Chapter 21

advertisement
1
Transition Metal Chemistry
2
Transition Metal Chemistry
3
Gems & Minerals
Citrine and amethyst are quartz (SiO2) with a
trace of cationic iron that gives rise to the
color.
4
Gems & Minerals
Reactions: Transition Metals
Fe + Cl2
5
6
Periodic Trends: Atom Radius
Fe + HCl
Fe + O2
Rhodochrosite, MnCO3
1
Periodic Trends: Density
7
Periodic Trends: Melting Point
8
9
Periodic Trends:
Oxidation Numbers
Most common
10
Metallurgy: Element Sources
11
Electron Configuration
• As you know from first semester
chemistry, the transition metals have a
little different electron configuration.
– So, lets go back.
• If the principle quantum number (n) is 3
what are the possibilities of l (orbital
shape)?
– That is right l can be 0, 1, or 2
– Which means that the d orbital exists in the 3rd
row of the periodic table, but it is not filled.
– Why?
12
Energy Levels
• What are the basic rules for filling the d and f
orbitals?
– Hund’s Rule
– Pauli Exclusion Principle
– When filling the d orbitals subtract the principle
quantum number by one.
– When filling the f orbitals subtract the principle quantum
number by two.
• These are really an over simplification of what is
really going on.
• The reason why the d orbitals are filled where
they are is really do to the fact the energies of the
d orbitals are higher in energy than that of the s
orbital in the next row.
2
Examples of Electron
Configuration
13
Degenerate Energy Levels
• Give me the electron configuration of
¾V
¾[Ar] 4s2, 3d3
¾Fe
¾[Ar] 4s2, 3d6
¾Zn
¾[Ar] 4s2, 3d10
¾Cr
¾[Ar] 4s1, 3d5
¾Cu
¾[Ar] 4s1, 3d10
14
Same Family!
Oxidation States & Ionization
Energies
15
• The reason why there Cr and Cu
populate the d orbital first is really
not because Hund’s rule.
• It is because the 4s and 3d energy
levels are degenerate (have about the
same energy).
• This allows this strange population
of the 3d.
¾W
¾[Xe] 6s2, 4f14, 5d4
The 4d and 5d
16
Lanthanide Contraction
17
18
Section 21.2
• One way to convince yourself of these
trends is to look at the atomic radii of the
transition metals.
• But when we look the atomic radii of the
4d and 5d elements we find that two rows
have about the same atomic radii in each
family.
• As you can see the 2nd and 3rd series are about the
same size.
So
we will only worry about the 1st transition metal
• This is due to the extra protons in the nucleus from the
series!
lanthanides causing a contraction in the atomic size.
• Is a small section on descriptive
chemistry of the 1st row transition
metals.
• It gives you a little information about
the %’s found in the earth’s crust,
common uses, etc.
• MAKE SURE YOU READ THIS!
– Remember the core electrons vs. valence electrons
– Effective shielding.
3
19
Coordination Chemistry
CH2
21
CH2
Pt
– Complex ion = a transition metal ion with its
attached ligands
– Ligands = a neutral molecule or ion having a
lone pair of electrons that can be used to
form a bond to a metal ion; a Lewis base.
– Counterions = anions or cations as needed
to produce a compound with no net charge.
-
Cl
Cl
Cl
Coordination Chemistry
22
Coordination Chemistry
Pt(NH3)2Cl2
Heme
Co(H2O)62+
20
• These coordination complexes typically
consist of a complex ion and
counterions.
• Coordination
compounds
– combination of two
or more atoms, ions,
or molecules where
a bond is formed by
sharing a pair of
electrons originally
associated with only
one of the
compounds.
Two Parts to a Coordination
Complex.
23
24
Vitamin B12
A naturally occurring
cobalt-based
compound
“Cisplatin” - a
cancer
chemotherapy
agent
Cu(NH3)42+
Co atom
4
25
Nomenclature
Common Bidentate
Ligands
26
27
Inner coordination sphere
Ligand: monodentate
+
Bipyridine (bipy)
Acetylacetone (acac)
Cl-
Ligand: bidentate
Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules
Ethylenediamine (en)
Oxalate (ox)
Cis-dichlorobis(ethylenediamine)cobalt(II)
chloride
28
Acetylacetonat
e Complexes
Multidentate Ligands
EDTA4- - ethylenediaminetetraacetate ion
29
Multidentate
Ligands
30
Co2+
complex of
EDTA4Commonly called the
“acac” ligand. Forms
complexes with all
transition elements.
Multidentate ligands are sometimes
called CHELATING ligands
5
Naming Coordination
Compounds
31
[Co(NH3)5Cl]Cl2
32
[Co(NH3)5Cl]Cl2
• 2. Ligands are named before the metal
ion.
•
ammine, chlorine named before
cobalt
• 4. The prefixes mono-, di-, tri-, etc., are
used to denote the number of simple ligands.
• penta ammine
34
Naming Coordination
Compounds (continued)
33
[Co(NH3)5Cl]Cl2
• 3. For ligand, an “o” is added to the root
name of an anion (fluoro, bromo). For
neutral ligands the name of the molecule is
used, with exceptions.
• ammine, chloro
• 1. Cation is named before the anion.
• “chloride” goes last
Naming Coordination
Compounds (continued)
Naming Coordination
Compounds (continued)
35
• 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
36
[Co(NH3)5Cl]Cl2
• 7. If the complex ion has a negative
charge, the suffix “ate” is added to the
name of the metal.
• pentaamminechlorocobalt (III) chloride
6
Nomenclature
37
Co(H2O)62+
Nomenclature
Pt(
Name These
38
•
39
[Co(NH3)5Cl]Cl
– Pentaamminechlorocobalt(II) chloride
Tris(ethylenediamine)nickel(II)
• K3Fe(CN)6
– Potassium hexacyanoferrate(III)
• [Fe(en)2(NO2)2]2SO4
– Bis(ethylenediamine)dinitroiron(III) sulfate
Hexaaquacobalt(II)
Pt(NH3)2Cl2
Cu(NH3)42+
Tetraamminecopper(II)
What is the molecular formula of
these?
[Ni(NH2C2H4NH2)3]2+
IrCl(CO)(PPh3)2
diamminedichloroplatinum(II)
• Triamminebromoplatinum(II) chloride
Vaska’s compound
– [Pt(NH3)3Br]Cl
Carbonylchlorobis(triphenylphosphine)iridium(I)
• Potassium hexafluorocobaltate(III)
– K3[CoF6]
40
41
• Two forms of isomerism
– Constitutional
– Stereoisomerism
Isomerism
• Constitutional (Structural)
– Same empirical formula but different
atom-to-atom connections
• Coordination Isomerism
• Linkage Isomerism
• Stereoisomerism
– Same atom-to-atom connections but
different arrangement in space.
• Geometrical Isomerism
• Optical Isomerism
Coordination Isomerism
• Composition of the complex ion varies.
• Example:
– [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4
Linkage Isomerism
• Composition of the complex is the
same, but the point of attachment of at
least one of the ligands differs.
Example:
42
Structural Isomerism
Structures of Coordination
Compounds
– [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4
7
43
Snp.swf
Coordination Isomerism
Aldehydes & ketones
H 2O
H 2O
OH2
Cl Cl
Cl
OH2
Cr
green
O
CH3-CH2-CH
H 2O
H 2O
Linkage Isomerism
NH3 2+
H 3N
NO2
sunlight
Co
H 3N
NH3
NH3
O
H3C C CH3
44
Optical Isomerism
• The isomers have opposite effects on
plane-polarized light.
• What?!
violet
Peyrone’s chloride: Pt(NH3) 2Cl2
Magnus’s green salt: [Pt(NH3)4][PtCl4]
Stereoisomerism
• One form is commonly called
geometric isomerism or cis-trans
isomerism. Occurs often with square
planar complexes.
cis
trans
Note: there are VERY few tetrahedral
complexes. Would not have geometric isomers.
45
• A.K.A. cis-trans isomerism
• Occurs when atoms of groups of atoms
can assume different positions around a
rigid ring or bond.
2+
NH3
H 3N
ONO
Co
H 3N
NH3
NH3
Such a transformation could be used as an energy
storage device.
OH2
OH2 Cl3
OH2
OH2
Cr
Geometrical Isomerism
46
47
Geometric Isomerism
Cis and trans-dichlorobis(ethylenediamine)cobalt(II)
chloride
48
Geometric Isomerism
Fac isomer
Mer isomer
8
Figure 21.12: Unpolarized light consists of waves
vibrating in many different planes (indicated by the
arrows). The polarizing filter blocks all waves except
those vibrating in a given plane.
49
50
Figure 21.13: The rotation of the plane of polarized light
by an optically active substance. The angle of rotation is
called theta (θ).
51
Stereoisomerism
• Enantiomers: stereoisomers that have a
non-superimposable mirror image
– Two molecules that are related as object and
mirror image, and to convert into the other
would require the breaking of bonds.
• Diastereoisomers: stereoisomers that do
not have a non-superimposable mirror
image (cis-trans isomers)
– Steroisomers that are not related as object and
mirror image are called diasteromers.
• Asymmetric: lacking in symmetry—will
have a non-superimposable mirror image
• Chiral: an asymmetric molecule
52
53
An Enantiomeric Pair
Figure 21.16: Isomers I and II of Co(en)33+ are mirror
images (the image of I is identical to II) that cannot be
superimposed. That is, there is no way that I can be
turned in space so that it is the same as II.
54
[Co(NH2C2H4NH2)3]2+
9
Figure 21.17: (a) The trans isomer of Co(en)2Cl2+ and
its mirror image are identical (superimposable). (b) The
+
cis isomer of Co(en)2Cl2 and its mirror image are not
superimposable and are thus a pair of optical isomers.
55
56
Stereoisomerism
N
Cl
Co
2+
NH3
NH3
OH2
NH3 2+
NH3
Co
N
Cl
OH2
N
58
Bonding in Coordination Compounds
• Model must explain
– Basic bonding between M and ligand
– Color and color changes
– Magnetic behavior
– Structure
• Two models available
– Molecular orbital
– Electrostatic crystal field theory
Stereoisomerism
[Co(en)(NH3)2(H2O)Cl]2+
N
57
NH3 2+ These two isomers have
Cl
a plane of symmetry.
Co
N
OH2 Not chiral.
NH3
N
These two are
NH3 2+
NH3 asymmetric. Have
Co
non-superimposable
N
OH2 mirror images.
Cl
N
These are non-superimposable mirror images
[Co(en)(NH3)2(H2O)Cl]2+
59
Bonding in Coordination Compounds
60
Bonding in Coordination Compounds
• As ligands L approach the metal ion
M+,
– L/M+ orbital overlap occurs
– L/M+ electron repulsion occurs
• Crystal field theory focuses on the
latter, while MO theory takes both
into account
– Combination of the two ---> ligand field
theory
10
61
Octahedral Ligand Field
62
Crystal Field Theory
63
• Consider what happens as 6 ligands
approach an Fe3+ ion
[Ar]
↑ ↑ ↑ ↑ ↑
five 3d orbitals
4s
All electrons have
the same energy in
the free ion
Orbitals split into two groups as the ligands approach.
energy
• Look at the locations of the orbitals of
the dz2 and dx2-y2.
• Because Crystal Field Theory want to
minimize electron repulsion, the d
orbitals rearrange
Tetrahedral & Square Planar
Ligand Field
t2g
64
Figure 21.26: (a) Tetrahedral and octahedral
arrangements of ligands shown inscribed in
cubes.(b) The orientations of the 3d orbitals
relative to the tetrahedral set of point charges.
65
eg
↑
↑
d(x2-y2)
dz2
↑
dxy
↑
dxz
Value of ∆o
depends on
L: e.g.,
H2O > Cl-
∆ E = ∆o
↑
dyz
Crystal Field Theory
66
•Tetrahedral ligand field
•Note that ∆t = 4/9 ∆o and so ∆t is small
•Therefore, tetrahedral complexes tend to blue end
of spectrum
energy
e
↑
dxy
↑
dxz
↑
dyz
∆ E = ∆t
t2
↑
↑
d(x2-y2)
dz2
11
67
Figure 21.28: (a)
The crystal field
diagram for a
square planar
complex oriented
in the xy plane
with ligands along
the
x and y axes.
(b) The crystal
field diagram for a
linear complex
where the ligands
lie along the z
axis.
Crystal Field Theory
68
• Why are complexes colored?
Crystal Field Theory
69
• Why are complexes colored?
– Note that color observed is transmitted
light
Fe3+
Absorption
M + hν Æ M*
70
Co2+
Ni2+
Cu2+
Zn2+
Absorption
71
M + hν Æ M*
• Absorption = the process in which a chemical species in a
transparent medium selectively attenuates (decreases the
intensity of) certain frequencies of electromagnetic radiation
When a photon of radiation passes near an elementary particle,
absorption is probable ONLY if the energy of the photon (hν)
EXACTLY matches the energy difference between the ground
state and one of the higher energy states of the particle
• According to quantum theory, every elementary particle
(atom, ion, molecule) has a unique set of energy states, the
lowest of which is called the ground state
If the energy EXACTLY matches, the energy of the photon is
transferred to the atom, ion, or molecule, converting to a
higher energy state
•These energy states are discrete, quantized energy states
This higher energy state is called the excited state (M*)
• At room temp, most particles are in their ground state (M)
If the incident radiation has too much or too little energy to
satisfy one of the allowed energy transitions, it will be
transmitted through the sample without absorption
Crystal Field Theory
72
• Why are complexes colored?
– Note that color observed is transmitted light
12
Crystal Field Theory
73
• Why are complexes colored?
Spectrochemical Series
• d orbital splitting (value of ∆o)
is in the order
I- < Cl- < F- < H2O < NH3 < en <
phen < CN- < CO
– Note that color observed is transmitted
light
– Color arises from electron transitions
between d orbitals
– Color often not very intense
– d1, d4, d6, and d9 --> 1 band
– d2, d3, d7, and d8 --> 3 bands
Weak-field
Ligands
(small ∆)
• Spectrochemical series
Magnetic Properties/Fe2+
Paramagnetic
eg
t2g
High spin
Weak ligand field
∆E small strength and/or lower
Mn+ charge
↑
dxy
↑
dxz
↑
dyz
– Aquamarine and kyanite
are examples
– Prussian blue
• Color centers
Strong-field
Ligands
(large ∆)
I- > Br- > Cl - > F- > OH- > H2O > NH3 > en > NO2- > CN-
– Amethyst has Fe4+
– When amethyst is heated, it
forms citrine as Fe4+ is
reduced to Fe3+
75
The magnitude
of ∆ for a given
ligand increases
as the charge on
the metal ion
increases.
76
Diamagnetic
d(x2-y2)
↑
eg
↑
dxy
↑
t2g
↑
dz2
↑
dxz
Low spin
dz2
∆E large
↑
energy
↑
d(x2-y2)
↑
energy
Other Ways to Induce Color
• Intervalent transfer bands
(IT)
As ∆ increases, the absorbed light
tends to blue, and so the
transmitted light tends to red.
• Spectra can be complex
74
↑
dyz
Stronger ligand field
strength and/or higher
Mn+ charge
13