Chapter 22 The Chemistry of the Transition Elements

John C. Kotz • State University of New York, College at Oneonta

John C. KotzPaul M. TreichelJohn Townsend

http://academic.cengage.com/kotz

Chapter 22The Chemistry of the Transition Elements





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Transition Metal Transition Metal ChemistryChemistry

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Transition Metal Transition Metal ChemistryChemistry

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Gems & MineralsGems & Minerals

Citrine and amethyst are quartz (SiOCitrine and amethyst are quartz (SiO22) with a trace of cationic iron that gives rise to the color.) with a trace of cationic iron that gives rise to the color.

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Gems & MineralsGems & Minerals

Rhodochrosite, MnCORhodochrosite, MnCO33

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Reactions: Transition Reactions: Transition MetalsMetals

Fe + O2

Fe + Cl2 Fe + HCl

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Periodic Trends: Atom Periodic Trends: Atom RadiusRadius

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Periodic Trends: DensityPeriodic Trends: Density

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Periodic Trends: Melting Periodic Trends: Melting PointPoint

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Periodic Trends: Periodic Trends: Oxidation NumbersOxidation Numbers

Most commonMost common

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Metallurgy: Element Metallurgy: Element SourcesSources

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PyrometallurgyPyrometallurgy• Involves high temperature, such as Involves high temperature, such as Fe Fe

• C and CO used as reducing agents C and CO used as reducing agents in a blast furnacein a blast furnace

• FeFe22OO33 + 3 C + 3 C ff 2 Fe + 3 CO 2 Fe + 3 CO• FeFe22OO33 + 3 CO + 3 CO ff 2 Fe + 3 CO 2 Fe + 3 CO22

• Lime added to remove impurities, Lime added to remove impurities, chiefly SiOchiefly SiO22

SiOSiO22 + CaO + CaO ff CaSiO CaSiO33

• Product is impure cast iron or pig Product is impure cast iron or pig ironiron

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MetallurgyMetallurgy::

Blast Blast FurnaceFurnace

See Active Figure 22.8See Active Figure 22.8

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MetallurgyMetallurgy::

Blast Blast FurnaceFurnace

Molten iron is Molten iron is poured from a basic poured from a basic oxygen furnace.oxygen furnace.

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Metallurgy: Copper OresMetallurgy: Copper Ores

Native copperNative copper

Azurite, 2CuCOAzurite, 2CuCO33·Cu(OH)·Cu(OH)22

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• Uses aqueous solutionsUses aqueous solutions

• Add CuClAdd CuCl22(aq) to ore such as CuFeS(aq) to ore such as CuFeS22 (chalcopyrite)(chalcopyrite)CuFeSCuFeS22 (s) + 3 CuCl (s) + 3 CuCl22 (aq) (aq)

ff 4 CuCl(s) + FeCl 4 CuCl(s) + FeCl22 (aq) + 2 S(s) (aq) + 2 S(s)

• Dissolve CuCl with xs NaClDissolve CuCl with xs NaClCuCl(s) + ClCuCl(s) + Cl--(aq) (aq) f f [CuCl[CuCl2]]--

• Cu(I) disproportionates to Cu metalCu(I) disproportionates to Cu metal2 [CuCl2 [CuCl22]]-- ff Cu(s) + CuCl Cu(s) + CuCl2 (aq) + 2 Cl (aq) + 2 Cl--

Metallurgy: Metallurgy: HydrometallurgyHydrometallurgy

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Electrolytic Refining Electrolytic Refining of Cuof Cu

SeeFigure 22.11SeeFigure 22.11

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Coordination ChemistryCoordination Chemistry

• 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.

Pt

Cl

Cl

Cl

CH2

CH2

-

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Co(HCo(H22O)O)662+2+

Pt(NHPt(NH33))22ClCl22

Cu(NHCu(NH33))442+2+

““Cisplatin” - a Cisplatin” - a cancer cancer chemotherapy chemotherapy agentagent

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An iron-porphyrin, the basic unit of hemoglobinAn iron-porphyrin, the basic unit of hemoglobin

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Vitamin Vitamin B12B12A naturally A naturally occurring occurring cobalt-based cobalt-based compoundcompound

Co atomCo atom

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NitrogenaseNitrogenase• Biological nitrogen fixation contributes about Biological nitrogen fixation contributes about

half of total nitrogen input to global half of total nitrogen input to global agriculture, remainder from Haber process.agriculture, remainder from Haber process.

• To produce the HTo produce the H22 for the Haber process consumes for the Haber process consumes about 1% of the world’s total energy.about 1% of the world’s total energy.

• A similar process requiring only atmospheric T and A similar process requiring only atmospheric T and P is carried out by N-fixing bacteria, many of P is carried out by N-fixing bacteria, many of which live in symbiotic association with legumes.which live in symbiotic association with legumes.

• N-fixing bacteria use the enzyme nitrogenase — N-fixing bacteria use the enzyme nitrogenase — transforms Ntransforms N22 into NH into NH33..

• Nitrogenase consists of 2 metalloproteins: one Nitrogenase consists of 2 metalloproteins: one with Fe and the other with Fe and Mo. with Fe and the other with Fe and Mo.

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CoordinatiCoordination on

Compounds Compounds of Niof Ni2+2+

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NomenclatureNomenclature

Ni(NHNi(NH33))66]]2+2+

A NiA Ni2+2+ ion ion surrounded by 6, surrounded by 6, neutral NHneutral NH33 ligandsligands

Gives Gives coordination coordination complex ion with complex ion with 2+ charge.2+ charge.

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++

Inner coordination sphereInner coordination sphere

Ligand: monodentateLigand: monodentate

Ligand: bidentateLigand: bidentate

ClCl--

CoCo3+3+ + 2 Cl + 2 Cl-- + 2 neutral ethylenediamine molecules + 2 neutral ethylenediamine molecules

Cis-Cis-dichlorobis(ethylenediamine)cobalt(II) dichlorobis(ethylenediamine)cobalt(II)

chloridechloride

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Common Bidentate Common Bidentate LigandsLigands

Acetylacetone (acac)Acetylacetone (acac)

Ethylenediamine (en)Ethylenediamine (en)

Bipyridine (bipy)Bipyridine (bipy)

Oxalate (ox)Oxalate (ox)

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AcetylacetonAcetylacetonate ate

ComplexesComplexes

Commonly called the Commonly called the “acac” ligand. Forms “acac” ligand. Forms complexes with all complexes with all transition elements.transition elements.

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Multidentate LigandsMultidentate LigandsEDTAEDTA4-4- - ethylenediaminetetraacetate ion - ethylenediaminetetraacetate ion

Multidentate ligands are Multidentate ligands are sometimes called sometimes called CHELATINGCHELATING

ligandsligands

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MultidentaMultidentate Ligandste Ligands

CoCo2+2+ complex complex of EDTAof EDTA4-4-

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NomenclatureNomenclatureCis-Cis-

dichlorobis(ethylenediamine)cobalt(IIIdichlorobis(ethylenediamine)cobalt(III) chloride) chloride1. Positive ions named first1. Positive ions named first

2. Ligand names arranged alphabetically2. Ligand names arranged alphabetically3. Prefixes -- di, tri, tetra for simple ligands3. Prefixes -- di, tri, tetra for simple ligands

bis, tris, tetrakis for complex ligandsbis, tris, tetrakis for complex ligands4. If M is in cation, name of metal is used4. If M is in cation, name of metal is used5. If M is in anion, then use suffix -ate5. If M is in anion, then use suffix -ate

[CuCl[CuCl44]]2-2- = tetrachlorocuprate = tetrachlorocuprate6. Oxidation no. of metal ion indicated6. Oxidation no. of metal ion indicated

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[Co(H[Co(H22O)O)66]]2+2+

Pt(NHPt(NH33))22ClCl22

[Cu(NH[Cu(NH33))44]]2+2+

Hexaaquacobalt(II)Hexaaquacobalt(II)

Tetraamminecopper(II)Tetraamminecopper(II)

diamminedichloroplatinum(II)diamminedichloroplatinum(II)

HH22O as a ligand is O as a ligand is aquaaqua

NHNH33 as a ligand is as a ligand is ammineammine

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Pt(Tris(ethylenediamine)nickel(II)Tris(ethylenediamine)nickel(II)

IrCl(CO)(PPhIrCl(CO)(PPh33))22

Vaska’s compoundVaska’s compound

Carbonylchlorobis(triphenylphosphine)iridium(I)Carbonylchlorobis(triphenylphosphine)iridium(I)

[Ni(NH[Ni(NH22CC22HH44NHNH22))33]]2+2+

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Structures of Structures of Coordination CompoundsCoordination Compounds

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IsomerismIsomerism• Two forms of isomerismTwo forms of isomerism

– ConstitutionalConstitutional– StereoisomerismStereoisomerism

• ConstitutionalConstitutional– Same empirical formula but different Same empirical formula but different atom-to-atom connectionsatom-to-atom connections

• StereoisomerismStereoisomerism– Same atom-to-atom connections but Same atom-to-atom connections but different arrangement in space.different arrangement in space.

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Constitutional Constitutional IsomerismIsomerism

Aldehydes & ketonesAldehydes & ketonesCH3-CH2-CH

O

C

O

CH3H3C

CrH2OH2O Cl

Cl

OH2

OH2

CrH2OH2O OH2

OH2

OH2

OH2

Cl3Cl

green violet

Peyrone’s chloride: Pt(NHPeyrone’s chloride: Pt(NH33) ) 22ClCl22

Magnus’s green salt: [Pt(NHMagnus’s green salt: [Pt(NH33))44][PtCl][PtCl44]]

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Linkage IsomerismLinkage Isomerism

CoH3NH3N NO2

NH3

NH3

NH3

2+

CoH3NH3N ONO

NH3

NH3

NH3

2+

sunlightsunlight

Such a transformation could be used Such a transformation could be used as an energy storage device.as an energy storage device.

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StereoisomerismStereoisomerism• One form is commonly called One form is commonly called geometric geometric isomerismisomerism or or cis-trans isomerismcis-trans isomerism. Occurs . Occurs often with often with square planar complexessquare planar complexes..

Note: there are VERY few Note: there are VERY few tetrahedral complexes. Would not tetrahedral complexes. Would not

have geometric isomers.have geometric isomers.

ciscis transtrans

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Geometric IsomerismGeometric Isomerism

Cis and trans-Cis and trans-dichlorobis(ethylenediamine)cobalt(II) dichlorobis(ethylenediamine)cobalt(II)

chloridechloride

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Geometric IsomerismGeometric Isomerism

Fac isomerFac isomer Mer isomerMer isomer

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StereoisomerismStereoisomerism• Enantiomers:Enantiomers: stereoisomers that have stereoisomers that have a non-superimposable mirror imagea non-superimposable mirror image

• Diastereoisomers:Diastereoisomers: stereoisomers that stereoisomers that do not have a non-superimposable do not have a non-superimposable mirror image (cis-trans isomers)mirror image (cis-trans isomers)

• Asymmetric:Asymmetric: lacking in symmetry—will lacking in symmetry—will have a non-superimposable mirror have a non-superimposable mirror imageimage

• Chiral:Chiral: an asymmetric molecule an asymmetric molecule

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An Enantiomeric PairAn Enantiomeric Pair

[Co(NH[Co(NH22CC22HH44NHNH22))33]]2+2+

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StereoisomerismStereoisomerism[Co(en)(NH3)2(H2O)Cl]2+

CoNN NH3

NH3

Cl

OH2

2+

CoNN Cl

OH2

NH3

NH3

2+

CoNN NH3

Cl

NH3

OH2

2+

CoNN NH3

OH2

NH3

Cl

2+

These two isomers These two isomers have a plane of have a plane of symmetry. Not symmetry. Not chiral.chiral.

These two are These two are asymmetric. Have asymmetric. Have non-non-superimposable superimposable mirror images.mirror images.

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StereoisomerismStereoisomerism

These are non-superimposable mirror imagesThese are non-superimposable mirror images

[Co(en)(NH[Co(en)(NH33))22(H(H22O)Cl]O)Cl]2+2+

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Bonding in Coordination Bonding in Coordination CompoundsCompounds

• Model must explainModel must explain– Basic bonding between M and ligandBasic bonding between M and ligand– Color and color changesColor and color changes– Magnetic behaviorMagnetic behavior– StructureStructure

• Two models availableTwo models available– Molecular orbitalMolecular orbital– Electrostatic crystal field theoryElectrostatic crystal field theory– Combination of the two Combination of the two ff ligand field ligand field theorytheory

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• As ligands L approach the metal As ligands L approach the metal ion Mion M++, , – L/ML/M++ orbital overlap occurs orbital overlap occurs– L/ML/M++ electron repulsion occurs electron repulsion occurs

• Crystal field theory focuses on Crystal field theory focuses on the latter, while MO theory the latter, while MO theory takes both into accounttakes both into account

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Crystal Field TheoryCrystal Field Theory• Consider what happens as 6 ligands approach an

Fe3+ ion

4s five 3d orbitals[Ar] ↑ ↑ ↑ ↑ ↑

All electrons All electrons have the same have the same energy in the energy in the free ionfree ion

Orbitals split into two groups as the ligands approach.Orbitals split into two groups as the ligands approach.

Value of ∆Value of ∆oo depends on depends on ligand: ligand: e.g., He.g., H22O > O > ClCl--

↑eg

t2g

↑

↑ ↑ ↑

∆E = ∆o

energy

d(x2-y2) dz2

dxy dxz dyz

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Octahedral Ligand FieldOctahedral Ligand Field

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Tetrahedral & Square Planar Tetrahedral & Square Planar Ligand FieldLigand Field

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Crystal Field TheoryCrystal Field Theory

↑ ↑d(x2-y2) dz2

↑ ↑ ↑dxy dxz dyz

∆E = ∆t

e

t2

energy

• Tetrahedral ligand field Tetrahedral ligand field • Note that ∆Note that ∆tt = 4/9 ∆ = 4/9 ∆oo and so ∆ and so ∆tt is is smallsmall

• Therefore, tetrahedral complexes Therefore, tetrahedral complexes tend to blue end of spectrumtend to blue end of spectrum

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Ways to Distribute Ways to Distribute ElectronsElectrons

• For 4 to 7 d electrons in octahedral complexes, For 4 to 7 d electrons in octahedral complexes, there are two ways to distribute the electrons.there are two ways to distribute the electrons.– High spinHigh spin — maximum number of unpaired e- — maximum number of unpaired e-

– Low spinLow spin — minimum number of unpaired e- — minimum number of unpaired e-

• Depends on size of ∆Depends on size of ∆oo and P, the pairing and P, the pairing

energy.energy.

• P = energy required to create e- pair.P = energy required to create e- pair.

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Magnetic Magnetic Properties/FeProperties/Fe2+2+

•High spinHigh spin• Weak ligand Weak ligand field strength field strength and/or lower Mand/or lower Mn+n+ chargecharge

• Higher P Higher P possible?possible?

•Low spinLow spin• Stronger ligand Stronger ligand field strength field strength and/or higher and/or higher MMn+n+ charge charge

• Lower P Lower P possible?possible?

ParamagneticParamagnetic

DiamagneticDiamagnetic

eg

t2g↑ ↑ ↑

∆E large

energy

d(x2-y2) dz2

dxy dxz dyz

eg

t2g↑ ↑ ↑

energy

d(x2-y2) dz2

dxy dxz dyz

eg

t2g ↑ ↑ ↑

∆E sm all

energy

d(x2-y2) dz2

dxy dxz dyz

↑

↑ ↑

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High and Low Spin Octahedral High and Low Spin Octahedral ComplexesComplexesSee Figure 22.25See Figure 22.25

High or low spin octahedral complexes High or low spin octahedral complexes only possible for donly possible for d44, d, d55, d, d66, and d, and d77

configurations.configurations.

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Crystal Field TheoryCrystal Field Theory

Why are complexes colored?

FeFe3+3+ CoCo2+2+ CuCu2+2+NiNi2+2+ ZnZn2+2+

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Crystal Field TheoryCrystal Field TheoryWhy are complexes colored?

– Note that color observed for Ni2+ in water is transmitted light

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Crystal Field TheoryCrystal Field Theory• Why are complexes colored?Why are complexes colored?

– Note that color observed is Note that color observed is transmittedtransmitted lightlight

Absorption bandAbsorption band

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Crystal Field TheoryCrystal Field Theory• Why are complexes colored?Why are complexes colored?

– Note that color observed is Note that color observed is transmittedtransmitted light light– Color arises from electron transitions between Color arises from electron transitions between d orbitalsd orbitals

– Color often not very intenseColor often not very intense

• Spectra can be complexSpectra can be complex– dd11, d, d44, d, d66, and d, and d99 --> 1 absorption band --> 1 absorption band– dd22, d, d33, d, d77, and d, and d88 --> 3 absorption bands --> 3 absorption bands

• Spectrochemical series — Spectrochemical series — ligand dependence ligand dependence of light absorbed.of light absorbed.

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Light Absorption by Light Absorption by Octahedral CoOctahedral Co3+3+ Complex Complex

eg

t2g↑ ↑ ↑

energy

d(x2-y2) dz2

dxy dxz dyz

+ energy (= ∆o)

(light absorbed) ↑

eg

t2g↑ ↑ ↑

energy

d(x2-y2) dz2

dxy dxz dyz

↑

↑

Ground stateGround state Excited stateExcited state

Usually excited complex returns to ground Usually excited complex returns to ground state by losing energy, which is observed state by losing energy, which is observed as heat.as heat.

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Spectrochemical SeriesSpectrochemical Series

• d orbital splitting d orbital splitting (value of ∆(value of ∆oo) is in the ) is in the orderorderII-- < Cl < Cl-- < F < F-- < H < H22O < NHO < NH33 < en < phen < CN< en < phen < CN-- < CO < COAs ∆ increases, As ∆ increases,

the absorbed the absorbed light tends to light tends to blue, and so the blue, and so the transmitted transmitted light tends to light tends to red.red.

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Other Ways to Induce ColorOther Ways to Induce Color• Intervalent transfer bands Intervalent transfer bands (IT) between ion of adjacent (IT) between ion of adjacent oxidation number.oxidation number.– Aquamarine and kyanite are Aquamarine and kyanite are examplesexamples

– Prussian bluePrussian blue• Color centersColor centers

– Amethyst has FeAmethyst has Fe4+4+

– When amethyst is heated, it forms When amethyst is heated, it forms citrine as Fecitrine as Fe4+4+ is reduced to Fe is reduced to Fe3+3+

Prussian Prussian blue blue contains contains FeFe3+3+ and and FeFe2+2+

Documents

Chapter 22 The Chemistry of the Transition Elements