Download - Cobalt Synthesis 0
-
8/2/2019 Cobalt Synthesis 0
1/28
Cobalt (III) CoordinationCompounds
Synthesis Reactions
-
8/2/2019 Cobalt Synthesis 0
2/28
-
8/2/2019 Cobalt Synthesis 0
3/28
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
-
8/2/2019 Cobalt Synthesis 0
4/28
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.
-
8/2/2019 Cobalt Synthesis 0
5/28
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
-
8/2/2019 Cobalt Synthesis 0
6/28
Cobalt coordination complexes are known since 1850s areimportant in history of inorganic chemistry, Crystal Field
Theory (CFT), redox, isomerism etc.
-
8/2/2019 Cobalt Synthesis 0
7/28
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
-
8/2/2019 Cobalt Synthesis 0
8/28
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-
-
8/2/2019 Cobalt Synthesis 0
9/28
Isomers
Cis vs. Trans
Facial (fac) vs.
Meridional (mer)
Geometric
Linkage
Nitrito vs. nitro
-
8/2/2019 Cobalt Synthesis 0
10/28
Characterization Tests
Molar mass
Number of ammonia ligands
Identity of non-ammonia ligands
Charge of complex ion
But more on these in another lecture
-
8/2/2019 Cobalt Synthesis 0
11/28
Labile and Inert Compounds
-
8/2/2019 Cobalt Synthesis 0
12/28
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
-
8/2/2019 Cobalt Synthesis 0
13/28
OxidationLabile to Inert
d7 d6
-
8/2/2019 Cobalt Synthesis 0
14/28
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+
-
8/2/2019 Cobalt Synthesis 0
15/28
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
-
8/2/2019 Cobalt Synthesis 0
16/28
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.
-
8/2/2019 Cobalt Synthesis 0
17/28
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
-
8/2/2019 Cobalt Synthesis 0
18/28
Working in the Hood
Keep the sash down.
Keep your heads out of the hood.
-
8/2/2019 Cobalt Synthesis 0
19/28
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
-
8/2/2019 Cobalt Synthesis 0
20/28
Ammonium Fluoride
NH4F can form HF
HF can etch glass
HF can absorb through your skin
HF can eat at your bones
-
8/2/2019 Cobalt Synthesis 0
21/28
Waste
Organic waste (acetone, ethanol)
Acidic waste
Basic waste
Dont mix these!
-
8/2/2019 Cobalt Synthesis 0
22/28
Dropwise means dropwise
When the directions say dropwise, we mean dropwise
When the directions say slowly, we mean slowly
-
8/2/2019 Cobalt Synthesis 0
23/28
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
-
8/2/2019 Cobalt Synthesis 0
24/28
Filtration
Bchner funnels
Dont use too much water
Dont scratch sintered glass filters
Filtrate or solid?
-
8/2/2019 Cobalt Synthesis 0
25/28
Vacuum filtration using a Crucible
The Vacuum Filtration set-up you will be using
in this experiment.
A glass sintered crucible.
-
8/2/2019 Cobalt Synthesis 0
26/28
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
-
8/2/2019 Cobalt Synthesis 0
27/28
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.
-
8/2/2019 Cobalt Synthesis 0
28/28
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