Prentice-Hall © 2002 Complex Ions and Coordination Compounds

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 2 of Werner’s Theory of Coordination Compounds: An Overview Compounds made up of simpler compounds are called coordination compounds. CoCl 3 and NH 3. –CoCl 3 · (NH 3 ) 6 and CoCl 3 · (NH 3 ) 5. –Differing reactivity with AgNO 3.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 3 of 55 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. Based on the number of e - an atom loses in forming the ion. –Secondary valence. Responsible for the bonding of other groups, called ligands, to the central metal atom.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 4 of 55 Coordination Number

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 5 of 55 Example 25-1 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.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 6 of 55 Example 25-1 Charge on the metal ion:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 7 of Ligands Ligands are Lewis bases. –Donate electron pairs to metals (which are Lewis acids). Monodentate ligands. –Use one pair of electrons to form one point of attachment to the metal ion. Bidentate ligands. –Use two pairs of electrons to form two points of attachment to the metal ion. Tridentate, tetradentate…..polydentate

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 8 of 55 Table 25.2 Some Common Monodentate Ligands.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 9 of 55 Table 25.3 Some Common Polydentate Ligands (Chelating Agents)

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 10 of 55 Ethylene Diamine

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 11 of Isomerism Isomers. –Differ in their structure and properties. Structural isomers. –Differ in basic structure. Stereoisomers. –Same number and type of ligands with the same mode of attachement. –Differ in the way the ligands occupy space around the metal ion.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 12 of 55 Examples of 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 © 2002General Chemistry: Chapter 25Slide 13 of 55 Linkage Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 14 of 55 Geometric Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 15 of 55 Geometric Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 16 of 55 Optical Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 17 of 55 Optical Isomerism

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 18 of 55 Mirror Images

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 19 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 © 2002General Chemistry: Chapter 25Slide 20 of 55 Octahedral Complex and d-Orbital Energies

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 21 of 55 Electron Configuration in d-Orbitals Hund’s rule Δ > P low spin d 4 Δ < P high spin d 4 pairing energy considerations Δ P

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 22 of 55 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 © 2002General Chemistry: Chapter 25Slide 23 of 55 Weak and Strong Field Ligands Two d 6 complexes:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 24 of 55 Energy Effects in a d 10 System

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 25 of 55 Tetrahedral Crystal Field

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 26 of 55 Square Planar Crystal Field

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 27 of Magnetic Properties of Coordination Compounds and Crystal Field Theory. Paramagnetism illustrated:

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 28 of 55 Example 25-4 Using the Spectrochemical Series to Predict Magnetic Properties. How many unpaired electrons would you expect to find in the octahedral complex [Fe(CN) 6 ] 3- ? Solution: Fe [Ar]3d 6 4s 2 Fe 3+ [Ar]3d 5

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 29 of 55 Example 25-5 Using the Crystal Field theory to Predict the Structure of a Complex from Its Magnetic Properties. The complex ion [Ni(CN 4 )] 2- is diamagnetic. Use ideas from the crystal field theory to speculate on its probably structure. Solution: Coordination is 4 so octahedral complex is not possible. Complex must be tetrahedral or square planar. Draw the energy level diagrams and fill the orbitals with e -. Consider the magnetic properties.

Prentice-Hall © 2002General Chemistry: Chapter 25Slide 30 of 55 Example 25-5 Tetrahedral:Square planar: