Transition Metals

Occupy the d-block of periodic table Have d-electrons in valence shell Some characteristics of Transition Metals and their compounds 1.

2.

3.

4.

Exhibit more than one oxidation state Many of their compounds are colored They exhibit interesting magnetic properties.

They form an extensive series of compounds known as metal complexes or coordination compounds.

Transition Metals Exhibit

more than one

oxidation state e.g., Reduction of V

5+

by metallic Zn

VO 2 (H 2 O) 4 + VO(H 2 O) 5 2+ V(H 2 O) 6 3+

yellow-orange

blue

green

V(H 2 O) 6 2+

violet Many of their compounds are

colored

ELECTRON CONFIGURATIONS 3d elements: Sc



Zn

Ar 3s 2 3p 6 K [Ar]4s 1 Ca [Ar]4s 2

Sc [Ar] 3d 1 4s 2 Ti [Ar] 3d 2 4s 2 .

.

.

.

. .

Zn [Ar] 3d 10 4s 2

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

Ti Ti Ti Ti Ti 2+ 3+ 4+ 5+ [Ar]3d 2 4s 2 [Ar]3d 2 4s 0 [Ar]3d 1 4s 0 [Ar]3d 0 4s 0 does not exist!

Transition Metals TRANSITION METALS: Sc



Mn

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

Sc [Ar]3d 1 4s 2 Mn [Ar]3d 5 4s 2 Sc 3+ [Ar] Mn 7+ [Ar] maximum maximum Trend from Sc  Mn: The max. oxidation state becomes increasingly unstable.

Sc 3+ , Ti 4+ are stable (maximum oxidation states).

Sc 2 O 3 Mn 7+ MnO 4 Stable oxide.

Exists but is easily reduced.

Strong oxidizing agent.

Magnetic Properties

Diamagnetic:

unaffected by a magnetic field no unpaired electrons

Paramagnetic:

influenced by a magnetic field unpaired electrons Transition metals and their compounds are often paramagnetic  Have unpaired d-electrons Eg. Ti 2+ Mn 2+

TRANSITION METAL IONS Transition metal ions are Lewis acids



they accept electron pairs.

Ligands are Lewis bases



molecules or ions which donate electron pairs.

Ligands bonded to metal ions



metal complexes or coordination compounds.

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

Chelates are ligands possessing two or more donor atoms.

COORDINATION COMPOUNDS

• Metals Lewis acids • Ligands Lewis bases.

Ligand molecules have lone pair electrons.

– –

Anions -

F  , Cl  , Br  , CN  , SCN  , NO 2  , etc.

Neutral ligands: NH 3 , H 2 O, CO

• mono-dentate (single claw to hold onto metal d orbital) Ex. :NH 3 , H-:O:-H , CH 3 -:O:-H • Bi-dentate -(has 2 claws to hold onto metal d orbitals).

Has 2 or more functional groups on ligands that have lone pairs Example :NH 2 -CH 2 -CH 2 -H 2 N: (= en or ethylenediammine )

COORDINATION COMPOUNDS

Coordination # = 4

Tetrahedral,

e.g.

[Zn(NH 3 ) 4 ] 2+ Square Planar,

e.g.

[Ni(CN) 4 ] 2  Square Planar,

e.g.

[PtCl 3 (C 2 H 4 )]  Cl Cl H C H Pt C Cl H H

COORDINATION COMPOUNDS

Coordination # = 6

Octahedral, e.g. [CoF 6 ] 3 Octahedral, e.g. [Co(en) 3 ] 3+

F F F Co F F F N N Co N N N N

Porphine IMPORTANT CHELATING LIGANDS EDTA O HOCCH 2 HOCCH 2 O NCH 2 CH 2 N O CH 2 COH CH 2 COH O

CHELATE EFFECT

Chelating ligands form more stable compounds.

[Ni(H 2 O) 6 ] 2+ + 6NH 3  [Ni(NH 3 ) 6 ] 2+ + 6H 2 O K f = 4x10 8 [Ni(H 2 O) 6 ] 2+ + 3en  [Ni(en) 3 ] 2+ + 6H 2 O K f = 2x10 18

CHELATE EFFECT IS AN ENTROPY EFFECT

Cd 2+ + 4CH 3 NH 2  G ° =  37.2kJ

 [Cd(CH 3 NH 2 ) 4 ] 2+  H ° =  57.3kJ  S ° = 

67.3J/K

Cd 2+ + 2

en

 [Cd(

en

) 2 ] 2+  G ° =  60.7kJ

 H ° =  56.5kJ  S ° =

+14.1J/K

PROPERTIES OF TRANSITION METALS

Transition Metal Complexes have different properties –

•

color (all except Zn or Sc 3+ 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

Co 3+ (3d 6 ) F F F F Co 3+ F F F F Co F F F F

CRYSTAL FIELD SPLITTING

d-electron energy dx 2 -y 2  dz 2 d xy d yz d xz  = crystal field splitting energy Spectrochemical series: CN  > NO 2  > en > NH 3 > H 2 O > OH > F  > Cl 

decreasing



UV IR

SPECTROCHEMICAL SERIES

Absorbed light CN CO NO 2 en NH 3 H 2 O Oxalate OH F SCN Cl Br I -

Strong field ligands Weak field ligands

Color seen is

complementary

absorbed color to

VIOLET

COLOR WHEEL

RED ORANGE BLUE GREEN YELLOW

CRYSTAL FIELD SPLITTING ENERGY

 depends on 1. Metal 2. Oxidation state 3. Ligands P = spin pairing energy P does not depend on the ligands P <   P >   Low Spin Complex High Spin Complex

SPIN PAIRING

OCTAHEDRAL COMPLEXES

E CoF 6 3 High spin Paramagnetic

Co(CN)

Low spin (spin paired) diamagnetic 6 3-

USES OF TRANSITION METALS Ti Lighter and stronger than steel.

Ti and its alloys are used in jet engines, planes, and in special high temp applications, e.g. in the reentry shield on the Apollo capsules.

TiO 2 is a white pigment in all white paints.

V Vanadium steel (Fe/V alloy) is the toughest steel known. It is used in car springs.

V 2 O 5 is a catalyst used in sulfuric acid production.

Cr Stainless Steel = 73% Fe,18% Cr, 8% Ni, 1% C Chromium is electroplated to make shiny metal parts.

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

CHROMIUM OXIDES

Cr(III) Oxide, Cr 2 O 3 Abrasive, Refractory Semiconductor, Green pigment Amphoteric Cr(IV) Oxide, CrO 2 Recording tape (magnetic material) Cr(VI) Oxide, CrO 3 Red Chrome plating, corrosion inhibitor Na 2 Cr 2 O 7 Tanning, metal corrosion inhibitor