Blue Acid Chemistry (8): K6[Co2O2Bl10].H2O

Я вчера был живой...

——Мертвый город. Рождество by DDT

Our first attempt on making a complex that can undergo further transformation!

In this complex, the bridge is a peroxo ligand, which contains an O-O single bond and bears 2 negative charges.

Two cobalts are connected to different oxygens, so the structure is [...Co-O-O-Co...].

Due to the disgusting nature of CoBl2 found before in (5) and the extreme accurate stoichiometry required in this experiment, we decided to use another way.

Co2+ + 5Bl- = [CoBl5]3-

2[CoBl5]3- + O2 = [Bl5CoOOCoBl5]6-

Attempt 1

We decided to use Co(OAc)2 instead of CoBl2 as precursor. Acetates are soluble in ethanol and can be removed from product easily.

First, 4.0g(0.01mol) (NH4)2[Co(H2O)6](SO4)2 and 1.4g(0.01mol) K2CO3 was dissolved separately and mixed together. Purple CoCO3 was formed immediately.

Then CoCO3 was put in minimal water and carefully dissolved with AcOH which is added dropwise. Pure AcOH is very pungent like chlorine and don't get too close. You can use white vinegar of course. Dissolution is somewhat slow so add slowly. No large excess is allowed or you will die!!! Now it's a red solution and is nearly neutral. Test pH to verify this.

3.2g(0.05mol) KBl was added, and the solution turned into a green opaque stuff. This is weird as we observed K3[CoBl5] to be orange-red before. Maybe 1) two different Co(II) complexes exist, depending on conditions 2) some CoBl2 is still there due to deficiency of KBl, as our electronic balance was down as said before. Different sources claimed both olive-green and reddish-brown color. This claimed that, probably in aqueous solution the sixth position can also be occupied by something though weakly, which affects spectrum significantly. This claimed that, color is dependent on concentration and temperature.

Then, air was bubbled quickly into the solution for 10min. Solution turned brown. Large amount of solid remained and this is the beginning of a disaster...

We thought the solid to be product, so we added much water to dissolve it but nothing happened. Papers claimed the product to be "very soluble" in fact. Upon heating the solution turned yellow so we didn't boil it to dry to prevent decomposition, and we are unable to get any product after addition of i-PrOH(as EtOH was run out). Obviously, the solution is too dilute now!

About the weird brown solid: it is possibly residual CoBl2, or Co3[Co2O2Bl10], or Co3[CoBl6]2, Co[CoBl5(H2O)], K2Co[CoBl6] or anything caused by deficiency of KBl. Many formulas can be suggested, but something becomes clear...

In fact in the paper a little (0.4M Co2+, 2.1M Bl-) excess was used and they still made it, so a little excess might be needed to prevent formation of stuff said above. Also they mentioned that cooling to 0℃(273K) could increase yield, so we should try next time.

Very sad, but, let's just, have a rest... I have lost almost everything during the past years and days, my dream, my life, my love, my motherland, my family, my friends, my idol, my ethanol, my electronic balance, my blue salt, my product... but I can't stop fighting just because of a miserable failure, my [removed]-Sensei once told me, only be alive then you can do something. Not a big deal, I said these just because of mania, not for any meaningful reasons.

Attempt 2

We're back! This time we followed the same procedure to make CoCO3 and used 1.20g(0.02mol) AcOH to dissolve it. Then the solution was cooled to 0℃(273K) and 3.57g(0.055mol) KBl was added. After dissolution air was quickly pumped into it for 10min. Color turned from deep red to yellow(red photo was not taken since I am busy pumping air).

Then EtOH was added to it, and solution was again cooled to ice cool and then filtered to collect the yellowish-brown product. Since the product is said to be hygroscopic I dried it in a sealed box with CaCl2. Yield: 2.32g(70%).

 

To be honest I was confused at first time since I thought it has the same color as K3[CoBl6] which means something went wrong. However I made a comparison and found that this product has a much deeper color.

After drying it looks like this, still much different

It dissolves in water to form a deep yellow, slightly basic solution. NaClO can't oxidize it. H2O2 turned the solution colorless and cloudy. I am confused.

However, if it is dissolved in a strong solution of KOH, NaClO definitely oxidize it into a red solution, which clearly proved its identity. According to papers quoted before, this complex decomposes quickly in water if no base is there.