Transition Metals and Coordination
Chemistry
• What is a transition metal?
• What are the characteristics of a transition
metal?
Transition Metals
• A transition metal is a metal which forms at
least one ion with a partially filled d orbital.
Properties
•
•
•
•
•
High melting point
Good conductors
Display variable oxidation states
Form complexes
Usually coloured
Coordination Compounds
• A coordination compound, sometimes
called a coordination complex, contains a
central metal atom or ion surrounded by
ligands.
Ligands
• A ligand is a neutral molecule or ion which
must possess at least one lone pairs of
electrons to bond to the metal.
• Lewis acid?
• Lewis base?
Transition metal ions are Lewis acids Þ they accept
electron pairs.
Ligands are Lewis bases Þ molecules or ions which
donate electron pairs.
Ligands bonded to metal ions Þ metal complexes or
coordination compounds.
Coordination number:
number of electron donor atoms attached to the metal.
Coordinate Covalent Bond
• Bond resulting from the interaction
between a Lewis base (the ligand) and a
Lewis acid (the metal ion).
LIGANDS
Ligands can be classified as monodentate or polydentate.
Polydentate ligands are also called chelates.
Chelates are ligands possessing two or more donor atoms.
MONODENTATE LIGANDS
•
Monodentate ligands are Lewis bases that donate a single pair of
electrons to a metal atom.
Anions F-, Cl-, Br-, CN-, SCN-, NO2-, etc.
Neutral ligands:
NH3, H2O, CO
BIDENTATE LIGANDS
BIdentate ligands are Lewis bases that donate two electron pairs to a metal atom.
(ox)
(en)
The Bidentate
Ligand
Ethylenediamine
and the
Monodentate
Ligand Ammonia
HEXADENTATE LIGANDS
Hexadentate ligands are Lewis bases that donate two electron pairs to a metal
atom.
The Coordination
of EDTA with a 2+
Metal Ion
ethylenediaminetetraacetate
Ligands
• Neutral molecule or ion having a lone electron
pair that can be used to form a bond to a metal
ion.
§ Monodentate ligand – one bond to a metal ion
§ Bidentate ligand (chelate) – two bonds to a
metal ion
§ Polydentate ligand (chelate) – more than two
bonds to a metal ion
Common Coordination Numbers
Common Coordination
Number
Geometry
2
linear
4
Tetrahedral, square planar (d8)
6
Octahedral
4 and 6 are the most common coordination numbers.
Nomenclature of complexes
• The name of a transition metal complex must
include the following:
• The name of the metal atom and its oxidation state.
• The names and numbers of the ligands
• The overall charge on the ion
Nomenclature of complexes
Metal
The name of the metal atom actually depends on the nature of the charge on
the ion. If the transition metal is part of a positive ion then the element keeps its
usual name. eg. iron, copper, chromium etc, followed by the oxidation state.
However, if the ion is negative overall the transition metal atom changes its
name (once again followed by the oxidation state):
Element
part of a negative ion
vanadium
vanadate
titanium
titanate
chromium
chromate
manganese
manganate
iron
ferrate
cobalt
cobaltate
nickel
nickelate
copper
cuprate
Nomenclature of complexes
Ligands
The names and numbers of the ligands must be stated. The ligands have
special names to differentiate them from non-complexed systems.
The Complex Ion Co(NH3)63+
A Coordination Compound
• Typically consists of a complex ion and
counterions (anions or cations as needed to
produce a neutral compound):
[Co(NH3)5Cl]Cl2
[Fe(en)2(NO2)2]2SO4
K3[Fe(CN)6]
Rules for Naming Coordination Compounds
[Co(NH3)5Cl]Cl2
1. Cation is named before the anion.
“chloride” goes last (the counterion)
2. Ligands are named before the metal ion.
ammonia (ammine) and chlorine
(chloro) named before cobalt
Rules for Naming Coordination Compounds
[Co(NH3)5Cl]Cl2
3. For negatively charged ligands, an “o” is
added to the root name of an anion (such as
fluoro, bromo, chloro, etc.).
4. The prefixes mono-, di-, tri-, etc., are used to
denote the number of simple ligands.bis-, tris, tetrakis
penta ammine
Rules for Naming Coordination Compounds
[Co(NH3)5Cl]2+ Cl2
x + 0 + -1 = +2
5. The oxidation state of the central metal ion is
designated by a Roman numeral:
cobalt (III)
6. When more than one type of ligand is present,
they are named alphabetically:
pentaamminechloro
Rules for Naming Coordination Compounds
[Co(NH3)5Cl]Cl2
7. If the complex ion has a negative charge, the
suffix “ate” is added to the name of the metal.
The correct name is:
pentaamminechlorocobalt(III) chloride
Exercise
Name the following compounds:
(a) [Cu(H2O)6]2+ hexaaquacopper(II) ion
(b) [Co(H2O)4(NH3)2]Br3
diamminetetraaquacobalt(III) bromide
(c) Na2[PtCl4] sodium tetrachloroplatinate(II)
(d) [Cr(NH3)3(H2O)3]Cl3 triamminetriaquachromium(III)
chloride
(e) [Co(H2NCH2CH2NH2)3]2(SO4)3
tris(ethylenediamine)cobalt(III) sulphate
Complete the table below:
Complex
shape
coordination
number
name
Electron configuration
[Fe(H2O)6]3+
octahedral
6
Hexaaquairon (II) ion
[Ar]3d5
K4[Fe(CN)6]
octahedral
6
Potassium hexacyanoferrate(II)
[Ar]3d6
[CuCl4]3-
tetrahedral
4
Tetrachlorocuprate(I) ion
[Ar]3d10
[Cu(NH3)4]2+
tetrahedral
4
Tetramminecopper(II) ion
[Ar] 3d9
[Co(ox)2(NH3)2]
octahedral
6
Diamminebis(oxalato)cobalt(
[Ni(CO)4]2+
Sq. planar
4
Tetracarbonylnickel(II)
[Ar]3d8
Give the formulas of the following coordination compounds?
1. hexaammineiron(III) nitrate [Fe(NH3)6](NO3) 3
2. ammonium tetrachlorocuprate(II) (NH4)2 [CuCl4]
3. sodium monochloropentacyanoferrate(III) Na3 [Fe(CN)5Cl]
4. potassium hexafluorocobaltate(III) K3[CoF6]
• http://www.chemistry.wustl.edu/~edudev/LabTuto
rials/naming_coord_comp.html