Isomerism: two main kinds

Structural Isomers: Coordination Isomerism

Structural Isomers: Linkage Isomerism

Stereo Isomers: Geometric (cis-trans) square planar octahedral

Stereo Isomers: Geometric (cis-trans)

Stereo Isomers: Optical Optical activity: opposite effects on plane-polarized light. Molecules have nonsuperimposable mirror images.

Stereo Isomers: Optical

Stereo Isomers: Optical

The Localized Electron Model The cobalt(III) ion possesses empty hybrid orbitals which can accept electrons. The metal ion is considered a Lewis Acid. The ligands possess lone pairs of electrons which can be donated to form coordinate covalent bonds. The ligands are considered Lewis Bases.

MO Diagram (octahedral) Orbitals with lone pairs on the ligands overlap with the metal ion orbitals. Only sigma bonds are considered here. The 3d is lower in energy than the 4s for transition metal ions. For reference we have kept the d-orbital labels on this diagram. Note the non-bonding d-orbitals.

MO Energy Diagram for [Co(NH3)6]3+ If ligands are “lone pairs”, with 6 lone pairs (octahedral) we always have 12 electrons from the ligands. Thus, the number of electrons in the “d-orbital” range of the MO = the number of electrons in the metal ion.

MOs: What Do We Notice?

Crystal Field Theory: Important Points We only need concern ourselves with the “d-orbitals” as seen in our consideration of MO theory. Consider ligands to be negative point charges. Bonding is considered to be ionic (with the metal ion the cation and the ligand the anion – even neutral ligands). Electron-electron repulsion causes an increase in energy in the d-orbitals on the metal. The greater the overlap, the greater the repulsion, the higher the energy (overlap = “bad”). We don’t “need” hybrid orbitals or MOs – we assume the d-orbitals are unchanged.

CFT: Color?

CFT: Ligands affect splitting Consider Co3+ (d?).

MOs: What Do We Notice?