Jor - 9-9-2008 at 10:43
In an attempt to get nickel in the 4+ oxidation state in solution, I did research on the subject. One of my inorganic textbooks said it was possible
to have a stable paraperiodate-complex of nickel(IV), as Ni(IO6)-. It did not tell me how to prepare the complex. I tried two different methods:
Method 1:
Nickel sulfate hexahydrate was dissolved in a small quantity of water. To this a small spatula of periodic acid (H5IO6) was added, and dissolved. Next
a solution of an excess sodium peroxydisulfate in water was added to the test tube. The solution remained green. The test tube was then heated and
drop by drop an 10% KOH-solution was added to raise the pH. At some point a light green precitipate formed, wich redissolved on shaking and heating.
This green precitipate formed everytime and redisolved everytime I added a drop of KOH-solution. But at some point the precitipate did not redissolve.
I added a few more drops of the alkaline solution and let stand for a few minutes. A small amount of precitipate has formed wich is strangely enough
not green but white/yellowish. This must be either some nickel(IV)-salt, or simply some nickel(II)_periodate precitipate, but if the latter is true,
why doens't nickel(II) hydroxide precitipate?
Method 2:
Some nickel sulphate hexahydrate was dissolved in water, and KOH-solution was added until no more precitipate formed (and maybe I added a bit too
much, I'm not sure). To this a sodium peroxidisulfate-solution was added, until all green precitipate turned into black NiO2.nH2O. To this a solution
of periodic acid is water is added. No bubbles of oxygen can be seen (but I'm not sure how alkaline the liquid was before periodate addition). the
solution remains completely black (even when diluted) and it is hard to seen if there's any color present or any NiO2.nH2O has dissolved. But a
precitipate is formed wich can be seen clearly and is on the bottom of the test tube. This precitipate is not black, but grey, and looks a littel bit
metallic in my opinio, but ofcourse it's not nickel metal.
So has ideas what to do next, or has a patent wich describes the synthesis of Ni(IV) species in solution?
I have found a patent, but it reserved to members , can anyone download it? Go to google and type : ''nickel(IV) in solution periodate''. It's the one
on the bottom of the page. the one on top is also interesting one, wich discusses tellurate complexes of nickel, platinum and palladium, but also the
periodate complex of nickel. However, they did not succesfully isolate the compounds MNiIO6.H2O, where M is sodium or potassium.
This is picture of the grey precitipate from method 2. On top of it is the black NiO2.nH2O, wich has now settled.
http://img233.imageshack.us/my.php?image=p1090616qr2.jpg
[Edited on 9-9-2008 by Jor]
[Edited on 9-9-2008 by Jor]
Jor - 9-9-2008 at 12:08
please ignore the colour of the liquid above the solids, as it is not indicative of the real color. in real it's basically colorless.
not_important - 9-9-2008 at 17:15
According to several papers, including this one http://www.ksu.edu.sa/sites/Colleges/CollegeofScinces/Chemis... you use the procedure in Inorganic Synthesis V5, page 201. That has you
adding the Ni(II) salt to a boiling solution of the alkali periodate, then slowly adding the corresponding alkali peroxidisulfate while continuing
boiling and vigorous stirring.
Precipitate is described as starting as red, darkening to near black, metallic looking crystals. Wash 10 times with hot 1% peroxidisulfate solution,
then water containing a little nitric acid to prevent peptizing the ppt.
Sorry, not near a scanner or I'd put up a copy of the relevent pages.
[Edited on 10-9-2008 by not_important]
woelen - 12-9-2008 at 12:24
I have done the following experiment:
Mix some dry KOH and KIO4 (approximately equal amounts) and dissolve this mix in some distilled water. A colorless solution is obtained. The KIO4 also
quickly dissolves, an ortho-periodate is obtained in solution.
To this, add a solution of Ni(NO3)2.xH2O. A pale green precipitate is formed.
Heat this liquid with the precipitate. The precipitate darkens. It becomes dark brown. The liquid becomes dark red/brown. Even after a few hours of
standing, the liquid still is turbid.
Split the dark brown and turbid liquid in two parts. To one part add some K2S2O8 and to the other part add nothing. Heat both liquids. The liquid with
the K2S2O8 becomes much clearer and becomes very dark red/brown, but not all of the precipitate dissolves. The other test tube remains dark and
turbid. The test tube with the dissolved K2S2O8 shows slow formation of bubbles.
Let settle for several hours. The test tube with the K2S2O8 in it has a clear dark red/brown solution over a dark brown, almost black precipitate. The
test tube without the K2S2O8 still is somewhat turbid.
A drop of the deep red/brown solution, added to some water gives a clear yellow/brown solution.
So, periodate definitely affects Ni(OH)2, even without persulfate added. It most likely is true that persulfate is better at oxidizing the nickel and
that this is the reason that more of the deep red/brown complex is formed.
woelen - 13-9-2008 at 05:13
Now, after one day of standing, the test tube with the persulfate added and the other one are almost the same. Both have a black precipitate with a
deep red clear liquid above it.
So, persulfate is not needed for making the red nickel-complex.
It is funny to see that this nickel complex also is red and has a color, which is very similar to the copper complex. I also already did an experiment
with silver(I) ions and these also give a red complex with periodate. So, apparently, the color of these periodate complexes is more determined by the
ligands than by the central metal ion. More investigation of this is ongoing 
Jor - 13-9-2008 at 05:45
Very nice Wilco!
I did not do this last experiment, because I do not have much periodic acid (about 25 grams), and I will do it, when I get my chloroprene tubing, so i
can bubble chlorine in solution, forming KIO4 (I have lots of potassium hydrogen diiodate and also about 100g KIO3. I also have a wash bottle but then
there will be a lot of chlorine lost abouve the KLO3/KIO4 solution, and as you know, acids will be impossible to get in NL, so HCl is not to waste
Im also impressed by these periodate complexes. Why dont you update your webpage on Cu(III) and add this nickel complex ? 