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Transition Metal Chemistry and Coordination Compounds
Lecture 18-20
Harminder Singh
The Transition Metals
Harminder Singh
Harminder Singh
Harminder Singh
Oxidation States of the 1st Row Transition Metals(most stable oxidation numbers are shown in red)
Harminder Singh
Ionization Energies for the 1st Row Transition Metals
Harminder Singh
Aqueous oxoanions of transition elements
Mn(II) Mn(VI) Mn(VII)
V(V)Cr(VI)
Mn(VII)
One of the most characteristic chemical properties of these elements is the occurrence of multiple oxidation states.
Harminder Singh
Effects of the metal oxidation state and of ligand identity on color
[V(H2O)6]2+ [V(H2O)6]3+
[Cr(NH3)6]3+ [Cr(NH3)5Cl ]2+
Harminder Singh
Scandium Titanium Vanadium
Chromium Manganese Iron
Cobalt Nickel CopperHarminder Singh
Chemistry of Iron and Copper
•Iron ore- Magnetite Fe3O4
•6.2% in earth’s crust after AlHaematite-Fe2O3
Siderite-FeCO3
•Prepration in Blast Furnace•Iron react with HCl to give H2 Conc. Sulfuric and nitric acid renders the metal passive by forming a thin layer of Fe3 O4
•some imp. Compounds: in +2 and +3 FeO (black), FeSO4.7H2O (green), FeCl2 (Yellow), FeS (Black) etc.
•Copper ore- Chalcopyrite CuFeS2
•Rare element 6.8 x 10-3 %•Obtained by roasting and can be purified by electrolysis.•After silver, Cu has the highest electrical conductivity and is a good thermal conductor.•Used in alloys, cables, plumbing and coins.•It reacts only with hot conc. Sulfuric and nitric acids.•+1 and +2 componds in which +1 are diamagmetic.•CuO (Black), CuSO4.5H2O (blue) and CuS (black)
Harminder Singh
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
• ••• • •
H
N
HH• •
••Cl• •
••
-
••C O••
Harminder Singh
Coordination Compounds
The atom in a ligand that is bound directly to the metal atom is the donor atom.
H
O
H
• ••• • •
H
N
HH
The number of donor atoms surrounding the central metal atom in a complex ion is the coordination number.
Ligands with:
one donor atom monodentate
two donor atoms bidentate
three or more donor atoms polydentate
H2O, NH3, Cl-
ethylenediamine
EDTA
Harminder Singh
Coordination Compounds
H2N CH2 CH2 NH2
• • • •
bidentate ligand polydentate ligand(EDTA)
Bidentate and polydentate ligands are called chelating agentsHarminder Singh
Harminder Singh
EDTA Complex of Lead
Harminder Singh
What are the oxidation numbers of the metals in K[Au(OH)4] and [Cr(NH3)6](NO3)3 ?
OH- has charge of -1
K+ has charge of +1
? Au + 1 + 4x(-1) = 0
Au = +3
NO3- has charge of -1
NH3 has no charge
? Cr + 6x(0) + 3x(-1) = 0
Cr = +3
Harminder Singh
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 H2O (aqua), CO (carbonyl), and NH3 (ammine).
• When several ligands of a particular kind are present, the Greek prefixes di-, tri-, tetra-, penta-, and hexa- are 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. Harminder Singh
Harminder Singh
What is the systematic name of [Cr(H2O)4Cl2]Cl ?
tetraaquodichlorochromium(III) chloride
Write the formula of tris(ethylenediamine)cobalt(II) sulfate
[Co(en)3]SO4
Harminder Singh
What is the systematic name of Na[AuF4] ?
Sodium tetrafluoroaurate(III)
Potassium hexacyanoferrate(III)
What is the systematic name of [Cr(en)3]Cl 3?
Tetracarbonylnickel(0)
What is the systematic name of K3[Fe(CN)6] ?
What is the systematic name of [Ni(CO)4] ?
tris(ethylenediamine)chromium(III) chloride
Harminder Singh
Transition Metal Chemistry and Coordination Compounds
Lecture 21-22
Mr. Harminder Singh
Harminder Singh
Structure of Coordination Compounds
Coordination number Structure
2
4
6
Linear
Tetrahedral or Square planar
Octahedral
Harminder Singh
Structure of Coordination Compounds
Stereoisomers are compounds that are made up of the same types and numbers of atoms bonded together in the same sequence but with different spatial arrangements.
a. Geometric isomers b. Optical isomers
Geometric isomers are stereoisomers that cannot be interconverted without breaking a chemical bond.
•They usually come in pairs (cis & trans).
•They have quite different colors, melting points, dipole moments and chemical reactivities.
cis-[Pt(NH3)2Cl2] trans-[Pt(NH3)2Cl2]
Harminder Singh
Structure of Coordination Compounds
cis-[Co(NH3)4Cl2] trans-[Co(NH3)4Cl2]
Are these additional geometric isomers of [Co(NH3)4Cl2]?
cis
trans
Harminder Singh
Structure of Coordination CompoundsOptical isomers are nonsuperimposable mirror images.
cis-[Co(en)2Cl2] trans-[Co(en)2Cl2]
optical isomers
chiral
not optical isomers
achiral
Harminder Singh
Structure of Coordination Compounds
Chiral molecules are optically active.
Dextrorotatory (d) & levorotory (l) (collectivelly enantiomers: equimolar mixture is called racemic mixture , the net rotation is zero.
Achiral molecules are optically in active
Harminder Singh
Bonding in Coordination compounds: Old theories: Werner and Sidgwick
New theories: VBT, CFT, LFT, MOT
CRYSTAL FIELD THEORY
Accounts for color and magnetic properties
Harminder Singh
Crystal field splitting in Octahedral complexes
All equal in energy in the absence of ligands!
Harminder Singh
Crystal-Field Theory• Model explaining bonding for transition Model explaining bonding for transition
metal complexesmetal complexes– • Originally developed to explain properties for
crystalline material– • Basic idea:– Electrostatic interaction between lone-pair
electrons result in coordination.
Harminder Singh
Energetics• CFT - Electrostatic between CFT - Electrostatic between
metal ion and donor atommetal ion and donor atom
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.
i
ii
iii
iv
Harminder Singh
Bonding in Coordination Compounds
Isolatedtransition metal
atom
Bondedtransition metal
atom
Crystal field splitting ( ) is the energy difference between two sets of d orbitals in a metal atom when ligands are present.
The magnitude of depends on the metal and the nature of the ligands; it has a direct effect on the color and magnetic properties of complex ions.
Harminder Singh
d-Orbitals and Ligand Interaction(Octahedral Field)
•Ligands approach metal
d-orbitals not pointing directly at axis are least affected (stabilized) by electrostatic interaction
d-orbitals pointing directly at axis are affected most by electrostatic interaction
Harminder Singh
Ligand-Metal Interaction•Crystal Field Theory - Describes bonding in Metal Complexes• Basic Assumption in CFT:• Electrostatic interaction between ligand and metal
• d-orbitals align along the d-orbitals align along the octahedral axis will be affected the octahedral axis will be affected the most.most.
• More directly the ligand attacks the More directly the ligand attacks the metal orbital, the higher the the metal orbital, the higher the the energy of the d-orbital.energy of the d-orbital.
• In an octahedral field the In an octahedral field the degeneracy of the five d-orbitals is degeneracy of the five d-orbitals is liftedlifted
Harminder Singh
Splitting of the d-Orbitals• Octahedral field Splitting Pattern:•
The energy gap is The energy gap is referred to as referred to as (10 Dq) (10 Dq) , the , the crystal field crystal field splitting energy.splitting energy.
The dThe dzz22 and d and dxx
22yy
22 orbitals lie on the same axes as negative charges.orbitals lie on the same axes as negative charges.
Therefore, there is a large, unfavorable interaction between ligand (-) orbitals.Therefore, there is a large, unfavorable interaction between ligand (-) orbitals.
These orbitals form the degenerate high energy pair of energy levels.These orbitals form the degenerate high energy pair of energy levels.
The dThe dxyxy , d , dyxyx and d and dxzxz orbitals bisect the negative charges. orbitals bisect the negative charges.
Therefore, there is a smaller repulsion between ligand & metal for these orbitals.Therefore, there is a smaller repulsion between ligand & metal for these orbitals.
These orbitals form the degenerate low energy set of energy levels.These orbitals form the degenerate low energy set of energy levels.
Harminder Singh
Color of a Substance
Harminder Singh
Absorption and Reflection
If the sample If the sample absorbsabsorbsall but all but orangeorange, , thethesample appears sample appears orange.orange.
Further, we also perceive orange Further, we also perceive orange color when visible light of all colors color when visible light of all colors except except blue blue strikes our eyes. In a strikes our eyes. In a complementary fashion, if the complementary fashion, if the sample absorbed only orange, it sample absorbed only orange, it would appear blue; blue and orange would appear blue; blue and orange are said to be complementary are said to be complementary colors.colors.
750
430
650 580
560
490
400
Harminder Singh
Light absorption Properties of Metal Complexes
•Recording the absorption SpectrumRecording the absorption Spectrum
Harminder Singh
Colour in Coordination Compounds
E = h
Harminder Singh
Harminder Singh
The absorption maximum for the complex ion [Co(NH3)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.
= hhc=
(6.63 x 10-34 J s) x (3.00 x 108 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 1023 atoms/mol
= 255 kJ/mol
Harminder Singh
Complex Influence on Color•Compounds of Transition metal complexes solution.Compounds of Transition metal complexes solution.
[Fe(H2O)6]3+
[Co(H2O)6]2+
[Ni(H2O)6]2+
[Cu(H2O)6]2+
[Zn(H2O)6]2+
800
430
650 580
560
490
400
Harminder Singh
Color Absorption of Co3+ Complexes
• The Colors of Some Complexes of the CoThe Colors of Some Complexes of the Co3+ 3+ IonIon
The complex with fluoride ion, [CoFThe complex with fluoride ion, [CoF66]]3+3+ , is high spin and has one absorption band. , is high spin and has one absorption band.
The other complexes are low spin and have two absorption bands. In all but one 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 case, one of these absorptionsis in the visible region of the spectrum. The wavelengths refer to the center of that absorption band.wavelengths refer to the center of that absorption band.
Complex IonComplex Ion Wavelength of Wavelength of Color of Light Color of Light Color of ComplexColor of Complex light absorbed light absorbed Absorbed Absorbed
[CoF[CoF66] ] 3+3+ 700 (nm)700 (nm) RedRed GreenGreen
[Co(C[Co(C22OO44))33] ] 3+3+ 600, 420600, 420 Yellow, violetYellow, violet Dark greenDark green
[Co(H[Co(H22O)O)66] ] 3+3+ 600, 400600, 400 Yellow, violetYellow, violet Blue-greenBlue-green
[Co(NH[Co(NH33))66] ] 3+3+ 475, 340475, 340 Blue, violetBlue, violet Yellow-orangeYellow-orange
[Co(en)[Co(en)33] ] 3+3+ 470, 340470, 340 Blue, ultraviolet Blue, ultraviolet Yellow-orangeYellow-orange
[Co(CN)[Co(CN)66] ] 3+3+ 310310 Ultraviolet Ultraviolet Pale YellowPale Yellow
Harminder Singh
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- < H2O < SCN- < NH3 < en < NO2- < CN- < CO
WEAKER FIELD STRONGER FIELD
LARGER SMALLER
LONGER SHORTER
Harminder Singh
o
3/5 o
2/5 o
o is the crystal field splitting
t2g
eg
E(t2g) = -0.4o x 3 = -1.2o
E(eg) = +0.6o x 2 = +1.2o
Splitting of d orbitals in an octahedral field
Harminder Singh
The magnitude of the splitting(ligand effect)
Strongfield
Weakfield
The spectrochemical series
CO, CN- > phen > NO2- > en > NH3 > NCS- > H2O > F- > RCO2
- > OH- > Cl- > Br- > I-
Harminder Singh
The magnitude of the splitting(metal ion effect)
Strongfield
Weakfield
increases with increasing formal charge on the metal ion
increases on going down the periodic table
Harminder Singh
Electron Configuration in Octahedral Field
• Electron configuration of metal Electron configuration of metal ion:ion:
• s-electrons are lost first. s-electrons are lost first. • TiTi3+3+ is a d is a d11, V, V3+3+ is d is d22 , and , and
CrCr3+3+ is d is d33 • Hund's rule:Hund's rule:• First three electrons are in First three electrons are in
separate d orbitals with their separate d orbitals with their spins parallel.spins parallel.
• Fourth e- has choice:Fourth e- has choice:• Higher orbital if Higher orbital if is small; is small;
High spinHigh spin• Lower orbital if Lower orbital if is large: is large:
Low spin.Low spin.• Weak field ligandsWeak field ligands• Small Small , High spin complex , High spin complex• Strong field LigandsStrong field Ligands• Large Large , Low spin complex , Low spin complex
Harminder Singh
d1 d2
d3 d4
Placing electrons in d orbitalsStrong field Weak field Strong field Weak field
Harminder Singh
d4
Strong field =Low spin
(2 unpaired)
Weak field =High spin
(4 unpaired)
< o > o
When the 4th electron is assigned it will either go into the higher energy eg orbital at an energy cost of 0 or be paired at an energy cost of , the pairing energy.
Harminder Singh
Pairing Energy,
The pairing energy, , is made up of two parts.
1) Coulombic repulsion energy caused by having two electrons in same orbital. Destabilizing energy contribution of 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 e for each pair having same spin and same energy
= sum of all c and e interactions
Harminder Singh
Placing electrons in d orbitals
1 u.e. 5 u.e.
d5
0 u.e. 4 u.e.
d6
1 u.e. 3 u.e.
d7
2 u.e. 2 u.e.
d8
1 u.e. 1 u.e.
d9
0 u.e. 0 u.e.
d10
Harminder Singh
To sum up•Electron Configuration for Octahedral complexes of metal ion Electron Configuration for Octahedral complexes of metal ion having dhaving d11 to d to d1010 configuration [M(H configuration [M(H22O)O)66]]+n+n. . •Only the dOnly the d44 through d through d77 cases have both high-spin and low spin configuration cases have both high-spin and low spin configuration..
Electron configurations for octahedral complexes of metal ions having from d1 to d10 configurations. Only the d4 through d7 cases have both high-spin and low-spin configurations.
Harminder Singh
Harminder Singh
Bonding in Coordination Compounds
Harminder Singh
Harminder Singh
Splitting of d orbitals in a tetrahedral field
t2
e
t
t = 4/9o
Always weak field (high spin)
Harminder Singh
Bonding in Coordination Compounds
Harminder Singh
A crystal-field aproach: from octahedral to tetrahedral
LM
L L
L
L
L
LM
L L
L
Less repulsions along the axeswhere ligands are missing
Harminder Singh
Octahedral, Tetrahedral & Square Planar
•CF Splitting pattern for CF Splitting pattern for various molecular geometryvarious molecular geometry
M
dz2dx2-y2
dxzdxydyz
M
dx2-y2 dz2
dxzdxy dyz
M
dxz
dz2
dx2-y2
dxy
dyz
OctahedralOctahedral
TetrahedralTetrahedral Square planarSquare planar
Pairing energy Vs. Weak field < Pe
Strong field > Pe
Pairing energy Vs. Weak field < Pe
Strong field > Pe
Small High SpinSmall High SpinMostly d8
(Majority Low spin)
Strong field ligands
i.e., Pd2+, Pt2+, Ir+, Au3+
Mostly d8
(Majority Low spin)
Strong field ligands
i.e., Pd2+, Pt2+, Ir+, Au3+
Harminder Singh
Harminder Singh
Harminder Singh
Harminder Singh
Harminder Singh
Harminder Singh
Harminder Singh
Harminder Singh
Applications of coordination compounds
• Colour of transition metal complexes
• Number of unpaired electrons and magnetic properties
• Coordination compounds in living systems
• Coordination compounds in medicine
Harminder Singh
Harminder Singh
Harminder Singh
Chemistry In Action: Coordination Compounds in Living Systems Hemoglobin
Harminder Singh
Chlorophyll a & b•Chl a has a methyl group •Chl b has a carbonyl group
Porphyrin ring delocalized e-
Phytol tailHarminder Singh
Harminder Singh
Chemistry In Action: Cisplatin – The Anticancer Drug
Harminder Singh