Complex Ions & Coordination Compounds Unit 3

Coordination Compound

• Neutral compounds that contain TM

• Formed from simpler compounds

• Usually have color and are paramagnetic

• Ex: [Co(NH3)5Cl]Cl2

Complex Ion

• TM ions with ligands

• Used when the TM species has a nonzero charge

• Ex: [Co(NH3)5Cl]2+

Counter Ions

• Anions/ cations needed to produce a compound with no charge

• When added to a complex ion, this turns it into a compound ion

• Ex: [Co(NH3)5Cl] + Cl2 —> [Co(NH3)5Cl]Cl2

Ligands

• Groups that surround the TM ion (excludes counter ions)

Coordination number (CN)

• The number of NEAREST neighbors (ligands) to the TM ion

• CN = # of ligands around the TM

• Usually 2,4, or 6(6 being the most common)

Complex

• General term

• Used to describe any species that involves ligands bonded to a TM

Oxidation state

Primary valence of a TM

Monodentate

• A ligand with ONE pair of e- to attach/ bond to the TM

Bidentate

• Ligand with TWO lone pairs of e- ready to donate to the TM

Polydentate

• A ligand having 2 or MORE lone pairs of e- to donate to a TM

• Polydentate ligand is also known as “chelating”

Composite ligands

• Ligands that have a prefix in its name

• Ex: EDTA^4-, (en)

• Requires a composite prefix when being named

Structural isomers

A compound that can have a different connectivity

Stereoisomers

compound that can have a different arrangement of its atoms in space

Ionization isomer

• A structural isomer where a ligand and counter iron switch

• Ex: [Cu(H2O)5Br]CN —> [Cu(H2O)5CN]Br

Coordination isomer

• Structural isomer where the transition metals of a bimetallic species switch ligands

• Think double replacement rxn, except the metals are the ones that are switched

• Ex: [A(BCD)2][W(XYZ)] —> [W(BCD)2][A(XYZ)]

Linkage isomer

• Structural isomer where a multi-atom ligand (e.g. ONO, SCN, CN) connected to the TM through different atoms

• Ex: M — XYZ —> M — ZXY

Geometric isomers

• Stereoisomer where the arrangement of the ligands are either neighboring or across from each other

• Ligands neighboring each other: cis- or fac-

• Ligands across from each other: trans- or mer-

What is cis/ trans isomerism

• Occurs only in square planar and octahedral molecular geometries

• Two IDENTICAL ligands involved

• cis - Ligands are neighboring

• trans - Ligands are across from each other

What is trans/ mer isomerism

• Only occurs in octahedral complexes

• Involves THREE identical ligands

• Fac - The three ligands are neighboring each other

• Mer - Two of the three ligands are across from each other

Isomer

Compounds that contain the same numbers of the same atoms, but in different arrangements

Optical isomers

• Subcategory of stereoisomers where the arrangement of atoms results in a non-superimposable mirror image

• Also known as chiral

• Basically, the mirror image of a molecule is different

• Only occurs with tetrahedral and octahedral isomers

How to know if a tetrahedral isomer is optical/ chiral

• All 4 ligands are different

How to know if an octahedral isomer is chiral/ optical

• All 6 ligands are different

• 3 cis- PAIRS or 3 BIdentate ligands are present

• Either only 2 MONOdentate ligands are the same and are cis-, or 3 MONOdentate ligands are the same and are fac-

• 2 bidentate ligands are cis

• 1 bidentate ligand if the monodentate ligands that are trans- are different and the other cis- monodentate ligands are different