Transcript PowerPoint for Part 1

Transition Metals and
Coordination Compounds
Transition Metals
• The transition metals are the d-block
elements.
• The Inner Transitions metals are the
lanthanides and actinides, or the f-block.
• Many transition metals form highly
colored compounds.
• Many are critical for our health!
d-block & Valence Electrons
• How many valence electrons does iron
have?
• How many valence electrons does gold
have?
• For the d-block, there are (n-1)d + ns
valence electrons.
• Why do we count the d electrons???
d-block & Valence Electrons
• How about ions?
• How many valence electrons does Cu
have and how many does Cu+1 have?
• What are their electron configurations?
Oxidation States
• Many transition metals are found in
more than 1 oxidation states, even Ag
and Zn!
• Here are some common states:
Oxidation States
• We can assign oxidation states using the
rules you already learned to love!
• Determine the oxidation states for the
transition metals in the following
complexes:
Coordination Compounds
• The preceding complexes are examples
of coordination compounds or
coordination complexes.
• Note that they may be neutral or
charged.
• What do you notice? What do you think
is the central atom?
Coordination Compounds
• In coordination compounds, the central
atom is a metal atom or ion, and it is
covalently attached to 2 or more
molecules or ions.
• The molecules or ions covalently
attached to the transition metal are
called ligands.
Coordination Compounds
• In a ligand, the atom(s) which are
directly attached to the metal are called
the ligand donor atoms or simply the
donor atoms.
• Look at the following and determine
what the ligands are, and what the donor
atoms are.
Complex Ions
• If the coordination compound has a
charge, it is a complex ion.
• We write it in brackets with the charge
outside.
• But if it’s an ion, what can it do?
• Complex ions can form ionic salts.
• How do we write the formulas for these
complex salts?
Coordination Numbers
• We also talk about coordination numbers
for coordination compounds.
• The coordination number for a
transition metal is the number of ligand
donor atoms directly attached to it.
Coordination Numbers
• Common coordination numbers are 2, 4,
or 6, but they may be anything from 2 to
8 (including odd).
Coordination Numbers
• What is the coordination number for the
following:
Common Ligands
• Ligands may actually form more than 1
bond or attachment to the transition
metal.
• Ligands which form only 1 bond are
called monodentate ligands.
• Ligands which form more than 1 bond
are called polydentate ligands.
• Bidentate ligands are fairly common.
Common Ligands
• Let’s look at some polydentate ligands
and how they bond or attach.
Common Ligands
• You do need to know the most common
ligands so you can name transition
compounds.
• The following table has all that you need
to know except the pyridine ligand which
is abbreviated py.
Structure
• Before we switch to nomenclature, what
about the structures?
• As the most common coordination
numbers are 2, 4, and 6, there are 4
common geometric shapes:
–
–
–
–
linear
tetrahedral
square planar
octahedral
Structure
• What’s the transition metal
hybridization associated with these
shapes?
Nomenclature
•
There are some rules to name the
simpler coordination compounds.
1. If the complex is a salt, name the cation
portion first, then name the anion.
Nomenclature
2. When naming a complex ion or a neutral
complex, name the ligands using the
appropriate prefix (di, tri, tetra, etc), then
name the metal. If a ligand is an anion, it
name ends in -o (like chloro or cyano).
Specify the metal oxidation # with a
Roman numeral inside ( ). If there are
more than 1 different ligands, name them
alphabetically, ignoring the prefixes.
Nomenclature
3. If the ligand atom itself contains a prefix
(for you this is ethylenediamine), then put
the name inside ( ), and use one of the
following prefixes to specify the number
of these ligands: 2 is bis, 3 is tris, 4 is
tetrakis.
4. If the complex ion is an anion, give the
metal an -ate ending.
Isomers
•
Isomers are compounds with the same
molecular formula but have the atoms
arranged differently.
There are several types of isomers:
•
–
–
–
Conformational or Structural
Geometric or Diasteorisomers
Enantiomers
Transition Metals and Color
• Why are so many transition metal complexes
colored?
• Usually only metals with d0 or d10 form
colorless compounds (Zn, Ag).
• Colors in metal complexes (or any compound)
is due to their absorption spectrum.
Transition Metals and Color
• When a metal complex absorbs light, an
electron undergoes an electronic transition
from a ground state to an excited state.
• Remember:
∆E = hc/ OR  = hc/ E
• We see the color which is NOT absorbed, but
which was reflected or transmitted.
• We see the complementary color of what was
absorbed.
Colors of Visible Light
Crystal Field Theory
• Why do metal complexes absorb light in the
Vis light spectrum?
• Crystal Field Theory tries to explain this.
• When a ligand approaches a free metal atom
or ion in order to form a bond, e-e repulsions
occur between the metal’s d-electrons and the
ligands electrons.
• This causes the metal’s 5 degenerate dorbitals to increase in energy AND to split.
• So they are no longer degenerate.
d-Orbital Splitting by Ligands
Octahedral Complexes and Orbitals
Crystal Field Theory
• Different ligands cause more of an energy
split in the d-orbitals.
• Ligands which cause the d-orbitals to split
more with a higher E are called strong-field
ligands.
• Ligands which cause the d-orbitals to split less
with a lower E are called weak-field ligands.
• Ligand Series from Weak to Strong:
I-<Br-<Cl-<F-<H2O<NH3<en<CN-
Octahedral Complexes:
Weak Field / Strong Field Ligands
Crystal Field Theory
• Ligand splitting of a metal’s d-orbitals also
explains why some complexes are highly
paramagnetic and others are diamagnetic or
weakly paramagnetic.
• Highly Paramagnetic: These are weak field
complexes with a low E, so the d-e are easily
promoted. The result is a complex with many
unpaired electrons, or a high-spin complex.
Tetrahedral & Square Planar Complexes