chapter 21 transition metals and coordination chemistry

Chapter 21

Transition Metals and Coordination

Chemistry

Chapter 21

Table of Contents

Copyright © Cengage Learning. All rights reserved 2

21.1The Transition Metals: A Survey

21.2 The First-Row Transition Metals

21.3 Coordination Compounds

21.4 Isomerism

21.5 Bonding in Complex Ions: The Localized Electron Model

21.6 The Crystal Field Model

21.7 The Biologic Importance of Coordination Complexes

21.8 Metallurgy and Iron and Steel Production

Section 21.1

The Transition Metals: A Survey

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Industry : Fe , Cu , Ti , Ag , table 21.1

Biosystem : transport , storage , catalyst ,

20.1 The Transition Metals - I

Section 21.1


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Transition Metals

• Show great similarities within a given period as well as within a given vertical group.

(1) General Properties ( Sc → Cu )

a) Great similarities within a period as well as a group

∵ d subshells incomplerely filled.

distinctive coloring

formation of paramagnetic compounds

catalytic behavior

tendency to form complex ions.

Section 21.1


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Section 21.1


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Cations are often complex ions – species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases). The Complex Ion Co(NH3)6

3+ :

Section 21.1


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b) difference : m.p : W / Hg

Hard / soft : Fe , Ti / Cu , Au , Ag

Reactivity & oxides : Cu / Fe ; Fe2O3 / CrO3

(2) Electron configurations : 4s before 3d

( Cr / Cu )

Table 21.2 p.931

(3) Oxidation states

most common : +2 , +3 ( +2 ～ +7 )

more than one oxidation states

Section 21.1


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Section 21.1


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(4) Ionization energies

(5) Reduction Potentials

─────→ period ， reducing ability ↓ ( Zn , Cr )

∵ Zeff ↑ r ↓ ; IE ↑

Section 21.2

Atomic MassesThe First-Row Transition Metals

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• 3d transition metals Scandium – chemistry strongly resembles lanthanides Titanium – excellent structural material (light weight) Vanadium – mostly in alloys with other metals Chromium – important industrial material Manganese – production of hard steel Iron – most abundant heavy metal Cobalt – alloys with other metals Nickel – plating more active metals; alloys Copper – plumbing and electrical applications Zinc – galvanizing steel

Section 21.3

The Mole Coordination Compounds

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A Coordination Compound

• Typically consists of a complex ion and counterions (anions or cations as needed to produce a neutral compound):

[Co(NH3)5Cl]Cl2[Fe(en)2(NO2)2]2SO4

K3Fe(CN)6

Section 21.3


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└→ colored & paramagnetic (often)

consists of a complex ion

(1) Coordination compounds are neutral species in which a small number of molecules or ions surround a central metal atom or ion.

ex.

[Co(NH3)5Cl]Cl2complex ion : [Co(NH3)5Cl]2+

Section 21.3


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coordinate covalent bond

Complex ion = metal cation + ligands

e acceptor e donor

center (one) surrounding

( 2 )

transion metal

Lewis acid Lewis base

[ Co(NH3)5Cl ]Cl2

H2O , NH3 , :Cl －....

.. ....

ionic force

counter ionscentral metal ligands

complex ion

Section 21.3


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(2) Coordination number :

The # of donor atoms surrounding the central metal

The most common : 4 or 6

Section 21.3


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Chelating agents

(3) Ligands :

A neutral molecule or ion having a line pair that can be used to from a bond to a metal ion.

monodentate : H2O, NH3

bidentate : en , ox

polydentate : EDTA

Section 21.3


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p. 939, Table 21-13

Section 21.3


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(4) Nomenclature :

Rules for naming coordination compounds : p.940

oxidation number :Net charge = charges on (central metal + ligands)[ PtCl6]2 － [Cu(NH3)4]2 ＋

└→ +4 └→ +2

ex. (a) [Co(NH3)5Cl]Cl2Pentaammine chloro cobalt(III) chloride

cation anion

Section 21.3


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p. 940, Table 21-14

Section 21.3


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(4) Nomenclature :

ex. (b) K3[Fe(CN)6]

potassium hexacyanoferrate (III)

cation anion

ex. (c) [Fe(en)2(NO2) 2]2SO4

bis (ethylenediamine) dinitro iron(III) sulfate

cation anion

Section 21.3


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Exercise

Name the following coordination compounds.

a) [Co(H2O)6]Br3

b) Na2[PtCl4]

hexaaquacobalt(III) bromide

sodiumtetrachloro-platinate(II)

Section 21.4

Isomerism

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Section 21.4

Isomerism

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Structural Isomerism

• Coordination Isomerism: Composition of the complex ion varies. [Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4

• Linkage Isomerism: Composition of the complex ion is the same,

but the point of attachment of at least one of the ligands differs.

Section 21.4

Isomerism

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Linkage Isomerism of NO2

–

Section 21.4

Isomerism

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Stereoisomerism

• Geometrical Isomerism (cis-trans): Atoms or groups of atoms can assume

different positions around a rigid ring or bond.

Cis – same side (next to each other) Trans – opposite sides (across from each

other)

Section 21.4

Isomerism

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Geometrical (cis-trans) Isomerism for a Square Planar Compound

a) cis isomerb) trans isomer

Section 21.4

Isomerism

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Geometrical (cis-trans) Isomerism for an Octahedral Complex Ion

Section 21.4

Isomerism

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Stereoisomerism

• Optical Isomerism: Isomers have opposite effects on plane-polarized light.

Section 21.4

Isomerism

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Optical Activity

• Exhibited by molecules that have nonsuperimposable mirror images (chiral molecules).

• Enantiomers – isomers of nonsuperimposable mirror images.

Section 21.4

Isomerism

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p. 947, Fig. 21-17

Section 21.4

Isomerism

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Section 21.4

Isomerism

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p. 948, Fig. 21-13

Ex. 21.3 at p 948

Section 21.4

Isomerism

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Concept Check

Does [Co(en)2Cl2]Cl exhibit geometrical isomerism?

Yes

Does it exhibit optical isomerism?

Trans form – No

Cis form – Yes

Explain.

Section 21.5

Bonding in Complex Ions: The Localized Electron Model

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Bonding in Complex Ions

1. The VSEPR model for predicting structure generally does not work for complex ions. However, assume a complex ion with a

coordination number of 6 : octahedral two ligands : linear. a coordination number of 4 : tetrahedral or

square planar.

2. The interaction between a metal ion and a ligand : Lewis acid–base reaction

Section 21.5

Bonding in Complex Ions: The Localized Electron Model

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Hybrid Orbitals for 6,4, and 2 ligands

Section 21.6

The Crystal Field Model

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• Focuses on the energies of the d orbitals.

Assumptions

1. Ligands are negative point charges.

2. Metal–ligand bonding is entirely ionic:• strong-field (low–spin):

large splitting of d orbitals• weak-field (high–spin):

small splitting of d orbitals

Section 21.6


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(1) Explains the bonding in complex ions solely in terms of electrostatic forces.

(2) Two types of electrostatic forces :attraction : ( M ＋ ) & ( ligand ion － or ligand ： )repulsion : ( ligand ： ) & ( metal e in d orbitals )

(3) Consider : octahedral complexes

● ●

● ● ●

● ● ● ● ●

Section 21.6


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An Octahedral Arrangement of Point-Charge Ligands and the Orientation of the 3d Orbitals

Section 21.6


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The Energies of the 3d Orbitals for a Metal Ion in an Octahedral Complex

Section 21.6


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Possible Electron Arrangements in the Split 3d Orbitals in an Octahedral Complex of Co3+

• Strong–field (low–spin):• Yields the minimum number

of unpaired electrons.

• Weak–field (high–spin):

• Gives the maximum number of unpaired electrons.

Section 21.6


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Spectrochemical Series

• a list of ligands arranged in order of their abilities to split the d orbital energies

• Strong–field ligands to weak–field ligands.

(large split) (small split)CN– > NO2

– > en > NH3 > H2O > OH– > F– > Cl– > Br– > I–

• Magnitude of split for a given ligand increases as the charge on the metal ion increases.

Section 21.6


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Color : arise when complexes absorb light in some portion of the visible spectrum.

(Table 21.16)

ex. [Cu(H2O)6]2+ → blue = E = h

Section 21.6


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ex. [Ti(H2O)6]3+ max absorption at 498 nm

molkJ

J

nmmnm

smJschh

/240

1099.3

/10498

)/1000.3)(1063.6(

19

9

834

Section 21.6


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p. 954, Table 21-17

color of gems

Section 21.6


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Concept Check

Which of the following are expected to form colorless octahedral compounds?

Zn2+ Fe2+ Mn2+

Cu+ Cr3+ Ti4+ Ag+

Fe3+ Cu2+ Ni2+

Section 21.6


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Tetrahedral Arrangement

• None of the 3d orbitals “point at the ligands”. Difference in energy between the split d

orbitals is significantly less.• d–orbital splitting will be opposite to that for the

octahedral arrangement. Weak–field case (high–spin) always applies.

Section 21.6


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The d Orbitals in a Tetrahedral Arrangement of Point Charges

Section 21.6


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The Crystal Field Diagrams for Octahedral and Tetrahedral Complexes

Tetrahedral Complexes:

Difference in energy between the split d orbitals is significantly less,

Weak–field case (high–spin) always applies for.

Section 21.6


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Concept Check

Consider the Crystal Field Model (CFM).

a) Which is lower in energy, d–orbital lobes pointing toward ligands or between? Why?

b) The electrons in the d–orbitals – are they from the metal or the ligands?

Section 21.6


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Concept Check

Using the Crystal Field Model, sketch possible electron arrangements for the following. Label one sketch as strong field and one sketch as weak field.

a) Ni(NH3)62+

b) Fe(CN)63–

c) Co(NH3)63+

Section 21.6


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Concept Check

A metal ion in a high–spin octahedral complex has 2 more unpaired electrons than the same ion does in a low–spin octahedral complex.

What are some possible metal ions for which this would be true?

Metal ions would need to be d4 or d7 ions. Examples include Mn3+, Co2+, and Cr2+.

Section 21.6


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Concept Check

Between [Mn(CN)6]3– and [Mn(CN)6]4– which is more likely to be high spin? Why?

Section 21.6


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The d Energy Diagrams for Square Planar Complexes

Section 21.6


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The d Energy Diagrams for Linear Complexes Where the Ligands Lie Along the z Axis

Section 21.7

The Biologic Importance of Coordination Complexes

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• Metal ion complexes are used in humans for the transport and storage of oxygen, as electron-transfer agents, as catalysts, and as drugs.

Section 21.7


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First-Row Transition Metals and Their Biological Significance

Section 21.7


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Biological Importance of Iron

• Plays a central role in almost all living cells.• Component of hemoglobin and myoglobin.• Involved in the electron-transport chain.

Section 21.7


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The Heme Complex

Section 21.7


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Myoglobin

• The Fe2+ ion is coordinated to four nitrogen atoms in the porphyrin of the heme (the disk in the figure) and on nitrogen from the protein chain.

• This leaves a 6th coordination position (the W) available for an oxygen molecule.

Section 21.7


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Hemoglobin

• two α chains and two β chains

• complex with four O2 molecules.

Section 21.7


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p. 959, Fig. 21-22

Hb(aq) + 4O2(g) Hb(O2)4(aq)

About high altitude sickness

Section 21.7


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p. 960, Fig. 21-24

About Supercharge Blood: EPO at page 960.

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