Ch18 II - L38 Isomers same composition but different...

L38. Isomers: same composition but different structure
Isomers
Structural isomers
Stereoisomers
Coordination
isomers
Linkage
isomers
geometric
isomers
optical
isomers
[Cr (NH
3
)
5
Cl ] SO
4
and
[Cr (NH
3
)
5
SO
4
] Cl
[Co(NH
3
)
4
( NO
2
)Cl]Cl
and
[Co(NH
3
)
4
( ONO )Cl]Cl
cis-Pt(NH
3
)
2
Cl
2
and
trans-Pt(NH
3
)
2
Cl
2
D-alanine
and
L-alanine

Today: Colors of coordination complexes:
both ligand and ion affect color
Crystal Field Theory

d-orbital energy splitting for octahedral complexes:
proximity of ligand increases energy (e-e- repulsion)
Energy and splitting
depends on:
Orientaion of d orbital
Nature of ligand
Charge of metal ion
Octahedral complex

Crystal field theory:
Magnetic properties and colors of coordination compounds
1. Octahedral field splittings of d-orbitals:
Δ
o
2/5Δ
3/5Δ
d
z2
d
x2-y2
(e
g
)
d
zy
d
yx
d
xz
(t
2g
)
d-orbital is:
near atoms: more repulsion
between atoms:
less repulsion

Strength (magnitude) of splitting ( Δ
o
or Δ
t
):
Spectrochemical series
Determines color in light absorption
Ligand effect:
CN
-
> NO
2
-
> en > NH
3
>
> H
2
O > OH
-
> F
-
>
> Cl
-
> Br
-
> I
-
Also, charge on the metal,
e.g., splitting in Fe
3+
> Fe
2+
Small negative ligands close to
metal ion
and metal ions with large charge
increase repulsion

Filling in electrons: Aufbau pinciple
Two electrons: in one or two orbitals
ε
1
E
ε
2
ε
1
E
ε
2
E= ε
1
ε
1
E
ε
2
Low spin case:
High-spin case:
low spin - large energy gap between orbitals
high spin (Hund’s rule) – (near)-degenerate orbitals
One electron: in the lowest energy orbital