COORDINATION COMPOUNDSCOMPLEX

Bys. r. ratnam

Alfred WernerSwitzerlandUniversity of ZurichSwitzerlandb. 1866 d. 1919

Alfred Werner (1866-1919)• 1893, age 26: coordination

theory• Nobel prize for Chemistry, 1913• Addition of 6 mol NH3 to

CoCl3(aq)Conductivity studies

Precipitation with AgNO3

Werner’s explanation of coordination complexes

Metal ions exhibit two kinds of valence: primary and secondary valences

The primary valence is the oxidation number (positive charge) of the metal (usually 2+ or 3+)

The secondary valence is the number of atoms that are directly bonded (coordinated) to the

metal

The secondary valence is also termed the “coordination number” of the metal in a

coordination complex

Werner Coordination Theory

Compound Moles of ions Moles of AgCl(s)

“CoCl3.6NH3”

“CoCl3.5NH3”

“CoCl3.4NH3”

“CoCl3.3NH3”

4 3

3

2

0

2

1

0

Co

NH3

NH3

NH3

Cl

NH3 NH3 NH3 Cl

Cl

Cl– attached to NH3 may be dissociated

Werner Coordination Theory

Compound Moles of ions Moles of AgCl(s)

[Co(NH3)6]Cl3

[Co(NH3)5Cl]Cl2

[Co(NH3)4Cl2]Cl

[Co(NH3)3Cl3]

4 3

3

2

0

2

1

0

• Proposed six ammonia molecules to covalently bond to Co3+

Coordination Chemistry

Definitions• Coordination compounds – compounds

composed of a metal atom or ion and one or more ligands (atoms, ions, or molecules) that are formally donating electrons to the metal center

Miessler, Tarr, p. 278

Coordination Chemistry

Definitions• Coordination compounds

NH3

Co

NH3

H3N NH3

NH3H3N

3+

3Cl–

H

N

HH

M

ligand

N forms a coordinate covalent bond to the metal

(coordination sphere)

(counterion)

Coordination Chemistry

Definitions• Ligands – simple, ‘complex’• Denticity – different number of donor atoms• Chelates – compounds formed when ligands

are chelating (Gk. crab’s claw)

H3C C

O

O

M

bidentate

Valence Bond Theory

Developed by Linus Pauling

Overlap of an empty orbital with a fully-filled orbital leads to the formation of a co-ordinate covalent bond or dative bond

Bonding in Coordination CompoundsValence Bond Theory

Tro, Chemistry: A Molecular Approach

15

• Geometry of complex• Magnetic properties of complex• Electronic configuration of Metal ion• Nature of Bonding

VBT explains

VBT Valence Bond Theory

Tro, Chemistry: A Molecular Approach

20

Geometries in Complex Ions

tetrahedral

octahedral

Polydentate Ligands

Ethylenediaminetetraacetate, mercifully abbreviated EDTA, has six donor atoms.

Valence Bond Theory

• Metal or metal ion: Lewis acid• Ligand: Lewis base• Hybridization of s, p, d orbitalsC.N. Geometry

4 tetrahedral

56

4

Hybrids

sp3

square planar dsp2

trigonal bipyramidal dsp3 or sp3doctahedral d2sp3 or sp3d2

Valence Bond Theory

Example 1: [Co(NH3)6]3+

Co [Ar] 3d7 4s2

Co3+ [Ar] 3d6

3d 4s 4p

if complex is diamagnetic

4d

d2sp3

octahedral

:

Valence Bond Theory

Example 2: [CoF6]3–

Co [Ar] 3d7 4s2

Co3+ [Ar] 3d6

if complex is paramagnetic

3d 4s 4p 4d

4sp3d2

octahedral

Valence Bond Theory

Example 3: [PtCl4]2–, diamagnetic

Pt2+ [Xe] 4f14 5d8

5d 6s 6p

dsp2

square planar

Valence Bond Theory

Example 4: [NiCl4]2–, tetrahedral

Ni2+ [Ar] 3d8

3d 4s 4p

4sp3

paramagnetic

Valence Bond Theory

• Ligands (Lewis base) form coordinate covalent bonds with metal center (Lewis acid)

• Relationship between hybridization, geometry, and magnetism

• Inadequate explanation for colors of complex ionse.g., [Cr(H2O)6]3+, [Cr(H2O)4Cl2]+