Download COORDINATION COMPOUNDS COMPLEX

COORDINATION COMPOUNDS
COMPLEX
By
s. r. ratnam
Alfred Werner (1866-1919)
• 1893, age 26: coordination
theory
• Nobel prize for Chemistry, 1913
• Addition of 6 mol NH3 to
CoCl3(aq)
Alfred Werner
Switzerland
University of Zurich
Switzerland
b. 1866
d. 1919
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
NH3 Cl
Co
NH3 NH3
Cl– attached to NH3 may be dissociated
NH3 NH3
Cl
NH3 Cl
Compound
Moles of ions
Moles of AgCl(s)
“CoCl3.6NH3”
4
3
“CoCl3.5NH3”
3
2
“CoCl3.4NH3”
2
1
“CoCl3.3NH3”
0
0
Werner Coordination Theory
• Proposed six ammonia molecules to
covalently bond to Co3+
Compound
Moles of ions
Moles of AgCl(s)
[Co(NH3)6]Cl3
4
3
[Co(NH3)5Cl]Cl2
3
2
[Co(NH3)4Cl2]Cl
2
1
[Co(NH3)3Cl3]
0
0
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
3+
NH3
H3N
Co
H3N
NH3
3Cl–
(counterion)
NH3
NH3
ligand
(coordination sphere)
H
N
H
H
M
N forms a coordinate covalent bond to the metal
Coordination Chemistry
Definitions
• Ligands – simple, ‘complex’
• Denticity – different number of donor atoms
• Chelates – compounds formed when ligands
are chelating (Gk. crab’s claw)
O
H3C
M
C
bidentate
O
Valence Bond Theory
Developed by Linus Pauling
Bonding in Coordination Compounds
Valence Bond Theory
Overlap of an empty orbital with a fullyfilled orbital leads to the formation of a
co-ordinate covalent bond or dative bond
VBT explains
•
•
•
•
Geometry of complex
Magnetic properties of complex
Electronic configuration of Metal ion
Nature of Bonding
Tro, Chemistry: A Molecular
Approach
15
VBT Valence Bond Theory
Geometries in Complex Ions
Tro, Chemistry: A Molecular
Approach
20
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 orbitals
C.N. Geometry
Hybrids
4
4
5
6
tetrahedral
square planar
trigonal bipyramidal
octahedral
sp3
dsp2
dsp3 or sp3d
d2sp3 or sp3d2
:
Valence Bond Theory
Example 1: [Co(NH3)6]3+
Co [Ar] 3d7 4s2
Co3+ [Ar] 3d6
3d
4s
d2sp3
octahedral
if complex is diamagnetic
4p
4d
Valence Bond Theory
Example 2: [CoF6]3–
Co [Ar] 3d7 4s2
Co3+ [Ar] 3d6
3d
4s
4p
4sp3d2
octahedral
if complex is paramagnetic
4d
Valence Bond Theory
Example 3: [PtCl4]2–, diamagnetic
Pt2+ [Xe] 4f14 5d8
5d
6s
dsp2
square planar
6p
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
ions
e.g., [Cr(H2O)6]3+, [Cr(H2O)4Cl2]+