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Coordination Chemistry

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Coordination Chemistry

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Werner/Jorgensen Controversy

Alfred Werner

“Probably the greatest conceptual contribution to inorganic chemistry—comparable in both direct and indirect impact to the concept of the tetrahedral carbon atom in organic chemistry—is Alfred Werner’s concept of coordination compounds and his general theory of how they behave.” Albert Cotton

Sophus Jorgensen

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Chelation

Metals are able to bind or chelate (greek to claw) to other molecules or ions in solution called ligands Common Ligands are Lewis bases (electron pair donors)

◦ Monodentate Bidentate

H N

H

H H N CH2CH2 N

H

H

H

Common Metal ions are Lewis acids (electron pair acceptors)

Coordinate Covalent bonds are formed L → M Complexes using polydentate ligands are called chelates

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Table 24.3 Some Common Polydentate Ligands (Chelating Agents)

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24-1Werner’s Theory of Coordination Compounds: An Overview

Compounds that contain metal complexes are called coordination compounds.

CoCl3 and NH3. [Co(NH3)6]Cl3 and [CoCl (NH3)5]Cl2

Differing reactivity with AgNO3.

Alfred Werner1866-1919

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Werner’s Experiment As a 26 year old lecturer Werner did the following experiment

Empirical formula # ions

Cl- ions

Ag+ ppt

Complex

Co(Cl)3(NH3)6

Orange/yellow

4 3 [Co(NH3)6]3+

+ 3 Cl-

Co(Cl)3(NH3)5

purple

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

+ 2 Cl-

Co(Cl)3(NH3)4

Green/violet

2 1 [Co(NH3)4Cl2]1+

+ 1 Cl-

Wener proposed that metals exhibit both primary and secondary valences

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Werner’s Theory

[Co(NH3)6]Cl3 → [Co(NH3)6]3+ + 3 Cl-

[CoCl(NH3)5]Cl2 → [CoCl(NH3)5]2+ + 2 Cl-

Two types of valence or bonding capacity. Primary valence (oxidation number).

◦ Based on the number of e- an atom loses in forming the ion.

Secondary valence (coordination number).◦ Responsible for the bonding of other groups, called

ligands, to the central metal atom.

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Coordination Number

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Ethylene Diamine

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Relating the Formula of a Complex to the Coordination Number and Oxidation State of the Central Metal. What are the coordination number and oxidation state of Co in the complex ion [CoCl(NO2)(NH3)4]+?

Solution:

The complex has as ligands 1Cl, 1NO2, 4NH3 .

The coordination number is 6.

EXAMPLE 24-1

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Charge on the metal ion:

EXAMPLE 24-1

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Isomerism

Werner predicted there would be only two isomers of [CoCl2(NH3)4]+ and mailed them to Jorgensen. He received the Nobel prize in 1913.

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Isomerism

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Examples of Structural Isomerism

Ionization Isomerism

[CrSO4(NH3)5]Cl [CrCl(NH3)5]SO4

pentaaminsulfatochromium(III) chloride pentaaminchlorochromium(III) sulfate

Coordination Isomerism

[Co(NH3)6][CrCN6]

hexaaminecobalt(III) hexacyanochromate(III)

[Cr(NH3)6][CoCN6]

hexaaminechromium(III) hexacyanocobaltate(III)

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Linkage Isomerism

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Stereoisomerism: Geometric Isomerism

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Geometric Isomerism

How many isomers would [CoCl3(NH3)3] have?

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Geometric Isomerism

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Optical Isomerism

Chiral shapes are not super imposable on their mirror image

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Chirality or Handedness

Triethylenediamine cobalt(III) is a chiral molecule it differs only in how it interacts with another chiral object. “You can not put a right handed glove on a left hand”. Left and right circularly polarized light is an example of a chiral object.

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Optical Isomerism

enantiomers

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Optical Activity

dextrorotatory d-

levorotatory l-

We are made up of chiral molecules –l-amino acids, protein alpha helix, the DNA duplex, and sugars.

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24-3 Nomenclature

In names and formulas of coordination compounds, cations come first, followed by anions.

Anions as ligands are named by using the ending –o. Normally:

◦ – ide endings change to –o.◦ – ite endings change to –ito.◦ – ate endings change to –ato.

Neutral molecules as ligands generally carried the unmodified name.

If the complex is an anion the ending –ate is attached to the name of the metal.

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Table 24.2 Some Common Monodentate Ligands.

– ide endings change to –o – ate endings change to –ato

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24-5 Bonding in Complex Ions: Crystal Field Theory

Consider bonding in a complex to be an electrostatic attraction between a positively charged nucleus and the electrons of the ligands. Electrons on metal atom repel electrons on ligands. Focus particularly on the d-electrons on the metal ion.

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Octahedral Complex and d-Orbital Energies

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Electron Configuration in d-Orbitals

Hund’s Rule Pairing Energy Considerations

ΔP

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Spectrochemical Series

CN- > NO2- > en > py NH3 > EDTA4- > SCN- > H2O >

ONO- > ox2- > OH- > F- > SCN- > Cl- > Br- > I-

Large ΔStrong field ligands

Small ΔWeak field ligands

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Electron Configuration in d-Orbitals

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Effect of Ligands on the Colors of Coordination Compounds

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Absorption Spectrum

max

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Light Absorption and Transmission

[Ni(H2O)6}2+ Ni(NH3)6]2+ [Ni(en)3]2+

Transmitted Green Blue Purple

Absorbed (red) (orange) (yellow)

700 nm 600 nm 570 nm

o hc/small medium large

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Werner’s Theory of Coordination Compounds

CoCl3 and NH3. [Co(NH3)6]Cl3 and [CoCl (NH3)5]Cl2

Alfred Werner1866-1919

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Presented by: Sudhir Kumar Maingi PGT CHEMISTRY

K.V. No. 1 PATHANKOT, JAMMU REGION