Experimental Details:
First and foremost, the safety precautions should be noted. Potassium permanganate is a strong oxidant. If the chemical is spilled on the skin, immediately wash off with water. All glassware must be cleaned properly. The first step is to make the Tris(acetylacetonato)manganese(III). In a 250 mL beaker, 3.75 grams of potassium permanganate was measured. 75 mL of distilled water was added to the beaker. The solution was stirred and heated to 80°C. The temperature should be monitored by using a thermometer and by checking the temperature every few minutes. Once the solution reached the desired temperature, cool the solution in an ice bath until the solution has reached around room temperature. After the solution has reached room temperature, stir the solution rapidly. The solution will thicken up so rapid stirring is necessary. Slowly, 17mL of acetyl acetone was added in several aliquots over ten minutes or so. Adding the acetyl acetone too fast will result in the solution foaming up and possibly overflowing. The color change should be noted moving from dark purple to black. The solution then must be boiled for five minutes. After the solution was boiled, the solution was chilled in the ice bath. Crystals should start to form on the surface of the solution. Next, the shiny brown-black crystals were collected on a coarse fritted filter. The crystals were washed with 10 mL of distilled water three times. The crystals were dried through the frit with the vacuum on for at least 30 minutes. The crystals were dried in the oven for another 30 minutes to fully dry the Tris(acetylacetonato)manganese(III).
The next part of the experiment involved doing magnetic susceptibility. Be aware that the magnetic susceptibility balance is very sensitive when taking readings. First the mass of the empty tube was recorded. I measured 0.76 grams. The balance must be zeroed. The balance was first calibrated. The constant was calculated to 1.0823. The temperature before and after the reading should be noted in order to see if any outside factors would be affecting the balance readings. The temperature remained fairly constant around 21°C. The balance reading for the empty tube, Ro was determined by inserting the tube and recording the out and in recordings. Next the tube was filled with sample of the Tris(acetylacetonato)manganese(III). The sample was transferred using a spatula and by gently tapping the tube against the desk. This was repeated until the height between 2.4-4.5 cm was obtained. The height of my sample was 2.90 cm. The sampled filled tube was weighed in order to determine the weight of the sample in the tube. The weight of the sampled tube was 0.87 grams. My total weight of sample used in the magnetic susceptibility balance was .11 grams. It was important to pack the sample efficiently so that an accurate reading can be taken from the balance. The final reading of the filled sample tube was taken. Also, the actual yield of the Tris(acetylacetonato)manganese(III) was measured to be 6.15 grams
Results:
Discussion:
Using the magnetic susceptibility balance was somewhat inaccurate. There were outside factors that were affecting the accuracy of the scale. As stated in the beginning, the scale is extremely sensitive. There may have been error due to unnecessary items on the desk where the scale was placed and the passing of people in and out of the room. For the most part, the standard deviation of the averages was helpful enough to give the scale credibility.
The results that I gathered lead me to the conclusion that manganese(III) has 4 d-electrons. Since the complex is octahedral, there was a possibility that it would have either 4 or 7 d-electrons. There are two different ways to distribute the electrons among the t2g and the eg orbitals. Whether a metal has high or low spin depends on how strong the ligands and their splitting with respect to the metal. Ligands, which cause large splitting, Δ , of the d- orbitals are referred to the strong field ligands. The spectrochemical series tells us how strong the ligands are with respect to the metal. We get splitting, according to the Crystal Field Theory, CFT. Mn(III) had 4 unpaired electrons. There was a weak field, thus resulting in high spin.
Conclusion:
The number of unpaired electrons can provide information about the bonding between the metal and the ligand. Determing the number of unpaired electrons is also useful for assigning symmetry. Octahedral ligands have the ability to cause a splitting of the orbitals. The spectrochemical series is a list of ligands that puts them in the order of their ability to cause large orbital separations. For d4 metals, Mn(III), two possible electron separations can occur depending on the gap, the field strength creating low or high spin. If the energy gap is large enough, all the electrons will be placed in the t2g (low-spin). If the energy gap is small, the four electrons will be paired in each orbitals first. Mn(acac)3 is a weak field/ high spin case. It has a configuration of 3 electrons in the t2g orbital and 1 electron in the eg orbital. In total there were 4 unpaired electrons.
References:
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WebQC Chemical Portal. (accessed February 3, 2011)
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Girolami, Gregory S., Rauchruss, Angelici. Synthesis and Technique in Inorganic Chemistry. 3rd Ed. California, 1996.
- Pchem lab manuel
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E.P. O’Reilly, Quantum Theory of Solids, Brighton, UK (2002), 128.