Transcript Document 7307416

Chapter 20
Transition Metals and
Coordination Chemistry
Chapter 20: Transition Metals and
Coordination Chemistry
20.1
20.2
20.3
20.4
20.5
20.6
20.7
20.8
The Transition metals: A Survey
The First-Row Transition Metals
Coordination Compounds
Isomerism
Bonding in Complex Ions: The localized Electron Model
The Crystal Field Model
The Molecular Orbital Model
The Biological Importance of Coordination Complexes
Vanadium metal (center) and in solution as
V2+(aq), V3+(aq), VO2+(aq), and VO2+(aq),
(left to right).
Figure 20.1: Transition elements on the periodic
table
Calcite with traces of Iron
Source: Fundamental Photographs
Quartz
Wulfenite
Rhodochrosite
Aqueous solutions containing metal ions
Co+2
Mn+2
Cr+3
Fe+3
Ni+2
Molecular model: The CO(NH3)63+ ion
Figure 20.2: plots of the first (red dots) and
third (blue dots) ionization energies for the
first-row transition metals
Figure 20.3: Atomic radii of the 3d, 4d,
and 5d transition series.
Transition
metals are often
used to
construct
prosthetic
devices, such
as this hop joint
replacement.
Source: Science Photo Library
Liquid titanium(IV) chloride being added to
water, forming a cloud of solid titanium oxide
and hydrochloric acid.
Colors of Representative Compounds of
the Period 4 Transition Metals
b
a
d
c
f
e
h
g
j
i
a = Scandium oxide
f = Potassium ferricyanide
b = Titanium(IV) oxide
g = Cobalt(II) chloride hexahydrate
c = Vanadyl sulfate dihydrate
h = Nickel(II) nitrate hexahydrate
d = Sodium chromate
i = Copper(II) sulfate pentahydrate
e = Manganese(II) chloride tetrahydrate j = Zinc sulfate heptahydrate
Orbital Occupancy of the Period 4 Metals–I
Element
Sc
Partial Orbital Diagram
4s
3d
Unpaired Electrons
4p
1
Ti
2
V
3
Cr
6
Mn
5
Orbital Occupancy of the Period 4 Metals–II
Element
Fe
Partial Orbital Diagram
4s
3d
Unpaired Electrons
4p
4
Co
3
Ni
2
Cu
1
Zn
0
Oxidation States and d-Orbital Occupancy of the
Period 4 Transition Metals
Oxidation
State
0
3B
(3)
Sc
4B
(4)
Ti
0
(d1)
0
(d2)
+1
+2
+3
+4
+5
+6
+7
+3
(d0)
5B
(5)
V
6B
(6)
Cr
0
0
(d3) (d5)
+1 +1
(d3) (d5)
+2
+2
+2
(d2) (d3) (d4)
+3
+3
+3
(d1) (d2) (d3)
+4
+4
+4
(d0) (d1) (d2)
+5
+5
(d0) (d1)
+6
(d0)
7B
(7)
Mn
8B
(8)
Fe
8B
(9)
Co
0
0
0
(d5) (d6) (d7)
+1
+1
(d5)
(d7)
+2
+2
+2
(d5) (d6) (d7)
+3
+3 +3
(d4) (d5) (d6)
+4
+4
+4
(d3) (d4 ) (d5)
+5
+5
(d2)
(d4)
+6
+6
(d1) (d2)
+7 (d0)
8B
(10)
Ni
1B
(11)
Cu
2B
(12)
Zn
0
0
0
(d 8) (d10) (d10)
+1
+1
(d8) (d10)
+2
+2
+2
(d8) (d9) (d10)
+3
+3
(d7) (d8)
+4
(d6)
Figure 20.4: Titanium bicycle
Figure 20.5: Structures of the chromium
(VI) anions
Manganese nodules on the sea floor
Source: Visuals Unlimited
Aqueous solution containing the Ni2+ ion
Alpine
Pennycress
This plant can thrive on soils
contaminated with Zn and Cd,
concentrating them in the stems,
which can be harvested to obtain
these elements.
Source: USDA photo
Figure 20.6:
Ligand
arrangements
for coordination
numbers 2, 4,
and 6
Figure 20.7:
a) Bidentate ligand
ethylene-diamine can
bond to the metal ion
through the lone pair on
each nitrogen atom, thus
forming two coordinate
covalent bonds. B)
Ammonia with one
electron pair to bond.
a)
b)
Figure 20.8: The coordination of EDTA
with a 2+ metal ion.
Rules for Naming Coordination Compounds - I
1) As with any ionic compound, the cation is named before the anion
2) In naming a complex ion, the ligands are named before the metal ion.
3) In naming ligands, an o is added to the root name of an anion. For
example, the halides as ligands are called fluoro, chloro, bromo, and
iodo; hydroxid is hydroxo; and cyanide is cyano. For a neutral the
name of the molecule is used, with the exception of H2O, NH3, CO,
and NO, as illustrated in table 20.14.
4) The prefixes mono-, di-, tri-, tetra-, penta-, and hexa- are used to
denote the number of simple ligands. The prefixes bis-, tris-, tetrakis-,
and so on, are also used, especially for more complicated ligands or
ones that already contain di-, tri-, and so on.
5) The oxidation state of the central metal ion is designated by a Roman
numeral in parentheses.
Rules for Naming Coordination Compounds - II
6) When more than one type of ligand is present, ligands are named in
alphabetical order. Prefixes do not affect the order.
7) If the complex ion has a negative charge, the suffix –ate is added to
the name of the metal. Sometimes the Latin name is used to identify
the metal (see table 20.15).
Example 20.1 (P 947)
Give the systematic name for each of the following coordination
compounds:
a) [Co(NH3)5Cl]Cl2
b) K3Fe(CN)6
c) [Fe(en)2(NO2)2]2SO4
Solution:
a) Ammonia molecules are neutral, Chloride is -1, so cobalt is +3
the name is therefore:
pentaamminechlorocobalt(III) chloride
b) 3 K+ ions, 6 CN- ions, therefore the Iron must have a charge of +3
the complex ion is: Fe(CN)6-3, the cyanide ligands are cyano, the
latin name for Iron is ferrate, so the name is:
potassium hexacyanoferrate(III)
c) Four NO2-, one SO4-2, ethylenediamine is neutral so the iron is +3
the name is therefore:
bis(ethylenediamine)dinitroiron(III) sulfate
An aqueous solution of [Co(NH3)5Cl]Cl2
Solid K3Fe(CN)6
Figure 20.9: Classes of isomers
Structural Isomerism
Coordination isomerism: the composition of the complex ion varies.
consider:
[Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4
another example is: [Co(en)3][Cr(ox)3] and [Cr(en)3][Co(ox)3]
ox represents the oxalate ion.
Linkage isomerism: the composition of the complex ion is the, but the
point of attachment of at least one of the ligands is different.
[Co(NH3)4(NO2)Cl]Cl
Tetraamminechloronitrocobalt(III) chloride
(yellow)
[Co(NH3)4(ONO)Cl]Cl
Tetraamminechloronitritocobalt(III) chloride
(red)
Figure 20.10: As a ligand, NO2- can bond to a
metal ion (a) through a lone pair on the
nitrogen atom (b) through a lone pair on one
of the oxygen atoms
Figure 20.11: (a)
The cis isomer of
Pt(NH3)2Cl2
(yellow). (b) the
trans isomer
of Pt(NH3)2Cl2
(pale yellow).
Cis - yellow
Trans – pale yellow
Figure 20.12: (a) The trans isomer of
[Co(NH3)4Cl2]1. The chloride ligands are
directly across from each other.
(b) The cis isomer of [Co(NH3)4Cl2]1.
Figure 20.13: Unpolarized light consists of
waves vibrating in many different planes
Figure 20.14: Rotation of the plane of
polarized light by an optically active
substance.
Figure 20.15: human hand has a
nonsuperimposed mirror image
Figure 20.15: human hand has a
nonsuperimposed mirror image (cont’d)
Figure 20.16: Isomers I and II of Co(en)33+ are
mirror images (the mirror image of I is
identical to II) that cannot be superimposed.
Figure 20.17: Trans isomer of Co(en)2Cl2+ and
its mirror image are identical(superimposable)
(b) cis isomer of Co(en)2Cl2+
No Optical activity
Does have Optical activity
Figure 20.18: Some cis complexes of
platinum and palladium that show significant
antitumor activity.
Figure 20.19: Set of six d2sp3 hybrid
orbitals on CO3+
Figure 20.20: Hybrid orbitals required for
tetrahedral square planar and linear
Complexes
Figure 20.21: Octahedral arrangement and
d-orbitals
Figure 20.22: Energies of the 3d orbitals
for a metal ion in a octahedral complex.
Figure 20.23: possible electron arrangements
in the split 3d orbitals of an octahedral
complex of Co3+
Example 20.4 (P958)
The Fe(CN)6-3 ion is known to have one unpaired electron. Does the CNligand produce a strong or weak field?
Solution:
Since the ligand is CN- and the overall complex ion charge is -3, the metal
ion must be Fe+3, which has a 3d5 electron configuration. The two
possible arrangements of the five electrons in the d orbitals split by the
octahedrally arranged ligands are:
The strong-field case gives one unpaired electron, which agrees with the
experimental observation. The CN- ion is a strong-field ligand toward the
Fe+3 ion.
The Spectrochemical Series
CN- > NO2- > en > NH3 > H2O > OH- > F- > Cl- > Br- > IStrong-field
ligands
(large )
Weak-field
ligands
(small )
The magnitude of
for a given ligand increases as the charge on
The metal ion increases.
Example 20.5 (P 959)
Perdict the number of unpaired electrons in the complex ion [Cr(CN)6]4-.
Solution:
The net charge of 4- means that the metal ion must be Cr2+ (-6+2=-4),
which has a 3d4 electron configuration. Since CN- is a strong-field
ligand, the correct crystal field diagram for [Cr(CN)6]4- is
The complex ion will have two unpared electrons. Note that the CNligand produces such a large splitting that two of the electrons will be
Pared in the same orbital rather than force one electron up through the
Large energy gap .
Figure 20.24: Visible spectrum
Figure 20.25:
(a) when white light
shines on
a filter that absorbs
wavelengths
(b) because
the complex ion
Figure 20.26: The complex ion Ti(H2O)63+
Figure 20.27: Tetrahedral and octahedral
arrangements of ligands shown inscribed in
cubes.
Figure 20.28: Crystal field diagrams for
octahedral and tetrahedral complexes
Figure 20.29: Crystal field diagram for a
square planar complex oriented in the xy
plane (b) crystal field diagram for a linear
complex
Figure 20.30: Octahedral arrangement of
ligands showing their lone pair orbitals
Figure 20.31:
The MO energylevel diagram
for an
octahedral
complex ion
Figure 20.32: MO energy-level diagram for
CoF63-, which yields the high-spin
Figure 20.33:
The heme
complex in
which an Fe2+
ion is
coordinated to
four nitrogen
atoms of a
planar
porphyrin
ligand.
Figure 20.35: Representation of the
myoglobin molecule
Figure 20.36: Representation of the
hemoglobin structure
Figure 20.37: Normal red blood cell (right)
and a sickle cell, both magnified 18,000 times.
Source: Visuals Unlimited
Hemoglobin and the Octahedral
Complex in Heme
Figure 20.34: Chlorophyll is a
porphyrin complex
The Tetrahedral Zn2+ Complex in
Carbonic Anhydrase