The Transition Metals

Oxidation States of the 1 st Row Transition Metals
( most stable oxidation numbers are shown in red )

Mn(II)
Aqueous oxoanions of transition elements
One of the most characteristic chemical properties of these elements is the occurrence of multiple oxidation states.
Mn(VI) Mn(VII)
V(V)
Cr(VI)
Mn(VII)

Effects of the metal oxidation state and of ligand identity on color
[V(H
2
O)
6
] 2+
[V(H
2
O)
6
] 3+
[Cr(NH
3
)
6
] 3+ [Cr(NH
3
)
5
Cl ] 2+

Ionization Energies for the 1 st Row Transition Metals

Scandium Titanium
Chromium Manganese
Vanadium
Iron
Cobalt Nickel Copper

Coordination Compounds
A coordination compound typically consists of a complex ion and a counter ion.
A complex ion contains a central metal cation bonded to one or more molecules or ions.
The molecules or ions that surround the metal in a complex ion are called ligands .
A ligand has at least one unshared pair of valence electrons
H
O
H
• •
N
H
H
H
• •
••Cl
C O
22.3

Coordination Compounds
The atom in a ligand that is bound directly to the metal atom is the donor atom .
O
• •
N
H H H
H
H
The number of donor atoms surrounding the central metal atom in a complex ion is the coordination number .
Ligands with: one donor atom two donor atoms monodentate bidentate three or more donor atoms polydentate
H
2
O, NH
3
, Cl ethylenediamine
EDTA

Coordination Compounds bidentate ligand
H
2
• •
N CH
2
CH
2
• •
NH
2 polydentate ligand
(EDTA)
Bidentate and polydentate ligands are called chelating agents

EDTA Complex of Lead

What are the oxidation numbers of the metals in
K[Au(OH)
4
] and [Cr(NH
3
)
6
](NO
3
)
3
?
OH has charge of -1
K + has charge of +1
? Au + 1 + 4x(-1) = 0
Au = +3
NO
3
has charge of -1
NH
3 has no charge
? Cr + 6x(0) + 3x(-1) = 0
Cr = +3

Naming Coordination Compounds
• The cation is named before the anion.
• Within a complex ion, the ligands are named first in alphabetical order and the metal atom is named last.
• The names of anionic ligands end with the letter o . Neutral ligands are usually called by the name of the molecule. The exceptions are H
2
O (aqua), CO (carbonyl), and NH
3
(ammine).
• When several ligands of a particular kind are present, the
Greek prefixes di, tri, tetra, penta -, and hexaare used to indicate the number. If the ligand contains a Greek prefix, use the prefixes bis , tris , and tetrakis to indicate the number.
• The oxidation number of the metal is written in Roman numerals following the name of the metal.
• If the complex is an anion, its name ends in –ate .
22.3

What is the systematic name of
[Cr(H
2
O)
4
Cl
2
]Cl ?
tetraaquodichlorochromium(III) chloride
Write the formula of tris(ethylenediamine)cobalt(II) sulfate
[Co(en)
3
]SO
4

– • Originally developed to explain properties for crystalline material
– • Basic idea:
–
Electrostatic interaction between lone-pair electrons result in coordination.

i i) Separate metal and ligand high energy ii) Coordinated Metal - ligand stabilized iii) Destabilization due to ligand -d electron repulsion iv) Splitting due to octahedral field.
ii iii iv

d-orbitals pointing directly at axis are affected most by electrostatic interaction d-orbitals not pointing directly at axis are least affected
(stabilized) by electrostatic interaction

d-orbitals align along the octahedral axis will be affected the most.
More directly the ligand attacks the metal orbital, the higher the energy of the d-orbital.
In an octahedral field the degeneracy of the five d-orbitals is lifted

The energy gap is referred to as
 (10 Dq) , the crystal field splitting energy.
The d z
2 and d x
2 y
2 orbitals lie on the same axes as negative charges.
Therefore, there is a large, unfavorable interaction between ligand (-) orbitals.
These orbitals form the degenerate high energy pair of energy levels.
The d xy
, d yx and d xz orbitals bisect the negative charges.
Therefore, there is a smaller repulsion between ligand & metal for these orbitals.
These orbitals form the degenerate low energy set of energy levels.

Splitting of d orbitals in an octahedral field
3/5  o e g
2/5  o t
2g
 o is the crystal field splitting
E( t
2g
) = -0.4
 o x 3 = -1.2
 o
E( e g
) = +0.6
 o x 2 = +1.2
 o
 o

The magnitude of the splitting
(ligand effect)
Strong field
Weak field
The spectrochemical series
CO, CN > phen > NO
2
> en > NH
3
> NCS > H
2
O > F > RCO
2
> OH
-
> Cl > Br > I -

The magnitude of the splitting
(metal ion effect)
Strong field
Weak field
 increases with increasing formal charge on the metal ion
 increases on going down the periodic table

The spectrochemical series
•For a given ligand, the color depends on the oxidation state of the metal ion.
•For a given metal ion, the color depends on the ligand.
I < Cl < F < OH < H
2
O < SCN < NH
3
< en < NO
2
< CN < CO
WEAKER FIELD STRONGER FIELD
SMALLER

LONGER

LARGER
SHORTER


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• Electron configuration of metal ion:
• s-electrons are lost first.
• Ti 3+ is a d
• Hund's rule:
1 , V 3+ is d 2 , and Cr 3+ is d 3
• First three electrons are in separate d orbitals with their spins parallel.
• Fourth e- has choice:
• Higher orbital if  is small; High spin
• Lower orbital if  is large: Low spin.
• Weak field ligands
• Small  , High spin complex
• Strong field Ligands
• Large  , Low spin complex

d 1
Placing electrons in d orbitals
Strong field Weak field
Strong field Weak field d 2 d 3 d 4

When the 4 th electron is assigned it will either go into the higher energy e g orbital at an energy cost of  cost of P , the pairing energy.
0 or be paired at an energy d 4
Strong field =
Low spin
(2 unpaired)
Weak field =
High spin
(4 unpaired)
P
<
 o
P
>
 o

P
The pairing energy, P , is made up of two parts.
1) Coulombic repulsion energy caused by having two electrons in same orbital. Destabilizing energy contribution of P c for each doubly occupied orbital.
2) Exchange stabilizing energy for each pair of electrons having the same spin and same energy. Stabilizing contribution of P e for each pair having same spin and same energy
P = sum of all P c and P e interactions

Placing electrons in d orbitals d 5 d 6 d 7
1 u.e.
5 u.e.
d 8
0 u.e.
4 u.e.
d 9
1 u.e.
3 u.e.
d 10
2 u.e.
2 u.e.
1 u.e.
1 u.e.
0 u.e.
0 u.e.

• Electron Configuration for Octahedral complexes of metal ion having d 1 to d 10 configuration [M(H
2
O)
6
] +n .
• Only the d 4 through d 7 cases have both high-spin and low spin configuration .
Electron configurations for octahedral complexes of metal ions having from d 1 to d 10 configurations. Only the d 4 through d 7 cases have both high-spin and low-spin configurations.

Colour in Coordination Compounds

E = h n
22.5

The absorption maximum for the complex ion
[Co(NH
3
)
6
] 3+ occurs at 470 nm. What is the color of the complex and what is the crystal field splitting in kJ/mol?
Absorbs blue, will appear orange.

= h n
= hc

=
(6.63 x 10 -34 J s) x (3.00 x 10 8 m s -1 )
470 x 10 -9 m
= 4.23 x 10 -19 J

(kJ/mol) = 4.23 x 10 -19 J/atom x 6.022 x 10 23 atoms/mol
= 255 kJ/mol
22.5

3+
[CoF
6
]
3+
Red Green
600, 420 Yellow, violet Dark green [Co(C
2
O
4
)
3
] 3+
[Co(H
2
O)
6
] 3+
[Co(NH
3
)
6
] 3+
[Co(en)
3
] 3+
[Co(CN)
6
] 3+
600, 400
475, 340
470, 340
310
Yellow, violet
Blue, violet
Blue, ultraviolet Yellow-orange
Ultraviolet
Blue-green
Yellow-orange
Pale Yellow
The complex with fluoride ion, [CoF
6
] 3+ , is high spin and has one absorption band.
The other complexes are low spin and have two absorption bands. In all but one case, one of these absorptionsis in the visible region of the spectrum. The wavelengths refer to the center of that absorption band.

650
800
Artist color wheel showing the colors which are complementary to one another and the wavelength range of each color.
400
430
580
560
490

[Fe(H
2
O)
6
] 3+
[Co(H
2
O)
6
[Ni(H
] 2+
2
O)
6
] 2+
[Cu(H
2
O)
[Zn(H
6
] 2+
2
O)
6
] 2+
800
400
650
430
580
560
490