodic table.

Figure 12.39: Special names for groups

in the periodic table

Figure 12.39: Special names for groups

in the periodic table (cont’d)

Figure 20.1: Transition elements on the periodic table

Figure 12.28: The orbitals filled for

elements in various parts

Some Transition Metals Important to the U.S. Economy and Defense

20.1 A Survey of the Transition Metals

→ Recall the Representative Elements, Groups 1A – 8A:

• Chemical similarities occur within the vertical groups E.g. LiCl

NaCl

KCl

RbCl

CsCl

all ionic compounds

• Large changes in chemistry across a given period as the number of valence

electrons changes

E.g. Na Mg Al Si P S Cl Ar

— increasing metallic character

— decreasing ionization energy

NaCl MgCl2 AlCl3 … PCl5

Ionic Covalent

molecules

→ Transition Metals

• Similarities within a given period as well as within a given vertical group.

this huge contrast with the representative elements is due to the fact that the

last electrons added to the transition metal elements are inner electrons:

• d electrons in d – block transition metals

• f electrons in the lanthanides and actinides

– the inner d and f electrons cannot participate in bonding as readily as

the s and p electrons.

• Characteristics of the transition metals

– typical metals

• metallic luster

• high electrical and thermal conductivities

• Differences in Physical Properties among the transition metals can be large

– E.g. W, tungsten (mp = 3400℃) vs Hg, mercury (mp < 25℃)

– hard and high strength vs soft

Fe, iron and Ti Cu, Au, Ag

– ready rxn w/ O2 to form oxides vs no rxn with O2

Cr, Ni, Co, Al, Fe Au, Ag, Pt, Pd

• Ionic compounds with nonmetals

– Often more than one oxidation state

E.g. FeCl2 FeCl3

+2 +3

– the cations are often complex ions, species in which the transition

metal ion is surrounded by a number of ligands.

Molecular model: The CO(NH3)63+ ion

— Ligands are molecules or ions that behave

as Lewis bases, i.e. have a lone pair of electrons.

• Most compounds of the transition metals are colored.

— the transition metal ion can absorb visible light.

• Many transition metal compounds are paramagnetic.

— because they contain unpaired electrons

Electron Configurations (See Section 12.13)

• The 3d orbitals begin to fill after the 4s orbital is complete.

e.g. Sc: [Ar]4s23d1

Ti: 4s23d2

Y: 4s23d3

Cr: 4s13d5

Mn: 4s23d5

:

Cu: 4s13d10

Zn: 4s23d10

• for most elements of the first-row transition metals 4s23dn has a lower energy

than 4s13dn+1 except chromium and copper.

•The 4s and 3d orbital energies are very similar.

(See Table 20.2)

4s13dn+1 exceptions to 4s23dn electron

configuration

Co2+, Mn2+, Cr3+, Fe3+, & Ni2+

Table 20.2 Selected Properties of the First-Row Transition Metals

• Electron configurations of ions of the first-row transition metals

— the energy of the 3d orbitals is significantly less than that of the 4s orbital.

E.g. Sc: 4s23d1 Sc2+: 3d1

Ti: 4s23d2 Ti3+: 3d1

Zn: 4s23d10 Zn2+: 3d10

— these ions do not have 4s electrons (since the 3d orbitals are lower in energy)

• Oxidation States and Ionization Energies

• Various ions formed by losing electrons

E.g. Ti → Ti2+, Ti3+, Ti4+

4s23d2 most common

(See Table 20.2)

— to the right of the row the higher oxidation states are not observed because the

3d orbitals become lower in energy as the nuclear charge increases, making

electrons difficult to remove.

e.g. Zn → Zn2+ {Zn3+, Zn6+, Zn10+, etc ← NOT OBSERVED}

4s23d10 observed

(See Figure 20.2)

Figure 20.2: plots of the first (red dots) and third (blue

dots) ionization energies for the first-row transition metals

Standard Reduction Potentials

• The potential of the half-reaction

M(s) → Mn+ + ne-

characterizes the reducing ability of the metal.

• this is the reverse of usually

tabulated half-reactions and the

potentials are opposite in sign to

tabulated values in Table 20.2.

• Since by definition ξo = 0 for:

2H+ + 2e- → H2

all the first-row transition metals, except copper, can reduce H+ ions to hydrogen

gas in 1M aqueous solutions of strong acids:

M(s) + 2H+(aq) → H2 (g) + M2+

(aq)

The 4d and 5d Transition Series

• Comparison of the atomic radii of 3d, 4d, and 5d elements

See Figure 20.3

— general decrease in size in going from left to right across each

series

— significant increase in size from 3d to 4d

— 4d and 5d metals are very similar in size

this is due to the lanthanide contraction.

lanthanide series: elements between lanthanum (La) and

hafnium (Hf)

↑

filling of 4f orbitals which are in the interior of the atoms do

not affect size of the 5d elements

• 4d and 5d transition metals, though not as common as 3d metals,

have some very useful properties.

E.g. The platinum group metals – Ru, Os, Rh, Ir, Pd and Pt – are

widely used as catalysts in many industrial processes.

Figure 12.28: The orbitals filled for

elements in various parts

Figure 12.31: The positions of the elements considered

in Example 12.8

Figure 20.3: Atomic radii of the 3d, 4d,

and 5d transition series.

Figure 20.1: Transition elements on the periodic table

20.2 The First-Row Transition Metals Highlights of some properties or chemistry of the 10 3d transition metals.

1. Scandium, Sc

+3 oxidation state in compounds, e.g. ScCl3, Sc2O3, etc

most of its compounds are colorless and diamagnetic.

2. Titanium, Ti

fairly abundant (0.6% by mass of the earth’s crust) low density + high strength + high mp (1,672℃)

excellent structural material: jet engines, Boeing 747 jetliners, etc.

titanium (Ⅳ) oxide (or titanium dioxide), TiO2 is the most common

compound.

-- white pigment used in many products: paper,

paint, linoleum, plastics, cosmetics, etc.

3. Vanadium, V

The most common oxidation state is

+5 as in V2O5 (orange, mp =

650 ℃) and VF5.

Figure 20.4: Titanium bicycle

5. Manganese, Mn

– The only member of the 3d metals that can exist in all oxidation states from +2 to +7.

– Manganese (VII) ion: MnO4-

permanganate ion

( a strong oxidizing agent in solution)

Ferrochrome

added directly to iron in steel making process • common oxidation states in compounds: +2, +3, and +6

• Cr2+ (chromous ion)

• Cr3+ (chromic ion)

• chromium (IV) oxide + conc. sulfuric acid

cleaning solution

4. Chromium, Cr

– Main ore is chromite (FeCr2O4)

– FeCr2O4 (s) + 4 C (s) → 4 CO (g) + Fe (s) + 2Cr (s)

Manganese nodules on the sea floor

Source: Visuals Unlimited

6. Iron, Fe

• Quite abundant (4.7% of the

earth’s crust) • Its chemistry mainly involve its

+2 and +3 oxidation states.

7. Cobalt, Co

• mainly +2 and +3 states

• compounds with 0, +1 and +4

states are also known

8. Nickel, Ni

• mainly in the +2 oxidation state.

• aqueous solutions of nickel (II)

salts contain Ni(H2O)62+ ion,

— characteristic emerald

green color

Aqueous solution containing the Ni2+ ion

9. Copper, Cu

• widely available in ores (sulfides,

chlorides, carbonates etc.)

• used in electrical applications (wires,

cables, etc)

• also used in water pipes in homes

• many common alloys contain copper

e.g. brass, bronze, sterling silver, 18- and 14-

Karat gold

chemistry involves +2 oxidation state,

but also some compounds with the +1

oxidation state.

10. Zinc, Zn

• +2 oxidation state only

• used mainly for producing

galvanized steel.

• Zinc (II) salts are colorless.

20.3 Coordination Compounds

• A coordination compound consists of a complex ion and counter ions.

– it is an ionic compound, electrically neutral.

– complex ion = transition metal ion + attached ligands.

E.g. [Co(NH3)5Cl]Cl2

Co(NH3)5Cl2+ ← complex ion

2 Cl- ← counter ions (anions) – coordination compounds ionize in solutions (similar to simple salts)

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

• Coordination Number of Metal Ions

– The number of bonds formed between a metal ion and the ligands in

the complex ion is termed the coordination number.

– depending on the size, charge, and electron configuration of the

transition metal ion, the coordination number can be from 2 to 8.

H2O

– many metal ions show more than one coordination number.

– for the typical geometries for the various typical coordination numbers

see Figure 20.6.

Ligands

– a neutral molecule or ion having a lone pair that can be used to form a

bond with a metal ion.

• Lewis bases by definition are ligands

• the metal ion is a Lewis acid

– a metal – ligand bond is called a coordinative covalent bond.

• it results from a Lewis acid – base interaction in which a ligand

donates an electron pair to an empty orbital on a metal ion.

Figure 20.6: Ligand

arrangements for

coordination numbers 2,

4, and 6