Atom Config Electrons

H 1s1 1He 1s2 2

Li 1s22s1 3Be 1s22s2 4B 1s22s22p1 5C 1s22s22p2 6N 1s22s22p3 7O 1s22s22p4 8F 1s22s22p5 9Ne 1s22s22p6 10

n = 2

n = 1

Na 1s22s22p63s1 11Mg 1s22s22p63s2 12Al 1s22s22p63s23p1 13Si 1s22s22p63s23p2 14P 1s22s22p63s23p3 15S 1s22s22p63s23p4 16Cl 1s22s22p63s23p5 17Ar 1s22s22p63s23p6 18

K 1s22s22p63s23p63d04s1 19Ca 1s22s22p63s23p63d04s2 20Sc 1s22s22p63s23p63d14s2 21Ti 1s22s22p63s23p63d24s2 22V 1s22s22p63s23p63d34s2 23Cr 1s22s22p63s23p63d54s1 24Mn 1s22s22p63s23p63d54s2 25Fe 1s22s22p63s23p63d64s2 26Co 1s22s22p63s23p63d74s2 27Ni 1s22s22p63s23p63d84s2 28Cu 1s22s22p63s23p63d104s1 29Zn 1s22s22p63s23p63d104s2 30

n = 3

3d metals(8 First transition series metals constitute the bulk of

essential microminerals to life)

An element in the periodic table characterized by having partially filled d orbitals, created by having the adjoining s orbitals filled before the d.

Definition: What is a transition element?

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.

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

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.

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

Oxalate C C

OO

O O

CH2-CH2

NH2H2N

Co3+

OO

OO

C - C

Cu2+ Ethylene diamine

CH2-CH2

NN

OOC

OOC

COO

COO

Ethylenediamine tetraacetic acid (EDTA)

..

..

.. ..

Z Z

Z Z

Z

X

X

X

X

XY

Y Y

Y

Y

dxy dyzdxz

d dX2-Y2 Z2

3d orbitals

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

Fe Ni

Co Mn

Cr

Transition metals that form octahedral complexes

Zn

Transition metals that form tetrahedral complexes

Zn Cu Co

Transition metals that form square planar and 5-coordination complexes

Cu Zn Cu

Orbital splitting

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

Insights into the properties of ligands

3d Orbitals

dz2

dx2

-y2

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.

xy xz yz x2-y2 z2

z2x2-y2

xy xz yz

o

eg

t2g

Octahedral Iron

Before splitting

After splitting

Energy difference

z2x2-y2

xy xz yz

Ti =

z2x2-y2

xy xz yz

hv

Ground state

[Ar]4s23d2 Ti(II) = [Ar]3d2 Ti(III) = [Ar]3d1

t12g

Excited state

e1g

Ti(III)

Ti2+ Ti3+

TiL

LL

L

L

L

One 3d

z2x2-y2

xy xz yz

z2x2-y2

xy xz yz

Feo [Ar]4s23d6

[Fe(H2O)6]2+

t62g

Low Spin(Highly energetic) Diamagnetic

High Spin(Low energetic) Paramagnetic

t42ge2

g

[Fe(CN)6]4-

Fe2+ [Ar]3d6

(water as a ligand)CN- as a ligand

Ionizes (loses 4s2 electrons to form Fe2+)

Fe(II)

V [Ar]4s23d3

Cr[Ar]4s13d5

Mn[Ar]4s23d5

High Spin Low Spin

No low spin possible

V(II)

Cr(II)

Mn(II)

Fe[Ar]4s23d6

Co[Ar]4s23d7

Ni[Ar]4s23d8

No low spin possible

Fe(II)

Co(II)

Ni(II)

Cu[Ar]4s13d10

Cu[Ar]4s13d9

Zn[Ar]4s23d10

Cu(I)

Cu(II)

No low spin possible

No low spin possible

No low spin possible

Zn(II)

Class Exercise: Draw the electronic configuration of octahedral [Zn(H2O)6]2+ and predict the color. Zn is [Ar]4s23d10

Solution

z2x2-y2

xy xz yz

All orbitals are filled, no color is possible

Upon ionization, Zn loses its 2, 4s electrons and becomes 3d10

Common Ligands

F- Fluoride FluoroCl- Chloride ChloroBr- Bromide BromoI- Iodide IodoCN- Cyanide CyanoNCS- Isothiocyanate IsothiocyanatoSCN- Thiocyanate ThiocyanatoOH- Hydroxide HydroxoO2- Oxide OxoONO- Nitrite NitroCO Carbon monoxide CarbonylH2O Water AquaNH3 Ammonia Ammine

Underline indicates atom bonded to metal

Ligand Name Name as ligand

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

Heme group

O=O

Interfere

Spherical-90% -helix

O2 binding to Heme

Histidine F8

Ferrous (Fe(II)

O2 binds abovethe ring planeHistidine binds below theplane of the ring

Only Fe(II) will bind O2

C O

A linear carbonmonoxide can bind with lessinterference

His E7

COLOR

garnet aquamarine

amethystruby

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 blue

Hmb 4O2

red (low spin) Hmbblue (high spin) + 4O2

Arterial blood Venous blood