D-block (Theory)

7/29/2019 D-block (Theory)

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3d Metal ComplexesSynthesis, Spectroscopic, Electronic,and Magnetic Properties

By Mark Justine R. Zapanta


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1. Introduction to transition metals

2. Nomenclature

3. Isomerism in coordinate compounds

4. Interpretation of metal complexes spectra

5. Overview of bonding in transition metals

6. Crystal Field Theory

7. Magnetic susceptibility8. Ligand Field Theory

9. Charge Transfer

10.Electron Transitions

11.Selection rules12.Tanabe-Sugano Diagram

WERE NOT GOING TO TALK ABOUT

MOLECULAR MODELING (I.E. MINIMIZED ENERGY)!

What were going to talk about


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elements that have at least one simple ion with anincomplete outer set of d electrons

What are transition metals?


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Zinc

Zn [Ar] 4s23d10

Zn2+ [Ar] 3d10 (definition is not satisfied)

Scandium

Sc [Ar] 4s13d1

Sc2+ [Ar] (definition is not satisfied)

d-block metals that are not transition metals


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Transition metal ion is usually covalently bonded to other

ions or molecules

Metal ion Lewis acid

Ligand Lewis base

Naked transition metals? Probably not.


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Whats in a name? Nomenclature rules


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Isomerism in transition metal complexes


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Orbital splitting and electron spin

Crystal Field Stabilization EnergyCrystal Field Splitting

Structural isomers

1. Ionization isomers [PtBr(NH3)3]NO2 and [Pt(NO2)(NH3)3]Br

2. Linkage isomers

[Co(ONO)(NH3)5]Cl and [Co(NO2)(NH3)5]Cl

3. Coordination isomers

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

4. Hydrate isomers [CrCl2(H2O)4]Cl2H2O

[CrCl(H2O)5]Cl2H2O

[Cr(H2O)6]Cl3


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Geometric isomers

1. Cis and trans

2. Fac and mer

Optical isomersnon-superimpossable mirror image


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Overview of bonding theories of transition metals

Valence Bond

Theory

Assumed that bonding of transition metals was similar to that of typical maingroup elements assigning different modes of hybridization to the metal ion

depending on the known geometry of the compound

Crystal Field

Theory

Assumed that the interaction between a metal ion and its ligand was totally

electrostatic in nature

Ligand Field

Theory

Modified form of CFT.

Takes the covalent character into account

Racah parameter (B)

Molecular

Orbital Theory

Most sophisticated theory

Not necessary for the discussion of conventional transition metal complexes


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A simple approach to Crystal Field Theory

Crystal Field Stabilization Energy

Crystal Field Splitting


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strong ligand field = large = low spin

weak ligand field = small = high spin


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Magnetic susceptibility


Diamagnetic

no unpaired electron

slightly repelled by magnetic field

Paramagnetic

has unpaired electron

attracted into magnetic field

Magnetic susceptibility measure of magnetism

s = 2 [S(S+1)]^.5 = [n(n+2)] .5


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A challenging approach: Ligand Field Theory

Pi b di


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Pi bonding

Addition of other ligand orbitals

allows the possibility of pi bonding

The ligand must have a

p orbital or pi* molecular orbitals

Types:

1. pi-acceptor ligands

-empty pi* orbitals

2. pi-donor ligands

Pi b di


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Pi bonding

C t l Fi ld Th


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Crystal Field Theory

Crystal Field Splitting depends on four factors:

1. Identity of the metal

first row < second row (50%) < third row (25%)

2. Oxidation state of the metal

higher oxidation state

3. Number of ligands

greater for more ligands

4. Nature of ligands

spectrochemical series


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Ch T f


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Charge Transfer

Metal to Ligand Charge Transfer

pi* orbitals on the ligands (pi-acceptor ligand) becomethe acceptor orbitals on the absorption of light

oxidation of the metal

CO, CN-, SCN-

El t i t f di ti d


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Electronic spectra of coordination compounds

Electronic transition absorption bands

Complementary

Selection r les


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Selection rules

Laporte selection rule

transition between states of the same parity is forbidden

In Oh symmetry, d to d transitions are forbidden!

Relaxation: bond vibration removes symmetry, orbital

mixing

Selection rules


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Selection rules

Spin selection rule

transition between states of different spin multiplicities is

forbidden

Relaxation: spin-orbit coupling


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Interpreting the spectra


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Tanabe-Sugano Diagram

we can often obtain values and sometimes B of

reasonable accuracy simply by using the positions of the

absorption maxima taken directly from the spectra

simplest cases: d1, d4 (h.s.), d6 (h.s.), d9



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What are those shoulders?


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What are those shoulders?

Jahn-Teller Effect

there cannot be

unequal occupation

of orbitals with identical

energies



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Cases: d3, d8

T2g A2g corresponds to



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Cases: d2, d7 h.s.

A2g T2g corresponds to


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QUESTIONS?


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Comments:

1. In the magnetic susceptibility part, discuss

how to calculate for spin-only

D-block (Theory)

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