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Valdosta State University Chapter 22 Transition Elements Valdosta State University

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Page 1: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Chapter 22Transition Elements

Valdosta State University

Page 2: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Transition Elements – d- and f-block

• Used in construction and manufacturing (iron), coins (nickel, copper, zinc), ornamental (gold, silver, platinum).• Densest elements (osmium d=22.49 g/cm3, iridium d=22.41g/cm3).• Highest melting point (tungsten, mp=3410oC) and lowest melting point (mercury, mp=-38.9oC).

Page 3: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Metal Chemistry

Valdosta State University

• Radioactive elements with atomic number less than 83 (technetium 43; promethium 61).• All elements are solids, but mercury.• Have metallic sheen, conduct electricity and heat.• Are oxidized and form ionic compounds.• Some are essential to living organisms: Cobalt (vitamin B12), iron (hemoglobin and myoglobin), molybdenium and iron (nitrogenase).• Compounds are highly colored and used as pigments: Fe4[Fe(CN)6)3 14 H2O (prussian blue), TiO2 (white).• Ions give color to gemstons: Iron(II) ions give yellow color in citrine and chromium(III) ions produce the red color of a ruby.

Page 4: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Electron Configurations

• General: [noble gas core] nsa (n-1) db

• Valance electrons for transition elements reside in the ns and (n-1) d subshells.

Page 5: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Reactions

Fe + O2

Fe + Cl2 Fe + HCl

• All metals undergo oxidation with oxygen, halogens, aqueous acids.• First the outermost electron is removed, followed by one or more d electrons.• Some generate cations with unpaired electrons = paramagnetism.• Are colored.• For first transition series common oxidation numbers are +2 and +3.

Fe2O3

Fe3+

[Ar]3d5

FeCl3Fe3+

[Ar]3d5

FeCl2 + H2

Fe2+

[Ar]3d6

Fe: [Ar]3d64s2

Fe + HCl

Fe + Cl2

Fe + O2

Page 6: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Trends: Oxidation number

Valdosta State University

Most commonMost common

Page 7: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Trends: Atom Radius

Valdosta State University

Page 8: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Trends: Density

Valdosta State University

Page 9: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Trends: Melting Point

Page 10: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Metallurgy: Element Sources

Valdosta State University

Page 11: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Pyrometallurgy

Valdosta State University

• Involves high temperature, such as Fe

• C and CO used as reducing agents in a blast furnaceFe2O3 + 3 C ---> 2 Fe + 3 CO

Fe2O3 + 3 CO ---> 2 Fe + 3 CO2

• Lime added to remove impurities, chiefly SiO2

SiO2 + CaO ---> CaSiO3

• Product is impure cast iron or pig iron

Page 12: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Hydrometallurgy

Valdosta State University

• Use aqueous solutions (flotation). Some use bacteria.• Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite)

CuFeS2(s) + 3 CuCl2(aq) --> 4 CuCl(s) + FeCl2(aq) + 2 S(s)

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

• Cu(I) disproportionates to Cu metal2 [CuCl2]- --> Cu(s) + CuCl2 (aq) + 2 Cl-

Azurite, 2CuCO3•Cu(OH)2 Native copper

Page 13: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Coordination Compounds

Valdosta State University

– 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

-

H••

H

H

N

H O H••

••

Page 14: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Coordination Chemistry

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

Pt(NHPt(NH33))22ClCl22

Cu(NHCu(NH33))442+2+

““Cisplatin” - a cancer Cisplatin” - a cancer chemotherapy agentchemotherapy agent

Page 15: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Coordination Chemistry

Valdosta State University

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

Page 16: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Myoglobin / Hemoglobin

p.1084

Page 17: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Coordination Chemistry

Valdosta State University

Vitamin B12Vitamin B12A naturally occurring A naturally occurring cobalt-based compoundcobalt-based compound

Co atomCo atomCo atomCo atom

Page 18: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Coordination Chemistry

Valdosta State University

• Biological nitrogen fixation contributes about half of total nitrogen input to global agriculture, remainder from Haber process.• To produce the H2 for the Haber process consumes about 1% of the world’s total energy.• A similar process requiring only atmospheric T and P is carried out by N-fixing bacteria, many of which live in symbiotic association with legumes.• N-fixing bacteria use the enzyme nitrogenase — transforms N2 into NH3.• Nitrogenase consists of 2 metalloproteins: one with Fe and the other with Fe and Mo.

Page 19: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nickel ion:coordination compounds

Coordination Chemistry

Page 20: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nomenclature

• [Ni(NH3)6]2+

• A Ni2+ ion surrounded by 6, neutral NH3 ligands

• Gives coordination complex ion with 2+ charge.

Ligand: monodentateCoordinate to the metal via a single Lewis base atom.

Page 21: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nomenclature++

Inner coordination sphereInner coordination sphere

ClCl--

Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules

Cis-dichlorobis(ethylenediamine)cobalt(II) chloride

Ligand: polydentateLigand: polydentatealso chelating ligandsalso chelating ligandsCoordinate with more Coordinate with more than one donor atom.than one donor atom.(Bidentate)(Bidentate)

Page 22: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Bidentate Ligands

Acetylacetone (acac)Acetylacetone (acac)

Ethylenediamine (en)Ethylenediamine (en)

Bipyridine (bipy)Bipyridine (bipy)

Oxalate (ox)Oxalate (ox)

Page 23: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Bidentate Ligands

Acetylacetonate Acetylacetonate ComplexesComplexes

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

Page 24: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Multidentate LigandsEDTAEDTA4-4- - ethylenediaminetetraacetate ion - ethylenediaminetetraacetate ion

Multidentate ligands are sometimes called CHELATING ligands

Page 25: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Co2+ complex of EDTA4-

Multidentate Ligands

Page 26: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Give the formula of a coordination compound

A Co3+ ion bound to one Cl- ion, one ammonia molecule, and two ethylenediamine (en) molecules.

1. Determine the net charge (sum the charges of the various components).

2. Place the formula in brackets and the net charge attached.

[Co(H2NCH2CH2NH2)2(NH3)Cl]2+

Page 27: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Determine the metal’s oxidation number and coordination numberPt(NH3)2(C2O4)

Oxalate: (C2O4)2-

Ammonia: NH3

Pt must be 2+ (oxidation number = +2)

Coordination number = 4 (two from oxalate and each ammonia filling one).

[Co(NH3)5Cl]SO4

Chloride: Cl-

Sulfate: SO42-

Overall complex must be 2+

Co must be 3+ (oxidation number = +3)

Coordination number = 6 (sulfate is not coordinated to the metal).

Page 28: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nomenclature

1. Positive ions named first2. Ligand names arranged alphabetically3. Prefixes -- di, tri, tetra for simple ligands

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

CuCl42- = tetrachlorocuprate6. Oxidation no. of metal ion indicated in roman

numerals.

Cis-dichlorobis(ethylenediamine)cobalt(III) chlorideCis-dichlorobis(ethylenediamine)cobalt(III) chloride

Page 29: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nomenclature

Valdosta State University

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

Pt(NHPt(NH33))22ClCl22

Cu(NHCu(NH33))442+2+

Hexaaquacobalt(II)

Tetraamminecopper(II)

diamminedichloroplatinum(II)

HH22O as a ligand is O as a ligand is aquaaqua

NHNH33 as a ligand is as a ligand is ammineammine

Page 30: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Nomenclature

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

Vaska’s compoundVaska’s compound

Carbonylchlorobis(triphenylphosphine)iridium(I)

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

Tris(ethylenediamine)nickel(II)

Page 31: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Geometry of Coordination Compounds

Valdosta State University

Defined by the arrangement of donor atoms of ligands around the central metal ion.

Page 32: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Isomerim of Coordination Compounds

• Two forms of isomerism– Constitutional– Stereoisomerism

• Constitutional– Same empirical formula but different atom-to-atom

connections

• Stereoisomerism– Same atom-to-atom connections but different

arrangement in space.

Geometric and Optical

Page 33: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Constitutional Isomers

Aldehydes & ketonesAldehydes & ketones CH3-CH2-CH

O

C

O

CH3H3C

3C, 1O, 6H

- Coordination isomerism: it is possible to exchange a ligand and the uncoordinated counterion.Example: [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br

(violet) (red)- Linkage isomerism: it is possible to attach a ligand to the metal through different atoms.Usually: SCN- and NO2

-

Page 34: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Constitutional Isomers

Valdosta State University

CoH3N

H3N NO2

NH3

NH3

NH3

2+

CoH3N

H3N ONO

NH3

NH3

NH3

2+

sunlightsunlight

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

Pentaamminenitritocobalt(III) Pentaamminenitrocobalt(III)

Page 35: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Stereoisomerism

Note: there are VERY few tetrahedral Note: there are VERY few tetrahedral complexes. Would not have geometric isomers.complexes. Would not have geometric isomers.

ciscis transtrans

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

Page 36: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Geometric Isomers

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

Page 37: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Geometric Isomers

fac isomer mer isomer

For octahedral complexes (MX3Y3):

fac isomer has three identical ligands lying at the corners of a triangular face of octahedron (fac=facial).

mer isomer ligands follow a meridian (mer=meridional).

Page 38: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Stereoisomers

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

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

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

• Chiral: an asymmetric molecule.

Valdosta State University

Page 39: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Enantiomers

[Co(NH2C2H4NH2)3]2+

Page 40: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Stereoisomers

CoN

N NH3

NH3

Cl

OH2

2+

CoN

N Cl

OH2

NH3

NH3

2+

CoN

N NH3

Cl

NH3

OH2

2+

CoN

N NH3

OH2

NH3

Cl

2+

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

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

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

Page 41: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Stereoisomers

These are non-superimposable mirror images:enantiomers

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

Page 42: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Bonding in Coordination Compounds

Valdosta State University

• 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– Combination of the two ---> ligand field theory

Page 43: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Bonding

• 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

Page 44: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Ligand Field Theory

• Consider what happens as 6 ligands approach an Fe3+ ion: Orbitals split into two groups as the ligands approach.

4s five 3d orbitals

[Ar] All electrons have the same energy in the free ion

Value of ligand field sppliting: ∆o depends on L: e.g., CN- > H2O > Cl-

eg

t2g

0

energy

d(x2-y2) dz2

dxy dxz dyz

Page 45: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Octahedral Ligand Field

Page 46: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Tetrahedral and Square Planar Ligand Fields

Page 47: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Crystal Field Theory

• Tetrahedral ligand field.

• Note that ∆t = 4/9 ∆o and so ∆t is small.

• Therefore, tetrahedral complexes tend to

absorb “red wavelengths” and be colored blue.

d(x2-y2) dz2

dxy dxz dyz

e

t2

energy

t

Page 48: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Ways to Distribute Electrons

• For 4 to 7 d electrons in octahedral complexes,

there are two ways to distribute the electrons.

– High spin — maximum number of unpaired e-

– Low spin — minimum number of unpaired e-

• Depends size of ∆o and P, the pairing energy.

• P = energy required to create e- pair.

Page 49: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Magnetic Properties of Fe2+

• High spin• Weak ligand field strength and/or lower Mn+ charge• 0 is smaller than P• [Fe(H2O)6]2+

• Low spin• Stronger ligand field strength and/or higher Mn+ charge• 0 is larger than P• [Fe(CN)6]4-

ParamagneticParamagnetic

DiamagneticDiamagnetic

eg

t2g

energy

d(x2-y2) dz2

dxy dxz dyz

eg

t2g

E small

energy

d(x2-y2) dz2

dxy dxz dyz

eg

t2g

E large

energy

d(x2-y2) dz2

dxy dxz dyz

Page 50: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

High and Low Spin Octahedral Complexes

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

Page 51: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Why are complexes colored?

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

Page 52: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Why are complexes colored?

– Note that color observed is transmitted light.

Red and blue are absorbed

Page 53: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Why are complexes colored?

– Note that color observed is transmitted light.

– Color arises from electron transitions between d orbitals (d-to-d transitions).

– Color often not very intense.

• Spectra can be complex– d1, d4, d6, and d9 --> 1 absorption band

– d2, d3, d7, and d8 --> 3 absorption bands

• Spectrochemical series — ligand dependence of light absorbed. The ability to split the d orbitals is determined by spectroscopy.

Page 54: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Light absorption by octahedral Co3+ complex

eg

t2g

energy

d(x2-y2) dz2

dxy dxz dyz

eg

t2g

energy

d(x2-y2) dz2

dxy dxz dyz

Ground stateGround state Excited stateExcited state

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

+ energy (= )

(light absorbed)

Page 55: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Spectrochemical Series

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

• d orbital splitting (value of ∆o) is in the order:

small ∆o large ∆o

I- < Cl- < F- < H2O < NH3 < en < phen < CN- < CO

Page 56: Valdosta State University Chapter 22 Transition Elements Valdosta State University

Valdosta State University

Other ways to induce color

• Intervalent transfer bands (IT) between ion of adjacent oxidation number.– Aquamarine and kyanite are examples

– Prussian blue

• Color centers– Amethyst has Fe4+

– When amethyst is heated, it forms citrine as Fe4+ is reduced to Fe3+

Prussian blue contains Fe3+ and Fe2+