Magnesium Platinocyanide, MgPt(CN)4.7H2O, is conveniently prepared by decomposing the barium salt with magnesium sulphate solution. On filtering off the insoluble barium sulphate and allowing to evaporate, the salt crystallises out in blood- or carmine-red tetragonal crystals, possessing a metallic-green surface sheen. The parameters of the crystals are:
a: с = 1: 1.06143.
There is no evidence that the salt can exist in two isomeric forms.
When maintained at 30° to 40°C., the pentahydrate, MgPt(CN)4.5H2O, is produced, which is yellowish green in colour. The same hydrate may be prepared by maintaining a hot saturated aqueous solution for some time at 45° to 50° C. until the salt separates out; as also by recrystallising the heptahydrated salt from alcoholic solution. The dihydrate, obtained at 100° C., is white, and the anhydrous salt, obtained by heating to 150° or 200° C., is yellow. The following table indicates the colour and fluorescent properties of anhydrous and hydrated salts:
| Colour | Fluorescence | | MgPt(CN)4.7H2O | Red with green reflection | None | | MgPt(CN)4.5H2O | Yellowish green | | | MgPt(CN)4.2H2O | White | None | | MgPt(CN)4 | Yellow | None | |