COMPLEX IONS

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COMPLEX IONS

• Compounds in which metal ion is surrounded by a
  group of anions or neutral molecules.

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Metal Ions. . .

• do not exist in isolation.
• are accompanied by anions whose negative charge
  balances the positive charge of metal ion,
  producing neutral compounds.
• have empty valence orbitals therefore act as
  electron pair acceptors.

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Metal Ions. . .

• act as Lewis acids.
• Anions or molecules with unshared pairs of
  electrons can act as Lewis bases and bind to
  metal center.
• ability to form complexes increases positive
  charge increases and size decreases.
• Weakest complexes formed by alkali metals.
• 2 and 3 ions of transition elements show
  greatest tendency to form complexes.
• Cr 3 forms more stable complexes than does Al 3

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Ligands. . .

• Molecules or ions surrounding the metal ion.
• Are known as complexing agents.
• Normally either anions or polar molecules.
• Must have at least one unshared pair of valence
  electrons.
• Therefore act as electron pair donors/Lewis bases.

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Coordination Sphere. . .

• The central metal and the ligands.
• Cu(NH3)4SO4
• Placed inside brackets to set it off from other
  parts of the compound.

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Complex Ions. . .

• Metal ions in water, the ligand is water.
• In aqueous solution, ligands such as SCN- and CN-
  replace H2O in the coordination sphere.
• Different properties than metal or ligands.
• Color.
• Oxidation state stabilized. Reduction potentials
  change.

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Charge. . .

• Is the sum of the charges on the central metal
  and surrounding ligands.

Cu(NH3)4SO4
SO4 2- (charge of the polyatomic ion)
NH3 0 (molecule therefore no charge)
Cu 2 (based on what is needed to balance the
charges)
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Practice determining charges

• 1. What is the oxidation number of the central
  metal in Co(NH3)5Cl(NO3)2?
• 2. What is the charge of the complex formed by a
  platinum (V) metal ion surrounded by three
  ammonia molecules and three bromide ions?
• Write the formula for this complex ion.
• 3. Given that a complex ion contains a chromium
  (III) bound to four water molecules and two
  chloride ions, write its formula.

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Nomenclature. . .

• Co(NH3)5ClCl2
• In naming salts, the name of the cation is given
  before the name of the anion.
• Co(NH3)5Cl2 Cl-
• Ligands are named before the metal.
• Co(NH3)5Cl2
• Ligands named in alphabetical order.
• Do not consider charge or prefix.
• In writing formula, metal is written first.

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• Anionic ligands end in the letter o. Others bear
  the name of the molecule.
• Ligand Ligand Name
• Azide,N3- azido
• Bromide, Br- bromo
• Chloride,Cl- chloro
• Cyanide, CN- cyano
• Hydroxide, OH- hydroxo
• Carbonate,CO3 2- carbonato
• Oxalate, C2O4 2- oxalato

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Neutral Molecules. . .

• Ligand Ligand Name
• Ammonia, NH3 ammine
• Ethylenediamine, en ethylenediamine
• Water,H2O aqua
• CH3NH2 methylamine
• CO carbonyl
• NO nitrosyl

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• A Greek prefix is used to indicate the number and
  kind of each ligand when more than one is
  present.
• Co(NH3)5ClCl2
• Pentaammine
• If the name of the ligand contains a prefix, then
  the name of the ligand is enlosed in parentheses.
  Alternate prefixes are used bis-, tris-,
  tetrakis, petakis-, and hexakis for the name
  enclosed in the parentheses.
• Co(en)3Cl3
• Tris(ethylenediamine)cobalt (III)

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Monodentate LigandUnidentate Ligand

• Form one bond to the metal ion.
• H2O
• NH3
• NO2-
• SCN-
• OH-
• X- (halides)

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Bidentate Ligand

• Form two bonds to the metal ion. . .
• Oxalate
• Ethylenediamine
• Use bis-, tris-, tetrakis-, etc.

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• If the complex is an anion, its name ends in
  ate K4Fe(CN)6
• The suffix ate is added to the latin stem.
• Fe(CN)6 4- hexacyanoferrate (II) ion.
• K4Fe(CN)6
• Iron Ferrate
• Copper cuprate
• Lead plumbate
• Silver argenate
• Gold aurate
• Tin stannate

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• The oxidation number of the metal is given in
  parentheses in Roman numerals following the name
  of the metal.
• hexacyanoferrate (II)
• Tris(ethylenediamine)cobalt (III)

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Practice. . .
Ni(C5H5N)6Br2
Hexapyridinenickel(II)bromide
Co(NH3)4(H2O)CNCl2
Tetraammineaquacyanocobalt(III)chloride
Na2MoOCl4
Sodium tetrachlorooxomolybdate(IV)
NaAl(OH)4
Sodium tetrahydroxoaluminate