Chm361-chapter 5 Coordination Compound.pdf

CHM361 CHAPTER 6: COORDINATION COMPOUND

LEARNING OUTCOMES

1)

Apply the knowledge of electron configuration of transition metals and ligand structures to name and determine the geometry, isomerism and hybridization of coordination compounds.

2)

Conduct, observe and report scientific investigation in selected areas of inorganic and coordination chemistry.

COORDINATION COMPOUNDS Compound that typically consist of a complex ion and counter ion. Most but not all, of the coordination compounds are transition metal.

metals

in

Complex ion

[Co(NH3)5Cl]Cl2

Counter ion Can be cation or anion

COMPLEX ION Species where transition metal ion is surrounded by a certain number of ligands. Complex ion

[Co(NH3)5Cl]Cl2 Metal atom

ligand

Counter ion

LIGANDS

Molecules or ions that surround the metal in a complex ions. Complex ion

[Co(NH3)5Cl]Cl2 Metal atom

Counter ion

ligand

Ligands as a Lewis base : donating electons Transition metal as a Lewis acid : accepting a pair of electron from Lewis base.

LIGANDS

Depending on the number of donor atoms present. Ligands are classified as: monodentate

:

one donor atom

bidentate

:

two donor atoms

polydentate

:

more than two donor atoms [tetradentate (4), pentadentate (5), hexadentate (6) ……..]

COORDINATION NUMBER Number of donor atoms surrounding the central metal atom in a complex ion.

Donor atoms : atom in a ligand that is bound directly to the metal atom. Complex ion

[Co(NH3)5Cl]Cl2 Metal atom

Counter ion

ligand

 Atom in ligand that bound directly to Co metal atom is N & Cl.  N & Cl are donor atom.  Number of N = 5, Number of Cl = 1  Coordination number = 6

SOME COMMON LIGANDS

NOMENCLATURE 1)

Cation is named before the anion. cation

anion

K3 [Fe(CN)6] = K+ is named first cation

anion

[Cr(NH3)3(H2O)3] Cl3 = Cr(NH3)3(H2O)3 is named first

2)

Within complex ion, ligands are named first, in alphabetical order, and metal ion is named last.

Cation & Anion (Counter Ion) CATION

FORMULA

ANION

FORMULA

ANION

FORMULA

Aluminum

Al+3

Fluoride

F-

Hypochlorite

Ammonium

NH4+

Chloride

Cl-

Nitride

Barium

Ba+2

Bromide

Br-

Carbonate

CO32-

Calcium

Ca+2

Iodide

I-

Hydrogen carbonate or Bicarbonate

HCO -

Lead(II)

Pb+2

Sulfate

SO42-

Amide

Lithium

Li+

Hydrogen sulfate

HSO4-

Chromate

CrO4 2Cr2O7 2-

OClN3-

3

NH2-

Magnesium

Mg+2

Thiosulfate

S2O32-

Dichromate

Nitronium

NO2+

Sulfite

SO32-

Iodate

IO3 -

Potassium

K+

Sulfide

S2-

Bromate

BrO3-

Sodium

Na+

Perchlorate

ClO4-

Nitrate

NO3-

Strontium

Sr+2

Chlorate

ClO3-

Nitrite

NO2-

Zinc

Zn+2

Chlorite

ClO2-

NOMENCLATURE 3) Names of ligands:  anionic ligands end with “o”.  Neutral ligands usually called by the name of the molecule.  Exception for H2O, CO, & NH3

Names of ligands: ANIONIC LIGAND LIGANDS NAMES

NEUTRAL LIGAND LIGANDS NAMES

Br-

bromo

NH3

ammine

Cl-

chloro

H2O

aqua

I-

iodo

NO

Nitrosyl

FCN-

fluoro

CO

Carbonyl

cyano

O2

dioxygen

OH-

Hydroxo

N2

dinitrogen

O2-

oxo

H2NCH2CH2NH2

ethylenediamine

SO42-

sulphato

P(C6H5)3

Triphenylphosphine

C2O42-

oxalato

C5H5N

pyridine

2CO3

carbonato -

CH COO 3

2 2-

acetato

NH

amido

NH

imido

ONO- (O-bonded) NO - (N-bonded)

nitrito

SCN- (S-bonded)

Thiocyanato

NCS- (N-bonded)

Isothiocyanato

glyN3

glycinato

2

Nitro

azido

NOMENCLATURE

4)

If more than one ligands present, use prefix.



di, tri, tetra, penta, hexa…



Prefix are ignored when alphabetizing ligands.

eg: [Co(NH3)4Cl2]+ = tetraamminedichloro 

For polydentate ligands, use prefix bis (2), tris (3), tetrakis (4)



eg: (en)2 = bis(ethylenediamine)

NOMENCLATURE 4)

Oxidation number of metal is written in roman (I, II, III) following the name of the metal. Example:

5) If

[Cr(NH3)4Cl2]+ = chromium (III)

complex ion is a cation, the metal is named same as the element. But, If complex ion is an anion, the name of the metal ends with the suffix – ate. Example : [Fe(CN)6]4- :hexacyanoferrate (II) ion

Transition Metal

Name if in Cationic Complex

Name if in Anionic Complex

Sc

Scandium

Scandate

Ti

Titanium

Titanate

V

Vanadium

Vanadate

Cr

Chromium

Chromate

Mn

Manganese

Manganate

Fe

Iron

Ferrate

Co

Cobalt

Cobaltate

Ni

Nickel

Nickelate

Cu

Copper

Cuprate

Zn

Zinc

Zincate

Pb

Lead

Plumbate

Ag

Silver

Argenate

Au

Gold /Aurum

Aurate

Sn

Tin

Stannate

Al

Aluminium

Aluminate

Pt

Platinum

Platinate

Example cation

anion

[Cr(NH3)3(H2O)3]Cl3 1)

Oxidation no of metal: Cr + 0 + 0 + (-1 x 3) = 0 Cr = +3

2)

Complex ion : triamminetriaquachromium (III)

2)

Counter ion : chloride

3)

Name: triamminetriaquachromium (III) chloride

Example cation

anion

K4[Fe(CN)6] 1)

Oxidation no of metal: (1 x 4) + Fe + (-1 x 6) = 0 Fe = +2

2)

Complex ion : hexacyanoferrate (II)

3)

Counter ion : potassium

4)

Name: potassium hexacyanoferrate (II)

EXERCISE 1

Write the systematic name for the following: 1.

K2[FeCl4]

2.

[Pd(NH3)3Cl]+

3.

K4[Fe(CN)6]

4.

[Co(en)2Cl2]NO3

5.

(NH4)2[Pt(NH3)2Br4]

6.

[Cr(en)2(SCN)2]+

EXERCISE 2

Write formula name for the following: 1)

Tetraaquodibromocobalt(III) nitrate

2)

Tetracyanonickelate(II) ion

3)

Tetraammineaquabromocobalt(III) bromide

4)

Hexamminechromium(III) tetrachlorocuprate(II)

5)

Pentaaquacyanoiron(III) chloride

6)

Tetrahydroxocuprate(II) ion

STRUCTURE 

 

Coordination number will determine the structure of the compounds. coordination COORDINATION NUMBER

STRUCTURE

2

Linear

4

 Tetrahedral  Square planar

6

Octahedral

Four-coordinate platinum(II) complexes are always square planar. Whereas 4-coordinate cobalt(II) complexes are tetrahedral.

STRUCTURE d electron

Ligand

Structure

d7, d8, d9

Strong

Square planar

d7, d8, d9

Weak

Tetrahedral

d4

Strong

Tetrahedral

d4

Weak

Square planar

2nd & 3rd period Cu+

Square planar Irrespective types of ligands

Tetrahedral

Cu2+

Square planar

Mn2+

Tetrahedral

6-co-ordinated complex ions



Four of the ligands are in one plane, with the fifth one above the plane, and the sixth one below the plane.

4-co-ordinated complex ions

Tetrahedral arrangement

Square Planar arrangement

ISOMERISM 

Compounds with same formula but different atom arrangement.



There is more than one way to arrange ligands around the central atom.



Will have distinctly different physical and chemical properties.

ISOMER

Compounds with different connections between atoms

HYDRATE

STRUCTURAL

IONIZATION

LINKAGE

Compounds with same connectivity but different spatial arrangement

COORDINATION SPHERE

STREOISOMER

GEOMETRIC

OPTICAL

STRUCTURAL ISOMER (HYDRATE) Coordination compound that have the same composition but differ number of water molecules present as ligands.

in the

STRUCTURAL ISOMER (IONIZATION) Two coordination compounds in which two different anions switch positions between the inner and outer coordination sphere.

STRUCTURAL ISOMER (LINKAGE) Coordination compound having the same complex ion structure but differ in donor atom attachment.

[Co(NH3)5(NO2)]Cl

[Co(NH3)5(ONO)]Cl

STRUCTURAL ISOMER (COORDINATION) Coordination compound having the same composition but occur through exchange of ligands between complex ion in the same coordination compound [Co(NH3)6] [Cr(C2O4)3]

&

[Co(C2O4)3] [Cr(NH3)6]

STREOISOMER (GEOMETRIC) 

Streoisomers that cannot be converted without breaking a chemical bond.



Comes in pair.



Use term cis & trans.



Cis = two groups of atoms are adjacent to each other.



Trans = two groups of atoms are on opposite side to each other.



Only square planar (4) & octahedral (6) have geometrical isomer.



Generally have different colors, melting points, & chemical reactivities.

STREOISOMER (GEOMETRIC)



ammonias and the chlorines are next door to each other.



ammonias and so are the chlorines are arranged opposite each other.

STREOISOMER (GEOMETRIC)



chlorines are next door to each other.



chlorines are arranged opposite each other.

STREOISOMER (OPTICAL) 

Coordination compounds that are mirror images & non-superimposable to each other.



Comes in pair.



Have identical physical & chemical properties.



Chiral molecule = nonsuperimposable with their mirror images.



Optical isomers are possible for both tetrahedral and octahedral complexes, but not square planar.



Only cis isomer can have optical isomer.

TRANS ISOMER SUPERIMPOSE

CIS ISOMER NON SUPERIMPOSE

NON SUPERIMPOSE

CIS ISOMER NON SUPERIMPOSE

TRANS ISOMER SUPERIMPOSE

BONDING IN COMPLEX ION 

Metal to ligand bonds formed when a filled orbital of a ligands overlaps with an empty hybrid orbital on the central metal atom.



The molecular geometry is predicted using VSEPR.

BONDING IN COMPLEX ION 

Strong field ligand will caused the d electron to be paired up.



Weak field ligand will not caused the d electron to be paired up. I-
WEAK LIGAND

CN-

I-

-

NO2

Br-

CO

Cl-

en (ethylenediamine)

F-

NH3

C2O4

-2

H2O OH-

VBT: sp3 - outer shell hybridization Four Coordinate Compounds (Tetrahedral Complexes) [CoCl4]2-

Consider:

Oxidation no of metal : Co + (-1 x 4) = -2 Co = +2 Co = [Ar] 3d7 4s2 Co2+ = [Ar] 3d7

Electron configuration :

Since Cl is a weak field ligand, 3d electrons are not paired up.

Co2+ = [Ar]

↑ ↓ ↑↓

↑

↑

↑

3d

X

X X X

4s

4p

hybridization

[Ar]

↑ ↓ ↑↓

↑

3d

↑

↑

↑↓

↑ ↓ ↑↓

sp3

↑↓

Since there are 4 ligands surround the central metal atom.

VBT: dsp2 - inner shell hybridization Four Coordinate Compounds (Square Planar Complexes) Consider:

[Ni(CN)4]2-

Oxidation no of metal : Ni + (-1 x 4) = -2 Ni = +2 Electron configuration :

Ni2+ = [Ar]

Ni = [Ar] 3d8 4s2 Ni2+ = [Ar] 3d8

↑ ↓ ↑↓

↑↓

↑

↑

↑↓

↑↓

4p

4s

3d

Since CN- is a strong field ligand, it caused the pairing of unpaired 3d electron.

[Ar]

↑ ↓

↑↓

3d

X

X

X X

4s

4p

hybridization

[Ar]

↑ ↓ ↑ ↓ ↑↓

3d

↑↓

↑↓

↑ ↓ ↑↓

dsp2

↑↓

Since there are 4 ligands surround the central metal atom

VBT: sp3d2 - outer shell hybridization Six Coordinate Compounds (Octahedral Complexes) [Fe(H2O)6] 3+

Consider:

Oxidation no of metal : Fe + (0 x 6) = +3 Fe = +3 Fe = [Ar] 3d6 4s2 Fe3+ = [Ar] 3d5

Electron configuration :

Since H2O is a weak field ligand, 3d electrons are not paired up.

Fe3+ = [Ar]

↑

↑

↑

↑

↑

3d

Since there are 6 ligands surround the central metal atom.

X

X X X

4s

4p

hybridization

[Ar]

↑

↑

↑

3d

↑

↑

↑↓

↑↓

↑↓

↑ ↓ ↑ ↓ ↑↓

sp3d2

X X 4d

VBT: d2sp3 - inner shell hybridization Six Coordinate Compounds (Octahedral Complexes) Consider:

[FeCN6]3-

Oxidation no of metal : Fe + (-1 x 6) = -3 Ni = +3 Electron configuration :

Fe3+ = [Ar]

↑

Fe = [Ar] 3d6 4s2 Fe3+ = [Ar] 3d5 ↑

↑↓

↑

↑

↑↓

X X

↑

4p

4s

3d

Since CN- is a strong field ligand, it caused the pairing of unpaired 3d electron.

[Ar]

↑

3d

X

X X X

4s

4p

Since there are 6 ligands surround the central metal atom

hybridization

[Ar]

↑↓

↑ ↓

3d

↑

↑↓

↑ ↓ ↑↓

↑↓

d2sp3

↑↓

↑↓

CRYSTAL FIELD THEORY



Explains that the bonding on complex ion purely in term of electrostatic forces.



Two types of electrostatic interaction involve.

1.

Attraction between the positive metal ion & negatively charged ligands.

2.

Electrostatic repulsion between the lone pair on the ligands & the electron in the d orbitals of the metals.

CRYSTAL FIELD THEORY (OCTAHEDRAL)

CRYSTAL FIELD THEORY (OCTAHEDRAL) 

Central metal atom surrounded by six electron lone pair (ligands).



So all five d orbitals experience electrostatic repulsion.



The magnitude of repulsion depends on the orientation of d orbital involved.



dx2-y2 & dz2 : the lobes point toward where the lone pair located. Thus it would experience greater lone pair-d orbital electron repulsion.



They will be higher in energy.



Thus, 5d orbitals are split between two sets of energy level.

• t2g set of orbitals (dxz, dyz, dxy) – lower in energy • eg set of orbitals (dz2 , dx2-y2 ) – higher in energy

CRYSTAL FIELD THEORY (OCTAHEDRAL) High energy eg

Crystal field splitting

d-orbitals

Lower energy t2g

•∆ = energy difference between two sets of d orbitals in a metal atom when

ligands are present. •Has direct effect on color & magnetic properties of complex ion.

CRYSTAL FIELD THEORY (TETRAHEDRAL)

CRYSTAL FIELD THEORY (TETRAHEDRAL) Central metal atom surrounded by four electron lone pair (ligands). The d orbitals of tetrahedral complexes also split into two groups.

the dxy, dyz, and dxz orbital point in the direction of the ligands. They will be higher in energy than the degenerate orbitals of the free metal atom or ion. The dz² and dx² -y² orbitals point between the ligands thus are lower in energy. Thus, 5d orbitals are split between two sets of energy level. • t2g set of orbitals (dxz, dyz, dxy) – higher in energy • eg set of orbitals (dz2 , dx2-y2 ) – lower in energy

CRYSTAL FIELD THEORY (TETRAHEDRAL) High energy

eg

d-orbitals

t2g Lower energy

CRYSTAL FIELD THEORY (SQUARE PLANAR) there are four ligands as well. the difference is that the electrons of the ligands are only attracted to the plane. There are four different energy levels for the square planar.

Tips!!!!!!

d7, d8, d9

d4 Pd, Pt

Strong field ligand

Square planar

Weak field ligand

Tetrahedral

Strong field ligand

Tetrahedral

Weak field ligand

Square planar Square planar

Strong Field Ligand VS Weak Field Ligands Strong Field Ligand

Weak Field Ligand

 the electrons of the metal ion pair in the lower-energy t2g orbitals.

 the electrons will occupy all five orbitals before pairing occurs.

 can be low spin - have few unpaired electrons.

 can be high spin - have more unpaired electrons.

↑ ↓

↑ ↓

↑ ↓

t2g

Energy

Energy

∆ large

↑

↑

eg

↑ ↓

↑

eg

↑

∆ small t2g

PROBLEM:

Iron forms an essential complex in hemoglobin. For each of the two octahedral complex ions [Fe(H2O)6]2+ and [Fe(CN)6]4-, draw an orbital splitting diagram, predict the number of unpaired electrons, and identify the ion as low or high spin.

1)

Identify oxidation no of transition metal

2)

Identify type of ligands (strong or weak)

3)

Fill e in the d orbital.

[Fe(H2O)6]2+ = weak ligand

[Fe(CN)6]4-= strong ligand

Fe + (0)6 = +2 Fe = +2

Fe + (-1)6 = -4 Fe = +2 Fe26 = [Ar]

↑ ↓

↑ ↓ ↑

↑

4s

Fe26 = [Ar]

↑ ↓ ↑ ↓

↑

3d ↑

↑

↑

↑

3d

Fe2+ = [Ar]

↑ ↓

↑

↑

↑

4s ↑

↑

3d ↑

↑ ↓

↑

eg

↑

∆ small

eg Energy

Energy

↑

∆ large ↑ ↓

↑ ↓

↑ ↓

t2g

 4 unpaired e  High spin

 0 unpaired e  Low spin

t2g

COLOR Many transition metal compounds absorb visible light in a process that promotes a d electron from lower-energy d orbitals to higher-energy d orbitals. Color in transition metal complexes is due to an electron being excited from one d-orbital to a higher-energy d-orbital. These electronic transitions are called d–d transitions. A color of a substance appear when it absorb visible light at certain wavelength. color observed = complementary color of color absorbed.

If no visible light been absorb, it appear as white or colorless.

COLOR

400 nm higher energy

absorbed color

700 nm lower energy

observed color

COLOR Different complexes exhibit different colors because color of light absorbed depends on . magnitude of  depends on:

ligand (Strong or weak field ligands) -The amount of d-orbital splitting depends on the ligands. thus different ligands have different splitting energies, and different colors result.

Metal

COLOR

Low light energy

High light energy

Example: Why is an aqueous solution of Ni(NH3)6 2+ deep blue while an aqueous solution of Ni(H2O)6 2+ is green.

Answer:  



 



Ni(NH3)62+ contain stronger ligand. Therefore will have larger ∆. Large ∆ will absorb light with higher energy and shorter wavelength. Ni(NH3)62+ are blue because the compound absorbs higher-energy (yellow) light. Ni(H2O)6 2+contain weaker ligand. Therefore will have smaller ∆. Small ∆ will absorb light with lower energy and longer wavelength. Ni(NH3)62+ are green because the compound absorbs lower-energy (red) light.

MAGNETISM 

Have to refer to the VBT & CFT



Low-spin complexes contain more paired electrons so, are more often

diamagnetic or weakly paramagnetic. Likewise, high-spin complexes usually contain more unpaired electrons thus, are often paramagnetic.

↑ ↓

↑ ↓

↑ ↓

diamagnetic

Energy

∆ large

↑

↑

eg Energy



↑ ↓

↑

eg

↑

t2g

∆ small t2g

paramagnetic

Answer For Exercise

Answers: Answer:

1.

[Co(H2O)4Br2]NO3

Triamminechloropalladium((II) ion

2.

[Ni(CN)4]2-

3.

Potassium hexacyanoferrate(II)

3.

[Co(NH3)4(H2O)Br] Br2

4.

Dichlorobis(ethylenediammine)cobalt(III) nitrate

4.

[Cr(NH3)6]2 [CuCl4]3

5.

Ammonium diamminetetrabromoplatinate(II)

5.

[Fe(H2O)5CN]Cl2

6.

Bis(ethylenediammine)dithiocyanatochromium(III) ion

6.

[Cu(OH)4]2-

1.

Potassium tetrachloroferrate(II)

2.