Transition Metals, Coordination
Compounds and Complex Formation
--Read Section 23.4 in Silberberg for an introduction to
coordination compounds and complexes.
--Do problems 23:45,46,47,48,53,55,58, 67,73
--Friday back to some equlibrium and formation constants
The Transition Metals
Order of orbitals
filling in multielectron atoms
Oxidation States of the 1st Row Transition Metals
(most stable oxidation numbers are shown in red)
Coordination compounds or consist of a complex metal ion
bounded to a anionic counter ion or ions called a ligand.
ligands
••
N
H H H
Co2+
••
••
•• Cl
••
complex
metal ion
A ligand has at least one unshared pair of valence
electrons. It is a Lewis base (e- donar) and the metal
ion a Lewis acid (e- acceptor).
Terminology of Coordination Compounds
Coordination Number - the number of ligands bonded
directly to the central metal ion.
• specific for a given metal ion and oxidation state
•indicative of a geometry around the central atom
Terminology of Coordination Compounds
The atom in a ligand that is bound directly to the metal atom is
the donor atom.
••
•• •
•O
N
H
Ligands with:
one donor atom
two donor atoms
three or more donor atoms
H
H H H
Are Called
monodentate
bidentate
Examples
H2O, NH3, Clethylenediamine
polydentate
EDTA
Examples of ligands and their nomenclature
bidentate ligand
••
H 2N
CH2
CH2
••
NH2
polydentate ligand
(EDTA)
Bidentate and polydentate ligands are also called chelating
agents as they tend to bind many types of metal ions.
Polydendate Ligands (>1 atom donating e-)
How do we communicate and represent Complex Ions?
[CoCl(H2O)(NH3)4]+Cl-What is the coordination number of the metal ion?
-What is the oxidation state of Co?
-What is the geometry of the complex?
-What is the net charge of the complex?
-Name the ligands that surround the central atom?
-What is the charge of the ligands?
Charge on the metal ion:
Common Ligands
What are the oxidation numbers of the metals
in K[Au(OH)4] and [Cr(NH3)6](NO3)3 ? Name
the ligands and their charge.
What are the oxidation numbers of the metals
in K[Au(OH)4] and [Cr(NH3)6](NO3)3 ?
OH- has charge of -1
K+ has charge of +1
? Au + 1 + 4x(-1) = 0
Au = +3
NO3- has charge of -1
NH3 has no charge
? Cr + 6x(0) + 3x(-1) = 0
Cr = +3
Naming Coordination Complexes
• The cation of the complex is named before the anion.
• Name the ligands first, in alphabetical order, without regard to
prefixes, followed by the name of the metal centre.
• Anions as ligands are named by using the ending –o.
• Some ligands have common names that must be learned (H2Oaqua, NH3 see table)
• The number of ligands of a given kind is given by a prefix mono,
di, tri, tetra, penta, hexa…
• If the ligand is a composite name we then use bis, tris = 3,
tetrakis = 4 and parenthesize the ligand
• The oxidation state of the metal centre is given by a Roman
numeral and must be determined by considering the ligand
charges.
• If the metal complex is an anion itself the ending –ate is attached
to the name of the metal.
25-3 Nomenclature
• In names and formulas of coordination compounds, cations
come first, followed by anions.
• Anions as ligands are named by using the ending –o.
– Normally
• – ide endings change to –o.
• – ite endings change to –ito.
• – ate endings change to –ato.
• Neutral molecules as ligands generally carried the
unmodified name.
Writing Coordination Complex Names
• When writing the formula
• the chemical symbol of the metal is written first,
• followed by the formulas of anions,
– in alphabetical order.
• and then formulas of neutral molecules,
– in alphabetical order.
What is the systematic name of
[Cr(H2O)4Cl2]Cl ?
tetraaquodichlorochromium(III) chloride
Write the formula of
tris(ethylenediamine)cobalt(II) sulfate
[Co(en)3]SO4