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Electrons
1s1
1s2
1
2
1s22s1
1s22s2
1s22s22p1
1s22s22p2
1s22s22p3
1s22s22p4
1s22s22p5
1s22s22p6
3
4
5
6
7
8
9
10
n=1
H
He
n=2
Li
Be
B
C
N
O
F
Ne
n=3
Na
Mg
Al
Si
P
S
Cl
Ar
1s22s22p63s1
1s22s22p63s2
1s22s22p63s23p1
1s22s22p63s23p2
1s22s22p63s23p3
1s22s22p63s23p4
1s22s22p63s23p5
1s22s22p63s23p6
11
12
13
14
15
16
17
18
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
1s22s22p63s23p63d04s1
1s22s22p63s23p63d04s2
1s22s22p63s23p63d14s2
1s22s22p63s23p63d24s2
1s22s22p63s23p63d34s2
1s22s22p63s23p63d54s1
1s22s22p63s23p63d54s2
1s22s22p63s23p63d64s2
1s22s22p63s23p63d74s2
1s22s22p63s23p63d84s2
1s22s22p63s23p63d104s1
1s22s22p63s23p63d104s2
19
20
21
22
23
24
25
26
27
28
29
30
3d metals
(8 First transition series metals constitute the bulk of
essential microminerals to life)
Definition: What is a transition element?
An element in the periodic table characterized by
having partially filled d orbitals, created by having the
adjoining s orbitals filled before the d.
Properties:
The 3d orbitals are split by ligands resulting in
orbitals with higher and lower energy states that
supersede the 5 degenerate orbitals. Characterized
by Multi-valence states
Importance:
Resulting complexes take on specific geometrical
shapes that relate to binding, color formation, and
functionality
Important Definitions
Ligand: (Lat: that which ties) A ligand is a charged or neutral
molecule that binds to a metal through either coordinate covalent or
ionic bonds. Water is a neutral ligand, CN is a charged ligand.
Chelator: (Lat. Claw) A chelator is an organic compound that is
capable of wrapping around a metal in multiple bonds thus competing
with other molecules (e.g., proteins, nucleic acids) for the metal.
Multidentate: ( Lat: dentate, teeth) Referring to a molecule that has
multiple binding groups within the same chain capable of forming
multiple bonds with the metal ion, e.g., bidentate (2) tridentate (3) etc.
Orbital Splitting: A process by which d orbitals are split into high
and low energy levels in response to the binding of a ligand.
Coordination Number: Referring to the number of ligands that attach
Coordinate covalent: A type of bond created when a ligand provides
the pair of bonding electrons (Lewis base) to share with the metal.
Multi-dentate Ligands
O
Oxalate
O
CH2-CH2
CC
NH2
H 2N
O
O
Co3+
Cu2+
Ethylene diamine
O
O
O
C-C
OOC
OOC
CH2-CH2
.. N
N ..
COO
COO
Ethylenediamine tetraacetic acid
(EDTA)
O
3d orbitals
Z
Z
Z
Z
X
Y
Y
X
dxy
Z
Y
X
dxz
dyz
X
dX2-Y2
Y
X
Y
dZ2
Octahedral Complex
3 of most common complexes with metal ions
are:
Octahedral (most common)
An 8 sided figure featuring 6 ligands, 4 in one plane
and two above and below the plane.
Square planar
A 4 sided figure with 4 ligands all in the same plane
Tetrahedral
4 ligands vectorially positioned to have minimum
interaction
Transition metals that form octahedral complexes
Fe
Zn
Ni
Co
Cr
Mn
Transition metals that form tetrahedral complexes
Zn
Cu
Co
Transition metals that form square planar and 5-coordination complexes
Cu
Zn
Cu
Orbital splitting
Insights into the properties of ligands
Take Home: By altering the energy state of electrons in
a metal ion, ligands are capable of determining valence,
reactivity, and even the color of the complex
3d Orbitals
dx2-y2
dz2
Octahedral Iron
Fe forms an octahedral (8 sided figure, six
ligands) complex by having its 5, 3d orbitals
split into two 2 new orbitals, eg and t2g.
eg
Before splitting
x2-y2
z2
o Energy
difference
xy
xz
yz x2-y2 z2
t2g
xy
xz
yz
After splitting
Ti = [Ar]4s23d2
x2-y2
Ti(II) = [Ar]3d2
Ti(III) = [Ar]3d1
Ti2+
Ti3+
hv
z2
x2-y2
z2
Ti(III)
One 3d
xy
xz
Ground state
t12g
L
L
L
Ti
L
L
L
yz
xy
xz
yz
Excited state
e1g
Feo [Ar]4s23d6
Ionizes (loses 4s2 electrons to form Fe2+)
CN- as a ligand
Fe2+ [Ar]3d6
(water as a ligand)
[Fe(CN)6]4-
x2-y2
xy
Fe(II)
z2
xz
t62g
Low Spin
(Highly energetic)
Diamagnetic
[Fe(H2O)6]2+
yz
x2-y2
xy
z2
xz
yz
t42ge2g
High Spin
(Low energetic)
Paramagnetic
V
[Ar]4s23d3
No low spin possible
V(II)
Cr
[Ar]4s13d5
Cr(II)
Mn
[Ar]4s23d5
Mn(II)
High Spin
Low Spin
Fe
[Ar]4s23d6
Fe(II)
Co
[Ar]4s23d7
Co(II)
Ni
[Ar]4s23d8
Ni(II)
No low spin possible
Cu
[Ar]4s13d10
No low spin possible
Cu(I)
Cu
[Ar]4s13d9
Cu(II)
Zn
[Ar]4s23d10
Zn(II)
No low spin possible
No low spin possible
Class Exercise: Draw the electronic configuration of
octahedral [Zn(H2O)6]2+ and predict the color. Zn is
[Ar]4s23d10
Solution
Upon ionization, Zn loses its 2, 4s electrons and becomes 3d10
x2-y2
xy
z2
xz
All orbitals are filled,
no color is possible
yz
Common Ligands
Ligand Name
FClBrICNNCSSCNOHO2ONOCO
H 2O
NH3
Fluoride
Chloride
Bromide
Iodide
Cyanide
Isothiocyanate
Thiocyanate
Hydroxide
Oxide
Nitrite
Carbon monoxide
Water
Ammonia
Name as ligand
Fluoro
Chloro
Bromo
Iodo
Cyano
Isothiocyanato
Thiocyanato
Hydroxo
Oxo
Nitro
Carbonyl
Aqua
Ammine
Underline indicates atom bonded to metal
Ligand Strength and Numbers as a determinant
Rule: Ligands differ in the strength of their orbital splitting. The
following has been determined experimentally
Cl < F- < H2O < NH3 < NO2- < CN- < CO
Rule: Low spin complexes are created by ligands with strong
orbital splitting properties
Rule: Octahedral complexes that have 3, 4, 5, or 6 electrons in the
t2g orbital tend to be very stable (inert). All others are labile.
Biological Relevance
Myoglobin
O=O
Heme group
Spherical90% -helix
Interfere
O2 binding to Heme
His E7
C O
A linear carbon
monoxide can
bind with less
interference
O2 binds above
the ring plane
Histidine binds
below the
plane of the
ring
Only Fe(II) will bind O2
Histidine F8
Ferrous (Fe(II)
COLOR
garnet
aquamarine
ruby
amethyst
topaz
kyanite
Red Blood vs Blue Blood
O2 binding to the heme ring of hemoglobin is
coordinated to iron (II). When O2 is bound to one of
the coordinates, Fe(II) is in a low spin (high energy)
state and the light emitted is a red. Without O2 the
iron binds water resulting in high spin (low energy)
and takes on a bluish color.
 red
Hmb 4O2
red (low spin)
Arterial blood
 blue
Hmb
+ 4O2
blue (high spin)
Venous blood