Review of variable valenceReview of variable valence

Transition metal ions have variable oxidation Transition metal ions have variable oxidation statestate

Electron configurationsElectron configurations 4s4s223d3dnn with some exceptions with some exceptions

Isomerism – same atoms, different Isomerism – same atoms, different arrangementarrangement

Constitutional and stereoConstitutional and stereo

ConstitutionalConstitutional Different connections between the atomsDifferent 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)

StereoisomersStereoisomers Same connections but different spatial Same connections but different spatial

arrangementsarrangements Diastereoisomers (geometric isomers)Diastereoisomers (geometric isomers) Enantiomers (handedness)Enantiomers (handedness)

Linkage isomersLinkage isomers The nitrite ion can use either the O or the N atom as the ligand The nitrite ion can use either the O or the N atom as the ligand

since both have non-bonding pairs.since both have non-bonding pairs. Indicate linkage in the name:Indicate linkage in the name:

Nitro (NONitro (NO22) links through N) links through N Nitrito (ONO) links through ONitrito (ONO) links through O

Obvious influence on physical propertiesObvious influence on physical properties

Ionization isomersIonization isomers

Different anions are linked to the central atomDifferent anions are linked to the central atom

In one, the free anion is SOIn one, the free anion is SO442-2-

In the second, the free anion is BrIn the second, the free anion is Br--

453 SOBrNHCo

BrSONHCo 453

Diastereo (geometric) isomersDiastereo (geometric) isomers

Same attachments but different arrangement 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 polarityInfluences physical properties through different polarity

Example with square planar: opposite or side-by-sideExample with square planar: opposite or side-by-side

Octahedral complexOctahedral complex

Not all complexes qualify for Not all complexes qualify for geometric isomersgeometric isomers

Square planar – Square planar – MLML22XX22 (cis and trans) (cis and trans)

MLML33X (none)X (none)

Tetrahedral – none with any compositionTetrahedral – none with any composition Octahedral –Octahedral –

MLML44XX22 (cis and trans) (cis and trans)

MLML33XX33

MLML55X (none)X (none)

More than two ligands…More than two ligands…

MLML22XY or MLXY or ML44XY can also have cis and trans XY can also have cis and trans

isomersisomers

Isomers or equal?Isomers or equal?

What hands are these…?What hands are these…?

Apparently all same connections and yet…Apparently all same connections and yet… Enantiomers are molecules or ions that form Enantiomers are molecules or ions that form

mirror images of each othermirror images of each other Tetrahedral C atoms with four different groupsTetrahedral C atoms with four different groups

Hands are enantiomers.Hands are enantiomers. They possess chiralityThey possess chirality Molecules that have no handedness are achiralMolecules that have no handedness are achiral

Testing for chiralityTesting for chirality

Presence of planes of symmetry – achiralPresence of planes of symmetry – achiral Absence of plane of symmetry – chiralAbsence of plane of symmetry – chiral

Handedness in complexes with Handedness in complexes with bidentate ligandsbidentate ligands

How many diastereoisomers and enantiomers are How many diastereoisomers and enantiomers are there of Co(en)there of Co(en)22ClCl22

++??

Getting a complex?Getting a complex?

Which are chiral?Which are chiral? Which are achiral?Which are achiral? What are the enantiomers?What are the enantiomers?