Complexes of metal ions and nomenclature for inorganic compounds

1
Complexes of metal ions and nomenclature for
inorganic compounds
ammonia ligands
Cobalt(III) ion
blue nitrogen donor atom
white hydrogen atom
Co(NH3)63
2
Complexes of metal ions.

• Prior to the work of Werner on coordination
  complexes, formulated at the time as CoCl3.6NH3,
  for example, there was no understanding of why
  the six ammonia molecules were so strongly bound
  in this compound. Werner showed that the ammonia
  molecules were in fact chemically bound to the
  cobalt, and that the three Cl- ions were present
  only to act as counter-ions to the 3 charge on
  the Co(NH3)63 cation.

Alfred Werner (1866-1919) Nobel prize 1913 for
his work on Coordination compounds
3
(a) (b)
(c)

• Co(NH3)63 Co(NH3)5Cl2 Co(NH3)3Cl3
• Werner proposed that Co(III) (trivalent cobalt)
  had a coordination number of six, which could be
  satisfied by six ammonias in a, five ammonias
  and a Cl- in b, and three ammonias and three
  Cl- in c. His theory explained why conductivity
  showed that in solution a was a 3 cation, b
  was a 2 cation, and c was neutral. The
  molecules or ions coordinated to the Co(III) are
  called ligands, from the Latin ligare meaning
  to join. The coordination geometry of the
  Co(III) is octahedral, which means that the six
  ligands are placed around the Co(III) at the
  corners of an octahedron.

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Some complexes of metal ions
cyanide ion
nickel
ammonia
Cobalt
water molecule
nickel
2
2
2-
C N
N
O
Co(H2O)62 Ni(NH3)62
Ni(CN)42-
Hexaaquacobalt(II) hexamminenickel(II)
tetracyanonickelate(II)
A complex is written such that everything inside
the square brackets is a ligand chemically bonded
to the metal ion. Everything outside the brackets
is a counter-ion or something simply present in
the crystal lattice. Thus, we might have
Co(H2O)6(NO3)2 where the NO3- ions are
counter-ions.
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Formal Oxidation State

• The formal oxidation state of metal ions in
  their complexes is determined by ascribing formal
  charges to all ligands which correspond to those
  they possess as the free molecules or ions
• Neutral NH3, H2O, CO, PH3, (CH3)2S
• Anionic OH-, F-, Cl-, Br-, I-, CN-, SCN-
• Cationic NO

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• Examples of oxidation states
• Co(NH3)63 Co(III)
• hexamminecobalt(III)
• K3Fe(CN)6 Fe(III)
• potassium hexacyanoferrate(III)
• Co(NH3)4Cl2Cl Co(III)
• tetrammiinedichlorocobalt(III) chloride
• FeNO(NH3)5Cl3 Fe(II)
• pentamminenitrosyliron(II) chloride
• Cr(CO)6 Cr(0)
• hexacarbonylchromium(O)
• KV(CO)6 V(-I)
• potassium hexacarbonylvanadate(-I)
• Mn(NO)3CO Mn(-III)
• trinitrosylcarbonylmanganese(-III)

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Identifying which are ligands

• In the formula for a complex, everything inside
  the square brackets (blue in formula below) is
  coordinated to the metal ion, everything outside
  (red) is a counterion or a lattice molecule.
• When the name of a complex is written, all the
  ligands that are coordinated to the metal ion
  come before it, while counter-ions come after the
  name of the metal
• Co(NH3)4Cl2Cl is
• tetramminedichlorocobalt(III)chloride

ligands bonded to metal ion counterion
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Naming of ligands in complexes Neutral ligands

• When naming a complex, the ligands are indicated
  by names as follows
• Neutral ligands NH3 ammine
• H2O aqua
• CO carbonyl
• The number of each type of ligand present is
  indicated by the Latin prefixes di-, tri-,
  tetra-, penta-, hexa-, hepta-, octa-, nona-, and
  deca-
• Co(NH3)6Cl3 hexamminecobalt(III) chloride
• La(H2O)9(NO3)3 nona-aqua lanthanum(III)
  nitrate
• K2Ti(CO)6 potassium hexacarbonyl
  titanate(-II)

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Naming of ligands in complexes anionic ligands

• Anionic ligands To indicate that they are
  anions, ligands in complexes are given an o
  ending fluoro, chloro, bromo, iodo, hydroxo,
  cyano, sulfato, nitro, etc. If the overall charge
  on the complex is negative, the metal ion is
  given an ate ending to indicate this
• K3Fe(CN)6 potassium hexacyanoferrate(III)
• or potassium hexacyanoiron(III)
• K4Fe(CN)6 potassium hexacyanoferrate(II)
• Na3AlF6 sodium hexafluoroaluminate(III)
• Co(NH3)3F3 triamminetrifluorocobalt(III)

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Nomenclature of complexes

• Cations, including complex cations, come first,
  anions, including complex anions come second
• Co(NH3)6Cl3 hexammine cobalt(III) chloride,
  Na3CrCl6 sodium hexachlorochromate(III),
  Ni(H2O)6Cl2 hexaaquanickel(II) chloride
• K3Rh(CN)6 potassium hexacyanorhodate(III)
• Co(NH3)6Co(CN)6 hexamminecobalt(III)
  hexacyanocobaltate(III)

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Naming more complex ligands

• Many ligands are more complex and have more than
  one donor atom, such as en (ethylenediamine),
  bipy (2,2-bipyridyl) and acac (acetyacetonate)
  below
• Where more complex ligands are present, one
  indicates the number of these present with
  prefixes bis-, tris-, tetrakis, pentakis, or
  hexakis, followed by the name of the ligand in
  parentheses. Thus, Co(en)3Cl3 is
  tris(ethylenediamine)cobalt(III) chloride.

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Some cobalt(III) complexes of more complex
ligands
tris(ethylenediamine) tris(2,2-bipyridyl) tr
is(acetylacetonato) cobalt(III)chloride
cobalt(III) nitrate cobalt(III)
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NOMENCLATURE

• 1.1 Formulas of Simple Ionic substances.
• For ionic compounds, the cation (more
  electropositive element) should always be first.
  (KCl, Na2S). If several cations are present, they
  should be listed in alphabetical order, followed
  by anions in alphabetical order (LiMgClF2). An
  exception is the proton, which is always listed
  last in the sequence of cations, (RbHF2).

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Nomenclature (contd.)

• 1.2. Sequence of atoms in formulas of polyatomic
  ions and molecules
• For polyatomic species with a central atom,
  these are generally listed first followed by the
  attached atoms in alphabetical order (SO42-,
  CCl2H2, PCl3O, SO3, -CF3, -SCN). An exception is
  the linear thiocyanate group (-SCN), where
  the atoms are placed in the order in which they
  occur in the thiocyanate ion
• -SCN

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Formulas and Names of Common substances.

• Acid Name Name of anion
• HNO3 Nitric acid nitrate
• H3PO4 Phosphoric acid phosphate
• H2SO4 Sulfuric acid sulfate
• HClO4 Perchloric acid perchlorate
• HClO3 Chloric acid chlorate
• HClO2 Chlorous acid chlorite
• HClO Hypochlorous acid hypochlorite
• HCl Hydrochloric acid chloride

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Chemical Names

• Names of the Elements These originated with
  Berzelius (1813) who developed the system that
  the symbol for an element was the first letter of
  its name, e.g., F, O, N, C, B. If there was more
  than one element whose name started with the same
  letter, then a second, lower-case letter, was
  added, which was usually the second letter of the
  name of the element. e.g. C for carbon, but Ca,
  Cd, Ce, Cf, Cl, Cm, Co, Cr, Cs, Cu. B for Boron,
  but Ba, Be, Bi, Bk, Br, and so on.

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Names of metallic elements you should know
(pretty much all of them)

• H
• hydrogen
• Li Be
• lithium beryllium
• Na Mg
• sodium magnesium
• K Ca Sc Ti V
• potassium calcium scandium titanium vanadium
• Rb Sr Y Zr Nb
• rubidium strontium yttrium zirconium niobiuim
• Cs Ba La Hf Ta
• cesium barium lanthanum hafnium tantalum

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Names of metallic elements you should know
(continued)

• Cr Mn Fe Co Ni Cu Zn
• chromium manganese iron
  cobalt nickel copper zinc
• Mo Tc Ru Rh Pd Ag Cd
• molybdenum technetium ruthenium rhodium
  palladium silver cadmium
• W Re Os Ir Pt Au Hg
• tungsten rhenium osmium
  iridium platinum gold mercury
• Lanthanides
• La Ce . Gd . Lu
• lanthanum cerium gadolinium lutetium
• Actinides
• Ac Th . U Np Pu Am
• actinium thorium uranium neptunium
  plutonium americium

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Geometrical Isomerism
ammonia
chloride
Pt
Pt
cis-diamminedichloro
trans-diamminedichloro- platinum(II)
platinum(II)
Geometrical isomers can exist with two identical
ligands placed next to each (cis) or at 180º to
each other (trans). Again, Werners theory could
explain how two different complexes
corresponding to (NH3)2Cl2Pt could exist.
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Cis and trans isomerism of octahedral complexes
green Cl
trans-Co(NH3)4Cl2 cis-Co(NH3)4Cl2
(green)
(violet)
An important aspect of Werners theory was that
it could explain how two compounds of identical
formula, i.e. Co(NH3)4Cl2Cl, could exist as two
entirely different forms, which we now know to be
the cis and trans forms above.
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fac (facial) and mer (meridional) geometrical
isomers of the Co(NH3)3Cl3 complex
mer
fac mer-Co(NH3)Cl3
fac-Co(NH3)Cl3
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Optical isomerism
mirror plane
? (lambda) form ? (delta) form
The tris(ethylenediamine)cobalt(III) complex
exists as optical isomers. the ? and ? forms,
which are non-superimposable mirror images of
each other. This will be discussed further under
group theory.