Chemical elements
    Physical Properties
    Chemical Properties
      Platinum Difluoride
      Platinum Tetrafluoride
      Platinum Dichloride
      Tetrachlor~platinous Acid
      Potassium Tetrachlor-platinite
      Trichlor-hydroxy-platinous Acid
      Silver Trichlor-hydroxy-platinite
      Platinum Trichloride
      Caesium Pentachlor-platinite
      Platinum Tetrachloride
      Ammonium Chlor-platinate
      Caesium Chlor-platinate
      Potassium Chlor-platinate
      Rubidium Chlor-platinate
      Silver Chlor-platinate
      Sodium Chlor-platinate
      Pentachlor-hydroxy-platinic Acid
      Barium Pentachlor-hydroxy-platinate
      Silver Pentachlor hydroxy-platinate
      Tetrachlor-dihydroxy-platinic Acid
      Dichlor-tetrahydroxy-platinic Acid
      Monochlor-pentahydroxy-platinic Acid
      Platinum Dibromide
      Brom platinous Acid
      Brom-platinic Acid
      Platinum Di-iodide
      Platinum Tetra-iodide
      Iodo-platinic Acid
      Ammonium Iodoplatinate
      Potassium Iodo-platinate
      Sodium Iodo-platinate
      Tetra-iodo-dihydroxy-platinic Acid
      Platinum Monoxide
      Triplatinum Tetroxide
      Platinum Sesquioxide
      Platinum Dioxide
      Hexahydroxy-platinic Acid
      Platinum Trioxide
      Platinum Monosulphide
      Platinum Sesquisulphide
      Platinum Disulphide
      Potassium Thio-platinate
      Platinum Oxysulphide
      Platinum Disulphate
      Platinum Monoselenide
      Platinum Triselenide
      Platinum Subtelluride
      Platinum Monotelluride
      Platinum Ditelluride
      Ammonium Platinonitrite
      Potassium Platinonitrite
      Silver Platinonitrite
      Platinum Subphosphide
      Platinum Monophosphide
      Platinum Diphosphide
      Platinum Arsenide
      Platinum Di-antimonide
      Monocarbonyl Platinum Dichloride
      Sesquicarbonyl Platinum Dichloride
      Dicarbonyl Platinum Dichloride
      Diphosgene Platinum Dichloride
      Carbonyl Platinum Dibromide
      Monocarbonyl Platinum Di-iodide
      Carbonyl Platinum Monoxide
      Carbonyl Platinum Monosulphide
      Carbonyl Platinum Thiocyanate
      Platinous Cyanide
      Cyanoplatinous Acid
      Aluminium Platinocyanide
      Ammonium Platinocyanide
      Barium Platinocyanide
      Calcium Platinocyanide
      Cerium Platinocyanide
      Copper Platinocyanide
      Hydrazine Platinocyanide
      Hydroxylamine Platinocyanide
      Indium Platinocyanide
      Lead Platinocyanide
      Magnesium Platinocyanide
      Potassium Platinocyanide
      Radium Barium Platinocyanide
      Rubidium Platinocyanide
      Sodium Platinocyanide
      Sodium Potassium Platinocyanide
      Strontium Platinocyanide
      Uranyl Platinocyanide
      Dichlorcyanoplatinic Acid
      Cyanoplatinic Acid
      Lithium Platinicyanide
      Potassium Platinicyanide
      Silver Platinicyanide
      Potassium Thiocyanoplatinite
      Ammonium Thiocyanoplatinate
      Potassium Thiocyanoplatinate
      Potassium Selenocyanoplatinate
      Platinum Subsilicide
      Platinum Monosilicide
    PDB 1a2e-2bho
    PDB 2ch8-3un9
    PDB 3vdk-5bna

Potassium Platinocyanide, K2Pt(CN)4

Potassium Platinocyanide or Gmelin's Salt, K2Pt(CN)4.3H2O, was the first platinocyanide to be discovered, namely, by Ittner, who allowed mixed solutions of potassium cyanide and platinic chloride to crystallise. Ittner, however, does not appear to have understood the nature of the compound he had prepared. Gmelin, who discovered the ferricyanides, observed that by heating to redness a mixture of platinum sponge and potassium ferrocyanide, a compound results in which platinum replaces iron. Analysis of the product crystallised from water showed it to have the formula K2Pt(CN)4.3H2O, when translated into modern symbols. Another method consists in mixing ammonium chlor-platinite with water, adding caustic potash and raising to 100° C. Finally, saturated potassium cyanide solution is added. Ammonia is evolved, and potassium platinocyanide passes into solution:

2KOH + (NH4)2PtCl4 + 4KCN = 2NH3 + 4KCl + K2Pt(CN)4 + 2H2O.

After prolonged boiling to remove all the ammonia the solution is allowed to crystallise, when the salt separates out in long rhombic needles, density 2.4548 at 16° C. Upon exposure to air the crystals effloresce, and at 120° C. lose three molecules of water, becoming pale golden yellow. The crushed crystals are sulphur-yellow in colour, but the crystalline faces exhibit a blue fluorescence. When dehydrated at ordinary temperatures the colour becomes reddish yellow. On heating, the salt becomes white, then yellow, and finally melts at 400-600° C. It is soluble in cold water, easily so in hot, as also in alcohol and ether. Dilute mineral acids do not affect it, but concentrated sulphuric acid effects the precipitation of platinous cyanide.

Wilm drew attention to the fact that the properties of potassium platinocyanide vary somewhat according to the method of preparation. When white, fluorescent crystals of the salt are boiled with hydrogen peroxide (20 volume solution) the crystals remaining after evaporation are pale yellowish green in colour, but devoid of fluorescence. They constitute, in fact, an isomeride, into which the white, fluorescent salt has been converted, probably through the catalytic agency of some impurity in the peroxide. This catalytic theory is supported by the fact that by boiling the white, fluorescent crystals with pure perhydrol, no change takes place.

Contrary to the statements of early investigators, oxidation of potassium platinocyanide with the halogens, nitric acid or lead peroxide, does not yield potassium platinicyanide. The halogens convert it into a dihalogenide, of general formula K2Pt(CN)4.X2. If, however, the solution of potassium platinocyanide is treated with hydrogen peroxide (20-volume solution) acidulated with dilute sulphuric acid, potassium platinicyanide, KPt(CN)4, is obtained united with three molecules of platinocyanide, thus: KPt(CN)4.3K2Pt(CN)4.6H2O.

The crystallographic elements of the hydrated salt are:

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