Chapter 20Chapter 20

Transition Metals and Transition Metals and Coordination ChemistryCoordination Chemistry

Chapter 20: Transition Metals and Coordination Chemistry

20.1 The Transition metals: A Survey20.2 The First-Row Transition Metals20.3 Coordination Compounds20.4 Isomerism20.5 Bonding in Complex Ions: The localized Electron Model20.6 The Crystal Field Model20.7 The Molecular Orbital Model20.8 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 c

d

e

f

g

h

i

j

a = Scandium oxideb = Titanium(IV) oxidec = Vanadyl sulfate dihydrated = Sodium chromatee = Manganese(II) chloride tetrahydrate

f = Potassium ferricyanideg = Cobalt(II) chloride hexahydrateh = Nickel(II) nitrate hexahydratei = Copper(II) sulfate pentahydrate j = Zinc sulfate heptahydrate

Orbital Occupancy of the Period 4 Metals–I

Element Partial Orbital Diagram Unpaired Electrons

Sc 1

Ti 2

V 3

Cr 6

Mn 5

4s 3d 4p

Orbital Occupancy of the Period 4 Metals–II

Element Partial Orbital Diagram Unpaired Electrons

Fe 4

Co 3

Ni 2

Cu 1

Zn 0

4s 3d 4p

Oxidation States and d-Orbital Occupancy of the Period 4 Transition Metals

3B 4B 5B 6B 7B 8B 8B 8B 1B 2BOxidation (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) State Sc Ti V Cr Mn Fe Co Ni Cu Zn

0 0 0 0 0 0 0 0 0 0 0 (d1) (d2) (d3) (d5) (d5) (d6) (d7) (d 8) (d10) (d10)+1 +1 +1 +1 +1 +1 +1 (d3) (d5) (d5) (d7) (d8) (d10)+2 +2 +2 +2 +2 +2 +2 +2 +2 +2 (d2) (d3) (d4) (d5) (d6) (d7) (d8) (d9) (d10)+3 +3 +3 +3 +3 +3 +3 +3 +3 +3 (d0) (d1) (d2) (d3) (d4) (d5) (d6) (d7) (d8)+4 +4 +4 +4 +4 +4 +4 +4 (d0) (d1) (d2) (d3) (d4 ) (d5) (d6)+5 +5 +5 +5 +5 (d0) (d1) (d2) (d4)+6 +6 +6 +6 (d0) (d1) (d2)+7 +7 (d0)

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

Source: USDA photo

This plant can thrive on soils contaminated with Zn and Cd,concentrating them in the stems,which can be harvested to obtainthese elements.

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 anion2) 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 IsomerismCoordination 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 CN-

ligand produce a strong or weak field?Solution: Since the ligand is CN- and the overall complex ion charge is -3, the metalion must be Fe+3, which has a 3d5 electron configuration. The two possible arrangements of the five electrons in the d orbitals split by theoctahedrally 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- > I-

Strong-field Weak-field ligands ligands (large ) (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 CN- ligand produces such a large splitting that two of the electrons will be Pared in the same orbital rather than force one electron up through theLarge 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 energy-level diagram for an octahedral complex ion

Figure 20.32: MO energy-level diagram for CoF6

3-, 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