Inorganic Chemistry Practical by Dr Deepak Pant (the reading strategies book txt) 📖

/> (ii) 0.5% dithyzone in chloroform solution is used. The paper chromatogram may also be developed by exposure to H2S gas but the results are not satisfactory as with dithizone .
(iii) K2CrO4 and ammonia solution.
Procedure
What man no.1 filter paper strip 25cm x 7cm is cut with a pair of stainless steel scissor .then a line is drawn horizontally across the width of filter paper strip using a lead pencil. This line should be about 2cm from the end of the filter paper. Location of the sports is marked with “x” on this line with pencil so that each “x” is at least 2cm from each other.
Pb (II),Ag (I)and Hg2 (II) salt solutions are applied at spots A,B and C respectively with fine capillary tubes .on the spot D, a mixtuxe of Pb (II),Ag(I) , Hg2(II) salt solution is applied .after drying the spotsthe filter paper strip is fixed vertically by means of a clip attached to the inner cover of the chromatography jar .
After this, the paper is lowered carefully into the chromatographic jar in such a way that the lower 1cm portion dips into the developing solvent which is either a mixture of tertiary butyl alcohol (40ml), aceton (40ml) , water (12ml)and nitric acid or methyl n-butyl ketone (85ml)and 10 N hydrochloric acid or n-butyl alcohol mixed with 5% (V/V) of glacial acetic acid .followed by water to turbidity.
When the solvent has travelled a reasonable distance (say 15 cm), it is taken out and allowed to dry. The spot can be visualised by using the visulising reagent.

1. If the spots are sprayed with ammonium sulphide solution , silver mercury and lead spots become dark brown
2. If the spots are sprayed with dithizene in chloroform the following spots are then obtained:
Pb2+ Orange
Ag2+ Pink
Hg22+ Rose pink

3. At the end of the run paper is removed from jar. Then it is dried and dipped into 0.25 molar K2CrO4 solution then following colour will be seen:
Pb2+ Yellow
Ag2+ Orange-red
Hg22+ Orange
The excess K2CrO4 is removed by washing with water . now the paper held over the top of ammonia bottle, the colour of silver will fade whereas mercurous will turn black.
Record the RF values. For solvent system involving n-butanol, glacial acetic acid and water the following values are obtained.
Cation RF Values Colour
Pb2+ Yellow Rose pink
Ag2+ Orange-red Orange
Hg22+ Orange Pink


Preparation of inorganic compounds
1. Preparation of Tris(2,4-pentanedionato)manganese(III) [Acetylacetonatomanganese(III)]

Introduction

Manganese is a first row transition metal that has a tremendous variety of oxidation states that appear in its compounds. The oxidation numbers range from Mn(–III) in compounds like
Mn(NO)3CO to Mn(VII) in KMnO4. Compounds of manganese range in oxidation number between these two extremes. This experiment involves the preparation of a Mn(III) complex of actylacetone (also named 2,4-pentanedione) which is a useful starting material for the preparation of other Mn(III) compounds. Manganese(III) complexes are relatively stable and can be prepared directly by reactions of the hydrous manganese(III) oxide or by oxidation of the hydrous manganese(II) oxide with air or an oxidizing agent. In aqueous solution Mn(III) is readily hydrolyzed.

Mn3+ + 2 H2O Mn(OH)2 + H+ K = 0.93
and is most stable in acid solutions. Manganese(III) is also slowly reduced by water.
4 Mn3+ + 2 H2O 4 Mn2+ + 4H+ + O2
In this experiment a solution of manganese(II) chloride is oxidized with potassium permanganate in the presence of acetylacetone giving the brown acetylacetonemanganese(III), Mn(acac)3.
Because the ground state for octahedral complexes like that of Mn(acac)3 is a 5Eg (t2g 3eg1) there exists considerable Jahn-Teller distortion. Therefore, the complexes are not “pure” octahedral. Two forms of Mn(acac)3 are known: one with substantial tetrahedral elongation (two Mn-O bonds at 212 pm, and four at 193 pm), the other with moderate tetragonal compression (two Mn-O bonds at 195 pm and four at 200 pm). The electronic spectrum of Mn(acac)3 shows a broad band at approximately 20,000 cm-1 (500 nm).1 The complex forms lustrous crystals which are black to dark brown by reflected light and green by transmitted light. The Mn(acac)3 complex can be reversibly oxidized to Mn(acac)3 + (0.96 V vs SCE), or reduced to Mn(acac)3– (–0.06 V vs SCE) in acetonitrile solution (0.1 M tetraethylamonium perchlorate). It has been shown that many electron transfer reactions like those above are ligandcentered rather than metal-centered.3 This implies that in many transition metal complexes electron transfer reactions are facilitated by stabilization of the ligand-radical product via covalent bond formation with an unpaired d electron of the transition metal center. The covalent bond energy is proportional to the negative shift in the potential for the ligand oxidation relative to that for the free ligands anion.3 The Mn(acac)3 prepared here may be used in a later magnetic susceptibility experiment.

Procedure
In a 250-mL conical flask prepare a solution of 1.00 g (5.05 mmol) manganese (II) chloride tetrahydrate and 2.72 g (17.1 mmol) of sodium actetate trihydrate in 40 mL water. To this solution add by digital pipet 3.79 mL (4.10 g or 40.0 mmol) acetylacetone. Place a small magnetic stirring bar in the solution and place the flask on a magnetic stirrer in the hood. To the stirred mixture add dropwise a solution of 0.21 g (1.3 mmol) of potassium permanganate in 10 mL water. (Note 1: Because of the color intensity of the permanganate solution it is difficult to determine if all the solid has dissolved; therefore, stir thoroughly and check for undissolved solute.) After the addition of the potassium permanganate solution continue stirring for 5 minutes. Prepare a solution containing 2.72 g (17.1 mmol) sodium acetate trihydrate in 10 mL of water and add this in approximately 1-mL portions to the stirred solution of crude Mn(acac)3.
Heat the reaction mixture to near boiling (hot plate) for 10 minutes and cool to room temperature. Filter the dark solid on a small Buchler funnel and wash with three 10-mL portions of water. (Note 2: Do not used sintered glass filters for this step.) Spread out the product on a porcelain dish and dry the product in a drying oven at 60 oC to 70 oC for at least one-half hour.
Weigh the dry product and determine the percent yield. Under the hood dissolve the dried acetylacetonatomanganese(III) in 4.0 mL of benzene contained in a 25-mL conical flask. Filter the solution through a 30-mL medium porosity glass filter. Transfer the filtrate to a 30-mL beaker and cool in an ice bath, being careful not to get any water in the benzene solution. Add 15 mL of petroleum ether to the solution to reprecipitate the product. Collect the recrystallized product on a 30-mL medium porosity filter funnel and place in a drying oven at 60 °C. (Note 3: Place the filtrate in a proper lab waste container, not down the drain.) Weigh the recrystallized product and calculate the percent yield from starting material.
References
1. Cotton, F., A., Wilkinson, G., Murillo, C. A., Bochmann, M., Advanced Inorganic Chemistry, 6th Ed., Wiley and Sons, New York, 1999.
2. Charles, R. G., Inorg. Synth., 1963, 7, 183.
3. Richert, S. A., Tsang, P. K. S., Sawyer, D. T., Inorg. Chem., 1989, 28, 2471.


2. VO(acac)2 Preparation (Five coordinationated)
Most of the complexes prepared in experiments 1 to 6 have been 6-coordinate with octahedral or at least pseudooctahedral inner coordination spheres. These have also been the most studied complexes historically. Nevertheless, there are many examples of coordination chemistry with coordination numbers ranging from 3 to 9, and a variety of structures can be found. (See reference 1.) After 6-coordinate octahedral, the next moststudied geometries have been 4-coordinate systems, which may be tetrahedral or square planar. Considerably effort has gone into elucidating the relationship between these two geometries. Some complexes can easily interconvert between the two geometries, and in fact the halogen complexes of Ni(II) [NiX2{P(CH2C6H5)(C6H5)2}2] can be crystallized in both forms.
Five coordinate complexes are much less common than either four or six-coordinate ones, but have received intensive study in recent years. They are more common for some metals, and often for one oxidation state, than others.There are two principal geometries, trigonal bipyramidal and square pyramidal. It is interesting and highly important that these two structures are similar enough in energy to be easily converted. Consequently, the deformation energy is low, and many complexes exist with some intermediate shape. The interconversion process, called Berry pseudorotation, is used to explain the stereochemical non-rigidity (fluxionality) of many five coordinate complexes.

In this experiment we will prepare a five-coordinate complex of V (IV) using the chelating acetylacetonate ligand, the anion of acetylacetone, or 2,4-pentanedione.Consequently, the IUPAC name for this complex is bis-(2,4- pentanedionato)oxovanadium(IV). Although all five donor atoms to the metal are oxygen atoms, they are of different type. The terminal V=O bond is extremely short (1.55-1.68 Å), and this always remains the axial ligand. In other words, vanadyl acetylacetonate is not subject to Berry pseudo-rotation. On the other hand, this complex does show a common reaction of 5-coordinate compounds, vis à vis the addition of a sixth ligand to achieve a pseudooctahedral geometry. The effect of the coordination change can be monitored by visible spectroscopy (a colour change) as well as by IR spectroscopy.
Vanadium(IV), d1, is paramagnetic with a single unpaired electron. This oxidation state is most commonly found as the vanadyl ion, and the complex prepared in this experiment can be thought of as a derivative of the vanadyl group. Vanadyl has a very characteristic "signature" in the electron paramagnetc resonance (EPR) spectrum. This is due to coupling of the electron spin with the nuclear spin of the metal atom.
Procedure
To 2.5 g of pure vanadium(V) oxide in a large Erlenmeyer flask are added 6 mL distilled water, 4.5 mL concentrated sulfuric acid and 12.5 mL of 95% ethanol. The mixture is heated to boiling on a steam or boiling-water bath and stirred. As the reaction proceeds the initial slurry of vanadium (V) oxide darkens, becomes light green and finally turns dark blue. The reduction of vanadium (V) is completed in 30 minutes. 10 mL of water is addded, and the solution is filtered by gravity and the filtrate is collected in a 600 mL beaker. 6.5 mL of acetylacetone (2,4-pentanedione) is added and the solution is stirred for 10 minutes. The solution is neutralized by adding a solution of 10 g of sodium carbonate dissolved in 60 mL of water slowly with continuous stirring to avoid excessive frothing. The precipitated product is collected by filtration on a Büchner funnel and dried by drawing air through it.

Recrystallize the product by dissolving in the minimum amount of hot chloroform (about 4 mL) in a small Erlenmeyer flask, filtering hot by gravity through fluted filter-paper, cooling to room temperature and adding 10 mL of diethyl ether to complete the precipitation. Filter and allow to dry in air.
References
1. D.E. Shriver, P.W. Atkins and C.H. Langford, Inorganic chemistry, (N.Y.: Freeman, 1990), 192ff.
2. M.C. Browning, J. Chem. Soc. (1962), 693.
3. I.S. Butler and J.F. Harrod, Inorganic Chemistry, (Redwood City, Cf.: Benjamin/Cummings, 1989), p. 221ff. (A simple introduction to ESR spectroscopy.) [QD151.2.B88]
4. G. Wilkinson, R.D. Gillard and J.A. McClevery, Comprehensive coordination chemistry (Oxford: Pergamon Press, 1987). Vol. 1, pp. 47ff; Vol. 2, 365ff and Vol. 3, p. 504. [QD474.C65]
5. G. Wilkinson and F.A. Cotton, Advanced Inorganic Chemistry (N.Y.: Wiley, 1988), 5th ed., p. 671ff. [QD151.2.C68]
6. A.B.P. Lever, Inorganic electronic spectroscopy, 2nd edition (Amsterdam: Elsevier, 1984), p. 389ff. [QD96.E44.L49]
7. K. Nakamoto, Infrared spectra of inorganic and coordination compounds (NY: Wiley,