coordination compounds complex by s. r. ratnam
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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
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
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