chemistry and spectroscopy of the transition metalschem1/lecture notes pdfs/series 13 transition...

Chemistry and Spectroscopy of the Transition Metals

• Structure of metal complexes

• Oxidation states of metals

• Color/Spectroscopy

• Magnetic Properties

• Chelate Effects

• Electron Transfer Chemistry

Alfred Werner

Nobel Prize in Chemistry, 1913

"in recognition of his work on the linkage of atoms in molecules by which he has thrown new light on earlier investigations and opened up

new fields of research especially in inorganic chemistry”

Zurich University

Pt (NH3)2Cl2

Stereochemistry of Coordination Complexes

Pt

Cl

Cl NH3

NH3

Pt

NH3

Cl NH3

Cl

Orange-Yellow(dipole moment)(cis-platin)

Pale Yellow No dipole

Co

H3N

NH3

NH3

NH3

H3N

H3NCo

H3N

Cl

NH3

NH3

H3N

H3N

Co

H3N

NH3

Cl

Cl

H3N

H3NCo

H3N

NH3

Cl

NH3

H3N

Cl

[Cl-3] [Cl-

2]

[Cl- ] [Cl-]

[ [

[ [

] ]

] ]

Inner Sphere vs Outer Sphere Coordination

Transition Metal Chemistry• Multiple Oxidation States• Coordination Chemistry/Stereochemistry• Crystal Field Splitting: Optical and Magnetic Properties• Ligand Field Splitting: Spectrochemical Series• Distortion to Tetragonal, Square Planar• Ligand Field Stabilization Energy• Hard and Soft Acids and Bases• Chelate Effect• Stereochemical Control of Binding Affinity• Water Exchange• Electron Exchange

1s2s3s4s5s6s7s

1s2p3p4p5p6p

3d4d5d6d

4f5f

Organization of Periodic Chart

Shielding

3d orbitals are shielded and not exposed much;Outside world won’t know as much how many d e- there are

r2Ψ2

r

1s 3d 3p3s

Penetration:3s > 3p > 3d

Faraday (1830):discovered this phenomenon and determined the charge to mass ratio of ions

Transition Metals Are Foundin Several Oxidation States

M+

M+

M+M+

Charge to mass ratioof ions: currentwhich passesthrough circuitdivided by massgained on electrode. Ammeter

e-

Fe(II)Fe(III)Fe(IV)

Indicate oxidation state by Roman numerals in parentheses

Transition Metals Are Foundin Several Oxidation States

M+

M+

M+M+

Charge to mass ratioof ions: currentwhich passesthrough circuitdivided by massgained on electrode. Ammeter

e-

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

He

Ne

Ar

Kr

Xe

Rn

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Exceptions to Filling Order

23. V (4s)2(3d)3

24. Cr (4s)1(3d)5

25. Mn (4s)2(3d)5

Exceptions occur because electrons don’t like to pair up in orbitals; so the highlighted atoms have lower energy.

↑ ↑ ↑ ↑ ↑ ↑

2s 2p3s

4s 3d3p

4p

4s3d

↑↓ ↑ ↑ ↑

4s 3d ↑

higher energy

Cr(0) ground state

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

He

Ne

Ar

Kr

Xe

Rn



All Metal Ions Have dn Configurations

23. V (4s)2(3d)3

24. Cr (4s)1(3d)5

25. Mn (4s)2(3d)5

4s becomes higher than 3din all of the metal ions

↑ ↑ ↑ ↑ ↑ ↑

2s 2p3s

4s 3d3p

4p

4s3d

Cr(0) ground state

↑ ↑ ↑4s

3d

Cr(III) ground state- 3e-Cr(III) (4s)1(3d)2?NO: (3d)3 (4s)0

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

He

Ne

Ar

Kr

Xe

Rn




40. Zr (5s)2(4d)2

41. Nb (5s)1(4d)4

42. Mo (5s)1(4d)5

2s 2p3s

4s 3d3p

4p

Zr(II) (4d)2 (5s)0

↑ ↑ ↑

5s4d

Zr(0) ground state

↑ ↑ 5s

4d

Zr(II) ground state- 3e-

↑

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

He

Ne

Ar

Kr

Xe

Rn




40. Zr (5s)2(4d)2

41. Nb (5s)1(4d)4

42. Mo (5s)1(4d)5

2s 2p3s

4s 3d3p

4p

Zr(II) (4d)2 (5s)0

Nb(III) (4d)2 (5s)0

Mo(IV) (4d)2(5s)0

↑ ↑ ↑ ↑ ↑

5s 4d

Nb(0) ground state

↑ ↑ 5s

4d

Nb(III) ground state- 3e-

Cr(III)

Cr(III)

[Ni(H2O)6 ] 2+ + 6 NH3 [Ni(NH3)6 ] 2+ + 6 H2O Ni(II) d8

Green Blue-violet

Reactions of Coordination Complexes

Fe(H2O)62+ + 6 K(CN) K4[Fe(CN)6]4- + 6 H2O Fe(II) d6

Fe(H2O)63+ + 6 K(CN) K4[Fe(CN)6]3-+ 6 H2O + 2 K+ Fe(III) d5

Cu(H2O)42+ + 4 KCl K2[CuCl4]2- + 4 H2O + 2 K+ Cu(II) d9

Oxidation state stays the sameColors are very different

[Co(NH3)4Cl2]

[Co(NH3)5Cl]2+[Co(NH3)6]3+

+

Nobel Prize in Physics, 1966

Hans Bethe, Cornell

Discovery of the C/N cycle that supplies energy to brilliant stars, 1935-1938Atomic physics and collision theoryNuclear forces acting on the nucleon

Lamb shift in the H-spectrum; modern quantum electrodynamicsΠ mesons and their production by electromagnetic radiation

Crystal Field theory: 1929

Crystal Field SplittingOctahedral Complexes

d

Cr C OCO

CO

CO

C O

O C

Extra electron densityxz yz xy

z2 x2-y2

∆oNon-sphericalsymmetry

I- < Br - < Cl - < F -

Spectrochemical Series

σ Donors

xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

Yellow beryl(Heliodor) is colored by the presence of F3+ions. Beryl includes emerald , aquamarine, and lesser known varieties: goshenite(colorless), morganite(pink), Heliodor (yellow), and bixbite(red).

Red ruby. The name ruby comes from the Latin "Rubrum" meaning red. The ruby is in the Corundum group, along with the sapphire. The brightest red and thus most valuable rubies are usually from Burma. Violet

Green emerald. The mineral is transparent emerald, the green variety of Beryl on calcite matrix. 2.5 x 2.5 cm. Coscuez, Boyacá, Colombia

Cr(III) in Al2O3

Cr(III) in Be2Al2Si6Ol8

beryllium aluminum silicate Be2Al2Si6Ol8

Colors of Minerals/Gemstones

Spectrochemical Series

Mn2+ < Ni2+ < Rh3+ < Co2+ < Fe2+ < Fe3+ < Cr3+

< Co3+ < Ir3+ < Pt4+

xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

∆o:

I- < Br - < Cl - < F - < OH - < H2O < NH3 < CN - <CO

Magnetic Properties ofOctahedral Complexes

xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d1



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d2



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d3



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d4



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d5



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d6



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d7



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d8



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d9



xz yz xy

z2 x2-y2

∆o

xz yz xy

z2 x2-y2

∆o

High Spin Low Spin

d10

Crystal Field Theory For Tetrahedral Complexes

Crystal Field SplittingTetrahedral Complexes

d

xz yz xy

z2 x2-y2

∆t

∆t= -4/9 ∆o


dxz yz xy

z2 x2-y2

∆o

z2 x2-y2


d

z2 x2-y2

xz yz xy

z2 x2-y2

∆t

xz

yzxy

xz yz xy

z2 x2-y2

∆o

xz

yzxy

xz yz xy

z2 x2-y2

∆t

Crystal Field SplittingTetrahedral Complexes

d

xz yz xy

z2 x2-y2

∆t

No low spin tetrahedral complexes

∆t= -4/9 ∆o

Transition Metal Chemistry• Multiple Oxidation States• Coordination Chemistry/Stereochemistry• Crystal Field Splitting: Optical and Magnetic Properties• Ligand Field Splitting: Spectrochemical Series• Ligand Field Stabilization Energy• Chelate Effect• Stereochemical Control of Binding Affinity• Electron Exchange

Ligand Field Stabilization EnergyHigh Spin Octahedral Complexes

dxz yz xy

z2 x2-y2

∆o

Extra electron density

Non-sphericalsymmetry

M

H2OH2O

H2OH2O

H2O

H2O

2/5 ∆o

3/5 ∆o

dn ∆od1, d6 2/5 d2, d7 4/5 d3, d8 6/5d4, d9 3/5d0, d5, d10 0

Ligand Field Stabilization Energy

Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn

HydrationEnergy(kJ/mol)

2500

3000

M2+(g) + ∞ H2O [M(H2O)6]2+

• Energy of hydration always favorable• Energy increases as ionic radius decreases (to right)• Additional stabilization due to crystal field energy

Binding Constants for Multiple Ligands

Cd2+ + NH3 [Cd(NH3)]2+

[Cd(NH3)]2+ + NH3 [Cd(NH3)2]2+

[Cd(NH3)2]2+ + NH3 [Cd(NH3)3]2+

[Cd(NH3)3]2+ + NH3 [Cd(NH3)4]2+

K

102.05

102.10

101.44

100.93

107.12

Decrease mostly statistical: as ligand count increasesmore changes to lose L as opposed to gaining L

Cd2+ + 4 NH3 [Cd(NH3)4]2+

Chelate Effect

Ni

NH3

NH3

NH3NH3

NH3

NH32+

Ni2+

6 NH3

+

K = 108.6

Ni

NH2N

NH2NH2

NH2

NH22+

Ni2+

3 H2NCH2CH2NH3

+

K = 1018.3

H2

Chelate Effect

M

OO

OO

N

N2+

Useful chelating ligands: en, sepulchrate, edta,

M(edta)2-

C-CH2 CH2-CNCH2CH2N

C-CH2 CH2-C

OOOO

OOOO

--

--: :

M

NHNH

NHNH

NH

NH2+

M(sep) 2+

edta

M2+

NHNH

NHNH

NH

NH

M2+

Ionic Radii and Charge Densities for the Alkali Metal Cations

Ion Ionic radius/Å Charge Density/C Å-3

Li+ 0.66 12.1x10-20

Na+ 0.95 4.46x10-20

K+ 1.33 1.62x10-20

Rb+ 1.48 1.18x10-20

Cs+ 1.69 0.79x10-20

So how do we get ligands to preferentially bind Na+ or K+ vs Li+?

Donald Cram Charles J. Pedersen Jean-Marie Lehn

1987 Nobel Prize in Chemistry

"for their development and use of molecules with structure-specificinteractions of high selectivity"

Chelate EffectUseful chelates: crown ethers (host/guest chemistry)

M+

18-crown 6

Fits Cs+ nicely (used to separate Cs in radioactive waste)

Crown Ethers

15-crown 5

(C10H20O5)

Fits Na+ and K+ nicely

Crown Ethers

12-crown 4 + Li+

Crown EthersUseful chelates: crown ethers (host/guest chemistry)

Also used to “bring along” pertechnetate anion intonon-aqueous solvents

Transports K+ through lipid membranes

Biological Host-Guest Complexes

Top View Side View

K+-Valinomycin Complex

Biological Ionophores

Li+ Na+ K+ Rb+ Cs+

Valinomycin <0.7 0.67 4.90 5.26 4.42

Monactin <0.3 2.60 4.38 4.38 3.30

Enniatin B 1.28 2.42 2.92 2.74 2.34

Nigericin - 4.7 5.6 5.0 -

Monensin 3.6 6.5 5.0 4.3 3.6

Henry Taube

"for his work on the mechanisms ofelectron transfer reactions,especially in metal complexes"

Nobel Prizes in Chemistry(and “nice guys finish first”)

1983

Rudy Marcus

"for his contributions to the theoryof electron transferreactions in chemical systems"

1992

“Nuclei do all the work, then the electrons move”

Electron Exchange

[Co (NH3)6]3+ [Co (NH3)6]2+

[Ru(NH3)6]3+ [Ru(NH3)6]2+

+ e-

+ e-

k = 10-6 M-1 s-1

k = 104 M-1 s-1

Simplest chemical reaction, yet enormous rate differences

Electron Exchange

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

[Co (NH3)6]3+ [Co (NH3)6]2+

[Ru(NH3)6]3+ [Ru(NH3)6]2+

+ e-

+ e-

Electron Exchange

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

[Ru(NH3)6]3+ [Ru(NH3)6]2++ e-

Ru

NH3NH3

NH3NH3

NH3

NH33+ Ru

NH3NH3

NH3NH3

NH3

NH32+

Electron Exchange

Co

NH3NH3

NH3NH3

NH3

NH33+ Co

NH3

NH3

NH3NH3

NH3

NH3

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

[Co (NH3)6]3+ [Co (NH3)6]2++ e-

2+

Electron Exchange

Co

NH3

NH3

NH3NH3

NH3

NH33+ Co

NH3NH3

NH3NH3

NH3

NH33+

Co

NH3

NH3

NH3NH3

NH3

NH3

2+Co

NH3

NH3

NH3NH3

NH3

NH3

2+

+ +

Electron Exchange

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

[Co (NH3)6]3+ [Co (NH3)6]2++ e-

Electron Exchange

xz yz xy

z2 x2-y2

xz yz xy

z2 x2-y2

[Co (NH3)6]3+ [Co (NH3)6]2++ e-

xz yz xy

z2 x2-y2

[Co (NH3)6]*3+

xz yz xy

z2 x2-y2

[Co (NH3)6]*2+

The Nature of the Chemical Bondin Chem 1a

• Atomic Structure• Explain Atomic Line Spectra, Galaxies, etc.• Shapes of Orbitals in Atoms for Bonding• Ionization Energies and Trends in Chemical

Reactivity (e.g., Li+ vs Li)• Which Molecules are Likely to Exist and Their

Shapes and Reactivities (Ozone, Glo. Warm.)• Covalent Bonding Properties of Organic Molecules• Special Properties of Resonance Stabilization• Directionality of Covalent Chemical Bonds• Bonding in Solids• Bonding of the Transition Metals (Optical and

Magnetic Properties, Electron Transfer Reactions)

chemistry and spectroscopy of the transition metalschem1/lecture notes pdfs/series 13 transition...

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