Ligands/Coordination compounds (Openstax Ch. 19)

Complex ion

Consist of metal cations that form coordinate covalent bonds with ligands

Ligand

Molecules that have at least one e- pair that it can share in a LAB interaction

Coordination number

Gives the total number of e- pairs shared with the metal cation

Coordination compound

Formed when complex ions are combined with 1 or more counterions

Monodentate ligand

Share ONE e- pair with the metal cation (ex. NH3, Cl-, CN-)

Bidentate ligand

Share TWO e- pairs with the metal cation (ex. C2O42-, H2NCH2CH2NH2 (en))

Polydentate ligand

Share MORE THAN TWO e- pairs with the metal cation (ex. EDTA)

Octahedral geometry coordination number

6

Tetrahedral geometry coordination number

4

Square planar geometry coordination number

4

Isomer of coordination compounds

Compounds with the same formula, but different structures

Structural isomers

Different connectivity

Coordination sphere isomer (type of structural isomer)

When the ligands exchange places with uncoordinated counter ions

linkage isomers (type of structural isomer)

Contain ligands that coordinate to the metal cation in different ways (NO2-, CN-, OCN-, SCN-)

Stereoisomers

Have the SAME connectivity but different spatial arrangements

Geometric isomer (type of stereoisomer)

Have ligands in different spatial arrangements around the metal cations

Cis geometric isomer

The two atoms are on the same side (90 degrees)

Trans geometric isomer

The two atoms are on opposite sides (180 degrees)

fac geometric isomer

Any two identical ligands are adjacent to one another (cis)

mer geometric isomer

A combination of a cis/trans isomer

Optical isomers

Mirror image of one another

Crystal Field Theory for Octahedral Complexes

When a metal cation is in an octahedral electric field created by the ligands, the d orbitals will INCREASE in energy

Crystal Field energy

The difference in energy between the two groups of d orbitals

Small crystal field energy

absorb long wavelengths, reflect short wavelengths; high spin (crystal field energy < e pairing energy), orbitals not filled

Large crystal field energy

absorb short wavelengths, reflect long wavelengths; low spin (crystal field energy > e pairing energy), orbitals all filled