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Transition Metals and Coordination:

Homework:

Read Chapter 24

Bonus Ch 24: 19, 23, 25, 43, 47, 51, 59

Check for the MasteringChemistry.com assignment and complete before due date

For Fun:

How are transition metal reactions similar to Reality TV?

Gemstones:

The colors of rubies and emeralds are both due to the presence of Cr3+

ions. The

difference lies in the crystal hosting the ion…

Transition Metals:

Many colorful compounds have transition metals.

Both ionic and [complex coordination] compounds can be formed

The properties of the transition metals are similar to each other and very different to

the properties of the main group metals

high mp, high densities, moderate to very hard, very good electrical conductors

Transition metals have electron configurations that fill the d orbitals last, yet when

losing electrons the valence s electrons are generally lost first. When the atom zinc

loses two electrons to become Zn+2

it is the 4s2 electrons that are lost…

Zn [Ar] 4s23d

10 Zn

+2 [Ar] 3d

10

Similarities in properties come from similarities in valence electron configuration

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Electron Configurations:

The difference in energy between ns and (n-1)d orbitals is not very large. This

causes some transition metal atoms to have irregular electron configuration patterns

like those below…

Cr = [Ar]4s13d

5 Cu = [Ar]4s

13d

10

Mo = [Kr]5s14d

5 Ru = [Kr]5s

14d

7

Pd = [Kr]5s04d

10 Ag = [Kr]5s

14d

10

Electron configurations are experimentally determined.

Ni, Tc+2

, and W behave predictably…

Ni

Tc2+

W

Atomic size:

The atomic radii of all the transition metals are very similar, with a small increase

in size down a column and a dip in size in the middle.

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Ionization Energy: The 1

st IE of the transition metals slowly increases across a series.

Electronegativity:

The electronegativity of the transition metals slowly increases across a series,

except for last element in the series

Oxidation States:

Unlike main group metals, transition metals often exhibit multiple oxidation states

Highest oxidation state is the same as the group number for Groups 3B to 7B

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Complex Ions:

Complex ion formation is a type of Lewis acid–base reaction. A bond forms

when a pair of electrons is donated by one atom creating a coordinate covalent

bond

When a transition metal cation combines with multiple anions or neutral molecules

it makes a complex ion

The attached anions or neutral molecules are called ligands

The overall charge on the complex ion can be positive or negative, depending on

the numbers and types of ligands attached

Names of Common Metals in Complex Ions:

Name in Cationic Complex, follow

with Roman numeral ( -- )

Name in Anionic Complex, follow

with Roman numeral ( -- )

chromium (-?-), Cr+?

chromate(-?-)

Cobalt (-?-), Co+?

cobaltate(-?-)

Copper (-?-), Cu+?

cuprate(-?-)

Gold (-?-), Au+?

aurate(-?-)

Iron (-?-), Fe+?

ferrate(-?-)

Lead (-?-), Pb+?

plumbate(-?-)

Manganese (-?-), Mn+?

manganate(-?-)

Molybdenum (-?-), Mo+?

molybdate(-?-)

Nickel (-?-), Ni+?

nickelate(-?-)

Platinum (-?-), Pt+?

platinate(-?-)

Silver, Ag+

argentate

Tin (-?-), Sn+?

stannate(-?-)

Zinc, Zn+2

zincate

Examples:

COMPLEX CATIONS:

[Cr(NH3)6]+3

hexaamminechromium(III)

[Fe(CO)6]+3

hexacarbonyliron(III)

[Pt(H2O)4]+2

tetraaquaplatinum(II)

COMPLEX ANIONS:

[Cr(CN)6]-3

hexacyanochromate(III)

[Fe(Br)6]-3

hexabromoferrate(III)

[Pt(OH)4]-2

tetrahydroxoplatinate(II)

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Ligands:

Ligands must have a pair of nonbonding electrons that can be shared to form the

coordinate covalent bond with the transition metal cation. Some ligands form more

than one coordinate covalent bond if they have lone pairs on different atoms that

are separated enough so that both can bond to the metal

A chelate is a complex ion containing a multidentate ligand and the ligand is

called the chelating agent (from Greek word chela = claw):

Example ligands:

Monodentate: H2O or NH3 (one atom in ligand has nonbonding electrons)

Bidentate: Polydentate:

Ethylenediamine (en) Ethylenediaminetetraacetate (EDTA)

Names and Formulas of Common Ligands:

Ligand (anions) Name in complex ion

Bromide, Br-1

bromo

Chloride, Cl-1

chloro

Hydroxide, OH-1

hydroxo

Cyanide, CN-1

cyano

Cyanate, OCN-1

cyanato (O to metal)

isocyanato(N to metal)

Nitrite, NO2-1

nitro (N attaches to metal),

nitrito(O attaches to metal)

Oxalate, C2O4-2

(ox) oxalato

Ethylenediaminetetraacetate

(EDTA)-4

ethylenediaminetetraaceto

Ligand (neutral molecules) Name in complex ion

Water, H2O aqua

Ammonia, NH3 ammine

Carbon monoxide, CO carbonyl

Ethylenediamine (en) ethylenediamine

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Geometries in Complex Ions:

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Coordination Compounds:

When a complex ion combines with counter-ions to make a neutral compound it is

called a coordination compound

The primary valence is the

oxidation number of the metal

Coordination number (also

called secondary valence) is the

number of bonds (not ligands) to

the metal. Coordination numbers

range from 2 to 12, with the most

common being 6 and 4

Example: [Co(NH3)6]Cl3

Naming Coordination Compounds:

1. Determine the name of the counter ions

2. Determine the ligand names and list them in alphabetical order

3. Determine the name of the metal cation

4. Name the complex ion:

a) naming each ligand alphabetically, adding a prefix in front of each

ligand to indicate the number found in the complex ion...

prefixes: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca,

dodeca (12)

b) following with the name of the metal cation

5. Write the name of the cation followed by the name of the anion

Name the coordination compound: [Co(NH3)6]Cl3

3 counter ions Cl-1

name____________

NH3 is neutral name____________

So the charge of cobalt must be +3

Co+3

(in a cationic complex)

name____________

Name the cation then the anion

Name of the coordination compound _________________________________

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Follow the naming rules Name [Cr(H2O)5Cl]Cl2 Name K3[Fe(CN)6]

Identify the cation and anion, and

the name of the simple ion

[Cr(H2O)5Cl]+2

is a

complex cation,

Cl-1

is chloride

K+1

is potassium,

[Fe(CN)6]-3

is a complex

ion

Give each ligand a name and list

them in alphabetical order

H2O is aqua

Cl-1

is chloro CN

-1 is cyano

Name the metal ion Cr

+3 is chromium(III)

complex ion is a cation

Fe+3

is ferrate(III)

complex ion is anionic

Name the complex ion by adding

prefixes to indicate the number of

each ligand followed by the name

of each ligand followed by the

name of the metal ion

[Cr(H2O)5Cl] +2

is

pentaquachloro-

chromium(III)

[Fe(CN)6]-3

is

hexacyanoferrate(III)

Name the compound by writing

the name of the cation before the

anion. The only space is between

ion names.

[Cr(H2O)5Cl]Cl2 is

pentaquachloro-

chromium(III) chloride

K3[Fe(CN)6] is potassium

hexacyanoferrate(III)

Try naming:

Na2CuBr4 and [Co(NH3)2(CO)4](NO3)3

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Isomers:

Structural isomers are molecules that have the same number and type of atoms,

but they are attached in a different order

Coordination isomers: ligand and counter ions exchange places

Linkage isomers: ligands attached to the central cation through different

ends of the ligand structure

[Co(NH3)5NO2]+2

, pentaamminonitrocobalt (III) and pentaamminonitritocobalt (III)

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Stereoisomers are molecules that have the same number and type of atoms, and

that are attached in the same order, but the atoms or groups of atoms point in a

different spatial direction

Geometric isomers: different special arrangements

Two identical ligands: tetrahedral or octahedral complex;

cis- adjacent , trans-opposite

Three identical ligand: octahedral complex; fac-all three ligands

adjacent, mer- the three ligands form an arc around the center

Optical isomers: nonsuperimposable mirror images

[Co(en)2Cl2]+1

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Bonding in Complex ions:

Valence Bond theory: Bonding takes place when the filled atomic orbital on the

ligand overlaps an empty atomic orbital on the metal ion. Explains geometries

well, but doesn’t explain color or magnetic properties.

Crystal Field theory: Bonds form due to the attraction of the electrons on the

ligand for the charge on the metal cation.

Electrons on ligands repel electrons in unhybridized d orbitals of metal ion

d orbitals are split

The difference in energy depends on complex formed and kinds of ligands

crystal field splitting energy

strong field splitting and weak field splitting

Octahedral Complex: Higher energy for positions with greater orbital overlap, ligands

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Size of the crystal field splitting energy, ,

Depends on the kinds of ligands and their relative positions on the complex ion, as

well as the kind of metal ion and its oxidation state

Large Small

Strong field ligands weak field ligands

CN-1

> NO2-1

> en > NH3 > H2O > OH-1

> F-1

> Cl-1

> Br-1

> I-1

Depends on the type of cation; increases as charge on metal increases and increases

down a group

Co3+

> Cr3+

> Fe3+

> Fe2+

> Co2+

> Ni2+

> Mn2+

Color and Complex Ions:

Transition metal ions show many intense colors in host crystals or solution

The color of light absorbed by the complex ion is related to electronic energy

changes in the structure of the complex

the electron “leaping” from a lower energy state to a higher energy state

The observed color is complementary color of one that is absorbed

Red-Purple: is least absorbed in

[Ti(H2O)6]+3

so that is the color

seen in a solution of [Ti(H2O)6]+3

Green and yellow are

absorbed the strongest,

the complementary colors

are “seen”

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Colors of complex ions:

Due to electronic transitions between split

d sublevel orbitals. The wavelength of

maximum absorbance can be used to

determine the size of the energy gap

between split d sublevel orbitals

Ephoton = h = hc/ =

h = 6.6262 x 10-34

J·s

c = 3.00 x 108 m/s

Try this:

[Cr(Cl)6]-3

has a maximum absorption spectrum at 735 nm.

Calculate the crystal field spitting energy in J/photon and kJ/mol.

Magnetic Properties and Crystal Field Strength: Octahedral-6 attached

The electron configuration of the metal ion with split d orbitals depends on the

strength of the crystal field

Weak field:

4th

and 5th electrons will go into the higher energy if the energy gap is small

unpaired electrons = paramagnetic complex

Strong field:

4th

thru 6th

electrons will pair the electrons in dxy, dyz, dxz if energy gap is large

paired electrons = diamagnetic complex

Try this: The complex ion [AlF6]-3

is paramagnetic. Is the F-1

ligand inducing a strong or

weak field?

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Tetrahedral - 4 attached (not on test)

Ligands repel more strongly with the dxy, dyz, dxz orbitals in the tetrahedral geometry

Reversing the order of energies compared to the octahedral geometry

Almost all tetrahedral complexes are high spin, d orbitals interact with only four

ligands, so is generally smaller.

Square Planar (not on test)

Occurs in d8 metals; Pt

2+, Pd

2+, Ir

+, Au

3+

The most complex splitting pattern

Almost all are low-spin complexes

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Applications:

Extraction of metals from ores; silver and gold as cyanide complexes

Use of chelating agents in heavy metal poisoning; EDTA for Pb poisoning

Chemical analysis; qualitative analysis for metal ions

blue = [CoSCN]+

red = [FeSCN]2+

Ni2+

and Pd2+

form insoluble colored precipitates with

dimethylglyoxime

Commercial coloring agents; Prussian blue = mix hexacyanoferrate(II) and (III)

Biomolecules

porphyrin ring

cytochrome C

hemoglobin

chlorophyll

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Transition Metal and Coordination Compounds Practice Problems:

1. For each of the complexes below, give the coordination number, oxidation state of the

metal and the formula for the phosphate salt (if the complex is a cation) or the

aluminum salt (if the complex is an anion), and name the compound.

a) [Mo(CN)2(en)2]+1

b) [Co(H2O)(OH)2Br]-1

c) [Ag(NH3)2]+1

d) [PtCl2(NO2)2]-2

2. Write out formulas, given the following names.

a) Pentaaquabromochromium(III) bromide

b) Sodium Hexacyanocobaltate(II)

c) Bis(ethylenediamine)dinitroiron(III) chloride

d) Tetraamminediiodoplatinum(IV) tetraiodoplatinate(II)

3. [PdCl4]-2

is found to be diamagnetic. Is this structure tetrahedral or square planar

according to crystal field theory? Draw the energy orbital diagram.

4. Draw two linkage isomers of [Mn(NH3)5(NO2)]+2

5. a) Three complex ions of cobalt (III) absorb light at wavelengths at 290 nm, 440 nm,

770 nm. Match each complex ion to the appropriate wavelength and predict the color

you would expect each solution to be. Refer to the color wheel for complements,

400nm to700nm is visible.

Choices: [Co(CN)6]-3

, [CoF6]-3

, [Co(NH3)6]-3

b) Solve for the crystal field splitting energy in kJ/mol for [Co(NH3)6]-3

.

For Fun: How are transition metal reactions similar to Reality TV?

When you mix two parties together you are not sure of the outcome. There are a

variety of possible reactions that the parties may undergo.