Chem 106 Thurs 4-21-2011

Ch. 22: Transition Metals

1. Review periodic table

2. Sources of the elements

3. Coordination compounds

Definitions and examples

Ni2+ complexes: H2O, NH3, ethylenediamine

Bi-dentate ligands

Naming coordination compounds

Complex geometry: linear, square planar, tetrahedral, octahedral

Geometric isomers (cis/trans)

Chiral complexes: mirror image isomers

Transition Metal Chemistry

Transition Metal Chemistry

Citrine and amethyst are quartz (SiO2) with a trace of

cationic iron that gives rise to the color.

Gems & Minerals

Rhodochrosite, MnCO3 (Mn2+ and CO32-)

(manganese (II) carbonate)

Reactions: Transition Metals

Fe + O2

Fe + Cl2 Fe + HCl

Periodic Trends: Atom Radius

Periodic Trends: Oxidation Numbers

Most common

Zn

2B

Electron Configurations and the Periodic Table

Metallurgy: Element Sources

Why the big block

of O2- ores among

the early transition

metals, and the S2-

ores in the late

transition metals??

This is explained by the “Hard-Soft- Acid-Base” (HSAB) Theory.

Smaller cations with higher positive charge tend form more stable compounds

with small anions having a high negative charge density. These compounds are

based more on ionic attractive forces.

Larger cations with smaller positive charge tend to form more stable

compounds with large anions with valence electrons in larger, more diffuse

orbitals. These compounds are based more on covalent bonding interactions.

Transition metals: Coordination chemistry

• Coordination compound:

– 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

-

Co(H2O)62+

Pt(NH3)2Cl2

Cu(NH3)42+

“Cisplatin” - a cancer

chemotherapy agent

More examples

More examples: natural coordination compounds

Heme = iron (Fe2+) and a porphyrin ring

Hemoglobin and many redox enzymes contain iron-porphyrin complexes

(web; HC examples folder)

Two different kinds of

bonding by N atoms.

Coordination Compounds of Ni2+

[Ni(H2O)6]2+

[Ni(NH3)6]2+

[Ni(H2NCH2CH2NH2)3]2+

Ni(NH3)6]2+

A Ni2+ ion surrounded by six

neutral NH3 ligands

Gives coordination complex ion

with 2+ charge.

Coordination number of Ni = 6.

NH3 , H2O , AND carbon

monoxide (C≡≡≡≡O) are

MONODENTATE LIGANDS.

These are referred to as

“ammine”

“aqua”

“carbonyl”

Bidentate Ligands

Ethylenediamine (en)

Bipyridine (bipy)

Oxalate (ox) (2-)

Acetylacetone (acac) (1-)

Nomenclature

Cis-dichlorobis(ethylenediamine)cobalt(III) chloride

1. Positive ions named 1st , negative ion 2nd

2. Ligand names arranged alphabetically

3. Prefixes -- di, tri, tetra for monodentate ligands

bis, tris, tetrakis for bi- and multi- ligands

4. If M is in cation, name of metal is used

5. If M is in anion, then use suffix -ate

[CuCl4]2- = tetrachlorocuprate

6. Oxidation no. of metal ion indicated as (II) etc

(board)

[Co(H2O)6]2+

Pt(NH3)2Cl2

[Cu(NH3)4]2+

Hexaaquacobalt(II)

Tetraamminecopper(II)

diamminedichloroplatinum(II)

H2O as a ligand is aqua

NH3 as a ligand is ammine

Pt(Tris(ethylenediamine)nickel(II)

IrCl(CO)(PPh3)2

Carbonylchlorodi(triphenylphosphine)iridium(I)

[Ni(NH2C2H4NH2)3]2+

Structures of Coordination Compounds

Isomers

• Constitutional Isomers

– Same empirical

formula but different

atom-to-atom

connections

• Stereoisomers

– Same atom-to-atom

connections but

different arrangement

in space.

CrH2O

H2O Cl

Cl

OH2

OH2

CrH2O

H2O OH2

OH2

OH2

OH2

Cl3Cl

green violet

Geometric Isomerism

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

Stereoisomerism

• Chiral (ky’ rul) objects (like certain molecules):

mirror images are not superimposable.

• example: L, R hands

• Enantiomers: the two non-superimposable mirror

image molecules.

• example: D and L amino acid.

Certain metal coordination complexes.

These are non-superimposable mirror images

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

See .hin file

The end