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Chem 410 Lab Report Grading Rubric for Abstract Only
Name:
Experiment Number:
Submission Date:
Possible Points
Section
Title & Author
Contact
Information
0
1
2
No Title or
Author Contact
Information
Missing a title
or author
contact
information
Incorrect author
contact
information or
title provided
0
2
No Abstract
Provided
Abstract
12
Abstract
references most
aspects of the
experiment, a
major and some
minor details are
missing
0
Grammar
Five or more
grammatical
errors
0
Answers to
Questions
Supporting
Information
Questions not
answered
0
No Supporting
Information
provided
0
TOC Graphic
No TOC Graphic
Provided
Student
displays a lack
of
understandin
g about how
to write an
abstract
14
4
Abstract is
present but
does not clearly
state the
hypothesis or
purpose or the
conclusions
1
2
2
4
Several
major
aspects of
the
experiment
are missing
Abstract is
less than 100
or greater than
250 words
Clearly states
the purpose or
the conclusions,
but not both
6
Two questions
answered
incorrectly
Missing more
than two items in
SI
Missing lab
notebook pages
in SI
TOC Graphic
doesn’t describe
the experiment
TOC Graphic
can’t be easily
read (not the
correct size)
1
4
2
8
18
3
Abstract contains
reference to all
major aspects of
carrying out the
experiment and the
results, but could
use some
improvement
Two
grammatical
errors
Three or more
questions
answered
incorrectly
2
5
All author
contact
information and
an attention
grabbing title
provided
Abstract
references most
of the major
aspects of the
experiment,
some minor
details are
missing
Three
grammatical
errors
4
All author
contact
information
and only a
generic title
provided
16
Abstract
references most
of the major
aspects of the
experiment, but
is missing a major
concept
Four
grammatical
errors
3
Author
contact
information
not
completely
provided
4
One
grammatical
error
10
20
Abstract contains
reference to all
major aspects of
carrying out the
experiment and
the results, wellwritten (100 – 250
words)
5
No grammatical
errors
6
8
One question
answered
incorrectly
All questions
answered correctly
6
8
Incorrect Table of
Contents or missing
one item in SI
All SI and Table of
Contents Provided
TOC Graphic is
missing a key result
TOC Graphic
succinctly
describes
experiment
3
Total
Points
4
Total Score:

Chem 410 (Spring 2019)
Experiment 8: Synthesis and O2 Uptake of Co(salen)
Time Required: Four Three Hour Laboratory Periods
Objective: In this experiment, you will synthesize a coordination complex of cobalt, and
demonstrate how it displays chemistry similar to that of metal-containing biological systems.
A simple apparatus will be used to quantitatively monitor the gas-uptake/release reaction.
Background: Bioinorganic chemistry is a growing field of inorganic chemistry that addresses
a number of significant biological issues. Much of the work in this area involves attempts to
model the activity of a complicated, or ill-characterized, metal- containing system with more
simple coordination complexes that can be prepared in the laboratory. The coordination
chemistry relevant to biological systems is reviewed in most inorganic textbooks, for example
Chapter 26 in Shriver (6th Ed).
This experiment involves use of a cobalt(II) complex, which serves as a model for oxygentransport systems. Oxygen transport and storage are accomplished in higher animals by the
iron-containing materials hemoglobin and myoglobin. The challenge in developing suitable
model systems to study this chemistry is in designing appropriate metal coordination complexes
which react with dioxygen simply by binding it intact, rather than by much more commonly
encountered redox processes, which can result in LnM=O (with a terminal oxo ligand) or LnMO-MLn (with a bridging µ-oxo ligand). Complexes of the latter type are usually inactive
toward release of O2. Cobalt(II) complexes are known to form two types of adducts with
dioxygen: a 1:1 adduct LnCo-O2, and a 2:1 peroxo structure LnCo-O-O-CoLn.
Biologically active metal centers are very often found in a coordination environment
that includes multidentate ligands. Therefore the synthesis of bioinorganic “model complexes”
often makes use of multidentate ligands that resemble those found in nature (e.g., as part of
a peptide chain). The multidentate ligand used in this experiment is tetradentate N,N’bis(salicylaldehyde)ethylenediimine (abbreviated H2salen). It is obtained by the condensation
reaction shown below:
OH
2
H
OH HO
+
H2N
NH2

N
2 H 2O
N
H
H
O
H2salen
The addition of a Co(II) salt to salenH2 results in formation of the Co(II) salen complex:
OH HO
N
O
+ Co(OAc)2
N
H
H

O
Co
2 HOAc
N
N
H
H2salen
H
Co(salen)
This four-coordinate Co(salen) complex is reactive toward addition of donor ligands in forming
five- or six-coordinate complexes. In the solid state it exists in two different forms (I, a dark
red isomer inactive toward oxygen binding, and II, the active isomer).
H
H
N
N
Co
O
O
O
Complex I (red isomer)
O
Co
N
H
N
H
The experiments below will be conducted in chloroform and dimethyl sulfoxide, Me2S=O
(DMSO) solvents. Chloroform (CHCl3) is not a good ligand for transition metals, whereas DMSO
is.
Briefly, we will prepare H2salen, and its complex with Co(II), Co(salen), as a mixture of the brown
and dark red forms. This mixture is heated to accomplish complete conversion to the dark red
form. This material is dissolved in DMSO in a closed system containing pure oxygen to generate
an active form. The oxygen uptake is quantitatively measured at constant temperature and
pressure. The oxygen adduct is then dissolved in chloroform to release the O2.
Additional literature references:
E. I. Ochiai, J. Inorg. Nucl. Chem. 1973, 35, 1727, 3375.
C. F. Floriani and F. Calderazzo J. Chem. Soc. (A) 1969, 946-953.
R. H. Bailes and M. Calvin J. Am. Chem. Soc. 1947, 69, 1886-1893.
W. L. Jolly, The Synthesis and Characterization of Inorganic Compounds, p. 466.
H. Diehl and C. C. Hach Inorg. Synth. 1950, 3, 196.
Experiment taken from: Appleton, T. G. J. Chem. Educ. 1977, 443.
Safety precautions: Co(salen) is reported to be toxic, therefore avoid inhalation of
particles of this material. While DMSO is not itself very toxic, it can transport dissolved
compounds through your skin. Therefore, avoid skin contact with DMSO.
Lab Period 1: Synthesis and Purification of H2salen
To a solution of 3.9 g (3.4 mL) of salicylaldehyde in 40 mL of boiling 95% ethanol (in an
Erlenmeyer flask) add 1.0 g (1.08 mL) of ethylenediamine in portions with a pipette (otherwise,
the reaction mixture may froth out of the flask). Stir the reaction mixture for 3.5 min, and
leave the solution to cool in an ice bath. Filter the bright yellow flaky crystals using house
vacuum, wash with a small volume of ethanol, and air-dry. Record the melting point and yield
of this product. Record an IR spectrum (vibrational spectrum; KBr pellet) and prepare an NMR
sample in CDCl3.
Lab Period 2: Synthesis and Purification of Co(salen)
Weigh 2.0 g of H2salen into a 100 mL 3-necked flask fitted with a magnetic stirring bar,
an addition funnel, and a condenser capped with a nitrogen inlet. Add 60 mL of 95% ethanol.
Stir using the magnetic stir bar, and flush the apparatus with nitrogen (the synthesis requires
the exclusion of oxygen, but extreme rigor is not necessary). Adjust the nitrogen flow to a
steady rate (ca. one bubble/sec) and provide a steady flow of cooling water through the
condenser. Immerse the flask in a water bath maintained at 70-80 °C. Cover the hot part of
the system with Al foil. Dissolve 1.86 g of Co(O2CMe)2.4H2O in 9 mL of hot water and put it
in the addition funnel. When the salenH2 has all dissolved, add the cobalt acetate solution
from the funnel. Continue heating and stirring for about an hour, during which time a red
precipitate should form. Cool the flask by immersing it in cold water. Discontinue the nitrogen
flow and filter off the solid in the air. Wash three times with 5 mL of water, then with 5 mL of
95% ethanol. Dry the solid on the funnel and wash it two times with 5 mL of diethyl ether. If
further drying is needed use the vacuum desiccator (over Drierite). Record your yield. Record
an IR spectrum (KBr pellet).
Lab Period 3: O2 Uptake with Co(salen)
Oxygen uptake will be measured with the apparatus diagrammed below. Stopper the
side-arm test tube with a #49 Suba Seal when necessary. The movable arm is used to keep the
pressure constant in the system. As oxygen is absorbed, the height of the movable arm must be
changed to keep the water level the same on both sides, which maintains a constant pressure
on both sides. The difference in initial and final volume readings gives the amount of O2 absorbed.
Weigh out 0.05-0.1 g of ground, dry Co(salen) into a side-arm test tube (1.5 x 15 cm). Place
approximately 5 mL of DMSO in a beaker and bubble oxygen through it for a few seconds to
saturate it with O2. Transfer the DMSO into a small test tube (1 x 7.5 cm) until it is filled to
about 2 cm from the rim. Tilt the side arm test tube and carefully lower the small test tube into
the side-arm tube without spillage.
Flush the side-arm tube with a gentle stream of O2. During flushing, the movable arm can be
moved up and down to aid in the replacement of air with pure oxygen. Insert a tight-fitting
rubber stopper in the mouth of the tube. Adjust the movable arm to make the water levels the
same in both tubes (i.e., pressure within the apparatus is atmospheric). Note the water level in
the graduated tube. Carefully invert the side-arm tube (holding near the stopper to minimize
heating by the hand, but being careful not to push the stopper further into the tube causing
a change in pressure) so that the DMSO is introduced onto the Co(salen) without spilling
any on the Tygon connecting tube. Gently shake the tube. As oxygen is absorbed the water
level in the graduated tube should begin to rise. Note the changes that occur. The tube can
be tipped to the side to increase the surface area of the solution and increase the rate of
oxygen absorption. Continue shaking until no further change in water level occurs (5-10 min).
Adjust the movable arm so that the water levels in the two tubes are again equal, and read off
the new level in the graduated tube.
From the decrease in volume at room temperature and atmospheric pressure, the number
of moles of O2 absorbed per mole of Co(salen) can be calculated. You should do two-three O2uptake experiments to test reproducibility.
Behavior of the oxygen adduct in chloroform. Remove the stopper from the side-arm tube in
the DMSO reaction, and remove as much as possible of the dark-brown suspension into a small
test tube. Carefully remove the supernatant DMSO. To the residue in the tube (drying is not
necessary) add 5-10 mL of chloroform without stirring. Observe the result and note your
observations in your notebook.
Chem 410 Lab Report Guidelines for
Experiment #8 – Synthesis and O2 Uptake of Co(salen)
Please use the lab report templates available on Blackboard prepare a report based on your
assigned section (please see table below).
Due Date
Experiment
3/22/19
8
Abstract
4,9,14
Lab Report Section Assignment
Results &
Introduction Experimental
Discussion
5,10,15
1,6,11
2,7,12
Conclusions
3,8,13
Questions to be Answered:
1) Why does the addition of DMSO activate the brown form of the Co(salen) complex?
2) Would the addition of chloroform to the red form cause similar activation?
3) What are the oxidation state, spin state, and electronic configuration of cobalt in the O2
adduct?
4) Draw three possible dioxygen binding modes for the mononuclear or dinuclear metaldioxygen complexes.
5) What does the ratio of Co(salen) to O2 say about the binding mode(s) of the
Co(O2)(salen) complex. Based on your average binding ratio, which is the dominant
adduct?
Data to be included in Supporting Information:
1)
2)
3)
4)
5)
6)
Drawing of O2 uptake apparatus (can be hand drawn)
NMR spectrum of H2salen
IR spectra of products
Sample % yield calculations
Sample calculations for determining O2 uptake
Carbon copies from lab notebook
1H
Experiment 8 – Synthesis and O2 Uptake of
Co(salen)




Three Lab Periods
First Lab Period: Synthesis and Purification of salen
Second Lab Period: Synthesis and Purification of Co(salen)
Third Lab Period: O2 Uptake with Co(salen)
• Concepts Learned: Gas reactions
• The synthesis of salen and Co(salen) can be completed in one laboratory
period
• The procedure can be found on Blackboard
1
Salen Ligands
• Show up everywhere in inorganic chemistry
• Are extremely popular due to the ease of synthesis
• Usually very pure product precipitates from the reaction material in
minutes
• Can also easily derivatize
• Schiff base ligands are able to coordinate metals through
imine nitrogen and another group, usually linked to the alcohol
• Schiff bases are able to stabilize many different metals in various
oxidation states
P. G. Cozzi. Chem. Soc. Rev., 2004, 33, 410-421.
2
Schiff-Base Reaction
• First described by Hugo Schiff as the condensation between
an aldehyde an amine in 1864
• Schiff bases are imines in which R3 is an alkyl or aryl group
(not a hydrogen). R1 and R2 may be hydrogens
• Reaction of an amine with a ketone/aldehyde generating a
hemiaminal
• Elimination of water generates an imine.
hemiaminal
3
Schiff-Base Generation








MgSO4 is often used as a dehydrating agent
The formation of aldimines often goes readily in ethanol
Generation of ketimines are more tricky
The water produced in the reaction can also be removed
from the equilibrium using a Dean Stark apparatus, when
conducting the synthesis in toluene or benzene
Chromatography of Schiff bases on silica gel can cause some
degree of decomposition of the Schiff bases, through
hydrolysis
Best to purify the Schiff-bases by crystallization
Are insoluble in hexane or cyclohexane
Can be purified by stirring the crude reaction mixture in
these solvents, sometimes adding a small portion of a more
polar solvent (Et2O, CH2Cl2), in order to eliminate impurities
Water
collects
here!
4
Synthesis of Metal Salen Complexes
• For early transition metals (M = Ti, Zr), alkoxide derivatives are desirable
metal sources for metal salen complexes
• Metal amides M(NMe2)4 (M = Ti, Zr) are also highly suitable precursors
for the preparation of Schiff base metal complexes of early transition
metals.
• The reaction occurs via the elimination of the acidic phenolic proton of
the Schiff bases, occurring at the same time as the formation of volatile
NHMe2.
• Metal alkyls of main group elements (AlMe3, GaMe3, InMe3) can be
used in the preparation of Schiff bases by a direct exchange reaction.
• Iron, manganese, vanadium and copper complexes can be generated
from M(mesityl)n (mesityl =2,4,6-trimethylbenzene) compounds
• Copper, cobalt, and nickel salen complexes are prepared using the
corresponding acetate M(OAc)2 by heating the Schiff base in the
presence of the metal salt under reflux conditions
• Deprotonation of the salen ligands and successive reaction with metal
halides can generate metal salen complexes
• Deprotonation step preferred with NaH or KH in coordinating solvents.
P. G. Cozzi. Chem. Soc. Rev., 2004, 33, 410-421.
5
Salen Ligands and Metal Salen Complexes
6
Metal Salen Complexes
• Most metal salen complexes are cupped (A) as opposed to stepped (B)
• The axial ligand can influence the geometry
P. G. Cozzi. Chem. Soc. Rev., 2004, 33, 410-421.
7
Metal Salen Compounds in Catalysis
P. G. Cozzi. Chem. Soc. Rev., 2004, 33, 410-421.
8
Metal Salen Complexes in the Generation of
Plastics
Nuc = N-heterocyclic amine
D. J. Darensbourg. Chem. Rev., 2007, 107, 2388-2410.
9
Jacobsen Epoxidation
• Mn(salen)Cl is prepared using Mn(OAc)2
and subsequent oxidation of the
intermediate Mn(II)(salen) by exposure to
air to generate Mn(III)(salen)Cl
• Complexes containing chloride ions are
obtained by an exchange reaction
performed during work-up, through
treatment with chloride-containing
aqueous solution.
• Chiral Mn(III)(salen) complexes are quite
efficient catalysts for the asymmetric
epoxidation of cis olefins.
• Oxidation takes place with iodosobenzene,
NaClO, H2O2, NaIO4, and peroxy acids
10
Redox Activity with Salen Ligands
• Steric bulk of tri-tertbutylphenoxyl radical aids in
the stabilization of the radical
species
• Suggests that the steric bulk
on a salen complex can lead to
ligand stabilized radicals
F. Thomas. Dalton Trans., 2016, 45, 10866-10877.
11
Redox Activity with Salen Ligands
• Addition of methanol or pyridine resulted in a metal-based radical
• Addition of dichloromethane resulted in a salen-based radical
F. Thomas. Dalton Trans., 2016, 45, 10866-10877.
12
Oxidation of a Ni(II) Salen Complex
• The presence of
excess pyridine
results in a metal and
salen-based radical
• In CH2Cl2 a salenbased diradical is
obtained
F. Thomas. Dalton Trans., 2016, 45, 10866-10877.
13
Metal Salen Complexes as Enzyme Mimics
Model complexes are often used
to aid in the understanding of
protein function
A. Erxleben. Inorg. Chim. Acta, 2018, 472, 40-57.
14
Dioxygen as a Ligand
Two classes of 1:1 bonding of O2 to
metal complexes
Class I compounds have known
structures from X-ray crystallography
Class II compounds have structures
inferred from EPR where M-O
distances are believed to be unequal
Valentine, J. S. Chem. Rev. 1973, 73, 235-245.
15
Structure of Co(salen)
• When Co(salen) was first prepared in 1933, the red-brown crystals were observed to darken
upon exposure to air
• Five years later the color change was established to be due to the reversible uptake of
dioxygen
• In 1944, it was found that different crystalline forms existed depending on the solvent used in
the preparation or for recrystallization
• These different crystalline forms had varying capacity for oxygenation in the solid state.
• This variation in oxygenation has been related to the presence of voids in the crystal lattice,
sufficient to allow the passage of molecular oxygen.
16
Structure of Co(O2)(salen)
• In solution under anaerobic conditions the cobalt(II) may be four, five or six coordinate
• For example, in a strongly coordinating solvent such as
pyridine, both [Co(salen)(py)] and [Co(salen)(py)2]
exist, whilst in chloroform, the major species appears
to be Co(salen)
• Irrespective of the solvent, the rate of dioxygen uptake
appears to be similar, however the product obtained may
be a 1:1 or a 2:1 (oxygen bridged) complex.
Goal of experiment: Determine which structure is preferred!
17
EPR of Co(salen) and Co(O2)(salen)
For Co = 7/2 (8 line pattern)
Co(salen)(py)
2400
2600
2800
3000
3200
3400
3600
Gauss (G)
g = 2.464, 2.244 and 2.024.
Co(O2)(salen)
3050
3100
3150
3200
3250
3300
3350
Gauss (G)
g =1.994, 2.010 and 2.081
18
Gas Reactions
• Fisher-Porter Bottle
• Parr Bombs
• J. Young Tubes
Often done
behind a blast
shield!
19
Toepler Pump
• Invented by August
Toepler in 1850
• Used to determine the
amount of gas that is
formed during a reaction
• Pumps gas into a
calibrated volume
• Can use a manometer
instead
20
Measuring O2 Uptake of Co(salen)
• The movable arm is used to keep the
pressure constant in the system
• As oxygen is absorbed, the height of
the movable arm must be changed to
keep the water level the same on
both sides to maintain a constant
pressure on both sides
• The difference in initial and final
volume readings gives the amount of
O2 absorbed
21
Oxygen Transport in Organisms
• Myoglobin
• Reversibly binds O2
• Controls O2 concentrations in tissues
• High-spin five-coordinate Fe(II) complex
• Bluish-red in color
• Low-spin six-coordinate Fe(II) complex upon
bindin …
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