Prentice-Hall © 2007Slide 1 of 59 Coordination Chemistry

Prentice-Hall © 2007Slide 2 of 59 Coordination Chemistry

Prentice-Hall © 2007Slide 3 of 59 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

Prentice-Hall © 2007Slide 4 of 59 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  Common Metal ions are Lewis acids (electron pair acceptors)  Coordinate Covalent bonds are formed L → M  Complexes using polydentate ligands are called chelates

Prentice-Hall © 2007Slide 5 of 59 Table 24.3 Some Common Polydentate Ligands (Chelating Agents)

Prentice-Hall © 2007Slide 6 of Werner’s Theory of Coordination Compounds: An Overview  Compounds that contain metal complexes are called coordination compounds.  CoCl 3 and NH 3.  [Co(NH 3 ) 6 ]Cl 3 and [CoCl (NH 3 ) 5 ]Cl 2  Differing reactivity with AgNO 3. Alfred Werner

Prentice-Hall © 2007Slide 7 of 59 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 (NH 3 ) 6 Orange/yellow 43[Co(NH 3 ) 6 ] Cl - Co(Cl) 3 (NH 3 ) 5 purple 32[Co(NH 3 ) 5 Cl] Cl - Co(Cl) 3 (NH 3 ) 4 Green/violet 21[Co(NH 3 ) 4 Cl 2 ] Cl -  Wener proposed that metals exhibit both primary and secondary valences

Prentice-Hall © 2007Slide 8 of 59 Werner’s Theory [Co(NH 3 ) 6 ]Cl 3 → [Co(NH 3 ) 6 ] Cl - [CoCl(NH 3 ) 5 ]Cl 2 → [CoCl(NH 3 ) 5 ] 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.

Prentice-Hall © 2007Slide 9 of 59 Coordination Number

Prentice-Hall © 2007Slide 10 of 59 Ethylene Diamine

Prentice-Hall © 2007Slide 11 of 59 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(NO 2 )(NH 3 ) 4 ] + ? Solution: The complex has as ligands 1  Cl, 1  NO 2, 4  NH 3. The coordination number is 6. EXAMPLE 24-1

Prentice-Hall © 2007Slide 12 of 59 Charge on the metal ion: EXAMPLE 24-1

Prentice-Hall © 2007Slide 13 of 59 Isomerism Werner predicted there would be only two isomers of [CoCl 2 (NH 3 ) 4 ] + and mailed them to Jorgensen. He received the Nobel prize in 1913.

Prentice-Hall © 2007Slide 14 of 59 Isomerism

Prentice-Hall © 2007Slide 15 of 59 Examples of Structural Isomerism Ionization Isomerism [CrSO 4 (NH 3 ) 5 ]Cl[CrCl(NH 3 ) 5 ]SO 4 pentaaminsulfatochromium(III) chloride pentaaminchlorochromium(III) sulfate Coordination Isomerism [Co(NH 3 ) 6 ][CrCN 6 ] hexaaminecobalt(III) hexacyanochromate(III) [Cr(NH 3 ) 6 ][CoCN 6 ] hexaaminechromium(III) hexacyanocobaltate(III)

Prentice-Hall © 2007Slide 16 of 59 Linkage Isomerism

Prentice-Hall © 2007Slide 17 of 59 Stereoisomerism: Geometric Isomerism

Prentice-Hall © 2007Slide 18 of 59 Geometric Isomerism How many isomers would [CoCl 3 (NH 3 ) 3 ] have?

Prentice-Hall © 2007Slide 19 of 59 Geometric Isomerism

Prentice-Hall © 2007Slide 20 of 59 Optical Isomerism Chiral shapes are not super imposable on their mirror image

Prentice-Hall © 2007Slide 21 of 59 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.

Prentice-Hall © 2007Slide 22 of 59 Optical Isomerism enantiomers

Prentice-Hall © 2007Slide 23 of 59 Optical Activity dextrorotatory d- levorotatory l- We are made up of chiral molecules – l-amino acids, protein alpha helix, the DNA duplex, and sugars.

Prentice-Hall © 2007Slide 24 of 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.

Prentice-Hall © 2007Slide 25 of 59 Table 24.2 Some Common Monodentate Ligands. – ide endings change to –o – ate endings change to –ato

Prentice-Hall © 2007Slide 26 of 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.

Prentice-Hall © 2007Slide 27 of 59 Octahedral Complex and d-Orbital Energies

Prentice-Hall © 2007Slide 28 of 59 Electron Configuration in d-Orbitals Hund’s Rule Pairing Energy Considerations Δ P

Prentice-Hall © 2007Slide 29 of 59 Spectrochemical Series CN - > NO 2 - > en > py  NH 3 > EDTA 4- > SCN - > H 2 O > ONO - > ox 2- > OH - > F - > SCN - > Cl - > Br - > I - Large Δ Strong field ligands Small Δ Weak field ligands

Prentice-Hall © 2007Slide 30 of 59 Electron Configuration in d-Orbitals

Prentice-Hall © 2007Slide 31 of 59 Effect of Ligands on the Colors of Coordination Compounds

Prentice-Hall © 2007Slide 32 of 59 Absorption Spectrum max

Prentice-Hall © 2007Slide 33 of 59 Light Absorption and Transmission [Ni(H 2 O) 6 } 2+ Ni(NH 3 ) 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

Prentice-Hall © 2007Slide 34 of 59 Werner’s Theory of Coordination Compounds  CoCl 3 and NH 3.  [Co(NH 3 ) 6 ]Cl 3 and [CoCl (NH 3 ) 5 ]Cl 2 Alfred Werner

Prentice-Hall © 2007Slide 35 of 59 Presented by: Sudhir Kumar Maingi PGT CHEMISTRY K.V. No. 1 PATHANKOT, JAMMU REGION