A Comprehensive Treatise on Inorganic and Theoretical Chemistry

374
PtBr4
1 „
INORGANIC AND THEORETICAL CHEMISTRY
formation of the bromide from platinum and found the stages are Pt—> PtBr->PtBr4.
Platinic bromide was analyzed by V. Meyer and H. Zublin, W. Halberstadt,
A. Gutbier and co-workers, L.. von Miiller, and A. Miolati and I. Bellucci. Dark
brown, amorphous platinic bromide is stable in air. W. Peters observed that when
it is dried in vacuo, it is somewhat moist. W. Halberstadt could not obtain it in
the crystalline state, but C. F. Rammelsberg did do so. R. Klement gave 5*687
for the sp. gr. at 25°/4°, and 90-6 for the mol. vol. W. Pullinger found that after
4 hrs.' heating at 310°, in a current of air, the salt was not completely converted into
1 JJBr3
^PtBr2
M -2 1
platinous bromide and bromine.
L.. Wohler and F. Mtiller's observations
on the range of stability
200 30 I , *".+ , * ,. 600 of the bromides are summarized
Fia. 90.-Range •g^Stob^hty of the Platxnum in F£g gQ Q Nogareda studied
the subject. L. Pigeon said that
the heat of formation of the solid is (Pt, 2Br2)=42-43 to 56-83 CaIs. according as
the bromine is liquid or gas ; the heat of formation of the salt in soln., (Pt, 2Br2Hq.,
H2O) =52-29 OaIs. ; and the heat of soln. is +9-86 CaIs. A. Gutbier and coworkers
said that hydrogen reduces platinic bromide, even at ordinary temp.,
forming hydrogen bromide. The salt is soluble in water, and L. Pigeon said that
1OO c.c. of water dissolve 0-4 grm. of the salt at ordinary temp., and W. Halberstadt
gave 0-41 grm. per 100 grms. of water at 20°. For the electrical conductivity,
vide infra, dihydroxy-tetrabromoplatinic acid. According to W. Halberstadt, the
salt is freely soluble in hydrobromic acid ; and soln. of potassium, sodium, or
calcium bromides give red precipitates.
An aq. soln. of the salt was found by W. Halberstadt to give a fawn-coloured
precipitate when treated with aq. ammonia, and a soln. of ammonium bromide gives
a red precipitate. According to W. Peters, the anhydrous salt rapidly absorbs
dry ammonia to form platinic hexamininobromide, [Pt(NH3)6]Br4, and this, in
vacuo, yields platinic pentamminobromide, PtBr4.5NH3. P. T. Cleve prepared
platinic dibromotetramminobromide, [Pt(NHg)4Br2]Br2, by mixing hot soln. of
the corresponding nitrate, and ammonium bromide ; and A. Werner, by the action
of bromine on a warm soln. of platinous tetramminosulphate. The orange-red
crystals are sparingly soluble in hot water. Silver nitrate precipitates silver
bromide from the aq. soln.—the hot filtered liquor on cooling furnishes pale yellow
crystals of what is considered to be [Pt(NH3)4(OH)Br](N03)2. L,. A. TschugaefE
prepared platinic bromoamidotetramminobromide, [Pt(NH3J4(NH2)BrJBr2 ; and
platinic cnloroamidotetramminobromide, [Pt(NH3)4(NH2)Cl]Br2. P. T. Cleve
obtained platinic trans-tetrabromodiammine, [Pt(NH3)2Br4], by adding bromine
to platinous trans-chlorodiammine. The orange-yellow powder consists of foursided
plates, or octahedra, which are sparingly soluble in water. The corresponding
platinic cis-tetrabromodiammine forms dark red prisms or rhombic or hexagonal
plates, sparingly soluble in cold water. A. R. Klien studied the action of water,
acids, and alkaline soln. According to E. G. Cox and G. H. Preston, the a- and
^8-diamminotetrabromides are isomorphous with the corresponding tetrachlorides.
H. Topsoe prepared platinic tetrabromonitrosylbromide, PtBr4.2NOBr, by
dissolving platinum in a mixture of hydrobromic acid and an excess of nitric acid.
The dark brown powder contains cubic crystals. Moisture decomposes the salt
with the evolution of nitrous fumes ; and when confined over calcium chloride
nitrosyl bromide is evolved. P. T. Cleve obtained platinic hydroxybromotetramminonitrate,
LPt(NH3)4(OH)Br](N03)2, by the action of silver nitrate on platinous
dibromotetramminonitrate. The straw-yellow powder consists of short prisms.
The salt loses nothing at 100°, but detonates like gunpowder when strongly heated.
It is sparingly soluble in cold water, and freely soluble in hot water ; hydrochloric
acid converts it into chlorobromotetramminochloride ; nitric acid forms bromonitratotetramminonitrate
; and an excess of oxalic acid gives a mixed precipitate.
W. Manchot and G. Lehmann observed that in carbon monoxide the halogen