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

Platinocyanides, M2Pt(CN)4

Cyanoplatinous acid, like chlorplatinous acid, yields a series of well- defined salts of general formula M2Pt(CN)4. By analogy they should be termed cyanoplatinites, but it is more usual to refer to them as platinocyanides. The salts definitely contain the negative radicle Pt(CN)2'', and are not, therefore, mere double salts of the type 2MCN.Pt(CN)2. They may be obtained by neutralising the free acid with their corresponding bases, but the method is not convenient. It is more usual to prepare them:
  1. By double decomposition of the metallic sulphate with barium platinocyanide solution. Thus, for example, the magnesium salt was first prepared by Martius as follows:

    MgSO4 + BaPt(CN)4 = MgPt(CN)4 + BaSO4.
  2. By precipitation of the metallic platinocyanide, when insoluble in water, by double decomposition of a soluble salt of the metal with potassium platinocyanide solution. In this manner Martius obtained the copper salt:

    CuSO4 + K2Pt(CN)4 = CuPt(CN)4 + K2SO4.
  3. By warming platinum salt solutions with alkali or alkaline earth cyanides and allowing to crystallise. In this manner the potassium salt, the first platinocyanide to be obtained, namely, by Ittner, was prepared:

    6KCN + PtCl4 = K2Pt(CN)4 + 4KCl + (CN)2.
  4. A more recent method consists in passing an alternating electric current through platinum electrodes immersed in aqueous solutions of the cyanides of the alkali or alkaline earth metals.

The platinocyanides are an interesting set of salts, remarkable, amongst other of their properties, for the tenacity with which they retain the electronegative metal (platinum) and disguise it to ordinary tests. Concentrated nitric or hydrochloric acid, alone or mixed, in the cold or on boiling, extracts no platinum from them. Even concentrated sulphuric acid only liberates platinum cyanide with difficulty.

The platinocyanides yield very beautiful hydrates. The magnesium salt is an excellent example. It yields, upon slow evaporation of its solution, large regular prisms which appear deep red by transmitted light, but viewed by reflected light the sides of the prisms exhibit a brilliant beetle-green, and the extremities a deep blue or purple. This is the heptahydrate, MgPt(CN)4.7H2O. When gently warmed, even under water, the crystals become yellow, which colour characterises the dihydrated crystals deposited from solution at 45° to 50° C.

Isomerism of Platinocyanides

In an interesting series of memoirs, Levy has shown that certain hydrated platinocyanides, notably those of barium and calcium, exist in two modifications, having the same chemical composition and crystalline form, but exhibiting a remarkable difference in their optical characters, differing in colour and in the intensity of their fluorescence. The barium and calcium salts show this most distinctly, and the cerium salt only to a small extent. Other platinocyanides do not show this at all.

It is not easy to account for this isomerism according to the ordinary methods of representation of the structure of the platinocyanides. Since samples of anhydrous barium platinocyanide, derived from the isomeric tetrahydrates respectively, are equally fluorescent, it seems fairly certain that any scheme must take into consideration the combined water. Levy therefore suggests that the isomerism of the tetrahydrate may be accounted for by assuming that two molecules of water are attached to the barium and two to the platinocyanide radicles, since, in the case of the latter radicles, two alternative positions are possible, namely:


It is conceivable that the (3 or asymmetrical form may be incapable of that movement under the stimulus of the incident radiations which, in the case of the a or symmetrical isomeride, are able to excite fluorescence.

Fluorescence of Platinocyanides

The majority of platinocyanides fluoresce under the stimulus of ultra-violet light or of radium radiations, although some salts show no sign of this property. Magnesium, erbium, yttrium, thallium and uranyl salts are cases in point.

It is certainly very remarkable that uranyl platinocyanide should fail to respond to the stimulus of ultra-violet light or to radium radiations. Both the uranyl and the platinocyanide groups can confer the property of fluorescence upon salts containing them, yet when they both occur in the same complex, there is no sign of fluorescence.

Fluorescence under the stimulus of radium emanations is usually exhibited in a marked degree by one hydrate of the platinocyanide whilst other hydrates either exhibit a feeble fluorescence or none at all. The anhydrous is frequently non-fluorescent also. For example, the heptahydrate of magnesium platinocyanide, MgPt(CN)4.7H2O, is not fluorescent, although the pentahydrate, MgPt(CN)4.5H2O, is markedly so. Again, the pentahydrate of calcium platinocyanide, CaPt(CN)4. 5H2O, exhibits intense fluorescence, whilst the anhydrous salt is only feebly fluorescent.

Oxidation of Platinocyanides

In early literature it is stated that by the action of chlorine, bromine, iodine, lead peroxide or nitric acid upon potassium platinocyanide, a new product, potassium platinicyanide, K2Pt(CN)5.3H2O, is obtained. Similar statements may be found in some recent text-books, but are nevertheless quite incorrect.

When potassium platinocyanide in aqueous solution is acted upon by chlorine or bromine, a halogenated product of composition corresponding to the formula (in the case of bromine)


is obtained, but no platinicyanide.

Oxidation of potassium platinocyanide with lead peroxide, acidulated with dilute sulphuric acid, yields a product containing the SO4 group, of formula xK2Pt(CN)4.K2Pt(CN)4.SO4, where x is probably 9; but again no platinicyanide is formed.

If, however, a 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 3K2Pt(CN)4.KPt(CN)4.6H2O. Lithium platinocyanide is more readily oxidised in this manner, yielding 2Li2Pt(CN)4.LiPt(CN)4, and if the hydrogen peroxide is replaced by Merck's pure perhydrol, complete oxidation to lithium platinicyanide, LiPt(CN)4, is obtained.

The platinocyanides of the rare earth metals are crystalline salts which may be divided into two classes.
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