CH 4311
INORGANIC CHEMISTRY LABORATORY
LABORATORY MANUAL
Compiled and Edited by
Rudy Luck, Bahne Cornilsen, and Eugenijus Urnezius
(Version: Aug 2007)
Michigan Technological University
Houghton, Michigan
Fall 2007 Semester
Teaching Assistant:
Louis R Pignotti
Table of Contents
Table of Contents ...........................................................................................................................................................i
General Comments ....................................................................................................................................................... ii
Laboratory Notebook................................................................................................................................................... iii
LABORATORY SAFETY...........................................................................................................................................iv
In case of an accident ...............................................................................................................................................iv
Compressed Gas Cylinders........................................................................................................................................v
Manipulation in an Inert Atmosphere..................................................................................................................... vii
Simple Purging with an Inert Gas........................................................................................................................... vii
EMERGENCY PROCEDURES IN CHEMICAL INJURY ...................................................................................... vii
ACIDS, BASES, and other CORROSIVE CHEMICALS...................................................................................... vii
EMERGENCY FIRE PROCEDURE .................................................................................................................... viii
EXPERIMENT 1..........................................................................................................................................................1
TETRAFLUOROBORATES ....................................................................................................................................1
A. SYNTHESIS OF AMMONIUM TETRAFLUOROBORATE (Time 1.5 hours)..............................................1
B. SYNTHESIS OF POTASSIUM TETRAFLUOROBORATE ..........................................................................2
EXPERIMENT 2..........................................................................................................................................................7
PENTAMMINECHLOROCOBALT(III) CHLORIDE ............................................................................................7
A. SYNTHESIS OF PENTAMMINECHLOROCOBALT(III) CHLORIDE........................................................7
B. TEST TUBE EXPERIMENTS..........................................................................................................................8
EXPERIMENT 3........................................................................................................................................................13
BIS(PYRIDINE)IODINE(I) NITRATE..................................................................................................................13
A. SYNTHESIS OF BISPYRIDINEIODINE(I) NITRATE ................................................................................14
B. IODINE TESTS...............................................................................................................................................14
EXPERIMENT 4........................................................................................................................................................17
REDUCED OXIDATION STATES OF TRANSITION METALS .......................................................................17
A. SYNTHESIS OF CHROMIUM(II) ACETATE HYDRATE..........................................................................19
B. REDUCTIONS WITH ZINC ..........................................................................................................................19
EXPERIMENT 5........................................................................................................................................................24
ORGANOMETALLIC CHEMISTRY....................................................................................................................24
A. Synthesis of 2.2'-bipyridinetetracarbonylmolybdenum(0), Mo(CO)4bipy. ......................................................24
B. Hydridotetrakis(triphenylphosphite)cobalt(I), HCo[P(OPh)3]4. .......................................................................24
C. Bistriphenylphosphinecopper(I)borohydride, (Ph3P)2Cu(BH4). .......................................................................25
EXPERIMENT 6........................................................................................................................................................26
PREPARATION OF VANADYL ACETYLACETONATE ..................................................................................26
Introduction .............................................................................................................................................................26
EXPERIMENTAL ..................................................................................................................................................28
A. Preparation of Vanadyl Acetylacetonate, [VO(acac)2] ..................................................................................28
B. Abduct with Pyridine ......................................................................................................................................28
C. Infrared Spectroscopy .....................................................................................................................................28
D. Visible Spectroscopy ......................................................................................................................................28
Safety Notes ............................................................................................................................................................29
EXPERIMENT 7........................................................................................................................................................30
PREPARATION OF SOME COBALT ACETYLACETONATE COMPLEXES .................................................30
Measurement of NMR Spectra ................................................................................................................................30
EXPERIMENTAL ..................................................................................................................................................30
A. Preparation of Na[Co(acac)2(NO2)2] ...............................................................................................................31
B. Preparation of trans-[Co(acac)2(NO2)py] ........................................................................................................31
C. Preparation of cis[Co(acac)2(NO2)(py)] ..........................................................................................................31
D. Preparation of [Co(acac)2(o-phen)]ClO4 .........................................................................................................31
i
General Comments
Modern inorganic chemistry and inorganic synthesis techniques are best learned "handson" in the lab. A paper (journal article) or report describing the synthesis of a "new" compound
must convince (prove) to the reader that the author did, indeed, prepare the material described.
"Characterization" of the product is critical to this proof. These statements define the spirit and
objective of this lab, synthesis and characterization. Your job in each lab report is to convince
the reader that you succeeded in preparing the product. In so doing, you also prove that you
have learned some inorganic chemistry, as well has how much! To succeed, the lab report must
be concise, well organized and well written. To clearly communicate your results a report must
be grammatically correct and follow the standard format. (Lab reports should consist of title,
abstract, experimental, results and discussion sections - more detail will be supplied.)
Timeline: Weeks 1 through 4: experiments 1-3 will be completed individually. 2) Starting
week 5 the class will be split into groups forming rotations for the rest of CH4311 experiments.
Those are: a) experiment 4, where you will learn working under inert atmosphere utilizing
glovebox techniques; b) “open end” experiment(s) utilizing mobile vacuum line setups
(suggested procedures will be provided from recent scientific literature); c) in addition to this,
one of the remaining experiments (5-7) will have to be completed. Time and equipment
permitting, these experiments can be replaced with continuation of the “open end” experiments.
Lab Reports: Lab reports must be completed and turned in no later than the next lab period ( a
week after the completion of your experiment). Your reports will be graded and returned to you;
a cumulative grade from individual reports will be your grade for the course. Late reports will
result in grade reductions; reports late 5 or more days will result in a failing grade for the
experiment.
Attendance: Since there is no formal make-up lab period scheduled, all students who
miss 3 or more lab periods will authomatically be considered for an “I” grade.
There are Question and Answer (Q&A) sheets (including a "reaction table") for you to
fill out in the Lab Manual for these first four experiments. These pages are to be included in
your reports with the questions answered. These Q&A sheets focus your thinking about
important aspects of each experiment. These are useful in two ways. First, certain chemical
tests may be appropriate to help in the analysis of your product. Secondly, these are intended to
guide you in the type of analysis you should carry our for any synthesis experiment, especially
for the last three experiments (e.g., the information contained in the "reaction tables"). The last
three experiments do not have these question and answer sheets, rather the actual chemical
literature references are provided for your reference. The lab reports for experiments 5-7 and
“open end” experiments should include the type of information that you have learned is
important in the answer sheets of labs 1 through 4. When questions are raised in these
experiments, these should also be addressed in your reports.
Each lab requires the synthesis of some molecule(s); these products are to be handed-in
for grading purposes in labeled sample vials. Each vial should contain your name, the
experiment number, the chemical name of the compound or the formula, and the % yield. "No
vial, no grade."
ii
Please note that we are aware of two ways to conduct these labs. One is to thoroughly
prepare for the lab in advance of the experiment. This would be the recommended procedure.
The other method is to arrive without any prior preparation or any idea of what to do. It is your
responsibility to plan ahead to effectively utilize your time in the lab. The teaching assistant for
the lab is primarily responsible for your safety in the laboratory, for lab preparation, the
arrangement of the chemicals, etc. He/she will demonstrate new and difficult techniques.
All lab work and reports will be conducted entirely individually. There will be a brief
quiz at the start of each lab, so be sure to arrive on time. Your pre-lab preparations and lab
notebook will be periodically checked during the lab periods.
Laboratory Notebook
A bound notebook should be used. The notebook is your permanent record of laboratory
observations and results. The purpose of this record is to allow you or someone else to learn
from what you did in the experiment and to help you or them to repeat your success or avoid
your failure. As you will soon learn in this course, detailed information about a synthesis or
measurement is much appreciated by someone wishing to repeat your experiment. The following
points are to guide you in keeping an acceptable notebook:
1. The first 1-3 pages of your notebook should be used for an index (or "contents") of the
experiments performed during the year. The page numbers for each can be included here.
2. Notebook pages should be numbered consecutively. Each page and entry in the notebook is
to be dated. If an entry is made at a later day, it should be dated. All records are to be made in
ink.
3. Before proceeding with any experiment, prepare a table of physical constants of all inorganic
and organic substances which take part in the main reaction and important side reactions. The
mass required, molar mass, number of moles, density, solubility and melting point or boiling
point are usually included. Include also flammability and toxicity of the chemicals when
applicable. The most convenient sources for these data are the Handbook of Chemistry and
Physics, Merck Index, and Safety in the Chemical Laboratory. Define the expected main and
side reactions, the physical properties of the products, and the theoretical yield calculation in
your notebook. "Reaction tables" are provided for this data for the first 4 experiments.
The following is a typical example of a notebook entry:
Experiment 3
Chemical:
(CH3)4NCl
ICl
(CH3)4NICl2
Mass:
No. of Moles:
Density:
Melting Point (mp)
1.1 g
0.010
-
2.0 g
0.012
3.2 g/mL
27.2
Attacks skin,
forming dark,
painful patches
calculate
calculate
search
search
Toxicity
iii
search
(CH3)4NCl
+
ICl
Theoretical Yield:
Æ
(CH3)4NICl2
0.01 x 271.9
=
2.7 g
Side Reaction: decomposition of ICl to I2
4. Long, extended write-ups are not necessary. During the course of the experiment, all
significant observations should be recorded immediately, such as color changes, temperatures of
reaction mixtures, difficulties encountered, weightings, and measurements. Drawings should be
made of apparatus if a complicated set-up is used.
5. Finally, a conclusion should be presented at the end. This should include calculations (when
an analysis is carried out), interpretation of results and spectral data used to characterize your
product, and general conclusions resulting from the study.
LABORATORY SAFETY
By its very nature, experimental work is potentially hazardous. You must remember this
ALL OF THE TIME that you are in any chemical laboratory.
We have made every effort to identify, and as far as possible eliminate, all risks.
However, it is not possible to cover every conceivable hazard in an experimental procedure, and
each year new toxic properties are being discovered in even the most common chemicals. For
this reason, the warnings contained in the lab manual should in no way be regarded as a
comprehensive guide to every hazard. It is your responsibility to exercise caution in handling all
chemicals.
You must also realize that you, and you alone, bear the ultimate responsibility for your
own personal safety in the lab. (Chemistry laboratories are by no means unique in this regard.
For example, you do not rely blindly on the traffic laws alone to keep you safe while crossing
the road - you step off the curb only when you have decided it is reasonable to do so.)
A copy of the Merck Index, which contains information on the toxicity of chemicals, is
available to you in the prep room. You are encouraged to seek a knowledge of chemical toxicity
as a part of your education in chemistry.
Give careful thought to your work before proceeding, exercise caution, and know
beforehand what you will do in the event of an emergency.
In case of an accident
Familiarize yourself with the location of various safety equipment in the laboratory; for
example, the fire extinguisher, shower, eye wash fountain, and the first aid kit.
Everyone who works in the laboratory should try their best to prevent possible accidents
and also should be on guard to prevent any accident which can inflict injury on anyone else. The
following are basic rules that MUST be practiced in order to achieve this.
1. Eye protection is absolutely necessary at all times. Safety glasses not only protect you from
your own experiment but also from your neighbor's.
iv
2. Fire hazards - when flammable solvents are used, avoid using flames, only hot plates or steam
baths should be used. During heating, always make certain that either a condenser is connected
to the heated container or make sure there is a means of allowing the solvent vapor to escape
safely and away from the lab, e.g. work in a fume hood or draw the vapor away by suction. Do
not keep excess solvent in open beakers. Be extremely careful with ether. This solvent should be
heated only with warm water baths.
3. Operations involving the release of poisonous fumes, e.g. Cl2, must be performed in a fume
hood.
4. Obnoxious liquids should not be poured into an open sink. If the liquid does NOT react
violently with water, it may be slowly flushed down a drain in a fume hood with large quantities
of water. The advice of the instructors should be sought regarding the disposal of all dangerous
chemicals. Metallic sodium waste, for example, should be reacted with butanol first and then
poured into the jar for collecting sodium waste. Sodium reacts explosively with water and should
never be placed in a wastebasket. Mercury also requires particular mention. It is a cumulative
poison giving rise to very distressing physical and mental symptoms. Be extremely careful when
handling it to avoid spillage. Recover any that is spilled with a suction device, and dust the site
liberally with sulfur. (Hg spill kits are available in Chem. Supply.)
5. Toxic chemicals - where toxic solutions are to be handled, always work in a fume hood.
Handle all chemicals with care. If you spill or splash a chemical or solution on your hands, wash
immediately with large quantities of water.
6. Always point the mouth of a test tube or flask away from yourself or others while conducting
a reaction. Never put your face too close to a vessel in which you are heating or mixing reagents.
Never leave a reaction unattended.
7. No one may work in the laboratory in the absence of an instructor.
8. Never eat, drink or smoke in the laboratory.
Compressed Gas Cylinders
In most laboratory applications, gases are bled from compressed gas cylinders into
systems that are near atmospheric pressure and that are provided with some sort of safety outlet
in case too high a pressure is reached. In CH 4311, the set-up shown in Fig. 1 will be used.
The main valve on a cylinder (see Fig. 2) is simply an on-off valve; it does not control the
gas flow rate. Some type of control valve must be used. A needle valve (Fig. 2) permits such
control. With this arrangement, the main cylinder valve must never be opened unless the needle
valve is closed. After opening the main valve, the needle valve is opened sufficiently to obtain
the desired flow rate. If a cylinder contains a compressed gas (i.e. gases having critical points
below room temperature), the cylinder pressure will decrease with time as the gas is used, and
the gas flow will likewise decrease. Thus, for compounds which exist as gases (e.g. CO, N2, Ar,
BF3 and CH4) in the cylinder, a given flow rate cannot be maintained without continuous
adjustment. Compounds which condense to form liquids under pressure exert their natural vapor
v
pressure as long as any liquid remains in the cylinder. For these gases (e.g. CO2, NH3, Cl2, SO2,
(CH3)3N, and HF), a continuous flow rate can be obtained with just a needle valve.
To achieve a constant flow rate for gases which do not condense under the pressure in the
cylinder, a pressure regulator (see Fig. 3) is required. Upon opening the main valve the gas
pressure in the cylinder is given on the right-hand gauge. The regulator valve is opened by
turning the lever clockwise. Finally the flow rate is adjusted to the desired level by opening the
needle valve. The pressure between the needle valve and the regulator valve is given on the lefthand gauge The regulator will maintain this pressure. During the experiment, closing the needle
valve can be used to halt the flow. However, when you are finished with the cylinder for the day,
the main valve is closed to prevent loss of the gas in case the regulator leaks slightly. Do not
empty a cylinder completely; leave approximately 25 psi (lbs/in2) so that the cylinder does not
become contaminated with air or other gases before it is returned to the supplier for refilling.
vi
Manipulation in an Inert Atmosphere
The preparation and manipulation of certain compounds; e.g., some of the
organometallic compounds, such as lithium alkyls and aryls, requires the use of an inert
atmosphere. Inert often implies that the atmosphere is free from water and oxygen because many
compounds are hydrolytically or oxidatively unstable. In many cases, the reaction is carried out
in an atmosphere of dry nitrogen. The inert atmosphere is maintained by utilizing "dry-box" or
“double manifold” Schlenk line techniques. Sometimes simple purging of the reaction vessel
with inert gas prior to the reaction is sufficient (for moderately sensitive reagents). We will use
all of these techniques in CH4311. General description of more advanced air-sensitive
techniques is provided in “Advanced Practical Inorganic and Metalorganic Chemistry”, (R.J.
Errington, printed by Chapman&Hall, QD 151.2 E77; available in our library; a copy of relevant
chapters attached). Simple purging technique is defined in the following section.
Simple Purging with an Inert Gas
Tubing and a T-tube are used in Figure 1 to connect a cylinder of inert gas to
a) the apparatus to be purged, and to b) one arm of a bubbler (the main leg of which dips into a
pool of mercury or mineral oil). Ground-glass equipment is convenient, but not necessary.
One of the joints of the apparatus or a stopper must be loosened, or a stopcock must
be opened slightly. A stream of inert gas is then passed through the apparatus until it is judged
that practically all the air has been flushed out. (When the reaction is extremely sensitive to
moisture, the glass walls of the apparatus can be heated with a Bunsen burner while flushing air
from the reaction system. This will not be necessary in CH4311.) When the system is judged to
be purged of air, the joint (or stopcock) is closed. The inert gas should then bubble through the
mercury or mineral oil "safety valve". The apparatus is then under a slight positive pressure of
relatively static inert gas, and is ready for operation. After the initial purging operation, the flow
of gas through the bubbler can be adjusted to a low value to minimize waste.
CAUTION: What will happen if the flow rate is not maintained and a negative pressure is
allowed to develop in the reaction vessel?
EMERGENCY PROCEDURES: CHEMICAL INJURY or FIRE
ACIDS, BASES, and other CORROSIVE CHEMICALS
The most frequent type of student injury is the acid burn. Burns also occur from
strongly alkaline solutions and other corrosive chemicals. With careful work, these injuries can
be avoided. Furthermore, the fact that you have acid spilled on you, or that you may have come
into contact with some other corrosive substances, does not necessarily mean that you will
vii
receive an injury. It does mean that you may have only a few seconds in which to act if you are
to avoid injury.
In all cases the emergency treatment is to:
GO IMMEDIATELY TO THE NEAREST TAP OR SHOWER AND FLOOD THE AFFECTED AREA
WITH COPIOUS AMOUNTS OF WATER.
There are no exceptions to this rule. It is the best emergency treatment in all cases.
Remember that speed is imperative. Do not hesitate to take the initiative to assist another person
who has been splashed - if their face has been splashed, they may be unable to get themselves to
the nearest tap.
Once the emergency treatment is underway, and only then, the instructor or a demonstrator
should be called. Yell loudly when calling for help - labs are inherently noisy places.
EMERGENCY FIRE PROCEDURE
In the event of a fire, you must quickly alert those nearby. Then warn all other students of
the danger, and also alert the instructor(s).
All students must then, without being asked, leave the laboratory by the nearest exit. This
should be done as quickly as possible, taking care not to run or push at the exits. Once outside,
form a group to make sure everyone is out. Do not stand near doors or block the corridor.
Under no circumstances should you, yourself, attempt to fight a laboratory fire. This is a
job for a professional trained to handle chemical fires. .
The only possible exception to the above procedure is if you, or someone next to you, is
involved in the fire.
If you are involved, and your clothing is on fire, DO NOT RUN. Lay on the floor to
keep the flames away from your face and hair, and roll to extinguish the flames.
If someone next to you is involved, and their clothes are on fire, help get them to the
floor and use your lab-coat (or a fire blanket or safety shower, if close by) to smother the flames.
Once the burning clothing is extinguished, help the person away from the general fire area.
As in all emergency procedures, speed is essential. You must therefore know exactly
what to do before the event.
viii
EXPERIMENT 1
TETRAFLUOROBORATES
A. Ammonium Tetrafluoroborate
B. Potassium Tetrafluoroborate
Although BF3 is very easily hydrolyzed because of the two-electron vacancy in the valence shell
of boron, the tetravalent anion BF4- is extremely stable. These preparations demonstrate the
persistence of BF4-, in a metathesis reaction.
Reagents and Products
Substance
Molar Mass
Amount
mmol
mp °C
Boric Acid
Ammonium Bifluoride
Potassium Chloride
Ammonium Tetrafluoroborate
Potassium Tetrafluoroborate
61.8
57.0
74.6
104.8
125.9
620 mg
1140 mg
500 mg
500 mg
10.0
20.0
6.7
169
126
Acids, Bases and Solvents
Ammonia (15 M), Ethanol and Ether
Safety Notes
Ammonium bifluoride: Toxic and destructive to skin and tissue; do not inhale. In case of
contact flush with large quantities of water. Will react with glass.
Boric Acid: Toxic if ingested.
A.
SYNTHESIS OF AMMONIUM TETRAFLUOROBORATE (Time 1.5 hours)
2NH4HF2 + H3BO3 → NH4BF4 + NH3 + 3H2O
1. Weigh out exactly 620 mg of H3BO3 and 1140 mg of NH4HF2.
2. Stir the mixture with a glass rod until a clear liquid is, obtained. This liquid is called a
eutectic mixture, i.e., a mixture of two substances which has a lower melting temperature than
either of its constituents. Tare the beaker used in this step for reference in step 6, below.
1
3. Heat the mixture slowly on a hot plate with constant stirring. Gas evolution begins at about
105 °C and becomes vigorous at 110 °C. Maintain the temperature at 115 °C, checking
periodically with a thermometer.
4. Continue stirring for several minutes until the mixture solidifies and the product no longer
adheres to the rod.
5. Break up the congealed mass, and drive off the remaining NH3 by heating in an oven at 140
°C for 15 minutes. (This product could be transferred to a tared ceramic dish or crucible for
heating; however, this is not necessary since we are not heating to "high" temperatures where a
ceramic would be needed.) If necessary, break the product into smaller pieces and continue
heating until a dry white solid remains. Store in a desiccator.
6. After it is dry, run the IR spectrum, weigh the product, and determine the % yield.
The IR interpretation will be discussed in a separate hand-out. Your analysis of the IR spectrum
will be written-up in a second report for this first use of FTIR spectroscopy. This IR report will
be due the week after the standard report for this experiment.
B.
SYNTHESIS OF POTASSIUM TETRAFLUOROBORATE
NH4BF4 + KCl → KBF4 + NH4Cl
1. Dissolve 500 mg NH4BF4 with 5 mL hot water in a 25 mL Erlenmeyer flask.
2. Add 4 drops 15 M NH3 and heat on the steam bath.
3. Filter the hot solution with a Hirsch funnel and pour the hot filtrate into a 25 mL Erlenmeyer
flask containing a solution of 500 mg KCl in 2 mL water.
4. Cool the solution in a salt-ice slush and filter the crystals through the Hirsch funnel. Wash
with two 0.5 mL portions of ice-cold water and with two 0.5-mL portions each of ethanol and
ether.
5. Place the product on a watch glass and dry it in an oven at 100 °C for 15 minutes. Store in a
desiccator.
6. After it is dry, run the IR spectrum. Transfer the product to a tared vial, weigh it and
calculate the % yield. Interpret this IR spectrum along with the IR spectrum of KBF4 (see part
1.A.6 above).
NOTE: Please remember the details regarding the submission of samples as written on
page (ii). These instructions must be followed in all experiments.
2
Experiment 1.A.
Tetrafluoroborates
Lab Report
PART A. NH4BF4
Reagent Formulae:
NAME_____________________________
H3BO3
NH4HF2
NH4BF4
Wt. Cpd. & Container (mg)
Wt. Container (mg)
Wt. Compound (mg)
Molar Mass (mg/mmol)
Mmols Reagent
1. Net Balanced Equation:
2. Limiting Reagent (show calculations):
3. Theoretical Yield of Product (mg):
Theoretical Yield =_______________
4. % Yield of Product:
% Yield =_________________
3
Questions: Part 1.A.
1.
What is the advantage of weighing out the specified amounts of reagents exactly?
2.
Record the handbook values of the melting points of NH4HF2 and H3BO3.
mp NH4HF2_______________
mp H3BO3_________________
Comment on the melting points of the two compounds and that of the mixture. What is the
special name applied to the mixture in step 2?
3.
Record the solubilities of NH4BF4, KCl, NH4Cl and KBF4 in both hot and cold solutions.
Solubilities (g/100 mL)
Compound
Cold H2O
Hot H2O
NH4BF4
KCl
NH4Cl
KBF4
4
Experiment 1.B.
Tetrafluoroborates
Lab Report
NAME_____________________________
PART B. KBF4
Reagent Formulae:
NH4BF4
KCl
KBF4
Wt. Cpd. & Container (mg)
Wt. Container (mg)
Wt. Compound (mg)
Molar Mass (mg/mmol)
Mmols Reagent
1. Net Balanced Equation:
2. Limiting Reagent (show calculations):
3. Theoretical Yield of Product (mg):
Theoretical Yield =_______________
4. % Yield of Product:
% Yield =_________________
5
Questions: Part 1.B.
1.
Why is it desirable to cool the solution with ice water in step 1.B.4 ?
solubility table in Part 1.A.
2.
Draw the Lewis electron-dot and the VSEPR structure of BF4-.
Indicate the bond angles and the shape of the molecule.
3.
A recent catalog gave the following prices for the reagents
used in this experiment: (a) NH4HF2, 500 g/$45.05;
(b) H3BO3, 500 g/$12.40; (c) KCl, 500 g/$8.35. Calculate
the cost of each reagent in this experiment.
(a)
(b)
(c)
6
Hint: Consult your
EXPERIMENT 2
PENTAMMINECHLOROCOBALT(III) CHLORIDE
The conversion of Co(II) to Co(III) is thermodynamically unfavorable in 1 M
acid. However in basic solution and in the presence of appropriate ligands this
transformation occurs with ease due to the great stability of Co(III) complexes.
The preparation of Co(NH3)5Cl2+ from CoCl2 and H2O2 illustrates this behavior.
Reagents and Product
Substance
(Conc.)
Cobalt(II) Chloride Hexahydrate
Ammonium Chloride
Ammonia
(12 M)
Hydrogen Peroxide
(30%)
Ammonium Oxalate (sat'd. soln.)
Potassium Iodide
(50%)
Pentamminechlorocobalt(III) Chloride
Molar Mass
237.9
53.5
17.0
34.0
Mass
mmol
2000 mg
1000 mg
6 mL
1.6 mL
8.4
18.2
180
15
mp °C
250.3
Acids. Bases and Solvents
Hydrochloric Acid (12 M), Sodium Hydroxide (12 M)
Safety Notes
Cobalt(III) Chloride: Harmful if swallowed, inhaled or absorbed through the
skin.
Hydrogen Peroxide: Causes skin burns; handle with care.
Part A: SYNTHESIS OF PENTAMMINECHLOROCOBALT(III) CHLORIDE
2CoCl2•6H2O + H2O2 + 2NH4Cl + 8NH3 → 2Co(NH3)5Cl3 + 8H2O
1.
Dissolve 1000 mg NH4Cl with 6 mL of 12M NH3 in a 50 mL Erlenmeyer
flask containing a magnetic stirring bar.
2.
Add 2000 mg of finely pulverized CoCl2•6H2O in small portions with vigorous stirring.
7
3.
Cool the slurry in ice and add dropwise 1.6 mL of 30% hydrogen peroxide. Turn off the
stirrer momentarily if the reaction mixture effervesces excessively. When effervescence
ceases, cautiously add 6 mL of 12 M HCl.
4.
Cover the flask with an inverted beaker and heat at 60 °C for 15 min with stirring.
5.
Add 5 mL of deionized water, cool the solution in an ice-salt slush and collect the
product in a sintered glass funnel or Hirsch funnel. Wash with three 1 mL portions of
ice-cold water and three 1 mL portions of ice-cold 95% ethanol.
6.
Transfer the product to a watch glass and allow to sit until dry. (After partial drying in
the open, it may be dried in the desiccator.) Weigh and calculate the % yield. Run the IR
spectrum.
Part B: TEST TUBE EXPERIMENTS
1.
Add 2 mL sat'd. ammonium oxalate solution to 2 mL of a 1% solution of the product.
Write a balanced equation for the reaction.
2.
Dissolve a pinch of the product in 2 mL water, add 1 mL 12 M HCl and heat to boiling.
Add 1 mL KI solution. Record observed color changes, if any. What conclusions do you
draw about the lability of Co(NH3)5Cl2+ in strong acid on the basis of your observations?
Note that the following reaction is rapid:
2 Coaq3+ + 3 I- → 2 Coaq2+ + I3-
3.
Heat a pinch of the product with 2 mL 12 M NaOH and note whether any ammonia is
given off. Describe the changes and write a balanced equation.
4.
Heat a pinch of the product in a dry test tube over a Bunsen burner until there is no
further change. Describe the changes and identify the products. Write a balanced equation
describing the chemical change.
8
Experiment 2
Pentamminechlorocobalt(III) Chloride
Lab Report
NAME_____________________________
Reagent Formulae:
CoCl2•6H2O
NH4Cl
Co(NH3)5Cl3
Wt. Cpd. & Container (mg)
Wt. Container (mg)
Wt. Compound (mg)
Molar Mass (mg/mmol)
Mmols Reagent
1. Net Balanced Equation:
2. Limiting Reagent (show calculations):
Limiting Reagent =_______________
3. Theoretical Yield of Product (mg):
Theoretical Yield =_______________
4. % Yield of Product:
% Yield =_________________
9
Questions:
Part A
1.
What is the chemical function of the H2O2 in step A.3? Why is the solution cooled prior
to adding H2O2 and what is the cause of the effervescence?
2.
Why is the solution containing the product acidified with HCl prior to filtration in step
A.4? Hint: Ksp for Co(OH)3 is 4x10-45; consider the results of the test in part B.3
3.
What is the function of ethanol in step A.5? Why is the solution cooled? Hint: Look up
the solubility of the product in cold and hot water.
Solubility of Co(NH3)5Cl3; Cold: ___________________, Hot: ____________________
10
4.
Draw a structural diagram for Co(NH3)5Cl2+. What is the nature of the bonds between Co
and NH3? Describe the geometrical configuration of bonds around the cobalt atom.
5.
The price of (a) CoCl2•6H2O is $25.00 per 100 g and (b) NH4Cl was $11.35 per 500 g.
Calculate the costs of each of these reagents used in this preparation. If cost were a
determining factor which of these would be used as a limiting reagent?
(a)
(b)
11
Test Tube Experiments:
1.
Part B
Observation:
Interpretation:
Balanced Equation:
2.
Observation:
Interpretation:
3.
Observation:
Interpretation:
Balanced Equation:
4.
Observation:
Interpretation:
Balanced Equation:
12
EXPERIMENT 3
BIS(PYRIDINE)IODINE(I) NITRATE
Iodine(1+) is prepared by forcing the disproportionation of iodine into I+ and I- through
stabilization of I+ by chelation with pyridine (C5H5N = py), and by stabilization of I- by
precipitation as AgI.
Reagents and Product
Substance
Iodine
Pyridine
Silver Nitrate
I(py)2NO3
Molar Mass
253.8
79.1
169.9
347.1
Mass
mmol
bp °C
mp °C
250 mg
500 µL
170 mg
1.0
6.2
1.0
164.3
115.5
d.440
113.5
-42
212
dens.
4.93
0.982
4.352
Acids. Bases and Solvents
Hydrochloric Acid (6M), Sodium Hydroxide (6M), Chloroform, Ether
Safety Notes
Pyridine: Irritant; dispense in hood and rinse apparatus that comes in contact with it in acetone.
Iodine: Lachrymator; corrosive to skin, membranes and most metals. Handle with a glass or
porcelain spatula, and do not allow it to come in contact with the balance pan.
Silver Nitrate Blackens skin on contact and is a heavy metal poison.
13
A.
SYNTHESIS OF BIS(PYRIDINE)IODINE(I) NITRATE
I2 + AgNO3 + 2py → I(py)2NO3 + AgI
1.
Weigh 170 mg silver nitrate onto a watch glass (or weighing paper), and dissolve it with
500 µL pyridine in a 25 mL Erlenmeyer flask containing a stirring bar.
2.
In another flask dissolve 250 mg iodine in 5 mL chloroform.
3.
Add the chloroform solution to the pyridine solution with stirring using a Pasteur pipette.
A yellow precipitate of silver iodide will form.
4.
Remove the precipitate by suction filtration through a Hirsch funnel protected by a water
trap.
5.
Transfer the filtrate to a clean 25 mL Erlenmeyer flask, add 5 mL ether, stopper the flask
and shake.
6.
Let the flask stand for 20 minutes as the yellow product crystallizes out. Cool the flask in
an ice slush for 10 minutes.
7.
Decant the supernatant liquid and wash the product with two 500 µL portions of ether.
Warm the solution cautiously on a hot plate to remove the residual ether.
8.
Weigh the product and calculate the percent yield. Run an IR spectrum.
B.
IODIDE TESTS
1.
Add two small portions of product to test tubes labeled A and B.
2.
Add 1 mL 6 M HCl to A and 1 mL 6 M NaOH to B. Note your observations.
3.
Add 1 mL 0.1 M KI solution to each test tube. Note your observations and your
conclusions about stability of I+ in acidic and basic solutions.
14
Experiment 3
Bis(pyridine)iodine(I) nitrate
Lab Report
NAME_____________________________
Reagent Formulae:
I2
AgNO3
I(py)2NO3
Wt. Cpd. & Container (mg)
Wt. Container (mg)
Wt. Compound (mg)
Molar Mass (mg/mmol)
Mmols Reagent
1. Net Balanced Equation:
2. Limiting Reagent (show calculations):
Limiting Reagent =____________________
3. Theoretical Yield of Product (mg):
Theoretical Yield =_______________
4. % Yield of Product:
% Yield =_________________
15
Part A. Questions
1. Indicate the formal oxidation state(s) of the underlined element(s) in each of the following
compounds or ions (given that hydrogen is +1 and oxygen is –2):
a)
I 3-
_____
c) Ag I
b) I(py)2NO3 _____
_____
_____
d) Ag NO3 _____
2. Compare the solubilities of the product in chloroform and ether.
3. Balance the following equations:
a)
I(py) 2+ +
b)
I+ +
H2O =>
I2 +
IO3- +
H+
c)
I2 +
OH- =>
I 3- +
IO3- +
H2O
I- +
I3- +
H+ =>
Hpy+
4. Why is it necessary to exclude water from this synthesis? (consider the previous reactions)
5. Determine the costs of the reagents used in this synthesis given the following prices:
a) iodine is $22.40 per 100 g, b) pyridine is $19.50 per 500 mL, and c) silver nitrate is
$82.15 per 100 g.
a)
b)
c)
Part B: Iodide Tests and Observations (consider the reactions in Question A.4., above)
Solution A, Observations (acidic solution + KI):
Solution B, Observations (basic solution + KI):
From these iodide tests, what can you conclude about the stability of I+ in acidic and basic
solutions?
16
EXPERIMENT 4
REDUCED OXIDATION STATES OF TRANSITION METALS (aka “Glovebox Experiment”)
Chromium(II) Acetate Hydrate
One of the principal difficulties in preparing chromium(II) compounds is the prevention of its
oxidation to Cr(III) by atmospheric oxygen. In this experiment Cr(II) is generated in a reducing
atmosphere and stabilized by chelation as the dimer, [Cr(OAc)2]2•H2O, in which the chromium
atoms are bound by a quadruple bond.
Reagents and Products
________________________________________________________________________
Substance
Conc.
Molar Mass
Mass
mmol
mp °C
________________________________________________________________________
Chromium(III) Chloride Hexahydrate
266.5
1000 mg
3.8
Zinc (mossy)
65.4
1g
15
419
Sodium Acetate Trihydrate
136.0
4g
30
Titanyl Sulfate
(0.1 M)
Ammonium Vanadate
(0.1 M)
Sodium Dichromate
(0.1 M)
Ammonium Molybdate
(0.1 M)
Chromium (II) Acetate Dihydrate
376.2
________________________________________________________________________
Acids and Solvents
Hydrochloric Acid (12 M), Ethanol and Ether
Safety Notes
Chromium(III) Chloride Hexahydrate: Mildly toxic
17
A. SYNTHESIS OF CHROMIUM(II) ACETATE HYDRATE
This reaction will be conducted in a glovebox, under the atmosphere of pure nitrogen. You will
be instructed by a TA or instructor on techniques how to transfer "things" to/from the glovebox.
Things to pay attention to: 1) glovebox must (MUST!!!) always be under positive pressure of
nitrogen. In other words, you shoud feel being sligtly "pushed out" all the time, while working.
Do not overpresurize it, as this may result in rupture of the gloves. 2) The pressure level should
be adjusted by regulating the valves on the left side panel of the box, and venting excess gas out
through a mercury bubler.
The experiment will require careful planning, as you will have to bring in all the necessary
equipment/reagents at once. (To take something into the glovebox takes about 45-50 minutes).
It is strongly recommend to prepare the list of "take-in" items beforehand, and check it with a
TA before you proceed.
The synthesis proceeds in two stages; reduction of Cr(III) with zinc, and chelation of Cr(II) with
acetate.
2 Cr3+ + Zn → 2 Cr2+ + Zn2+
2 Cr2+ + 4 OAc- + 2 H2O → [Cr(OAc)2]2·2H2O
The overall net reaction is the sum of the above reactions.
2CrCl3·6H2O + Zn + 4 NaOAc·3H2O →[Cr(OAc)2]2·2H20 + ZnCl2 + 4 NaCl + 22 H20
1.
Deaerated water will be brought into the glovebox for you. However, if your reaction
doesn’t work (instead of a maroon crystalline solid purple deposit is obtained), a quick
deaeration procedure may be applied. Shake 20 mL of water with 1 mL of ether in a stoppered
50 mL Erlenmeyer flask to remove dissolved oxygen; store and cool in ice. Use this water in all
subsequent operations.
2.
Weigh 4 g NaOAc·3H2, transfer to a 25 mL Erlenmeyer flask, and slurry it with 4 mL of
water.
3.
Dissolve 1000 mg CrCl3·6H2O in 5 mL of water; add 1 g mossy zinc.
4.
Add 3 mL 12 M HCl dropwise through a Pasteur pipette until the solution is a clear pure
blue-green color (about five minutes).
5.
While hydrogen is still evolving at a rapid rate, transfer the chromous solution into the
acetate slurry with a Pasteur pipette. A maroon precipitate forms.
6.
Stopper the flask and cool in ice.
7.
Filter the product on a filtration funnel, pressurizing it from the top with a rubber bulb;
this would replace suction on filter flask typically employed for filtrations. Wash the solid with
18
four 2 mL portions of oxygen-free cold water, and then with two 2 mL portions of ethanol and
two 2 mL portions of ether. Dry the product as dry as possible after washing with ether.
8.
Spread the product thinly on a watch glass until dry, and store in the vacuum desiccator.
Run an IR spectrum of the dry product. If a portion of the material turns black, isolate it from
the maroon product.
9.
Set a small portion of the product on a watch glass and expose it to the air. Record your
observations.
10.
Transfer the product to a tarred vial, seal tightly and weigh. Calculate the % yield.
B.
REDUCTIONS WITH ZINC (to be done outside the glovebox)
Pour 2 mL each of 0.1 M solutions of (a) TiO2+, (b) VO2+, (c) Cr2O72-, and (d) MoO42- into four
test tubes. Add to each, 1 mL 12 M HCl and a piece of mossy zinc. Record all color changes
and write a balanced equation for each reaction.
19
Experiment 4
Reduced Oxidation States of Transition Metals
Lab Report
NAME_____________________________
Reagent Formulae:
CrCl3•6H2O
NaC2H3O2•3H2O
[Cr(OAc)2]2•2H2O
Wt. Cpd. & Container (mg)
Wt. Container (mg)
Wt. Compound (mg)
Molar Mass (mg/mmol)
Mmols Reagent
1. Net Balanced Equation:
2. Limiting Reagent (show calculations):
Limiting Reagent =____________________
3. Theoretical Yield of Product (mg):
Theoretical Yield =_______________
4. % Yield of Product:
% Yield =_________________
20
Questions: Part A
1. Why is it necessary to remove dissolved oxygen from the water used in this experiment?
Illustrate your answer with a balanced equation.
2. Zinc undergoes two reactions each of which serves a specific function in this synthesis. Write
a balanced equation for each reaction and explain the corresponding function.
Function (1)___________________________________________________________
Balanced Equation:
Function (2)___________________________________________________________
Balanced Equation:
3.
Describe the visual changes that occur in the product when it is exposed to air. What
change occurs in the oxidation state of chromium? Balance the following equation.
[Cr(OAc)2]2 +
4.
O2
→
Cr(OAc)3 +
Cr2O3
Sketch the structure of [Cr(OAc)2]2•2H2O. Describe the unique character of the Cr-Cr
bond.
21
5. Given the standard electrode potentials:
E0 (Cr3+, Cr2+) = -0.41 v,
E0 (Zn2+, Zn) = -0.76 v,
E0 (H+, H2)
=
0.00 v,
calculate the E0 values for the following reactions.
(a)
Zn + 2 Cr3+ → Zn2+ + 2 Cr2+
(b)
Zn + 2 H+ → Zn2+ + H2
Part B. ZINC REDUCTIONS
1.
Observations:
Reagent
a.
TiO2+
b.
VO2+
c.
Cr2O72-
d.
MoO42-
2.
Color Changes
Balanced Equations
a.
TiO2+ +
Zn
+
________ → Ti3+ +
Zn2+ + ___________
b.
VO2+ +
Zn
+
________ → V2+ +
Zn2+ + ___________
c.
Cr2O72- +
Zn
+
________ → Cr2+ +
Zn2+ + ___________
d.
MoO42- +
Zn
+
________ → Mo3+ + Zn2+ + ___________
22
3.
Standard Electrode Potentials (1 M Acid)
0.10
TiO2+
Ti3+
1442443
E°= ? _
1.00
- 0.37
- 1.63
Ti2+
0.36
- 0.25
Ti
VO2+
VO2+
V3+
V2+
144444444244444443
E°= ? _
1.33
- 0.41
Cr2O72+
Cr3+
Cr2+
144444424444443
E°= ? _
+ 0.40
- 0.91
0.00
H2MoO4
MoO2+
Mo3+
144444424444443
E°= ? _
- 1.20
V
Cr
- 0.20
Mo
Calculate the E0 values for each of the reactions in Part 2 above. Show calculations.
a.
Ea0 = ________________________________
b.
Eb0 = ________________________________
c.
Ec0 = ________________________________
d.
Ed0 = ________________________________
23
Additional Experiments (to be performed after completion of Exp 4 and “open-end”
experiment)
EXPERIMENT 5
ORGANOMETALLIC CHEMISTRY
A. Synthesis of 2.2'-bipyridinetetracarbonylmolybdenum(0), Mo(CO)4bipy.
The preparation of this compound is discussed by M.H.B. Stiddard, J. Chem. Soc., 4712 (1962).
Weigh out Mo(CO)6 (1.4 g) and 2,2'-bipyridine (0.8 g) into a 100 mL flask fitted with ground
glass stoppers, and attach the flask to a water cooled condenser. There is a tendency for
Mo(CO)6 and the product to react with oxygen at high temperatures so the reaction will be
carried out under a nitrogen atmosphere. Flush the apparatus with a moderate stream of nitrogen
gas for approximately 10 mins., then add 40 mL of deoxygenated toluene to the flask by syringe.
Stop the N2 flow and heat the solution at a moderate boil for 1 1/2 h. Cool the reaction vessel to
O °C using an ice-water bath, and collect the orange-red product by filtration. Wash the product
with copious amounts of diethyl ether and air dry. Record % yield.
Record the infrared spectrum of Mo(CO)4bipy. Assign the bands due to vibrations associated
with the carbonyl and 2,2'-bipyridine ligands. Measure the electronic absorption spectrum of the
product using a chloroform solution. Record the proton NMR spectrum of the product.
B. Hydridotetrakis(triphenylphosphite)cobalt(I), HCo[P(OPh)3]4.
The preparation of this compound is discussed by J.J. Levison and S.D. Robinson,
J. Chem. Soc. A, 96 (1970).
The reaction should be performed under the hood as triphenylphosphite has an unpleasant odor.
A solution of sodium borohydride (0.35 g) in ethanol (15 mL) is to be added dropwise during a
10 min. period to a stirred solution of Co(NO3)2•nH2O (1.0 g) and triphenylphosphite (4.5 mL)
in ethanol (30 mL) at room temperature. The purple color of the solution will dissipate and a
24
pale yellow precipitate should form. After 15 min. the precipitate can be filtered off, washed
with ethanol, water, and methanol, and dried in vacuo. Record % yield. Recrystallize the
product from toluene-methanol to obtain pale yellow plates. Record the infrared spectrum of the
compound. Record the proton NMR spectrum.
C. Bistriphenylphosphinecopper(l)borohydride, (Ph3P)2Cu(BH4).
The preparation of this compound has been discussed by G.W.J. Fleet and P.J.C. Harding,
Tetrahedron Letters, (no. 11), 975 (1979) and J. M. Davidson, Chemistry and Industry, 2021
(1964).
Stir l.0 g of CuSO4•nH2O and 5.0 g of PPh3 in 175 mL EtOH for 30-45 min., until all solids have
dissolved. NOTE: If not all the CuSO4 has dissolved, filter to remove the remaining solid.
Carefully add a NaBH4/EtOH slurry (~2 spatulas NaBH4/10 mL EtOH) to the solution in small
portions allowing effervescence to cease before adding the next portion. Stop the addition when,
upon adding NaBH4, little effervescence occurs. Filter off the white solid and wash it with EtOH
and diethyl ether. Recrystallize half of the product from CHCl3/EtOH, and wash the crystals
with diethyl ether. Record % yield. The compound should be characterized by its infrared
spectrum and its melting point.
Note: It is important that you check the suggested references listed above in order to gain
more understanding about the use of IR spectroscopy in the characterization of these
compounds.
25
EXPERIMENT 6
PREPARATION OF VANADYL ACETYLACETONATE
Introduction
The early transition elements have a great affinity for electronegative donor atoms and
have a tendency to exist in high oxidation states. In neutral aqueous solutions they tend to
hydrolyze and form hydroxo- or even oxo-complexes and in many cases tend to polymerize to
give complex structures involving oxygen bridged species.
As far as oxygen donor atoms are concerned this hydrolytic behavior is in part related to
the ability of the empty d-orbitals to accept the lone pair electrons of the oxygen atoms to form
multiple bonds. This tendency toward multiple bond formation is related to the high
electropositivity of the metals which tends to be neutralized by the back-bonding; it is so strong
that it will strip off the protons from the coordinated water molecules.
It is then not surprising that V4+ does not exist in water as [V(H2O)6]4+ but rather as the
so called vanadyl ion (see Figure), and it is plausible to assume that the VO bond is a triple bond
involving a sigma bond and two π-bonds involving two lone-pair electrons of the oxygen. This
supposition is confirmed by the fact that the bond length is very "short" and while the five water
molecules can be readily substituted by a host of other ligands, the VO entity persists.
A spectroscopic consequence of this multiple bond formation is that the system has to be
treated by molecular orbitals and not as a simple crystal field system. The reason for this is that
the π-bonding of the VO group gives rise to electronic excited state levels which cannot be taken
into account by the simple crystal field theory. The [VO(H2O)5]2+ ion is d1.
The purpose of this experiment is first to make several of these vanadyl complexes and
then to characterize them using UV-Vis spectroscopy and IR spectroscopy. An approximate
molecular orbital diagram of the [VO(H2O)5]2+ ion is shown below, and it is to be used to
interpret the visible spectra obtained. This diagram is only slightly different if any , or all, of the
aquo-ligands are replaced by other ligands.
26
27
References:
(i)
C.J. Ballhausen, Introduction to Ligand Field Theory, McGraw-Hill, N.Y.,
1962, pp. 228-230.
(ii)
C.J. Ballhausen and H.B. Gray, Inorg. Chem., 1, 111 (1962).
(iii)
J. Selbin, L.H. Holmes, Jr. and S.P. McGlynn, J. Inorg. Nucl. Chem., 25,
1359 (1963).
(iv)
J. Selbin and T.R. Ortolano, J. Inorg. Nucl. Chem., 26, 37 (1964).
(v)
M.M. Jones, J. Am. Chem. Soc., 76, 5995 (1954).
(vi)
Adams and Raynor, Advanced Practical Inorganic Chemistry, p. 49.
EXPERIMENTAL
A.
Preparation of Vanadyl Acetylacetonate,
[VO(acac)2]
Boil a solution of 3.5 g vanadium pentoxide (V205) in 12 mL water to which has been
added 9 mL concentrated sulfuric acid and 25 mL ethanol. The color of the slurry changes from
green to blue. Stir the mixture during heating. Replenish with H2O if too much solvent has been
evaporated. After 30 minutes, gravity filter the mixture. Add 10 mL acetylacetone to the
solution. Neutralize the solution by adding slowly and with stirring a solution of 20 g anhydrous
potassium carbonate in 125 mL water. Filter the product, wash with H2O and dry in air. First
reserve about 1 g of crude, dry product for part b, and then recrystallize the rest from
chloroform.
B.
Abduct with Pyridine
Place 1 g of the crude VO(acac)2 in a 125 mL Erlenmeyer flask. Add 15 mL pyridine.
Reflux for 2 hours. Cool. Add 75-100 mL diethyl ether. Cool in ice bath. Scratch the sides of the
flask. Suction filter the product. Wash with some cold ether and dry in air.
What are the structures of vanadyl acetylacetonate and the pyridine adduct?
C.
Infrared Spectroscopy
Run an IR spectrum of VO(acac)2 and of [VO(acac)2py] as a Nujol mull. Note the
differences in the two spectra. Explain these differences.
D.
Visible Spectroscopy
Take 7 mL of chloroform, acetonitrile, pyridine and water respectively in four separate
test tubes. To each add 2 spatula tipfuls of VO(acac)2. Shake well to dissolve. Run the visible
spectrum of each solution from 450 mµ - 800 mµ. Also run a spectrum of VOSO4 in water.
28
Compare the spectra. Note the differences and assign the bands to electronic transitions in the
complex.
With the aid of the energy level diagram drawn for [VO(H2O)5]2+ and the IR spectral
data, discuss whether the sixth ligand causes a serious perturbation on the VO2+ entity.
Safety Notes:
General Warning about Organic Solvents
A lot of common organic solvents are poisonous by inhalation, irritable to skin and may cause
other effects.
To name a few here:
1.
Chloroform - Inhalation of large doses may cause hypotension, respiratory and myocardial
depression and death. Found to be carcinogenic in National Cancer Institute tests in mice
and rats.
2.
Acetonitrile - toxic, may cause skin irritation. Avoid breathing vapor.
3.
Pyridine - may cause CNS (central nervous system) depression, and irritation of the skin
and the respiratory tract. Large doses may cause G.I. (gastrointestinal) disturbances, kidney and
liver damage.
4.
Carbon tetrachloride - Poisonous by inhalation, ingestion or skin absorption.
5.
Benzene - toxic by inhalation and skin absorption. Carcinogenic by Chronic exposure.
Important::::: Note that the first part of the next experiment should be completed this
week, i.e., part 7A.
29
EXPERIMENT 7
PREPARATION OF SOME COBALT ACETYLACETONATE COMPLEXES
The purpose of this experiment is to prepare several cobalt acetylacetonate
complexes and then to apply proton magnetic resonance spectroscopy to solve stereochemical
problems in β-diketone chelate chemistry. This technique is particularly useful in studying the
geometrical isomers of bis(acetylacetonate) complexes of cobalt (III).
This experiment demonstrates that NMR spectroscopy is one of the chemist's very
valuable tools for the determination of structures of compounds. Although only 1H NMR will be
studied here, extensive NMR studies of 13C, 19F and 31P and other nuclei in a wide range of
inorganic compounds have contributed significantly to the understanding of structure and
bonding. You should read the references suggested in order to gain further theoretical
background upon which NMR spectroscopy is based.
Measurement of NMR Spectra
Most commercially available NMR instruments require liquid samples of
approximately 0.5 mL volume. If a compound is a liquid its spectrum can be measured neat.
Since many compounds are solids, they must first be dissolved in a solvent which itself does not
absorb in the region of the NMR spectrum of interest. The common solvents used for proton
NMR studies are CCl4, CS2, CDCl3, acetone-D6, and D2O. Generally solutions must be made up
relatively concentrated. For most inorganic complexes a saturated solution is used. A suitable
standard should then be chosen. The chemical shift values of the protons in a particular
compound are determined with reference to this standard. The reference compound that is
frequently used for 1H NMR is tetramethylsilane (TMS). It is dissolved in the same solution as
the sample (only a drop is necessary). Because TMS is insoluble in deuterium oxide, it cannot
be used with D2O. A suitable reference for aqueous solutions appears to be the methyl groups of
sodium 2,2-dimethyl-2-silapentane-5-sulfonate. Because TMS can sometimes interfere, TMSfree CDCl3 is often used, and the slight amount of CHCl3 impurity is used as a reference.
References:
(i)
L.J. Boucher, E.J. Battis and N.G. Paez, J. Inorg. Nucl. Chem., 33, 1373 (1971).
(ii)
L.J. Boucher, J.C. Bailar, J. Inorg. Nucl. Chem., 27, 1093 (1965).
(iii)
L.J. Boucher and N.G. Paez, Inorg. Chem., 9, 418 (1970).
(iv)
R.D. Archer and B.P. Cotsoradis, Inorg. Chem., 4, 1584 (1965).
(v)
R.D. Archer and B.P. Cotsoradis, Inorg. Chem., 6, 800 (1967).
(vi)
R.S. Drago, "Chapter 8,"Physical Methods in Inorganic Chemistry," p. 239.
(vii)
W.L. Jolly, The Synthesis and Characterization of Inorganic Compounds,
Prentice-Hall, Englewood Cliffs, N.J., 1970, pp. 350-368.
EXPERIMENTAL
30
A.
Preparation of Na[Co(acac)2(NO2)2]
Dissolve 15 g of Na3[Co(NO2)6] in 60 mL of water. Filter the solution if there is
still solid left after stirring for 15 minutes. Mix it with a solution of 3.2 g of sodium hydroxide
and 8 mL of acetylacetone in 50 mL of water. Stir the resulting solution for a few minutes.
Remove the red solid by filtration (see Note below*). Allow the filtrate to stand at room
temperature overnight, whereupon a reddish solid forms. Filter, wash with acetone to remove
[Co(acac)3] which is formed as a by-product, then with ether and air dry. Dissolve the crude
product in water. Immediately filter the solution into a flask cooled in an ice bath. Slowly add
(with stirring) a saturated NaNO2 solution to the cold filtrate. Leave in ice-bath for 1 hr. Filter.
Wash with ethanol, and ether. Air dry. Determine the yield. Measure the IR spectrum in Nujol
and the NMR spectrum in D2O. Can you derive some structural information from these spectra?
*Note: The red solid is a mixture of mostly Na[Co(acac)2(NO2)2], [Co(acac)2] and
[Co(acac)3]. Try to recover the Na[Co(acac)2(NO2)2] in the mixture.
B.
Preparation of trans-[Co(acac)2(NO2)py]
To a solution of 1.0 g of Na[t-[Co(acac)2(NO2)2]] in 20 mL of water, add 0.6 mL of
pyridine and 5 mL of methanol. Stir the resulting solution for 30 minutes. Filter. Wash with
three 10 mL portions of water, follow by methanol and ether. Air dry. Determine the yield.
Measure the NMR spectrum in CDCl3 and the IR spectrum as a Nujol mull.
C.
Preparation of cis-[Co(acac)2(NO2)(py)]
Reflux a solution of 0.8 g of trans-[Co(acac)2(NO2)(py)] in 40 mL of CHCl3 for 3 hours.
Filter. Reduce the filtrate to dryness. This residue is a mixture of the cis- and trans-isomers. A
tiny quantity of this red mixture will be separated by thin layer chromatography. Use the thin
layer plates (if provided) and first dissolve a small quantity of mixture in chloroform, place on
the plate, allow to dry and develop this with 25% methanol/benzene (see safety note on p. 29).
You should observe two spots. The dried plate should be submitted as evidence. The Rf values
based on one development of approximately 15 cm are cis-py, 0.70, trans-py 0.6. Measure the
NMR spectrum of the crude mixture in CDCl3.
D.
Preparation of [Co(acac)2(o-phen)]ClO4
Dissolve 4 g of Na[Co(acac)2(NO2)2] in 100 mL of water and 40 mL of methanol. Add to
this solution 3.0 g of activated charcoal and a solution of 1.98 g of 1,10-phenanthroline
monohydrate in 30 mL of methanol. Stir the resulting solution vigorously for 15 minutes at
room temperature. Filter by suction, using a Hirsch funnel (or Buchner filter). Wash the carbon
with two 5 mL portions of methanol. Combine the washing with the original filtrate. Add to
this a solution of 1.8 g of sodium perchlorate dissolved in 6 mL of water. Cool in ice-bath for 30
minutes. Wash the grey product with cold water and ether. Air dry.
The crude product is recrystallized as follows: Dissolve in a minimum amount of boiling
methanol, gravity filter while hot. Allow the solution to cool. Add 10 mL of anhydrous ether.
Filter. Wash with methanol, follow with ether. Determine the yield when dry. Measure the
NMR spectrum in CD2Cl2, and run the IR spectrum.
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