Chapter 24
Transition Metals &
Coordination Compounds
• 24.2 Properties of Transition Metals
o Review Electron Configuration
o Trends in the Periodic Table
• 24.3 Coordination Compounds
o The Basics
o Example of Naming
• 24.4 Structure and Isomerization
Transition Metals contain e- in d
Orbitals
http://www.can-do.com/uci/lessons98/Periodic.html http://www.can-do.com/uci/lessons98/Periodic.html
Why Are Transition Metals &
Coordination Compounds Important?
• Therapeutic drugs
• Chemical Sensors
• Coloring agents
o Paints
o Cosmetics
• Biological Molecules
o Hemeglobin
o Chlorophyll
• Gems (Jewelry & Technological
Applications)
o Rubies, Emeralds, Garnets, etc.
o Lasers
24.2 Properties of Transition Metals
• Moderate to High Densities
• Good Electrical Conductivity
• High Melting Points
• Moderate to Extreme Hardness
Due to the delocalization of d electrons in metallic bonding
Exceptions: Elements with filled d
orbitals, which prevents d-d bonding.
Hg has a low melting point and is liquid
at room temperature.
http://www.tutorvista.com/chemistry/shapes-of-d-orbitals
Electron Configuration
I
n
c
r
e
a
s
i
n
g
E
n
e
r
g
y
(n-1)d
(n-2)f
Electron Configuration
[noble gas] ns2 (n-1)dx
[noble gas] ns2 (n-2)f14 (n-1)dx
Electron Configuration
[Kr] 5s2 4d2
http://malaxoschemistry.wikispaces.com/Periodic+Table
Atomic Size
I
n
c
r
e
a
s
I
n
g
Decreasing Size
S
i
z
e
http://malaxoschemistry.wikispaces.com/Periodic+Table
Atomic Size
Exception to the trend: Electrons in the f-orbitals are not
effective at shielding outer shell electrons from nuclear
charge. So, the outer electrons are held in close – this is
known as lanthanide contraction.
Ionization Energy
Increases
D
e
c
r
e
a
s
e
s
http://malaxoschemistry.wikispaces.com/Periodic+Table
Ionization Energy
Exception to the trend: Note that 5d elements have a
greater ionization energy. This is again due to outer shell
electron being held closer to the nucleus, so it take more
energy to pull them away.
Electronegativity
Increases
D
e
c
r
e
a
s
e
s
http://malaxoschemistry.wikispaces.com/Periodic+Table
Electronegativity
Au: EN = 2.4
Compared to
P: EN = 2.1 !!
Exception to the trend: There is an increase in
electronegativity from the 3d (1st row transition
metals) to the 4d (2nd row transition metals).
Oxidation States
In general, stability is found in full or halffull shells, and in a configuration that
looks like a noble gas.
24.3 Coordination Compounds
• Complex Ion - Central Metal bound to one or more ligands
• Ligands are Lewis Base* (electron donors) and can be
either neutral or negatively charged
• The charge on the complex ion
is balance by counter ions
of opposite charge
The combination of a complex
ion and counter ions results in
a coordination compound
*Corrected 4/15/11 @ 2:30 pm)
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
A Little Background
• In 1893, Swiss chemist Alfred Werner came up with the
idea that a central metal could have 2 types of interactions
o Primary Valence – Oxidation State of the central metal
o Secondary Valence – Number of molecules or ions directly attached to the central
metal or Coordination Number
• Example: [Co(NH3)6]Cl3
o The Primary Valence or Oxidation State of Co is +3
o The Secondary Valence or Coordination Number is 6 (6 ammonia ligands are
directly attached to Co
• Other cobalt(III) coordination compounds
• [Co(NH3)6]Cl3
• [Co(NH3)5Cl]Cl2
• [Co(NH3)4Cl2]Cl
Coordinate Covalent Bonds
• Lewis Acid-Base Adduct – the ligand donates it’s electrons
to the empty metal orbitals to form a coordinate covalent
bond
M
:
L
Lewis Base
Lewis Acid
Adduct
Some Common Ligands
Chelating Agents
• Ligands can have one or more bonding pairs of electrons
o Monodentate
o Bidentate or Polydentate
• Complex ions with bidentate or polydentate ligands are
chelates, and the coordinating ligands are chelating agents
Co
EDTA is hexadentate
http://library.kiwix.org:4201/A/Inorganic_chemistry.htm
Geometries
Anne Marie Helmenstine, Ph.D., About.com Guide
Naming Coordination Compounds
• [Mn(CO)(NH3)5]SO4
(neutral ligands are written before charged ligands in the formula)
• Cation 1st
o Name the ligands in alphabetical order
• ammine
• carbonyl
o Add a prefix to indicate the number of ligands
• pentaammine
o Name the metal ion
• Manganese(II)
• Anion 2nd
o Sulfate
• Pentaamminecarbonylmanganese(II) sulfate
24.4 Structure & Isomerism
Isomers
Same formula –
different structures
Structural Isomers
Stereoisomers
Different
connectivities
Same connectivities
–different spacial
arrangements
Coordination Isomers
Linkage Isomers
Ligands & counter ions
trade places
Ligands coordinate
in different ways
Geometric Isomers
Optical Isomers
Different spacial
arrangements
Mirror images
cis-trans
fac-mer
Structural Isomers
Coordination Isomers
pentaamminesulfatochromium(III) bromide
pentaamminebromochromium(III) sulfate
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
Structural Isomers
Linkage Isomers
pentaamminenitrocobalt(III) ion
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
pentaamminenitritocobalt(III) ion
Stereoisomers
Geometric Isomers: cis-trans
cis
trans
cis-diamminedichloroplatinum(II)
trans-diamminedichloroplatinum(II)
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
Stereoisomers
Geometric Isomers: fac-mer
fac
fac-triamminetrichlorocobalt(III)
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
mer
mer-triamminetrichlorocobalt(III)
Stereoisomers
Optical Isomers
•
•
•
•
Mirror Images
Non-superimposable
Enantimomers
Chiral: optically active
(rotates polarized light)
http://en.wikipedia.org/wiki/Chirality_%28
electromagnetism%29
http://www.wikidoc.org/inde
x.php/Chirality_%28chemist
ry%29
Chirality
Determining Optical Activity
fac
mer
David N. Blauch - http://www.chm.davidson.edu/vce/index.htm
Chirality
Determining Optical Activity
Superimposable No optical activity