1
HCT 202: INORGANIC CHEMISTRY PRACTICAL
EXPERIMENT 1
The Chemistry of Chromium.Preparation of Potassium tris(oxalate)chromate(111)-K3[Cr(C2O4)3].3H2O
Experimental (Adams and Rayner,page 50)
1.Reactions of Chromium
Record all observations and interpret them as far as possible.
(a)Add a drop of sodium hydroxide to a solution of potassium dichromate.
(b)Add a few drops of concentrated sulphuric acid to solid potassium dichromate.Notice the colour change.Add solid solid sodium chloride and warm gently.
(c)Add hydrogen peroxide dropwise to a solution of potassium dichromate to which has been added an equal volume of ether.What occurs on shaking? Repeat this using an alkaline solution.
(d)Warm a mixture of 1g potassium dichromate in 1 ml concentrated hydrochloric acid and 1 ml water. Allow to stand, and recrystallize the product from acetone.
(e)Dissolve in dilute hydrochloric acid formaldehyde.Cool and add graduated zinc.
For the following tests use chrome alum solution:
(a)Reduce with zinc and hydrochloric acid.
(b)Add ammonium or potassium peroxidisulphate and one drop of silver nitrate solution and warm.
2. Synthesis and spectroscopy of k3[Cr(oxalate)3]3H2O
Preparation
To a solution of 2.0g H2C2O4.2H2O and 0.84g K2C2O4.2H2O in 30 ml of water, is added 0.7g of K2Cr2O7 in small portions with vigorous stirring.( The reaction mixture might not spontaneously warm, heating solution might be necessary).When the reaction is ended, the solution is evaporated nearly to dryness and allowed to crystallize.( A quick recrystallization can be achieved by dissolving the complex in minimum amounts of water and reprecipitating it with ethanol.This should be done quickly with minimal heating to minimize equation of the complex.Record the yield.
Spectral Assignments
- Prepare a 0.01 M solution of the above complex in water, and run its visible spectrum(350 nm – 750 nm). Interpret the results by assigning λmax(nm and cm-1), the extinction coefficient(Є) and the transitions (different states) of the various bands which you observe.
- Record the infrared spectrum of the compound and interpret the spectrum.
EXPERIMENT 2
Synthesis and Spectral study of Cu(11) Complexes
Purpose
To synthesize some Cu(11) complexes having water, ammonia, ethylenediamine, the acteylacetonate anion and the glycinate anion as the ligands.This selection gives some variety of oxygen and nitrogen donors as well as a mixed donor ligand.
Experimental
Preparation of cis-Bis(glycinate)copper(11) Monohydrate
A 1.5g sample (6.0 mmole) of copper(11) sulphate pentahydrate is dissolced in 17 ml of 1M HCl. To this solution 0.75g(10.0 mmole) of glycine is added and then warmed for about one hour.Sodium bicarbonate is added until precipitation is complete(avoid a large excess).The precipitate is suction filtered, recrystallised from hot wter and dried in an oven.
Preparation of Bis(acetylacetonate)Copper (11)
A solution of acetylacetone is prepared by adding 1.25g (12.5 mmol) of acac to 50ml of 0.25M NaOH solution (12.5 mmol). This solution is added to a solution of 1.55g (6.25 mmole) of CuSO4. 5H2O in 100 ml of water.The precipitate is suction filtered, recrystalised from dioxane and air-dried.
Spectra of Cu(11) Complexes
A)Prepare the following stock solutions:
1)A solution of 0.01M Cu(NO3)2 in 2M NH4NO3.
2)A solution of 0.01M Cu(NO3)2 in 1M KNO3.
3)0.1M NH3.
4)0.1M ethylenediamine.
B)Determine the spectra of the following nine solutions in the wavelength range 350-900nm:
1)Cu2+ in water
2)Cu2+-NH3 in 1:1, 1:2, 1:3 and 1:4 mole ratio (use stock solution 1).
3)Cu2+-en in 1:1 and 1:2 mole ratio(use stock solution 2).
4)Cu2+ glycine complex in a 0.01M aqueous solution.
5)Cu2+aca complex in a 0.01M chloroform or methylene chloride solution.
Lab Report
Your lab report should consist of the following:
(a)The yield of both your glycine and acac complexes.
(b)The spectra of the nine solutions.
(c)λmax of the solutions.
(d)1/λmax(cm-1) of the solutions.
(e)Literature values for 1/λmax(cm-1)
(f)The absorbing species in the various solutions.
(g)Order of spectrochemical series for the ligands used,i.e. for H2O, NH3, en, glycine, acac.
(h)Discussion.
References
1)Bjerrum etal.,Acta Chem.Scand.,8,1275(1954).
2)Bjerrum etal.,ibid., 2, 297 (1948).
3)Jorgensen, C.K., ibid.,9,1362 (1955).
General References
- Advanced Inorganic Chemistry, 3rd ed., F.A. Cotton & G.Wilkinson.
- Inorganic Chemistry,2nd ed., J. Huheey.
EXPERIMENT 3
Preparation of bis(cyclopentadienly) iron
A 250 cm3 three-necked flask equipped with a magnetic stirring bar and a concentration from one side to a source of nitrogen is charged in 70 cm3 of 1,2-dimethoxyethane and 25g of KOH powder.While the mixing is slowly stirred while flushing with a stream of nitrogen, 5.5 cm3 of freshly cracked cyclopentadiene is added. The other side neck is stoppered and the main neck fitted with a 100 cm3 dropping funnel with stop-cock open. After the air has been flushed out the stop-cock is closed and a solution of 7.5g of iron(11) chloride tetra hydrate in 25 cm3 of DMF is placed in the dropping funnel. The mixture is stirred vigorously. After five minutes drop-by-drop addition of the iron(11)chloride solution is begun.The rate of addition is adjusted so that all the solution is added in 20 minutes.Stirring is continued for another 15 minutes. The flow of nitrogen is then stopped and the mixture is added to 90 cm3 of 6M HCl containing about 100g of ice.After stirring for five minutes the precipitate is collected on a coarse sintered-glass funnel and washed with four 25 cm3 portions of water.Record the yield.
Complementary work
- Measure the melting point of your compound.
- Heat a small sample in a test tube and note what happens
- Note the solubility of the substance in toluene
- Give the overall reaction equation for the experiment.
- What is the role of the potassium hydroxide.
- Record the infrared spectrum of the compound as a Nujol mull and assign the peak.
- Add 0.2g of your compound to water (10 cm3) followed by concentrated nitric acid (10 cm3). Shake the tube gently for two minutes and record your obsvervations.
- What other compounds have a similar structure to ferrocene?
Reference: G. Wilkinson et al J.Amer.Chem.Soc. 1954, 76, 1970.
EXPERIMENT 4
Synthesis and Chromatography of ferrocene derivetives.
This experiment illustrates the ease with which ferrocene will undergo electrophilic substitution and many of these reactions resemble those of benzene.However, to effect substitution, milder reaction conditions are usually employed with ferrocene. It is considered to be more ‘aromatic’ than benezene but differs from this molecule in that it cannot be directly halogenated or nitrated. In these reactions electrophilic substitution takes place only with difficulty at a positively charged centre.
Materials required:
Concentrated phosphoric acid
Ferrocene
Acetic Anhydride
Sodium bicarbonate
Alumina for chromatography
Benzene
Petroleum ether(b.p. 40 – 60oC)
Diethyl ether.
Procedure:
Add ferrocene (1.5g, *.05 mmoles) to acetic anhydride 5 ml (5.25g, 87 mmoles) in a small Erlernmeyer flask and this mixture carefully add 1 ml of 85% phosphoric acid with constant stirring. Fit a calcium chloride guard tube to the flask and heat on a steam bath for 10 minutes. Pour the hot mixture on to ice( about 80g ) with stirring and when all has melted neutralize the mixture by adding solid bicarbonate. Cool the neutralized solution in ice for about 30 minutes and remove the brown solid that is deposited by filtration, using a Buchner funnel. Dry the orange- brown solid by suction.
Prepare a chromatography column, using alumina in petroleum ether( b.p 40-60oC).Dissolve the orange product in the minimum quantity of benzene(caution: benzene is a cancer suspecting agent, handle in a fumehood) and add it to the top of the column with a teat pipette. Allow solvent to run out of the bottom of the column until level has fallen to the top of the column( do not allow it to run dry).Add petroleum ether(b.p 40-60oC) to the column, allow the solvent to pass through and collect the yellow band which is eluted. When all of the first band has been eluted increase the polarity of the eluent by adding a mixture of ether-petroleum ether(2:1) to the top of the column.Elute the second red-orange band. Evaporate the solvent on a rotary evaporator from each fraction to leave red-orange crystals. Recrystallize the solid from the first band using an ether-petroleum ether mixture and the solid from the second band from petroleum ether.
Characterization:
(i)Determine the melyting points of each compound.
(ii) Record the infrared spectrum of each compound.
(ii) The NMR of one of the compounds is provided. Use the spectrum to identify the compound in conjuction with the melting point and infrared.
Your report should include the following:
(i) Percentage yield of the two components and their melting points.
(ii) Infrared spectra of the two compounds isolated. Point out differences and similarities and why?
(iii) NMR spectrum provided and interpretation.
Questions:
(i) Write a complete mechanism for the reaction carried out in this experiment.
(ii) What methods might be used to detect the elution of colourless compounds from a column?
(iii) Which of the two components of the mixture eluted first? Why?
(iv) Briefly describe how choice of solvents in column chromatography is made.
References
- B. Douglas, D.H. McDaniel and J.J. Alexander, Concepts and Models of Inorganic Chemistry, John Whiley and Sons. 2nd Edition, P.447.
- R.E. Bozak, J. Chem. Educ. 1966, 43,73
- R.J.Grahma, R.V.Lindsey, G.w.Parshall, M.L. Peterson and G.M. Whitman, J. Amer.Chem.Soc.1957, 79,3416.
- L.F. Druding and G.B.Kauffaman, Coord. Chem. Rev. 1968, 3,409.
EXPERIMENT 5
Carbonyl Stretching frequencies in metal carbonyls
Mesitylenetricarbonyl tungsten(O)
[1,3,5-C6H3(CH3)3]W(CO)3
The reaction is carried out using a 100 cm3 two-necked round bottomed flask.Place W(CO)6 0.5g (1.4 m.moles) and 10 cm3 (72 m.moles) mesitylene in the flask then flush out the apparatus with nitrogen gas for about 5 minutes. Adjust the flow of gas so that it is passing very slowly.(The gas passes out of the condenser which is fitted with a bubbler). Heat the mixture to reflux for 30 minutes using a heating mantle. Remove the heating mantle and increase the flow of ether (B.P. 60-80oC ) ( 10 cm3) which helps to precipitate the product.Collect by filtration the yellow product which contains some tungsten metal, and wash the product with petroleum ether (6 cm3). Recrystallize the product by dissolving it in the minimum quantity of dichloromethane (about 12 cm3) and filter this solution through a fluted filter paper.Add petroleum ether 30 cm3 to the filtrate and when the product has precipitetated collect it by filtration on a Buchner funnel. Wash the product with petroleum ether (5 cm3) and dry it in a vacuum desiccators.
Use the bulk of your product to prepare(Ph3P)3W(CO)3, this is used in place of cycloheptatriene W(CO)3 in Abel, Bennett and Wilkinson J.C.S.,(1959), p 2324 (Chemistry Depertment library).
- Record the I.R. Spectra of W(CO)6 and the two complexes prepared both as KBr discs and as solutions in CCl4.
Consult Cotton and Wilkinson Second edition, Nicholls and Whiting J.C.S.(1959) p 551 R.D.Fischer Chem. Ber. 93(1960) p 165.
Comment on your results and compare with those of free CO.
Questions
- If the reaction of Mo(CO)6 with mesitylene were conducted in the presence of air, what would probably be the decomposition products?
- How would you expect the C-O stretching frequencies in the compounds (C6H6)Mo(CO)3, [1,3,5-C6H3(CH3)3]Mo(CO)3 and [C6(CH3)6]Mo(CO)3 vary and why?
- How would you determine in an afternoon’s experiment whether or not your isolated [1,3,5-C6(CH3)3]Mo(CO)3 (or (C6H6)Cr(CO)3 was pure?
References
- E.O.Fischer, K. Ofele, H. Essler, W. Frohlich, J.P. Mortensen and W. Semmelinger, Chem. Ber. 1960, 93,165.
- B. Nicholls and M.C. Whiting J. Chem .Soc.1959,551
EXPERIMENT 6
The Chemistry of Nickel: Preparation of Cis-chlorobis(triphenylphosphine) nickel (11) NiCl2(PPh3)2
Experimental
- Reactions of Nickel
Use a solution of nickel sulphate or chloride.
Record all observations and interpret them as far as possible.
(i) Examine the effect of sodium hydroxide and ammonium hydroxide.
(ii) Investigate the effect of dimethylglyoxine at different pH. Do cobaltous solutions give a precipitate under similar conditions?
(iii) Add potassium cyanide solution dropwise and divide the solution into two parts:
(a)Add sodium hydroxide solution
(b)Crystallize and isolate any solid formed.
(iv) Record the visible and ultraviolet spectrum of a solution of nickel chloride in water. Now add ethylenediammine hydrate to the solution and repeat the spectrum.
(a)How many bands are there in the spectrum?
(b)Assign the transitions with reference to a Tanabe-Sugano diagram.
(c)Why is the spectrum shifted to higher frequencies when ethylenediammine is added?
- Dichlorobis(triphenylphosphine)nickel (11) NiCl2(PPh3)2
Materials required : nickel chloride hydrate
n-Butanol
Benzene
Nitromethane
Dean and Stark apparatus
Rotary evaporator
Dissolve nickel chloride hexahydrate (1.5g) in the minimum quantity of warm water (less than 10 cm3) and add n-butanol (50 cm3), benzene(6 cm3) and triphenylphosphine (3.2g). Distill this mixture azeotropically using a Dean and Stark apparatus until no more water passes over. Transfer the flask from the Dean and Stark apparatus to a rotary evaporator and evaporate the solution until crystals are deposited on cooling the solution.Collect the crystals by filtration on a Buchner funnel and immediately recystallize from nitromethane.The crystals should be stored in a desicator over calcium chloride.
Exercises
- Record the infra-red spectrum of the complex as a Nujol (paraffin oil) mull; does the spectrum confirm the presence of triphenylphosphine in the complex ?
- Record the ultra-violet and visible spectrum of the complex (0.005g) in nitromethane (10 cm3), using a 1 cm cell.
Determine the molar extinction coefficients for the bands observed.What do the spectrum and the values of the extinction coefficients indicate about the stereochemistry of the complex?
- Explain the observation of coluor changes during the recrystallization procedure and its significance on the structure of NiCl2(PPh3)2
EXPERIMENT 7
Complex ion composition by jobs method
Frequently it is possible to detect the interaction of two molecules in solution without being able to isolate a stable compound. For example, benzene and iodine interact in carbon tetrachloride.
C6H6 + I2 ↔ C6H6I2
to form a highly colored 1:1 adduct which is too unstable for isolation. The presence of an adduct is demonstrated by the intense color of these solutions, yet its composition is uncertain until it has been established that only one molecule of benzene react with one molecule of iodine.
The area of coordination chemistry has thrived on studies of complexes which have been identified in solution without being isolated. The interaction for example, of Ni2+ with NH3in water produces complexes of the compositions, Ni(NH3)(OH2)52+, Ni(NH3)2(OH)42+, Ni(NH3)3(OH2)32+, Ni(NH3)4(OH2)22+Ni(NH3)5(OH2)2+ and Ni(NH3)62+.Of this series only Ni(NH3)62+ has actually been isolated yet spectrophotometric and Potentiometric investigations leave little doubt concerning the existence of the others in solution. Because the complexes have not been isolated does not always imply that the interactions are weak. Indeed bond formation between transition metal ions and ligands is highly exothermic. For other reasons, however, it is frequently not possible to crystallize from solution all the species which may be present in solution. Their composition must then be established by other techniques. The procedure to be used in determining the solution composition of Ni2+-ethylenediamine complex in this experiment is known as the method of continuous variations for Job’smethod. In the general case, it is concerned with evaluating nfor the equilibrium,
Z + nl ↔ zLn…………………………………(1)
In the present experiment, Z is Ni2+ and L the ligand ethylenediamine(en). Both Ni2+ and the product
Ni(en)n2+ have absorptions in thevisible regionof the light spectrum but their spectra are different. Experimentally, the intensity of absorption at a given wavelength of a series of solutions containing varying amounts of Ni2+ and enis measured. This absorbance is related to the concentration of Ni(en)n2+ in solution. These solutions are prepared with the restriction that the sum of the concentrations of Ni2+ and en be the same in all solutions. In the case where the equilibrium constant for reaction (1) is very large, ie., the equilibrium lies far towards the right it is clear that the intensity of the Ni(en)n2+ absorption will be greatest when the en concentration in solution is exactly n times greater than of Ni2+ . As will be shown later, this is also true when the equilibrium does not lie far to the right. Sufficient concentrations of zLnmust, however, be produced so that accurate absorbance measurements maybe obtained on the solutions. It is therefore possible to determine n and the composition of Ni(en)n2+ by knowing the ratio of en to Ni2+in the solution which contains a maximum absorbance for Ni(en)n2+ .
For the Ni2+-en system, a series of complexes, Ni(en)2+ , Ni(en)22+ , Ni(en)32+ , Ni(en)42+ and so forth are possible. The purpose of this experiment is to determine which of the species are actually present in the solution, the possible equilibria involved follow:
K1
Ni2+ + en ↔ Ni(en)2+
K2
Ni(en)2+ + en ↔Ni(en)22+
K3
Ni(en)22+ + en ↔Ni(en)32+
K4
Ni(en)32+ + en ↔ Ni(en)42+
The values of the equilibrium constants will determine which species will predominate in solution. Thus if k2 is so much larger than k1,that virtually no Ni(en)2+ is present in solution, the Job procedure will identify Ni(en)22+without giving any evidenceof Ni(en)2+ . Likewise the relative size of K3 to K1and k2 will determine what species are characterized. One of the limitations of the method of continuous variations is the requirement that only one equilibrium of the type in equation (1) be present in a solution of Z and L. That is, it will give nonintegral values of n if addition to Z, L, and ZLn, another complex,ZLn+1 is also present.For the Ni2+-en reactions, this means that only 2 complexes(Ni2+ and Ni(en)2+ or Ni(en)2+ and Ni(en)22+, and so forth) can be present in any given solution. This will be true if K1, K2, and K3 are greatly different.From potentiometric studies of the interactions of Ni2+and en, the values of K1, K2, and K3 have been evaluated(see Experiment 13), and they in fact are separated by large factors.Although Job’s method allows the determination of complex compositions in this system, misleading or erroneous results might be obtained in a system where the K values for successive equilibria are unknown. For this reason, the method of continous variation is limited to relatively simple systems.
Theory
The purpose of this section is to prove that the value of n in zLnof equation (1) may be determined from spectrophotometric absorbance measurements on a series of solutions containing varying amounts of Z and L yet having the same total concentration of Z plus L. If the absorbance at a given wavelength of each solution is plotted vs the mole fraction,X, of L in solution, the maximum absorbance will occur at a mole fraction which corresponds to the composition of zLn. Hence n is determined.
Assume that substances Zand L react according to equation (1) . Equimolar solutions of Z nad L, each of M moles per litre concentration, are mixed in varying amounts so that the total concentration (Z L) is M. A series of these solutions may be prepared by the addition of X litres of L to (1-X) litres of Z(where X<1). The concentration of Z , L and zLn at equilibrium in these solutions are designated C1, C2,and C3, respectively. Thus for any solution the concentrations are expressed as follows: