• Depending on the?size of the ligands?and the?number of dative bonds?to the central metal ion, transition element complexes have different geometries
  • Dative bonds can also be referred to as?coordinate bonds, especially when discussing the geometry of a complex

Linear

• Central metal atoms or ions with?two coordinate bonds?form?linear?complexes
• The bond angles in these complexes are 180^o
• The most common examples are a copper (I) ion, (Cu⁺), or a silver (I) ion, (Ag⁺), as the central metal ion with two coordinate bonds formed to two ammonia ligands

Example of a linear complex

Tetrahedral

• When there are?four coordinate bonds?the complexes often have a?tetrahedral?shape
  • Complexes with four?chloride?ions?most commonly adopt this geometry
  • Chloride ligands are large, so only four will fit around the central metal ion
• The bond angles in tetrahedral complexes are 109.5^o

Example of a tetrahedral complex

Square planar

• Sometimes, complexes with?four coordinate bonds?may adopt a?square planar?geometry instead of a tetrahedral one
  • Cyanide ions (CN^-) are the most common ligands to adopt this geometry
  • An example of a square planar complex is?cisplatin
• The bond angles in a square planar complex are 90^o

Cisplatin is an example of a square planar complex

Octahedral

• Octahedral?complexes are formed when a central metal atom or ion forms?six coordinate bonds
• This could be six coordinate bonds with?six?small,?monodentate?ligands
  • Examples of such ligands are?water?and?ammonia?molecules and?hydroxide?and?thiocyanate?ions
• It could be six coordinate bonds with?three?bidentate?ligands
  • Each bidentate ligand will form two coordinate bonds, meaning six coordinate bonds in total
  • Examples of these ligands are?1,2-diaminoethane?and the?ethanedioate ion
• It could be six coordinate bonds with?one polydentate?ligand
  • The polydentate ligand, for example EDTA^4-_,?forms all six coordinate bonds
• The bond angles in an octahedral complex are 90^o

Examples of octahedral complexes

Types of ligands table

• The?coordination number?of a complex is the number of coordinate bonds that are formed between the?ligand(s)?and the central metal atom or ion
• Some ligands can form only one coordinate bond with the central metal ion (monodentate ligands), whereas others can form two (bidentate ligands?) or more (polydentate ligands)
• It is?not?the number of ligands which determines the coordination number, it is the number of coordinate (dative) bonds

Predicting complex ion formula & charge

• The formula and charge of a complex ion can be predicted if the following are known:
  • The central metal ion and its charge/oxidation state
  • The ligands
  • The coordination number/geometry