COORDINATION COMPOUNDS

COMPLEX IONS

COORDINATION COMPOUNDS

CoCl3 6NH3

[Co(NH3)6]Cl3

Alfred Werner introduced the 2 types of valences:

1) Primary valence – oxidation number/charge2) Secondary valence – coordination number

COMPLEXES

• Metal – usually transition metal either NEUTRAL or POSITIVELY CHARGED acting as LEWIS ACID

• Ligand – usually has at least one pair of unshared valence electrons and acts as LEWIS BASE

Metal-Ligand interaction forms a COORDINATE COVALENT BOND

LIGANDS

• DENTICITY (monodentate, bidentate, polydentate)

• CHELATING AGENTS (for bi/polydentate ligands)

• FIRST COORDINATION SPHERE as signified by []

EXAMPLES

1) [Cu(NH3)2(H2O)Cl]+

2) [Fe(H2O)2(CN)4]-

3) [Ni(H2NCH2CH2NH2)2]2+

Identify Primary Valence and Secondary Valence

NOMENCLATURE

RULES

• Cation Before Anion• Ligand before Central

Metal, reverse for formula

• Ligand Anions end in –o/-ido

• Neutral ligands retain their names

• Special Ligand Names

• [Co(en)3]Cl3, K2[CoCl4]

• Cl- • ethylenediamine• H2O, NH3, CO, NO

RULES

• Greek prefixes (di/bis)• Oxidation number in

Roman numeral after the Metal Name

• If complex is anion, end in –ate added to Latin name

• For multiple ligands, use alphabetical order regardless of prefix

• [CoCl4]2-, [Ni(en)2]2+

• [Co(NH3)3(NO2)3]

EXAMPLE

• [Ni(CO)4]

• [Co(H2O)4Cl2]Cl

• Na3[Ag(S2O3)2]

• [Fe(en)3](NO3)3

• [Cr(NH3)4[FeF6]2

SEATWORK

• [Ag(NH3)2]Cl

• [Co(NH3)3Cl3]

• K4[Fe(CN)6]

• [Ni(CO)4]

• [Cu(en)2]SO4

• [Pt(NH3)][PtCl6]

• [CoCl(NH3)4(H2O)]Cl2

STRUCTURAL ISOMERS

-compounds of same empirical formula but with different arrangement

4 TYPES- Ionization {[Co(NH3)5(SO4)]Br, [Co(NH3)5Br]SO4}

- Hydrate {[Cr(H2O)6]Cl3, [Cr(H2O)5Cl]Cl2H2O}

- Linkage {-NO2, -ONO}

- Coordination {[Cu(NH3)4][PtCl4], [Pt(NH3)4][CuCl4]}

STEREOISOMER

-with different spatial arrangement• GEOMETRIC – cis and trans {Co(NH3)4Cl}• OPTICAL – nonsuperimposable mirrors of each

other

VALENCE BOND THEORY

• Bond is formed with overlap of two orbitals• For complexes: overlap of ligand orbital

(containing an electron pair) and a metal orbital (empty)

• Number of Ligands GEOMETRY • Linear (2), Square Planar (4), Tetrahedral (4),

Octahedral (6)

EXAMPLES

OCTAHEDRAL COMPLEXES• [Cr(H2O)6]3+ (outer orbital complex)

• [FeF6]3- (inner orbital complex)

SQUARE PLANAR• [Ni(CN)4]2-

TETRAHEDRAL• [CoCl4]2-

CRYSTAL FIELD THEORY

• Electrostatic attraction (between metal and ligand)• Electrostatic repulsion (between electrons sharing

an orbital)• Electrical repulsion is dependent on orientation of d

orbitals and the incoming ligands causing splits in energy

• crystal field splitting (Δ) – dependent on metal and nature of ligand, affects color and magnetic properties

GEOMETRY

OCTAHEDRAL COMPLEX

___ ___

___ ___ ___

___ ______ ___ ___

Δ(high)

eg

t2g

Δ(low)eg

t2g

TETRAHEDRAL COMPLEX

___ ___ ___

___ ___Δ(high)

t2g

eg

SQUARE PLANAR COMPLEX

___

___

___

___ ___

d x2-y

2

d xy

d z2

d xz d yz

SPECTROCHEMICAL SERIES

Order of ligands based on ability to produce large Δ (strong field vs weak field)

I-<Br-<Cl-<F-<OH-<H2O<NH3<en<NO2-<CN-

PARAMAGNETISM and COLOR

• Presence of unpaired electrons of the metal• May usually lead to colored complexes

E = hc/λ• Fe3+ in [Fe(H2O)6]3+ vs Ca2+ or Cd2+

• [Fe(CN)6]3- vs [FeF6]3-

• [CoCl6]3- vs [Co(NH3)6]3+

SAMPLE PROBLEM

A compound contains 21.35% Cr, 28.70% N, 6.209% H and 43.68%Cl by mass.

(a) It does not react with HCl.(b) On reaction with AgNO3, it gives 2 moles of AgCl per

mole of compound.(c) It has an electrical conductivity corresponding to

3mols of ions per mole of compound.1. Give the inferences of a, b and c.2. Write the formula and give the name of the

compound.