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Author: Subject: Coordination chemistry of nickel(II)
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[*] posted on 4-12-2007 at 16:22
Coordination chemistry of nickel(II)

Ok, I have spent a great deal of time recently playing with various nickel salts but now I have reached the point where I can't figure where to go next.

I managed with difficulty to make Ni(NO3)2.6H2O as a green lump which could be ground up by heating it. I also managed to make some nice anhydrous NiCl2 - it is a beautiful yellow colour.

Nickel bromide is being a bit of a problem however. After roasting at a high but unknown temperature for ~12hrs I was able to separate and grind up some brown powder that resembles the trihydrate I used at uni once, however I am sure it was at more than 200*C, yet the anhydrous form was not produced (at least it is not "golden yellow"). It is the most hygroscopic substance I have ever seen. It is even worse than ground KOH. Upon leaving it to its own devices for some time in air a deep red solution is formed which I believe consists of [NiBr4]2- ions, in accordance with information from Cotton and Wilkinson which describes red or brown colours being formed by Br- and I- ligands - bringing a charge transfer band from UV down to blue. Upon slight dilution this stays deep red until at some point is starts changing to green. From here, a 2 fold dilution eliminates all red colour to form a deep green solution which I believe is a transition from tetrahedral halide complex to octahedral hexaaqua complex. I should also point out that you can at least see through the green solution, the red one is as opaque as a permanganate solution.

I was thinking of making some nickel ammonium bromide (if it exists as the chloride does) I was also wondering if anyone has any info on this, or indeed has made it or the chloride. I am wondering if the mixed chloride is blue which would imply that the chloride is coordinated or if water is coordinated?

I have also made some [Ni(en)3]SO4, which forms a nice purple mess (not good crystals). Is there anything else fun which can be done to nickel with ethylenediamine? such as controlling the concentration of the ligand? When I first added en to the solution it went blue, which would tend to suggest tetrahedral coordination, however with an excess of en octahedral coordination is inevitable.

Also, SCN- is an interesting ligand for nickel, but I don't know how to use it properly since I only have KSCN. In an experiment at uni once we added KSCN to Ni(NO3)2.6H2O in n-butanol and hot filtered the KNO3 so formed. Without vacuum or n-butanol I can't do this. Also, PPh3 is an interesting ligand but I would have to chew up an irreplaceable reagent to make any of this.

Any other fun things that I have missed?
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[*] posted on 4-12-2007 at 16:54

Not sure about nickel, but I've noticed zinc chloride is just about impossible to crystallize (even in my warm box!), whereas some potassium chloride added forms a combination salt, which should be KZnCl3 or K2ZnCl4. The crystals are acicular, and not too bad in diameter (despite the impure solution I've got).

Nickel, Fe(II), Mg, Co(II) and Mn(II) (and I think a few others I'm forgetting) tend to substitute in salts, so the potassium or ammonium nickel chloride salt ought to be not that hard to deal with.


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[*] posted on 4-12-2007 at 23:18

If you can get any phosphite esters or triphenylphosphine, you can make Ni(0) complexes which are useful. Or if you can get cyclooctadiene you can make Ni(COD)2.
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[*] posted on 5-12-2007 at 00:41

Is there anything else fun which can be done to nickel with ethylenediamine?

Certainly en would form energetic complexes with nickel nitrate, chlorate, perchlorate, iodate and bromate. These compounds can be made quite easily from NiSO4 and the corresponding barium salt. Insoluble BaSO4 precipates, and the clear liquid is decanted, filtered and added to the calculated amount of ethylenediamine.
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[*] posted on 5-12-2007 at 01:28

I have made some Ni[NH3]6Br2. This is the hexammine complex of nickel (II) with the bromide ion as counter ion. This material can fairly easily be made. I first took nickel nitrate (made from metallic nickel and HNO3), which I heated until I got a thick dark green syrup. To this, I added a concentrated solution of KBr and heated+mixed, in order to get a nice homogeneous solution. Then, I added excess 15% ammonia. This makes a deep blue/purple liquid. On cooling down, nice crystals of [Ni(NH3)6]Br2 separate from the liquid. I removed most real wetness by putting the crystals on tissue paper, and then I did a final rinse with diethyl ether (this dissolves quite some water) en then let them dry.

This material is remarkably nice and dry. It is not hygroscopic at all and also does not form big lumps. When added to water, it does not form a clear solution, the complex partly falls apart and the free NH3 causes the solution to become alkaline and Ni(OH)2 is formed. In order to get a clear solution, the solid must be dissolved in dilute ammonia.

EDIT(woelen): Changed link, such that it works again.

[Edited on 11-9-13 by woelen]

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[*] posted on 10-3-2011 at 08:43

I have managed to prepare the following three complexes of nickel II and ethylenediamine:

[Ni(en)(H2O)4]2+, [Ni(en)2(H2O)2]2+, [Ni(en)3]2+
(Second, third and fourth from the left respectively)

I followed the procedure given in "Classic Chemistry Demonstrations" Published by the Royal Society of Chemistry ISBN 1 870 343 38 7

[Edited on 10-3-2011 by strontiumred]

[Edited on 10-3-2011 by strontiumred]
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