Review of variable valence  Transition metal ions have variable oxidation state  Electron configurations 4s 2 3d n with some exceptions 4s 2 3d n with some exceptions

Isomerism – same atoms, different arrangement

Constitutional and stereo  Constitutional Different connections between the atoms Different connections between the atoms Linkage isomers (choice of linkage atom) Linkage isomers (choice of linkage atom) Ionization isomers (different anion bonding) Ionization isomers (different anion bonding)  Stereoisomers Same connections but different spatial arrangements Same connections but different spatial arrangements Diastereoisomers (geometric isomers) Diastereoisomers (geometric isomers) Enantiomers (handedness) Enantiomers (handedness)

Linkage isomers  The nitrite ion can use either the O or the N atom as the ligand since both have non-bonding pairs.  Indicate linkage in the name: Nitro (NO 2 ) links through N Nitro (NO 2 ) links through N Nitrito (ONO) links through O Nitrito (ONO) links through O  Obvious influence on physical properties

Ionization isomers  Different anions are linked to the central atom In one, the free anion is SO 4 2- In one, the free anion is SO 4 2- In the second, the free anion is Br - In the second, the free anion is Br -

Diastereo (geometric) isomers  Same attachments but different arrangement Cis- and trans- (analogous to bonding in alkenes) Cis- and trans- (analogous to bonding in alkenes)  Influences physical properties through different polarity  Example with square planar: opposite or side-by-side

Octahedral complex

Not all complexes qualify for geometric isomers  Square planar – ML 2 X 2 (cis and trans) ML 2 X 2 (cis and trans) ML 3 X (none) ML 3 X (none)  Tetrahedral – none with any composition  Octahedral – ML 4 X 2 (cis and trans) ML 4 X 2 (cis and trans) ML 3 X 3 ML 3 X 3 ML 5 X (none) ML 5 X (none)

More than two ligands…  ML 2 XY or ML 4 XY can also have cis and trans isomers

Isomers or equal?

What hands are these…?  Apparently all same connections and yet…  Enantiomers are molecules or ions that form mirror images of each other Tetrahedral C atoms with four different groups Tetrahedral C atoms with four different groups  Hands are enantiomers.  They possess chirality  Molecules that have no handedness are achiral

Testing for chirality  Presence of planes of symmetry – achiral  Absence of plane of symmetry – chiral

Handedness in complexes with bidentate ligands

 How many diastereoisomers and enantiomers are there of Co(en) 2 Cl 2 + ?

Getting a complex?  Which are chiral?  Which are achiral?  What are the enantiomers?