Cobalt Synthesis 0

8/2/2019 Cobalt Synthesis 0

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Cobalt (III) CoordinationCompounds

Synthesis Reactions


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The Cobalt Experience

Week 1: Synthesize a known compound, either J or Q. Begin

researching and writing.

Week 2: Synthesize an unknown compound. Keep

researching and writing

QS

T

J M

W

D


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The Cobalt Experience

Week 3: Complete two of four characterizations. Keep

researching and writing.

Week 4: Do the other two characterization tests. Keep

researching and writing

Week 5: Finish characterizations if you havent already.

Week 6: Spring Break for non-Chem 205 students.

Week 7: Turn in the report.


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Cobalt Coordination Chemistry

This is going to be a four week synthesis and

characterization lab. Basic idea we are going to make

some Co(III) complexes:

Then, youll make another, unknown complex, in which the

NH3 ligands, and the Cl- will be altered to e.g., F-, NO3

-,

SO42-, etc. Then well find the structure


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Cobalt coordination complexes are known since 1850s areimportant in history of inorganic chemistry, Crystal Field

Theory (CFT), redox, isomerism etc.


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Synopsis ofSynthesis

All compounds created will have an octahedral arrangement of

six ligands about Co3+.

Known Compound Q [Co(NH3)6]Cl

3

Known Compound J [Co(NH3)5Cl]Cl2

Unknown Compounds S, T, D, M, W

[Co(NH3)xLy]Xz nH2O


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Unknown Parameters[Co(NH3)xLy]Xz nH2O

x + y = 6

x 0

y 1

n 0

L = H2O, OH-, NO2-, NO3-, F-, Cl-, Br-[NO2

- = ONO- or NO2-]

X = NO3-, F-, Cl-, Br-


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Isomers

Cis vs. Trans

Facial (fac) vs.

Meridional (mer)

Geometric

Linkage

Nitrito vs. nitro


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Characterization Tests

Molar mass

Number of ammonia ligands

Identity of non-ammonia ligands

Charge of complex ion

But more on these in another lecture


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Labile and Inert Compounds


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What does this mean for Co?

Co(III) is inert, so we may have difficulty doing many inner

sphere reactions with it

So we use Co(II) which is kinetically labile

Co(III) is really stable due to large crystal field stabilization

energy (CFSE) associated with low spin d6 configuration.

However, you can

do reactions on some

inner sphere ligands

Mn+ inner outer intervening

sphere sphere medium

[Co(NH3)xLy]n+

(SO42-

)n


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OxidationLabile to Inert

d7 d6


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Known Synthesis

Q and J:

[Co(II)(H2O)6]Cl2 + NH4Cl + NH4OH [Co(II)(NH3)6]Cl2

[Co(II)(NH3)6]Cl

2+ H

2O

2 [Co(III(NH

3)5(H

2O)]Cl

3

J: [Co(III(NH3)5(H2O)]Cl3 + HCl [Co(III)(NH3)5Cl]Cl2

--(III) (III) [Co(NH3)5OH]2+

[Co(NH3)5(H2O)]3+


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Q:[Co(III(NH3)5(H2O)]Cl3 + C + HCl [Co(III)(NH3)6]Cl3

C

C

C+

(III)

[Co(II)(NH3)5(H2O)]2+

NH3[Co(II)(NH3)6]

2+

e-

[Co(III)

(NH3)6]3+

C+

C


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Some Concerns

You are dealing with some pretty dangerous

chemicals

Unwanted reactions are a possibility. Dont do that.

Watch your waste.

You are working with others under the hood for

extended periods of time.


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Cover ALL Chemicals

Concentrated ammonia and concentrated HCl react

in the air

Concentrated ammonia and concentrated HCl are notfun to breathe.

Even dry chemicals can have bad reactions when

exposed to open air, and possible spills


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Working in the Hood

Keep the sash down.

Keep your heads out of the hood.


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Important:

Must use hood as indicated!! SO2, SO3 choking gases, forms H2SO4 in lungs

NO2 choking gas, forms HNO3 in lungs

NaNO2 toxic

Oxalic acid toxic (rhubarb leaves)

Ethanol flammable, toxic

Acetone flammable, toxic

Work in hood as much as possible, use aspirators in lab

Coats on racks

Book bags well aware from hoods

Take care with acids


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Ammonium Fluoride

NH4F can form HF

HF can etch glass

HF can absorb through your skin

HF can eat at your bones


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Waste

Organic waste (acetone, ethanol)

Acidic waste

Basic waste

Dont mix these!


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Dropwise means dropwise

When the directions say dropwise, we mean dropwise

When the directions say slowly, we mean slowly


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30% H2O2

Hydrogen Peroxide in the store is 3%

Avoid contact with the skin

Do not allow H2O2 to contact unreacted solid on the inside of

the flask.

H2O2 is a great oxidizer and ethanol and acetone are reducing

agents DO NOT MIX THESE


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Filtration

Bchner funnels

Dont use too much water

Dont scratch sintered glass filters

Filtrate or solid?


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Vacuum filtration using a Crucible

The Vacuum Filtration set-up you will be using

in this experiment.

A glass sintered crucible.


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Care and Tips Great care with acids and bases: H2SO4, HNO3, NaOH

Keep coats, books, bags etc. well out of the way.

Record EVERYTHING in your notebook

Do calculations, and as much writing as you go Dont save

it all for the end

Take great care with acetone dont put it near the Bunsens!

First lab runs long, but later labs shorter


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Care and Tips

Label solutions well! (especially [Co(NCS)4]2- blue Co

standard solution

Use H2O2 very carefully, dont pour on compounds or sidesof flasks it will decompose dilute 30% to 3%

If you get black Co2O3 in synthesis, remove by filtration

Pour carefully!!

Vs.


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To-Do List

We will convert the Co complexes to [Co(NCS)4]2- which is

bright blue, and from its absorbance we can determine %Co

and molar mass by UV-Vis spectroscopy.

Well also find the number of NH3

by removing NH3

with

NaOH and titrating the NH3s

Plus, well find the charge on the cation by using it to

displace H+ from an Ion-Exchange resin column, and we

will titrate to get the charge.

This will give us a good chance of getting the total structure

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