Chapter 22 Metals and Coordination Chemistry

Basic Concepts

Lewis Acids and Bases

Lewis base: Substance that donates a lone pair of electrons.

Lewis acid: Substance that accepts a lone pair of electrons.

Lewis base: Substance that donates a lone pair of electrons.

Lewis acid: Substance that accepts a lone pair of electrons.

Complex Ions

Zn2+ ion: sp3 hybridization = tetrahedral

Complex Ions

Zn2+                                        +                              4  NH3                                                                  [Zn(NH3)4]2+

Coordinate bonds

(Ligands) (Complex  ion)

Coordinate bond bond formed when one anion/molecule donates a

pair of electrons to another ion/molecule to form a covalent bond.

Ligand a Lewis base bonded to the central metal ion of a

complex ion.

Complex ion ionic species consisting of a metal ion bonded to one

or more Lewis bases.

Inner coordination sphere ligands that are bound directly to a metal via

coordinate covalent bonds.

Common Ligands

Counter ions: Ions that balance the electrical charges of complex ions in

coordination compounds.

Coordination compound: Any compound that contains a complex ion.

Coordination number: Identifies the number of electron pairs surrounding a

metal ion in a complex.

Structure of Coordination Compounds

Structure of Coordination Compounds

Cr(NH3)63+, a typical complex ion.

A typical Coordination Compound [Cr(NH3)6]Cl3

Cu2+(aq) + 4 NH3(aq) ⇌ Cu(NH3)42+(aq)

[Cu(NH3)42+] [Cu2+][NH3]4Kf = = 5.0 x 1013

Complex-Ion Equilibria

Formation Constants (Kf) for Some Complex

Ions at 25ºC

1) Calculate the equilibrium concentration of Ag+ (aq) in a solution that is initially 0.100 M AgNO3 and 0.800 M NH3 after this reaction takes place:

Ag+(aq) + 2 NH3(aq) ⇌ Ag(NH3)2+(aq)

R

I

C

E

Ag+(aq) + 2 NH3(aq) ⇌ Ag(NH3)2+(aq)

Kf = 1.7 x 107

x

0.100 0.800 0.0

- (0.100 - x) - 2(0.100 - x) (0.100 - x)

(0.100 - x)0.800- 2(0.100 - x)

= 0.600 + 2x)

[Ag(NH3)2+] [Ag+][NH3]2Kf = = = 1.7 x 107

x = 1.6 x 10-8

(0.100 - x) (x)(.600+2x)2= (0.100)

(0.360x)

Naming Complex Ions and Coordination Compounds

Names and Structures of Common Ligands

X

N

O

O O

O H

O H

H

N H

H H

C N

C O

Names and Structures of Common Ligands

N

H

CH2CH2

NN H

H

H

N

NN

N

Naming Coordination Compounds

CationsNi(H2O)62+

[Cu(NH3)4(H2O)2]2+

Hexaaquanickel(II)

Tetraaminediaquacopper(II)

Fe(CN)63-Anions

[Fe(H2O)(CN)5]3-

Hexacyanoferrate(III)

Aquapentacyanoferrate(II)

Compounds[Zn(NH3)4]Cl2

K3[Fe(CN)6][Co(NH3)4(H2O)2](NO2)2

Potassium hexacyanoferrate(III)

2)

Tetraamminezinc chloride

Tetraamminediaquacobalt(II) nitrite

Polydentate Ligands

Monodentate ligand: Species that forms a single coordinate bond to a metal ion

in a complex (e.g., NH3, Cl–).

Polydentate ligand: Species that can form more than one coordinate bond per

molecule.

Chelation: Interaction of a metal ion with a ligand having multiple

donor atoms (chelating agent).

Chelating Agents

Ethylenediamine (en) (bidentate)

Triethylenediamine Nickel(II) [Ni(en)3]2+

2+ + 3

Nickel(II)

Chelating Agents

Diethylenetriamine (tridentate)

2+

Triaqua(diethylenetriamine) nickel (II)

NH2CH2

CH2NH

CH2CH2

NH2

Hexaaqua nickel (II)

Ethylenediaminetetraacetate (EDTA) Sequestering agent

7+

[Co(EDTA)]3+

Ligand Strength and Chelate Effect

Ligands with a higher affinity for metal cation will displace ligands with less affinity.

Metal ions generally have Greater affinity for polydentate ligands than for monodentate ligands.

Ni(H2O)62+* Ni(NH3)62+* Ni(en)32+*+*NH3* +*en*

Kf = 5×108 Kf = 1.1×1018