Transition metals

Objective

A comprehensive knowledge of transition elements

chemistry will be gained by understanding the structure of

metals and coordination compounds.

Transition Metals

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

Some characteristics of Transition Metals and their compounds

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 coordination compounds.

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

ELECTRON CONFIGURATIONS3d elements: Sc Zn

Ar 3s2

3p6

Sc [Ar]3d1

4s2

K [Ar]4s1

Ti [Ar]3d24s

2

Ca [Ar]4s2

. .

. .

. .

Zn [Ar]3d10

4s2

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

Ti [Ar]3d2

4s2

Ti2+

[Ar]3d2

4s0

Ti3+

[Ar]3d1

4s0

Ti4+

[Ar]3d0

4s0

Ti5+

does not exist!

TRANSITION METALS: ScMn

Oxidation States:

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

Sc [Ar]3d1

4s2

Sc3+

[Ar] maximum

Mn [Ar]3d54s

2Mn

7+[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

Magnetic Properties

Diamagnetic:unaffected by a magnetic fieldno unpaired electrons

Paramagnetic: influenced by a magnetic fieldunpaired electrons

Transition metals and their compounds are often paramagneticHave unpaired d-electrons

Eg. Ti2+

Mn2+

Nomenclature & Coordination Chem

Lewis Acid - Lewis Base Chemistry

•Lewis Acid : e- acceptor • (metals are good e- acceptor)•Lewis Base : e- donor • (Ligands with lone pair electrons)

•Ligands, atoms or cluster of atoms with lone pair electrons available to donate•Complexing Agent: H2O, NH3, Cl- CN-

Complex -

•Metal- Ligand compounds• [MLn] i.e., [Ag(NH3)2]+ or [Co(NH3)6] Cl3•[ ] denotes atoms bonded to each other through covalent bonds. These atoms are contained in the coordination sphere.

Coordinated sphere is the directly bonded to each other.

Counter ions are outside bracket, and are not part of the coordinate sphere.

A coordinated compound behaves like an electrolyte in water: the complex ion

and counter separates from each other. But the complex ion behaves like a

polyatomic ion: the ligands and central metal ion remain attached.

Coordinated Complexes and Coordination Number

•Coord Shape Example•Number• 2 Linear [CuCl2]-, [Ag(NH3)2]+, [AuCl2]-

• 4 Square Planar [Ni(CN)4] 2-, [PdCl4]2-

• [Pt(NH3)4] 2+, [Cu(NH3)4] 2+

• 4 Tetrahedral [Cu(CN)4] 3-, [Zn(NH3)4]2+

• [CdCl4] 2-, [MnCl4] 2-

• 6 Octahedral [Cu(H2O)6] 3+, [V(CN)6] 4-, • [Cu(NH3)4Cl2] +, [Co(en)3]

3+

F

F

Br

FF

F

F

F

S

F

F

F

Ligands• Example of Typical mono-, bi- and poly dentate Ligands

Name of Neutral and Anionic Ligands:

Neutral: Anionic

Aqua H2O Fluoro Fl-

Amine NH3 Chloro Cl-

Nitrosyl NO Bromo Br-

Carbonyl CO Iodo I-

Hydroxo OH-

Cyano CN-

Chelates • Chelating Ligands have two or more donor atoms that

simultaneously coordinate to a single metal ion.• Polydentate - (Many toothed - ligand) • Chelating agent (Claw)• Sequestering agent - sequester - to set apart or

separate

• en ethylenediamine (shown) - two toothed ligand:

– i.e., [Co(en)3]3+ [Pt(en)2]2+

• EDTA ethylenediaminetetraacetate– (picture) hexadentate– EDTA is the antidote for – heavy metal poisoning

Chelating agents in Living system

•Seven of 24 elements necessary for life, based on ability to formed complexes• V, Cr, Mn, Fe, Co, Cu, Zn•Fe - hemoglobin, chlorophyll (Mg)•Co - Vitamin B

Biological Coordinating Complexes• Chlorophyll

• Oxymyoglobin Ferrichrome

Nomenclature• Cation - Anion: Salts: name cation before anions i.e.,

[Co(HN3)5Cl]Br2, we name [Co(HN3)5Cl] complex ion before bromides counter ions .

• Complex: Within complex ion, the ligands are named in alphabetical order before the metal i.e., pentaaminechlorocobalt(II), note that tetra is an indication of the number of NH3 group, and not considered in the alphabetizing of the ligand.

• Ligand: Anionic ligands end in -o and neutral ligands are name based on their molecular name (excepts are aqua H2O, amine: NH3)–Greek prefixes are used to indicate number of ligands, di-, tri-, tetra-, penta-, hexa-. Exception occurs when ligand already has Greek prefix in its name, The prefixes bis-, tris-, tetrakis-, pentakis, & hexakis. are used instead.– i.e., Ir(bpy)3 trisbipyridineiridium (III) bipyridine already has bi in its name.

• If the complex is an anion, then its name ends with suffix -ate.• Further more, oxidation state of the metal is given in roman numerals in

parenthesis at the end of the name.

Nomenclature• Rules: • 1. The cation is written before the anion.• 2. The charge of the cation(s) is balanced by the charge of

the anion(s).• 3. For the complex ion, neutral ligands are written before

anionic ligands (negative charge), and the whole ion is placed in brackets.

• Procedure Outline:• 1. The cation is named before the anion.• 2. Within the complex ion, the ligands are named, in

alphabetical order.• 3. Neutral ligands generally have the molecule name.• Anionic ligands drop the -ide and add -o after the root

name.• 4. Numerical prefixes denote the number of a particular

ligand.• 5. Oxidation state of metal ion is in Roman numeral in

parenthesis.• 6. For anionic complex, the end of the metal name is replaced

by -ate.

Example: Naming from Formula

• Name from formula• a) K3[Au(CN)4]• Potassium Tetracyanoaurate(I)• d) K[Co(C2O4)2(NH3)2]• Potassium diaminedioxaloCobaltate(I)• f) [Cr(en)2F2]NO3

• Bis(ethylenediamine)difluorochromium(III) nitrate

• Naming anionic metals • Iron: Ferrate Copper:

Cuprate• Lead: Plumbate Silver:

Argentate• Gold: Aurate Tin: Stannate

Example: Formula from Name

• Name from formula• a) Hexaamminechromium(III) nitrate• [Cr(NH3)6] (NO3)3

• d) dichlorobis(ethylenediamine)platinum(IV) bromide• [PtCl2(en)2]Br2

• f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)• [Zn(en)2][HgI4]•

• More anionic metals • Osmium: Osmate Cobalt: Cobaltate• Amtimony: Antimonate Rhenium: Rhenate• Platinum: Platinate Rhodium: Rhodate

Co

FF F

F FF

Co3+

Co3+

F- F

-

F-

F-

F-

F-

(3d6)

CRYSTAL FIELD SPLITTING

CRYSTAL FIELD SPLITTING

dx2-y

2 dz2

dxy dyz dxz

= crystal field splitting energy

Spectrochemical series:

CN > NO2

> en > NH3 > H2O > OH

- > F

> Cl

decreasing

d-electron

energy

COLOR WHEEL

RED

GREEN

VIOLETORANGE

YELLOWBLUE

SPIN PAIRINGOCTAHEDRAL COMPLEXES

E

CoF63-

Co(CN)63-

High spin

Paramagnetic Low spin (spin paired)

diamagnetic