Sciencemadness Discussion Board

Diamminedinitritoplatinum (Platinum P-salt)

kilowatt - 27-4-2009 at 05:33

This platinum complex is the starting material for most platinum plating solutions. It seems to be pretty much standard practice, but how is it prepared? The salt is supplied by many chemical suppliers but there is virtually no information out there on the preparation which seems to be common knowledge in the industry. I would assume it would start from something like potassium tetrachloroplatinate and be similar to cis-diamminedichloridoplatinum, or possibly from PtCl4.

Sobrero - 27-4-2009 at 10:07

A useful reflex when it comes to inorganic preparation is immediately checking Brauer or Gmelin :).
Brauer's Handbook of Preparative Inorganic Chemistry (second volume), pg 1579-1580.

It goes
potassium tetra- or hexachloroplatinate --aqueous sodium nitrite--> potassium tetranitritoplatinate --aqueous ammonia--> cis-dinitrodiamineplatinum(II)

It's an explosive by the way; this should be moved to Energetic Materials! ^ ^

[Edited on 27-4-2009 by Sobrero]

Fleaker - 27-4-2009 at 11:01

I've made this one on many different occasions.

It's not all that energetic of an explosive. It doesn't do any thing when wet no matter how angry you get with it. It deflagrates when heated though.

Great for plating, and it does work on titanium (as I mentioned a long time ago in perchlorate thread) provided you've properly pretreated it.

You start from K2PtCl4, which can be made from either Na or KPtCl6 which is reduced with metabisulfite or SO2 or hydrazine hydrochloride in a warm solution to give a greenish solution of Pt (II), K+ precipitates it. Should want the rather insoluble K2PtCl4, start with KNO3/HCl and dissolve your Pt, removing nitrogen oxides, and bubble in the SO2; the solution will go from orange red to a sickly green and you'll get a pretty orange precipitate. Hydrazine works better provided it is not in excess.

You must use K2PtCl4: this is reacted with the nitrite, the precipitate filtered, and then reacted with concentrated ammonia.

It's pretty lossy though. Make sure you save all of your filtrate as it will certainly have Pt in it. Boil down the filtrate and add aqua regia to it until you're left with Pt (IV).

kilowatt - 27-4-2009 at 16:51

Excellent, thanks guys.

I've read several conflicting reports about the explosive properties of this compound, ranging from it being an unstable shock sensitive explosive, to quite stable. I think the moral of the story is keep it wet and away from light.

benzylchloride1 - 27-4-2009 at 20:43

The preparation of Pt(NO2)(NH3)2 is a good illustration of the trans effect. All the chloride ligands of PtCl4-2 are first replaced by the nitrite ion to form potassium tetranitritoplatinate. The complex is then treated with ammonia to produce trans Pt(NO2)2(NH3)2.

kilowatt - 5-5-2009 at 18:32

What is the intermediate precipitate formed when K2PtCl4 is reacted with nitrite? Is it K2Pt(NO2)2Cl2? How soluble is this? I am wondering because I don't see how you go from precipitating K2PtCl4 to precipitating something else from a solution of it with any decent yield. I know the solubility of K2PtCl4 increases a lot between room temp and 100C, so would the first precipitation be done in cold water and the second in hot?

Fleaker - 7-5-2009 at 12:55

I never said the yield was great. I suggest you check Brauer's for information on that, as I don't remember the numbers.

You can dissolve up the K2PtCl4 in warm dH2O, then add in the nitrite, then cool, which causes crystallization. You filter this, then react the ppt. with ammonia, which drops the cis diammine nitrite and you're left with potassium nitrite in solution. This is done very cold, the colder the better. This of course can be done one pot too. You can collect one or two crystal crops from the liquor even after a first precipitation but the quality is not as good. Really, it's just easier to make a bunch at one time (use 25 or 50g of K2PtCl4) and then take all of the platinum containing solutions and give them a boil in aqua regia to get tetravalent Pt again.