Transition Metals and Coordination Chemistry

Chapter 23Chapter 23

Transition Metals

Similarities Similarities within a given period within a given period and and within a given group. within a given group.

Last electrons added are inner electrons (Last electrons added are inner electrons (dd’s, ’s, ff’s).’s).

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Ce

Th

Pr

Pa

Nd

U

Pm Sm

Pu

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

Sc

Y

La

Ac

Ti

Zr

Hf

Unq

V

Nb

Ta

Unp

Cr

Mo

W

Unh

Mn

Tc

Re

Uns

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

Uno Une Uun Uuu

Np

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Sc

Y

La*

Ac†

Ti

Zr

Hf

Unq

V

Nb

Ta

Unp

Cr

Mo

W

Unh

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

d-block transition elements

*Lanthanides

† Actinides

f-block transition elements

Uns Uno Une Uun Uuu

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0.2

Ato

mic

radi

i (nm

)

Atomic number

La

Hf

TaW Re Os

Ir Pt

AuZr

Y

NbMo Tc Ru

Rh Pd

AgSc

Ti

VCr

Mn Fe Co Ni Cu

1st series (3d)

2nd series (4d)

3rd series (5d)

0.1

0.15

Multiple Oxidation States

Metallic Behavior/Reducing StrengthLower oxidation state = more metallicLower oxidation state = more metallic

Color and Magnetism

e- in partially filled d sublevel absorbs visible light moves to slightly higher energy d orbital

Magnetic properties due to unpaired electrons

Electronegativity increases down column

ChromiumChemical properties reflect oxidation state

Valence-State Electronegativity

Electronegativity, ENElectronegativity, EN::electron “pulling power”electron “pulling power”

Valence-state ENValence-state EN::metal in higher oxidation statemetal in higher oxidation state

is more positiveis more positivehas stronger pull on electronshas stronger pull on electronsis more electronegativeis more electronegative

““Effective ENEffective EN””

Manganese

Silver

Weak Reducing Agent, H2Q

Mercury

Coordination Compound

Consist of a Consist of a complex ion complex ion and necessary and necessary counter ionscounter ions[Co(NH[Co(NH33))55Cl]ClCl]Cl22

Complex ion:Complex ion: [Co(NH[Co(NH33))55Cl]Cl]2+2+

CoCo3+3+ + 5 NH + 5 NH33 + Cl + Cl--

== 1(3+) + 5 (0) + 1(1-)1(3+) + 5 (0) + 1(1-) = 2+= 2+

Counter ions:Counter ions: 2 Cl2 Cl--

Complex ion remains intact upon dissolution in water

[Co(NH3)6]Cl3 [Pt(NH3)4]Br2

Complex Ion

Species where transition metal ion is surrounded Species where transition metal ion is surrounded by a certain number of ligands.by a certain number of ligands.

Transition metal ion:Transition metal ion: Lewis acidLewis acidLigands:Ligands: Lewis basesLewis bases

Co(NHCo(NH33))663+3+

Pt(NHPt(NH33))33BrBr++

Ligands

Molecule or ion having a lone electron pair that Molecule or ion having a lone electron pair that can be used to form a bond to a metal ion can be used to form a bond to a metal ion ((Lewis baseLewis base).).

coordinate covalent bondcoordinate covalent bond: metal-ligand bond: metal-ligand bond

monodentatemonodentate: one bond to metal ion: one bond to metal ionbidentatebidentate: : two bond to metal iontwo bond to metal ionpolydentatepolydentate: : more than two bonds to a metalmore than two bonds to a metal

ion possibleion possible

Formulas of Coordination Compounds

1.1. Cation then anionCation then anion2.2. Total charges must balance to zeroTotal charges must balance to zero3.3. Complex ion in bracketsComplex ion in brackets

KK22[Co(NH[Co(NH33))22ClCl44]]

[Co(NH[Co(NH33))44ClCl22]Cl]Cl

Names of Coordination Compounds

1.1. Cation then anionCation then anion2.2. LigandsLigands

in alphabetical order before metal ionin alphabetical order before metal ionneutral:neutral: molecule name*molecule name*anionic:anionic: -ide -ide -o -o

prefix indicates number of eachprefix indicates number of each

3.3. Oxidation stateOxidation state of metal ion in () only if more of metal ion in () only if more than one possiblethan one possible

4.4. If complex ion = anion, metal ending If complex ion = anion, metal ending -ate -ate

Examples

KK22[Co(NH[Co(NH33))22ClCl44]]

potassium diamminetetrachlorocobaltate(II)potassium diamminetetrachlorocobaltate(II)

[Co(NH[Co(NH33))44ClCl22]Cl]Cl

tetraamminedichlorocobalt(III) chloridetetraamminedichlorocobalt(III) chloride

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Isomers(same formula but different properties)

Stereoisomers(same bonds, differentspatial arrangements)

Structuralisomers

(different bonds)

Opticalisomerism

Geometric(cis-trans)isomerism

Linkageisomerism

Coordinationisomerism

Structural Isomerism 1

Coordination isomerism: Coordination isomerism: Composition of the complex ion varies.Composition of the complex ion varies.

[Cr(NH[Cr(NH33))55SOSO44]Br ]Br

and and [Cr(NH[Cr(NH33))55Br]SOBr]SO44

Structural Isomerism 2

Ligand isomerism: Ligand isomerism: Same complex ion structure but point of Same complex ion structure but point of attachment of at least one of the ligands differs.attachment of at least one of the ligands differs.

[Co(NH[Co(NH33))44(NO(NO22)Cl]Cl)Cl]Cl

andand [Co(NH[Co(NH33))44(ONO)Cl]Cl(ONO)Cl]Cl

Linkage Isomers

[Co(NH[Co(NH33))55(NO(NO22)]Cl)]Cl22Pentaamminenitrocobalt(III)Pentaamminenitrocobalt(III)

chloridechloride

[Co(NH[Co(NH33))55(ONO)]Cl(ONO)]Cl22Pentaamminenitritocobalt(III)Pentaamminenitritocobalt(III)

chloridechloride

Stereoisomerism 1

Geometric isomerism (cis-trans):Geometric isomerism (cis-trans):

Atoms or groups arranged differently spatially Atoms or groups arranged differently spatially relative to metal ionrelative to metal ion

Pt(NHPt(NH33))22ClCl22

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H3N

Co

H3N

NH3

NH3

Cl

Cl

H3N

Co

H3N

NH3

Cl

Cl

NH3

Cl

Cl

Co

Cl

ClCo

(a) (b)

Stereoisomerism 2Optical isomerismOptical isomerism: :

Have opposite effects on plane-polarized lightHave opposite effects on plane-polarized light(no superimposable mirror images)(no superimposable mirror images)

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Unpolarizedlight

Polarizingfilter

Polarizedlight

Tubecontainingsample

Rotatedpolarized light

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Left hand Right hand

Mirror imageof right hand

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N

N

N

N

N

NCo

N

N

N

N

N

NCo

Mirror imageof Isomer I

Isomer I Isomer II

N

N

N

N

N

NCo

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Cl

Cl

N

N

N

NCo

Cl

Cl

N

N

N

NCo

Cl

Cl

N

N

N

NCo

Cl

Cl

N

N

N

NCo

Cl

Cl

N

N

N

NCo

Isomer IIIsomer I

cistrans

Isomer II cannot besuperimposed exactlyon isomer I. They arenot identical structures.

The trans isomer andits mirror image areidentical. They are notisomers of each other.

Isomer II has the samestructure as the mirrorimage of isomer I.(b)(a)

Crystal Field Theory

Focus:Focus: energies of the energies of the dd orbitals orbitals

AssumptionsAssumptions

1.1. Ligands:Ligands: negative point negative point chargescharges

2.2. Metal-ligand bonding:Metal-ligand bonding: entirely ionicentirely ionic

strong-fieldstrong-field (low-spin): large splitting of (low-spin): large splitting of dd orbitals orbitalsweak-fieldweak-field (high-spin): small splitting of (high-spin): small splitting of dd orbitals orbitals

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eg(dz2, dx2 – y2)

t2g(dxz, dyz, dxy)

Free metal ion3d orbitalenergies

E

= crystal field splitting

High spin Low spin

[V(H2O)6]2+ [V(H2O)6]3+

[Cr(NH3)6]3+ [Cr(NH3)5Cl]2+s

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–

–

–

– ––– ––

–

dz2 dx2 – y2

dxy dyzdxz

(a) (b)

Tetrahedral Complexes

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E

Free metal ion Complex

dz2

dxy

dxz dyz

dx2 - y2

M z

(b)

Free metal ion Complex

dx2 - y2

dxydz2

dxz dyz

M

(a)

x

y

E

Square Planar & Linear Complexes

Approach along x-and y-axes Approach along z-axis

Hemoglobin & Oxyhemoglobin