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Alfred Werner
1913 Nobel Prize in Chemistry
Theory of the structure of
coordination compounds
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20a–1
Werner's
Coordination Theory
• primary valence => ion charge
• secondary valence => coordination
number
• inner sphere => ligands bonded
directly to metal ion
• outer sphere => next sheath of ions
or molecules
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20a–2
Terminology
coordinate covalent bond - covalent bond
formed by one atom donated both electrons
of shared pair; Lewis acid-base reaction
ligand - electron pair donor; Lewis base
coordination number - number of electrons
pairs accepted by central metal atom
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20a–3
Coordinate Covalent Bond
+
+
H
H
N
H
+ H+
H
H
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N H
H
H
or
H
N
H
H
20a–4
Some Common Ligand
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20a–5
More Ligands
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20a–6
Some important aspects of transition metal ions:
1. The valence electrons are in d orbitals
2. The d orbitals do not have large radial
extension
3. The d orbitals are therefore mostly
nonbonding in complexes of transition metal
ions
4. For these reasons, the effects of redox
changes are substantially smaller for
transition metals than for main group elements
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20a–8
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20a–9
Coordination Compounds: Structure
and Nomenclature
Coordination Number => 2, 4 & 6 most
common
CN
Shape
2
linear
4
tetrahedral
4
square planar
6
octahedral
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20a–10
Coordination
Number 2
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20a–11
Coordination Number 4
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20a–12
Coordination
Number 6
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20a–13
Multiplicity
Monodentate
mono => 1
di => 2
tri => 3
tetra => 4
penta => 5
hexa => 6
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Bi- or tri- dentate
bis => 2
tris => 3
tetrakis => 4
20a–14
Names
1. In naming the entire complex, the name of the cation is
given first and the anion second (just as for sodium
chloride), no matter whether the cation or the anion is the
complex species.
2. In the complex ion, the name of the ligand or ligands
precedes that of the central metal atom. (This procedure is
reversed from writing formulae.)
3. Ligand names generally end with 'o' if the ligand is
negative ('chlorido' for Cl-, 'cyanido' for CN-, 'hydrido'
for H-) and unmodified if the ligand is neutral
('methanamine' for MeNH2). Special ligand names are
'aqua' for water, 'ammine' for ammonia, 'carbonyl' for CO,
'nitrosyl' for NO.
4. A Greek prefix (mono, di, tri, tetra, penta, hexa, etc.) indicates
the number of each ligand (mono is usually omitted for a single
ligand of a given type). If the name of the ligand itself contains the
terms mono, di, tri, eg triphenylphosphine, then the ligand name is
enclosed in parentheses and its number is given with the alternate
prefixes bis, tris, tetrakis instead. For example, NiCl2(PPh3)2 is
named dichloridobis(triphenylphosphane)nickel(II).
Again, one would use diammine, for (NH3)2, but bis(methylamine),
for (NH2Me)2, to make a distinction from dimethylamine. (Note
that this ambiguity does not arise if the preferred IUPAC name,
methanamine, is used instead of methylamine).
There is no elision of vowels or use of a hyphen, e.g. in
tetraammine and similar names. Some texts suggest that if a
ligand is "complicated" then use the bis, tris multipliers. What
constitutes "complicated" is not spelled out however, so a simpler
approach is to use them if the name of the ligand is three or more
syllables long!
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20a–16
5. A Roman numeral or a zero in parentheses is used to
indicate the oxidation state of the central metal atom.
6. If the complex ion is negative, the name of the metal ends in
'ATE' for example, ferrate, cuprate, nickelate, cobaltate etc.
7. If more than one ligand is present in the species, then the
ligands are named in alphabetical order regardless of the
number of each. For example, NH3 (ammine) would be
considered an 'a' ligand and come before Cl- (chlorido). (This
is where the 1971 rules differed from the 1959 rules. Some
texts still say that ligands are named in the order: neutral then
anionic).
Examples:
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20a–17
Nomenclature
Neutral molecule
[Ru(NH3)4(HSO3)2]
bis(bisulfite)tetraamineruthenium(II)
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20a–18
Nomenclature
Anionic coordination sphere
K3[Fe(CN)6]
potassium hexacyanoferrate(III)
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20a–19
Nomenclature
Cationic coordination sphere
[Cu(NH3)4]SO4
tetraaminecopper(II) sulfate
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20a–20
Nomenclature
Cationic coordination sphere & Anionic
coordination sphere
[Ti(H2O)6][CoCl6]
hexaaquatitanium(III)
hexachlorocobaltate(III)
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20a–21
Coordination Isomers
[Co(NH3)6][Cr(CN)6]
[Cr(NH3)6][Co(CN)6]
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20a–22
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20a–23