Chapter ____

Complexes: assemblies of a central metal ion bonded to a group of surroundings molecules or ions. Ex. [Ag(NH3)2]+

Complex Ion: If the complex carries a charge

Coordination Compounds: Compounds that contain complexes

Ligands: the molecules or ions that surround the metal ion in a complex and usually have at least one lone pair of electrons◦ Ex. The 2 NH3 ligands bonded to the Ag+

Coordination Number: The number of donor atoms attached to a metal

Form one or more stable ions that have a complete d orbitals◦ Recall how to write electron configurations for d orbital

elements. Block 2B will not be considered because its only

common oxidation state has a complete d orbital ‘S’ electrons are the first to be removed when

these metals form ions Atomic radius: decreases across the period

because the 3d electrons shield the 4s electrons

Electronegativity & Ionization energy: increases slightly

Closed packed structure and a very small atomic radii◦ Results in a very strong metallic bond ◦ Leads to transition metals have higher densities,

melting points, and boiling points. Form a variety of oxidation states in their

compounds

Metal +1 +2 +3 +4 +5 +6 +7Sc Colorless

Ti Violet Colorless

V Violet Green blue Yellow

Cr Blue Green Yellow (CrO4

2-) orange

(Cr2O7 2-

Mn Pale pink Brown Dark green

(MnO42-)

Intense purple (MnO4

-)

Fe Pale green

Yellow or brown

Co Pink Orange/yellow

Ni Green

Cu Blue

Zn colorless

They are either polar or anions Because ligands have lone pairs, they can

function as Lewis bases◦ This makes the metal a Lewis acid

Ligand coordiante to the metal◦ Ex. [Cu(NH3)4]SO4

[Cu(NH3)4]2+ CATION

SO42- ANION

The charge of a complex is the sum of the charges on the central atom on its surrounding ligands.

Try these: What is the oxidation number of the central atom in

1.[Co(NH3)5Cl](NO3)2

2.[Ru(NH3)5(H2O)]Cl23.[Cr(NH3)6](NO3)3

4. K4[Fe(CN)6]

The atom of the ligand bound directly to the metal is called the donor atom◦ Ex. [Ag(NH3)2]+ N is the donor atom

The coordination number (the number of donor atoms attached to the metal) in the above example is 2.

Dependent on the number of donor atoms present, ligands are classified as monodentate, bidentate, or polydentate◦ Ex. Monodentate: H2O Bidentate: ethylenediamine: H2N-CH2–CH2–NH2

Bidentate and polydentate ligands are called chelating agents:

They hold the metal atom like a claw.

1. In naming salts, the name of the cation is given before the name of the anion.

◦ Ex. In [Co(NH3)5Cl]Cl2, we name the [Co(NH3)5Cl]2+ and then Cl- .

2. Within a complex ion or molecule, the ligands are named before the metal. Prefixes that give the number of ligands are not considered part of the ligand name in determining alphabetical order.

◦ In [Co(NH3)5Cl]2+ion, the ammonia ligands are named first, then the chloride, then the metal: Pentaaminechlorocobalt (III)

Number of Ligands Prefix

1 Mono

2 Di

3 Tri

4 Tetra

5 Penta

6 Hexa

3. The names of anionic ligands end in the letter O, whereas neutral ones ordinarily bears the name of the molecule.

Ligand Name

Cl- Chloro

OH- Hydroxo

NO2- Nitrito

CN- Cyano

SO42- Sulfato

H2O Aquo or aqua

NH3 Ammine

CO Carbonyl

NO Nitrosyl

4. A Greek prefix is used to indicate the number of each kind of ligand when more than one is present. If the name of the ligand itself contains a Greek prefix, such as mono- or di-, the name of the ligand is enclosed in parentheses and alternate prefixes are used, Bis-, Tris-, tetrakis-,hexakis

Ex. [Co(en)3]Cl3 tris(ethylenediamine)cobalt (III) chloride

4. If the complex is an anion, its name ends in –ate. Ex. K4[Fe(CN)6] hexocyanoferrate (II) ionOthers: Copper: Cuprate

Silver: Argenate

6. The oxidation number of the metal is given in parentheses in Roman numerals following the name of the metal.

Try naming these:1. [Cr(H2O)4Cl2]Cl2. [Co(NH3)4(H2O)CN]Cl2 3. Na[Al(OH)4]4. K2[Ni(CN)4]5. (NH4)2[CuBr4]6. [Ni(H2O)6]SO4 7. [CoCl3(NH3)3]1-

8. [Co(NH3)6]Cl3 9. K3[Fe(CN)6]10. K4[Fe(CN)6]

☺Central ion is first

☺Ligands second ☺Neutral molecules first ☺Negative ions second

☺Neutral molecules and polyatomic ions are always surrounded by (parentheses), even if only 1 present

☺Entire complex ion formula surrounded by [brackets]

Write the formula for the diamminepalladium(II) ion

☺Central ion – palladium (Pd)

☺Ligands – NH3 (2)

☺Written in parentheses ☺Neutral charge

☺Brackets around entire formula☺Calculate the net charge

[Pd(NH3)2]2+

Write the formula for the carbonylpentacyanoferrate(II) ion

☺Central ion – iron (Fe)

☺Ligands ☺CN (5) 1- charge Written in parentheses ☺CO (1) Neutral Written in parentheses

☺Brackets around entire formula☺Calculate the net charge

[Fe(CO)(CN)5]3-

Tetraammineplatinum(II) ion

[Pt(NH3)4]2+

Tetraiodoaurate(III) ion

[AuI4]-

Pentacarbonylnitrosyliron(II) ion

[Fe(CO)5(NO)]2+

Ligand Exchange Reactions of Transition Metals (and Al3+)◦ Complex ions undergo ligand substitution

reactions in solutions◦ Ex. [Ni(H2 O)6]2+ + NH3 → [Ni(NH3)6]2+ + H2O or

Ni2+ + NH3 → [Ni(NH3)6]2+ How do you know the number of ligands that are in

the product?◦ Hint: Often, not all the time!!, the number of ligands is twice

the cation charge.◦ Also, helpful to know the following table

Metal Ion Ligand Number of Ligands

Fe3+ SCN- 1

Ni2+ NH3 Any between 1 and 6

Ag+ CN- 2

Ag+ NH3 1 or 2

Zn2+ NH3 4

Al3+ OH- 3 or 4

Zn2+ OH- 4

Cu2+ NH3 4

Co2+ Cl_ 4

Decomposition of complex by acid-base neutralization◦ Complexes containing NH3 can be broken down by

acid base decomposition by adding an acid◦ Ex. [Cu(NH3)4]2+ + H+ → Cu2+ + NH4

+ The NH3 acts as a base (accepts H+ ions to form NH4

+ ). The rest of the complex is broken down.

Go over sheet from the “Ultimate Chemical Equation Handbook.” Responsible for all the reactions listed in the transition metal section.