Complex Ions

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Complex Ions Co-ordination Compounds

• Definitions
• Overall Structure
• Ligands
• Formulas
• Isomerism
• Important Biological Examples

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Complex ions Co-ordination Compounds

• Complex ions
• Central metal ion (acting as Lewis acid) binds
  1 or more Lewis bases
• Lewis bases have one or more electron pairs
  Ligands
• Number of bound ligands is related to electronic
  structure of metal ion
• Co-ordination compounds
• Neutral salts of complex ions
• Nature of Interaction
• Bonding or Electrostatic?
• Overlap of empty d orbitals of transition metals
  with (usually) p orbitals of ligands
• Overlap of orbitals bonding ? co-ordinate
  covalent bonding
• One species provides all the electrons in bond

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Electronic Structure Strength of Complex Ions

• Geometries determined in complex ways
• Linear
• 2 ligand sites separated by 180o
• Square planar
• 4 ligand sites in plane separated by 90o
• Tetrahedral
• 4 ligand sites in 3-D separated by 109.5o
• Octahedral
• 6 ligand sites in 3-D separated by 90o
• Ligand sites can be filled by ligands with one
  electron pair or with multiple electron pairs
• The tendency of a metal ion to form a particular
  complex is called a formation constant, Kf
• Competitive with Ka, Ksp constants

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CuSO4
Cu(NH3)42
Cu(OH)2
Insoluble Cu(OH)2 forms after adding NH3
Hydroxide formed by ionization of NH3 with water
The precipitate dissolves upon adding more NH3
forming Cu(NH3)42
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Ligands

• Neutral Ligands
• H2O, NH3, amines, phosphines (like amines except
  with P)
• Anion Ligands
• Halides, CN-, OH-, carboxy groups
• Monodendate Ligands
• Ligands that have only one electron pair for
  bonding
• H2O, NH3 ,Halides, CN-, OH-
• Polydendate Ligands
• Ligands that have two or more electrons pairs for
  bonding
• ethylene diamine H2N-CH2-CH2-NH2 bidentate
• H2N(CH2)2NH(CH2)2NH2 tridentate
• Also known as chelates

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Formulas of Complex Ions

• General formula for complex ion
• Metal ion (ligand)a (ligand)b overall charge
• General formula for co-ordination compound
• Cation Metal ion (ligand)a(ligand)b OR
• Metal ion (ligand)a(ligand)b Anion
• Examples (complex ions)
• Co(NH3)3(H2O)2Cl Co 2 3 NH3 2 H2O 1
  Cl-
• Zn(OH)42- Zn 2 4 OH-
• Ni(en)3 2 Ni 2 3 en (ethylene diamine)
• Pt(en)2Cl2 2 Pt 4 2 en 2 Cl-
• Examples (co-ordination compounds)
• Co(NH3)3(H2O)2ClCl
• Na2Zn(OH)4

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Isomerism in Complex Ions - 1

• Isomers Same molecular formula, different
  structures due to geometry
• Isotope same element, different of neutrons
  in nucleus
• Resonance isomers structures different in terms
  of location of double bond

A
B

• In A Xs and Ys are across from each other trans
• Translation to change from one language across
  to another
• In B Xs and Ys are next to each other cis
• Possible for square planar and octahedral
  structures
• Have to be careful rotate to make sure
  structures are not equivalent

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Isomerism in Complex Ions - 2


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Biological Complex Ions

• Complex ions and co-ordination compounds have
  crucial roles in life processes
• Chlorophyll photo systems
• Harnessing of light energy (upon which all life
  depends)
• Mg 2 in center of square planar arrangement with
  N organic ligands
• Hemoglobin Myoglobin
• Oxygen transport and storage
• Fe 2 in center of octahedral arrangement with
  nitrogen ligands in plane and moveable arms that
  swing in and out of place as oxygen binds
• Cytochromes
• Electron transport chain uses oxygen to accept
  electrons at end of metabolism
• Fe 2 to Fe 3 shuttle in center of octahedral
  arrangement with nitrogen ligands
• Vitamin B12
• Essential vitamin Carbon 1 metabolism
• Co 2 to Co 3 redox reaction
• Superoxide dismutase P-450 enzymes
• Scavenger enzymes for toxins
• Fe S complexes
• Nitrogenase
• Fixation of nitrogen by bacteria
• Mo/Fe complexes with S and N groups

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