15.8 - Shapes of Complex Ions

• affects shape of complex ions?

  number of ligands
• factors affecting number of ligands

  size of ligand

  size of central metal ion

  bonding electrons in dative covalent bond repel each other so ligands are positioned as far away from each other as possible
• 6-fold coordination

  octahedral shape with 90 degree bond angle

  6 electron pairs around central atom repel as far as possible
• ligands that form 6-fold coordination

  H2O

  OH-

  NH3
• 4-fold coordination

  tetrahedral shape with 109.5 degree bond angle

  sometimes can be square planar with 90 degree bond angle - e.g.: cis-platin
• ligands that form 4-fold coordination

  Cl- and other large ligands
• 2-fold coordination

  linear shape

  180 degree bond angle
• what's the only complex ion that has a linear shape?

  diamminesilver(I)
• monodentate ligand

  ligands that only have/use one lone pair to form a dative covalent bond with central metal atom
• examples of monodentate ligands

  H2O

  NH3

  Cl-

  OH-

  CN-
• bidentate ligand

  ligands that can form two dative covalent bonds with central metal atom as they have two lone pairs
• example of bidentate ligands

  1,2-diaminoethane

  ethanedioate ion (C2O4)2-

  amino acids
• multidentate ligands

  ligands that form more than one dative covalent bond with central metal atom forming chelates
• examples of multidentate ligands

  haemoglobin

  EDTA4-
• chelates

  complex ions involving multidentate ligands
• what it EDTA4-

  a multidentate ligand

  forms 6 dative covalent bonds
• what does EDTA stand for?

  ethylenediaminetetraacedic acid
• uses of EDTA4-

  treat lead poisoning

  prevent foods from going off

  ingredient in bathroom cleaners
• how is EDTA4- used to treat lead poisoning?

  it forms a stable compound with lead ions so they can be excreted in urine
• how does EDTA4- preven food from going off?

  traps traces of metal ions by forming complex ions that would catalyse oxidation of vegetable oils
• why is EDTA4- used in bathroom cleaners?

  helps remove scale by dissolving CA2+ from CaCO3 left by hard water
• what is cis-platin?

  a neutral ligand complex with 2 isomers (cis/trans)
• shape of cis-platin

  square planar
• use of cis-platin

  anti-cancer drug

  it undergoes a ligand exchange reaction inside the cell forming a positive ion that binds to DNA strand in tumour so they can't separate so stops DNA replication
• why isn't trans-platin used to treat cancer?

  it's toxic