Laboratory Rules

1. Safety goggles or spectacles must be worn at all times when working in the laboratory.
Sunglasses will not be accepted.
2. Laboratory coats should be worn at all times when working in the laboratory.
3. No open shoes, sandals, slops or heels to be worn in the laboratory.
4. No eating, drinking or smoking is allowed in the laboratory.
5. Never inhale, sniff or taste chemicals. All chemicals must be handled with great care.
6. When working with concentrated acids or corrosive chemicals you must use gloves.
7. All solvent residues except acetone should be disposed of into the appropriate residue
bottles provided in the fume hood and not down the sink. Acetone must be discarded
in the acetone residue bottles provided.
8. All broken glassware must be reported and disposed of in the “broken glassware bin”
and not in the dustbin.
9. Do not leave cotton wool, filter paper, micropipettes or Pasteur pipettes in the sink.
10. All solid waste (MgSO4, CaCl2, silica gel etc.) must be disposed of in the appropriate
“solid waste” containers.
11. Do not heat flammable substances in an open container near a naked flame.
12. Do not leave spills unattended to.
13. Disconnect your heater-stirrer and tidy your benches at the end of each practical
session.
14. Always wash your hands before leaving the laboratory.
15. If in doubt about anything concerning the practical be sure to ask a lecturer or
demonstrator.

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 INTRODUCTION
The following laboratory experiments have been chosen to enhance your understanding of
coordination complexes, particularly with respect to coordination complexes with a tridentate
nitrogen-donor ligand. The main objective is to synthesize and characterize simple transition
metal complexes incorporating the tridentate propene bis (2-pyridylmethyl) amine (P-BPMA)
ligand and to compare the stabilities of the complexes. P-BPMA is identified as tridentate due
to the three nitrogen donor groups.

Figure 1: Structure of propene bis (2-pyridylmethyl) amine (P-BPMA)(1)

The experiments were designed to be carried out over a six week period in the following
sequence: Synthesis of the tridentate ligand, followed by its complexation with copper and iron
salts. After each synthesis information based on the characterization of the ligands and its
complexes will be attained by using a variety of instruments and instrumental techniques.
In order to synthesize P-BPMA it is necessary to first synthesize its precursor bis (2-
pyridylmethyl) amine or BPMA. Once this is done the actual ligand (P-BMA) can then be
synthesized with the use of 3-bromoethane and acetonitrile.

Figure 2. Synthesis of BPMA and P-BPMA(1)

Once the ligand is synthesized a series of complex reactions will be carried out to synthesize
iron, nickel, zinc, cobalt and copper complexes with the tridentate nitrogen-donor ligand. The
various metal complexes will then undergo a salt metathesis reaction and testing to identify its
magnetic properties.

Transition metal complexes often have spectacular colors caused by electron transitions by the
absorption of light. For this reason they are often applied as pigments. The stability of the
various metal complexes will be compared.

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 Experiment 1
Synthesis of propene-bis(2-pyridylmethyl)amine

Aim: The aim of this experiment is to synthesize bis(2-pyridylmethyl)amine and propene-

bis(2-pyridylmethyl)amine as well as to analyze it using NMR.

Chemical reagents:

▪ 2-pyridinecarboxaldehyde
▪ 2-pyridylmethylamine
▪ Dichloromethane
▪ Sodium carbonate
▪ 0.1M HCl
▪ Methanol
▪ NaBH4
▪ MgSO4
▪ Deionized water

Experimental:
Part A: Synthesis of Bis(2-pyridylmethyl)amine (BPMA)

▪ Measure 100 mL of methanol in a 250 mL conical flask and leave it to cool in an ice
bath. Measure 8.9 mL of 2-pyridinecarboxaldehyde and mix it with the already cooled
methanol in the 250 mL conical flask. Add 9.7 mL of 2-pyridylmethylamine to the
mixture and remove the flask from the ice bath to allow the reaction to proceed at room
temperature for 1 hour.
▪ Weigh out 3.5 g of NaBH4 and add it slowly to the mixture before placing it back in the
ice bath till it reaches 0 ̊ C. Once the mixture has reached a temperature of 0 ̊ C remove
it from the ice bath and leave it to mix for 12 hours at room temperature with the use of
a magnetic stirrer.
▪ After the 12 hours cool the mixture once more in an ice bath and add 0.1 M of HCl until
the solution reaches a pH of 4. This can be verified with blue litmus paper. (Blue litmus
paper should turn red in an acidic).
▪ Vacuum filter the solvent off and collect the resulting pale yellow residue and transfer
it to a 100 mL beaker.
▪ Add 50 mL of deionized water to the residue and transfer this to a separating funnel.
Add 20 mL of dichloromethane to the separating funnel until the organic layer becomes
clear. Collect the aqueous layer (bottom layer) in a separate beaker.
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 ▪ Add enough sodium carbonate to the aqueous layer in order to adjust the pH to 10. This
can be verified with red litmus paper (red litmus paper should turn blue in a base.).
Transfer the extracted aqueous layer to a new separating funnel.
▪ Add 20 mL of dichloromethane to the separating funnel and extract the organic layer
(bottom layer) as before into a new clean beaker.
▪ Add MgSO4 to the organic layer to dry it. After each addition of a small amount to the
beaker containing the organic layer, swirl the flask. If no “snowstorm” effect occurs
that means drying is not taking place and the addition of the drying agent should
continue.
▪ Filter off the MgSO4 by gravity filtration and remove the solvent in a rotary evaporator
at 32 ̊ C.

STOP HERE AFTER WEEK 1

Part B: Synthesis of Propene bis(2-pyridylmethyl)amine (P-BPMA) – Addition of allyl

halide group

▪ Dissolve 8.10 g of the previously synthesized BPMA in 15 mL of acetonitrile. Slowly

add 4.10 g of trimethylamine and 4.9 g of 3-Bromopropene. Allow the reaction mixture
to stand at room temperature for about 24 hours. The formation of triethylamine
hydrogen bromide salts will appear as white crystals in a brown coloured solution.
▪ Filter the solution under gravity, collect the desired product from the filtrate and transfer
it to a separating funnel.
▪ To the separating funnel add a 50/50% hexane-water (15 mL water and 15 mL hexane)
and isolate the hexane layer/ top layer. (This can be done by running the aqueous layer/
bottom layer out of the tap and collecting it in one beaker and then removing the hexane
layer out of the top of the funnel.)
▪ Transfer the hexane layer to a round bottom flask and then evaporate the solvent by the
use of a rotary evaporator.
▪ Dry the final product under vacuum for 2 hours to produce the ligand as a yellow
coloured oil ~ 8.5 g.

NOTE:
Do not discard your samples prepared as they will be used for the remaining duration of this
analysis.

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Part C: Instrumental Analysis for characterization of BPMA and P-BPMA

Apparatus used: Bruker

Experimental:
▪ Obtain IR spectrum using a NaCl crystal disks, the IR card must be washed with two
Pasteur pipettes full of acetone and ensure that NaCl disks is dried before applying a
drop of the yellow oil P-PBMA ligand prepared in the previous experiment.
▪ Obtain the 1H-NMR
Solvent: Deuterated methanol (CD3OD); 400 MHz.

Figure 3: Molecular Structure of P-BPMA (1)

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NOTE: Compare your obtained spectrum of BPMA with spectrum B (shown below) and
compare your obtained spectrum of P-BPMA with spectrum C only (shown below).

Figure 4: Room temperature H-NMR spectra (400 MHz, CD3OD) of b) BPMA ligand
precursor and c) P-BPMA ligand (1)

Experiment 2

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 Preparation of first row transition metal complexes

Aim: To prepare first row transition metal complexes of Fe(II), Ni(II), Co(II) and Cu(II) with
P-BPMA.

NOTE:
▪ Propene-bis(2-pyridylmethyl)amine isolated in the previous section serves as a
crucial starting material for the following experiments.
▪ Copper (II) complexes should be stored under inert atmosphere to prevent oxidation.
▪ NMR solvents are suspected carcinogens and should be handled with care.
▪ After each individual part carry out an instrument analysis for each complex. Refer
to page 9 for notes on the instrumental analysis.

Chemical reagents:
▪ Iron (III) Chloride hexahydrate
▪ Ethanol
▪ Aceonitrile

Experimental:

Part A: Preparation of [Fe (P-BPMA)Cl3]

▪ Accurately weigh out 0.20 g of propene-bis (2-pyridylmethyl) amine (P-BPMA) in a

250 mL conical flask
▪ Add 15 mL of ethanol and stir until the P-BPMA is dissolved.
▪ Prepare a solution of 0.23 g FeCl3.6H2O in 15 mL of ethanol and add this to mixture
above. A yellow precipitate should immediately be generated.
▪ Filter the mixture under vacuum filtration and wash the product with 2 x 20 mL portions
of ethanol.
▪ Collect the precipitate in an Erlenmeyer flask and recrystallize with acetonitrile. To
recrystallize add a small amount of acetonitrile into the flask containing the impure
solid. Heat the contents of the flask until the solid dissolves. Cool the solution and filter
using vacuum filtration. [1]
Part B: Preparation of [Ni(P-BPMA)Cl3]

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Chemicals reagents:

▪ Nickel (II) Chloride hexahydrate

▪ Ethanol

Experimental:

▪ Weigh out 0.60 g of NiBr2.4H2O salt in a 50 mL beaker and add 5ml of ethanol.
▪ Pour the mixture into a solution of 0.26 g P-BPMA in 10 mL ethanol.
▪ Allow the mixture to react for 30 minutes at room temperature.
▪ A blue precipitate should form. Filter the product under vacuum pump and wash
the precipitate with 5 mL of cold ethanol.
▪ Dry the precipitate in a vacuum desiccator of blue silica gel for 30 minutes.

STOP HERE AFTER WEEK 1

Part C: Preparation of [Co(P-BPMA)Cl2]

Chemicals reagents:
▪ Cobalt (II) Chloride Hexahydrate
▪ Ethanol

Experimental:

▪ Dissolved 0.60 g of CoCl2.6H2O in 5 mL ethanol in a 50 mL conical flask.

▪ Pour the mixture into a solution of 0.26 g of P-BPMA in 10 mL of ethanol.
▪ Allow the reaction mixture to react for 30 minutes at room temperature. A brown
precipitate should form.
▪ Filter the precipitate under vacuum pump and wash the precipitate with 5 mL of cold
ethanol.
▪ Dry the precipitate in a vacuum desiccator of blue silica gel for 30 minutes.

Part D: Preparation of [CuII(P-BPMA)Cl2]

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Chemical reagents:
▪ CuCl2
▪ Acetonitrile

Experimental:
▪ Dissolve 5.00 g of P-BPMA in 20 mL of acetonitrile in a 250 mL conical flask.
▪ Add 2.81 g CuCl2 to produce a green coloured solution and allow the contents of the
flask to mix for about 6 hours.
▪ Thereafter slowly add 20 mL of pentane to the solution and vigorously mix to generate
a bright green precipitate.
▪ Filter the precipitate under vacuum pump and wash it with 2 x 20 mL portions of
pentane.
▪ Dry the precipitate under vacuum desiccator for 2 hours to yield a green solid.

Instrumental Analysis

▪ Obtain an IR spectrum using a NaCl crystal disks, the IR card must washed with two
Pasteur pipettes full of acetone and ensure that NaCl disks is dried before applying the
compounds.
▪ Conduct an X-ray crystallography analysis on the complexes by slow diffusion of
diethyl ether into the complex solution made in acetonitrile at room temperature to
attain the single crystals. On a single crystal Bruker diffractometer using
monochromatic M0 Kα radiation (λ = 0.71069 A0) at room temperature, from selected
yellow single crystal. Then determine unit-cell parameters from centering of 25
reflection in the θ range 6.11 - 17.220 and refine by the least square method.

Experiment 3
Salts metathesis reactions in complexes
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Aim: The aim of the experiment is to perform anion metathesis reactions to exchange the
counter ions in the complexes.

NOTE:

Caution: Perchlorates should be handled with care because they are partially explosive.

Figure 5: Rotary evaporator used for obtaining crystals (5)

Chemical Reagents:
▪ NaBPH4
▪ Acetone
▪ Acetonitrile
▪ NaClO4.H2O

Experimental:

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Part A: Preparation of [Cu1(P-BPMA)Cl)ClO4]

▪ Dissolve 1.00 g Cu11 (P-BPMA)Cl2 in 10 mL acetonitrile in a 250 mL conical flask

and add 0.32 g NaClO,llmnb4 to the flask. You should obtain a green coloured
solution.
▪ Allow the reaction mixture to mix for 6 hours to generate a NaCl precipitate in
solution.
▪ Cool it in an ice-bath to facilitate the formation of crystals.
▪ Separate the heterogeneous mixture of the solid and liquid by spinning in a
centrifuge machine (refer to “how to centrifuge” below.).
▪ Filter under gravity to remove NaCl.
▪ Transfer the filtrate to the round bottom flask and removed solvent using rotary
evaporator to obtain green crystals.
▪ Wash the crystals with 20 mL of pentane while stirring continuously for 30 minutes
using a magnetic stirrer.
▪ Finally remove the solvent by filtration under vacuum pump and dry it under
vacuum for about 2 hours to yield a green coloured solid (~1.07 g = 92%) (6).

Figure 7: Molecular structure of [Cu1(P-BPMA)Cl)ClO4] (6)

How to centrifuge?
Centrifuge is the instrument that is used to separate heterogeneous mixture of solids and liquids
by spinning the mixture. After efficacious centrifugation precipitates of solid will start to settle
at the bottom of the test tube and the centrifuge is clear. Separation of the particles from the
centrifuge is based on the shape, size, density, viscosity of the medium and also on the speed
of the rotor. Few guidelines are used for operation of centrifuge which thus helps in preventing
the damage of the centrifuge.

The work surface must be level and firm. Make sure that the tubes are balanced in rotor ie. if
you want to run the tube for example with a 10 mL of liquid put another tube with 10 mL of
water in the opposite hole on the rotor if it happens that the liquid has a density that is higher
than that of water it would best that you must equalise the tubes by mass and not by volume. It
is very crucial to not open the lid while the rotor is still spinning. The rotor will still move
because of its inertia for a while until friction slows and eventually stop it. If you see it shaking,

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immediately turn it off or pull the plug. Small vibration is okay but excessive can result to
danger. Therefor if the centrifuge is shaking DO NOT continue to use it. When working with
centrifuge that is working you must always make sure that you wear goggles for eye protection.
DO NOT move centrifuge while the rotor is still spinning.

Operation:

▪ Use centrifuge that that is provided at the lab

▪ Balance the tubes
▪ Secure the lid and make sure that it is close. Check the speed of the rotor. Use the
following procedure to separate sodium chloride which is produced as the by-product
during the reaction.
1. Start at low speed.

2. Spin for 10 minutes if nothing is found settling at the bottom of the tube.
3. Change your settings to higher speed for about 10 minutes satiable speed is the one
that result in successful separation.

Part B: Preparation of [Cu11(P-BPMA)Cl)BPH4]

▪ Dissolve 1.00 g Cu11 (P-BPMA)Cl2 in 10 mL methanol in a 250 mL conical flask

and add 0.883 g NaBPH4 to reaction mixture. A green-blue precipitate in a green
coloured solution should form.
▪ Allow the reaction to mix for about 24 hours, in this time the green coloured
precipitate will turn clear.
▪ Transfer the content to a 250 mL round bottom flask. Remove the solvent by using
rotary evaporator at 40 – 45 ℃.
▪ Wash the crystals with 20 mL methanol while stirring continuously for 30 minutes
using a magnetic starrier.
▪ Finally remove the solvent by filtration under vacuum pump and dry it under
vacuum for 2 hours.

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 Figure 8: Molecular structure of [Cu11(P-BPMA)Cl)BPH4] (6)

Instrumental Analysis
(Conduct as mentioned in previous experiments)

▪ Conduct 1H-NMR, 1C-NMR and IR analysis on the complexes.

▪ Conduct X-ray crystallography analysis on the complexes
▪ Refer to spectrum F for the CuII(P-BPMA)Cl)BPH4 spetra and spectrum D for
[Cu(P-BPMA)Cl)ClO4] spectra below.

Figure 9: 1H NMR spectra for (refer to spectra D) [Cu(P-BPMA)Cl)ClO4] and (refer to

spectra F) [Cu11(P-BPMA)Cl)BPH4] (6)

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 Experiment 4
Determination of the magnetic properties of the complexes

Aim: the aim of this experiment is to determine the paramagnetic properties of the complexes
synthesised in experiment 3 using the Gouy method.

Apparatus used: Sestechno

Experimental:

▪ Fill the metal complexes samples to a dry & clean test tube to the mark.
▪ Suspend the tube between the magnet pole pieces and record the mass reading.
▪ Repeat the step with no magnetic force applied. The readings must be in triplicate.

Figure 10: Setup of a typical Gouy apparatus (7)

The Gouy balance is a device used to measure the magnetic susceptibility of a sample. The
region of high magnetic field between north and south poles of the magnet, either attracts or
repels the sample, which is suspended between the magnetic poles through an attached string
hung from the mass balance pan and the force exerted on the sample by the in homogeneous
magnetic fields is obtained by measuring the apparent change in the mass of the sample.

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NOTE:
Careful:

▪ Remove any magnetic/metallic wrist-ware, when working around the magnets.

▪ The tube hanging should have no contacted with either pole of the magnet.
▪ Ensure that the sample is well compacted in the hanging test tube.

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 References
1. Bussey, K.A., Cavalier, A.R., Connell, J.R., Mraz, M.E., Holderread, A.S., 2015.
Synthesis and Characterization of Copper Complexes with a Tridentate Nitrogen-
Donor Ligand: An Integrated Research Experiment for Undergraduate Students.
Journal of Chemical Education. B-CD. Nicholls, Complexes of the First -Row
Transition Elements, pp. 100 – 111.

2. Carvalho N.M.F., Horn Jr. A., Bortoluzzi A.J., Drago V., Antunes O.A.C., 2006.
Synthesis and characterization of three mononuclear Fe(III) complexes containing
bipodal and tripodal ligands: X-ray molecular structure of the dichloro[N-
propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate. Inorganica
Chimica Acta 359. 90–98

3. D. Nicholls, Complexes of the First -Row Transition Elements, pp. 100 – 111.

4. Bonding l1,3- (trans) vs l1,2- (cis) in squarato-bridging dinuclear copper(II)

complexes derived from pyridyl amine ligands. Polyhedron 85. 110–116

5. Harwood, Laurence M.; Moody, Christopher J. (1989). Experimental organic

chemistry: Principles and Practice (Illustrated ed.). pp. 47–51. ISBN 978-0-632-
020171.

6. Bussey, K.A., Cavalier, A.R., Mraz, M.E., Oshin K.D, Sarjeant A, Pintauer T. 2016.
Synthesis, characterization, X-ray crystallography analysis, and catalytic activity of
bis(2-pyridylmethyl)amine copper complexes containing coupled pendent olefenic
arms in atom transfer radical addition (ATRA) reactions. Pp. 260-261

7. Webber J.H, Busch D.H. complexes derived from strong field ligands XIX. Magnetic
properties of transition metal derivatives of 4, 4’, 4”, 4”’ – Tetrasulphophthalocyanine.

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 107.7
105
2177.03 892.15
100 1971.03 1224.96 849.70
1297.33

95 1120.30
2849.40 1754.47 1094.60
1149.72 506.01
90
1049.06

85 996.16
2917.12 1668.52 402.94
3308.38
80 1362.94 627.58

75 3014.44
%T 3066.34
70 1474.34

1591.86
65

60
1570.01
1433.92
55
753.82
50

45
BPMA OIL 2
39.5
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1

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