Although most of the dithiocarbamates are relatively easy to synthesize by addition of a sodium N,N-dithiocarbamate solution to the appropriate metal salt solution, there are a couple of things to consider. Here are some (hopefully) useful pointers:

1. Iron (not under inert gas)

Iron(III)c hloride (FeCl₃*6 H₂O, also called "ferric chloride") and not iron(II)chloride (FeCl₂*4 H₂O, also called "ferrous chloride") is used for the reaction. It is crucial to use the correct ratio of FeCl₃*6 H₂O to Nadtc*3 H₂O in the reaction because the intermediate FeCl_3-x(dtc)_x compounds would be formed in larger quantity if insufficient amounts of Nadtc was used. They are also black (why?) and are generally very difficult to separate from the target compound using recrystallization only.

The initially formed precipitate is almost black. Aside of target compound, it also contains significant amounts of hydroxides and other sulfur-containing species. These compounds can be removed by recrystallization (which steps does this process imply?) from hot toluene (~80-90 ^oC). The best strategy is probably to extract the crude product several times with hot toluene, combine the organic layers and then reducing the volume of the combined solutions to about 10 mL using the rotary evaporator. The solubility of the product is then lowered by the addition of 30 mL of 95% ethanol (what can be concluded about the polarity of the product based on that?). The purified product is filtered, washed with ice-cold ethanol and then dried at 50 ^oC in the oven. The final product can be stored in a closed vial at ambient temperature.


2. Manganese (not under inert gas)

The initially formed yellowish precipitate (Mn(dtc)2) is oxidized using an air stream, which causes a color change to dark purple. The air stream is applied by placing the solution in a filter flask connected to an aspirator or the house vacuum line. The air stream is introduced using a glass tube with a fritted disk to disperse the air more efficiently (shown on the right side). Alternatively, the air from the air supply in the hood (orange valve labeled "LA") can be bubbled through the solution using the same setup. Since the mixture foam heavily, the flow rate has to be carefully controlled to avoid a mess. It is also advisable to use a relative large container i.e., a 250 mL filter flask, etc. The crude product (a mixture of Mn(dtc)3, and some Mn-hydroxides/oxides/sulfur compounds) has to be extracted several times using small amounts of hot ethyl acetate. The volume of the combined extract should be reduced to ~5-10 mL before 30 mL of 95% ethanol are added to precipitate the final product. The final product is sensitive to hydrolysis, oxygen and light. It has to be stored in the freezer in a dark vial or bottle.

3. Cobalt (not under inert gas)

Most of the procedure is similar to the one above for manganese. However, the color change is not as pronounced during the oxidation (light green to dark green).

The extraction of the crude product is performed with warm toluene (60-70 ^oC). After the volume of the solution is reduced to ~10 mL, 30 mL of 95 % ethanol are added to precipitate the product. The final product is air stable.


4. Chromium (under inert gas!)

For this compound, anhydrous sodium dithiocarbamate is needed, which will be provided by the TA (please inform the TA ahead of time so that s/he can prepare it). Make sure that you handle the supply under inert gas. If you work quick enough, the required quantity can be weighted in a closed vial. You also will require dry THF (from the still) for this reaction as a solvent and anhydrous chromium chloride (How do you know that it is anhydrous?). Since this reaction will require more time due to the preparation of the glassware and the use of Schlenk techniques, it might be a good idea to start this one first, because this reaction will take some time to complete. The precipitate from the reaction forms a pretty fine powder, which implies that a Schlenk frit with a label (fine) is needed in order to remove it. The precipitate will usually clog the frit quickly, it is advisable to decant the solution in the beginning and transfer the precipitate onto the frit in the end (alternatively, a filter aid can be used). During this procedure, some of the product will precipitate as well. Thus, the solid part has to be extracted several times with some warm, dry THF. The volume of the combined organic layers should be reduced to ~10 mL before adding 30 mL of absolute ethanol to precipitate the product. The dark blue product can be stored in a closed vial.

If the anhydrous CrCl₃ is very pure, it will be non-reactive. In such a case, a small amount of zinc powder is added to the mixture to catalyze the dissolution of the CrCl₃. The zinc will reduce the Cr(III) to Cr(II), which makes it less kinetically inert.


5. Characterization

Read the appropriate appendices with the instructions how to use the FTIR spectrometers.

a. FTIR spectrum (YH 6076, YH 1033)

- Acquired using ATR setup (>450 cm^-1) and as Nujol mull in between CsI plates (250-500 cm^-1)
- Read the chapter on how to acquire infrared spectra (Appendix A and B, p. 145-154)

b. NMR measurements

- Solvent: CDCl₃
- Read the chapter on how to acquire NMR samples (with emphasis on paramagnetic compounds..why?) (Appendix C, p. 155-161)
- Review the NMR handout provided by the instructor
- Research the reference data for your compounds prior to running your sample to be able to measure the correct range

c. Electrochemical measurements

- Read the chapter about cyclic voltammetry in the reader (p. 39-44)
- Find the appropriate reference data in the literature before you start this part, so that you know what you are looking for
- Acquired in dry dichloromethane (from still)
- Prepare the following solutions:

• 1. ~0.1 M solution of tetraethylammonium tetrafluoroborate (=electrolyte solution)
  
• 2. ~5*10^-3 M solution of your Mdtc₃ compounds using the electrolyte solution above
  
• 3. 0.01 M solution of ferrocene using the electrolyte solution above
  

- three electrodes are needed: Pt-disk electrode (auxiliary electrode), Glassy carbon electrode (=working electrode) and Ag/AgCl-eletrode (reference electrode) using the LiCl solution above (What is its reference potential?) Do not break or lose the electrodes. The entire set is ~$1000! You will held responsible for any damages or losses caused by not following proper procedures!

- Important: The glassy carbon electrode has to be clean with an abrasive after each run. The TA will show you how.

You will have to acquire three spectra for each compound: One survey spectrum (large window: -1.5 V < E < 1.5 V, scan rate: 200 mV/s), two spectra focusing on the oxidation and the reduction step only (small window: +/- 0.3 V of the peak maximum and mininum in survey spectrum, scan rate: 20 mV/s)


6. Hints to questions

ad 3: How can you push an equilibrium to the side of the products in general?

ad 4: Many chromium minerals contain which other element? How about nickel? What can you conclude out of this?

ad 6: What determines the magnetic momentum?