complex formation

• complex :is a central metal ion surrounded by ligands.
• term ligand ~ An atom, ion or molecule which can donate a lone electron pair
• Co-ordinate bonding is involved in complex formation.

  • Co-ordinate bonding is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms.
• term co-ordination number ~The number of co-ordinate bonds formed to a central metal ion.
• ligands can be unidentate

  • (e.g. H2O, NH3 and Cl- )
  • form one coordinate bond per ligand
• ligands can be bidentate

  • (e.g. NH2CH2CH2NH2 and ethanedioate ion C2O4 2- )
  • have two atoms with lone pairs and can form two coordinate bonds per ligand
• ligands can be multidentate

  (e.g. EDTA4- which can form six coordinate bonds per ligand).
• draw the A complex with bidentate ligands e.g. [Cr(NH2CH2CH2NH2 )3 ]3+


  There are 3 bidentate ligands in this complex each bonding in twice to the metal ion It has a coordination number of 6

  
• A complex with bidentate ligands e.g. [Cr(NH2CH2CH2NH2 )3 ]3+

  • There are 3 bidentate ligands in this complex each bonding in twice to the metal ion
  • It has a coordination number of 6
• draw A complex with bidentate ethanedioate ligands e.g. [Cr(C2O4 )3 ]3-

  A complex with bidentate ethanedioate ligands e.g. [Cr(C2O4 )3 ]3

  
• Equations to show formation of bidentate and mutidentate complexes

  • Cu(H2O)6 2+ + 3NH2CH2CH2NH2  [Cu(NH2CH2CH2NH2 )3 ]2+ + 6H2O
  • Cu(H2O)6 2+ + 3C2O4 2- [Cu(C2O4 )3 ]4- + 6H2O
  • Cu(H2O)6 2+ + EDTA4- [Cu(EDTA)]2- + 6H2O