1

Transition Metals

Occupy the d-block of periodic tableHave d-electrons in valence shell

Some characteristics of Transition Metals and theircompounds

1. Exhibit more than one oxidation state2. Many of their compounds are colored3. They exhibit interesting magnetic properties.4. They form an extensive series of compounds

known as metal complexes or coordinationcompounds.

e.g., Reduction of V5+ by metallic Zn

VO2(H2O)4+ yellow-orange

VO(H2O)52+ blue

V(H2O)63+ green

V(H2O)62+ violet

Exhibit more than one oxidation state

Many of their compounds are colored

Transition Metals

2

ELECTRON CONFIGURATIONS3d elements: Sc → Zn

Ar 3s23p6 Sc [Ar]3d14s2

K [Ar]4s1 Ti [Ar]3d24s2

Ca [Ar]4s2 . . . . . .Zn [Ar]3d104s2

Note: 4s is filled before 3d, but when oxidized, 4s electrons are lostbefore 3d.

Ti [Ar]3d24s2

Ti2+ [Ar]3d24s0

Ti3+ [Ar]3d14s0

Ti4+ [Ar]3d04s0

Ti5+ does not exist!

TRANSITION METALS: Sc→Mn

Oxidation States:Highest oxidation states of Sc, Ti, V, Cr, Mn = number ofvalence (4s + 3d) electrons.

Sc [Ar]3d14s2 Sc3+ [Ar] maximumMn [Ar]3d54s2 Mn7+[Ar] maximum

Trend from Sc → Mn:The max. oxidation state becomes increasingly unstable.Sc3+, Ti4+ are stable (maximum oxidation states).Sc2O3 Stable oxide.Mn7+ Exists but is easily reduced.MnO4

- Strong oxidizing agent.

Transition Metals

3

Magnetic Properties

Diamagnetic:unaffected by a magnetic fieldno unpaired electrons

Paramagnetic:influenced by a magnetic fieldunpaired electrons

Transition metals and their compounds are oftenparamagnetic⇒Have unpaired d-electrons

Eg. Ti2+

Mn2+

TRANSITION METAL IONSTransition metal ions are Lewis acids ⇒ they acceptelectron pairs.

Ligands are Lewis bases ⇒ molecules or ions whichdonate electron pairs.

Ligands bonded to metal ions ⇒ metal complexes orcoordination compounds.

Coordination number:number of electron donor atoms attached to the metal.

Chelates are ligands possessing two or more donoratoms.

4

COORDINATION COMPOUNDS• Metals-Lewis acids• Ligands -Lewis bases.

Ligand molecules have lone pair electrons.– Anions -

F−, Cl−, Br−, CN−, SCN−, NO2−, etc.

– Neutral ligands: NH3, H2O, CO• mono-dentate -(single claw to hold onto metal d orbital)

Ex. :NH3, H-:O:-H , CH3-:O:-H• Bi-dentate -(has 2 claws to hold onto metal d orbitals). Has 2

or more functional groups on ligands that have lone pairsExample :NH2-CH2-CH2-H2N:(= en or ethylenediammine)

Coordination # = 4

Tetrahedral, e.g. [Zn(NH3)4]2+

Square Planar, e.g. [Ni(CN)4]2−

Square Planar,e.g. [PtCl3(C2H4)]−

Pt

Cl

Cl

Cl

C

H H

C

H H

COORDINATION COMPOUNDS

5

Coordination # = 6

Octahedral, e.g. [CoF6]3-

Octahedral, e.g. [Co(en)3]3+

Co

F

F F

F F

F

Co

N

N N

N N

N

COORDINATION COMPOUNDS

IMPORTANT CHELATING LIGANDS

NCH2CH

2N

: :

CH2COH

CH2COH

O

O

HOCCH2

HOCCH2

O

O

Porphine

EDTA

6

7

CHELATE EFFECTChelating ligands form more stable compounds.

[Ni(H2O)6]2+ + 6NH3 ↔ [Ni(NH3)6]2+ + 6H2O Kf = 4x108

[Ni(H2O)6]2+ + 3en ↔ [Ni(en)3]2+ + 6H2O Kf = 2x1018

CHELATE EFFECT IS AN ENTROPY EFFECT

Cd2+ + 4CH3NH2 ↔ [Cd(CH3NH2)4]2+

ΔG° = −37.2kJ ΔH° = −57.3kJ ΔS° = −67.3J/K

Cd2+ + 2en ↔ [Cd(en)2]2+

ΔG° = −60.7kJ ΔH° = −56.5kJ ΔS° = +14.1J/K

PROPERTIES OF TRANSITION METALS

Transition Metal Complexes have different properties –• color (all except Zn or Sc3+ white compounds)• solubility-depends on complex reduction potential

– lower than free ions

Ag+(aq) + e− → Ag(s) E°1/2= +0.80V

[Ag(CN)2]−(aq) + e− →Ag(s)+ 2CN−(aq) E°1/2 = −0.31V

8

Co

F

F F

F F

F

Co3+ Co3+

F- F-

F-

F-F-

F-

(3d6)

CRYSTAL FIELD SPLITTING

dx2-y2 dz2

dxy dyz dxz

Δ

Δ = crystal field splitting energySpectrochemical series: CN− > NO2

− > en > NH3 > H2O > OH- > F− > Cl−

decreasing Δ

d-electronenergy

9

SPECTROCHEMICAL SERIES

CN-

CONO2

-

enNH3H2OOxalateOH-

F-

SCN-

Cl-

Br-

I- Color seen is complementary toabsorbed colorAbsorbed light

Strong fieldligands

Weak field ligands

UV

IR

COLOR WHEEL

RED

GREEN

VIOLETORANGE

YELLOWBLUE

10

CRYSTAL FIELD SPLITTING ENERGY

Δ depends on1. Metal2. Oxidation state3. Ligands

P = spin pairing energyP does not depend on the ligands

P < Δ ⇒ Low Spin ComplexP > Δ ⇒ High Spin Complex

11

SPIN PAIRINGOCTAHEDRAL COMPLEXES

E

CoF63-

Co(CN)63-High spin

Paramagnetic Low spin (spin paired)diamagnetic

USES OF TRANSITION METALSTiLighter and stronger than steel.Ti and its alloys are used in jet engines, planes, and in special hightemp applications, e.g. in the reentry shield on the Apollo capsules.TiO2 is a white pigment in all white paints.

VVanadium steel (Fe/V alloy) is the toughest steel known. It is usedin car springs.V2O5 is a catalyst used in sulfuric acid production.

CrStainless Steel = 73% Fe,18% Cr, 8% Ni, 1% CChromium is electroplated to make shiny metal parts.

MnMn steel (Fe/Mn alloy) is very tough and can withstand shock andabrasion – used in bulldozer blades and armor plates on warships.

12

CHROMIUM OXIDES

Cr(III) Oxide, Cr2O3Abrasive, RefractorySemiconductor, Green pigmentAmphoteric

Cr(IV) Oxide, CrO2Recording tape (magnetic material)

Cr(VI) Oxide, CrO3RedChrome plating, corrosion inhibitor

Na2Cr2O7Tanning, metal corrosion inhibitor