Magnus' green salt

Magnus' green salt is the chemical compound with the formula [Pt(NH3)4][PtCl4]. This species has been of interest in materials chemistry and solid state physics because of its one-dimensional structure. It consists of a linear chain of Pt atoms separated by 3.25 Å. The Pt(II) centers are also coordinated to four molecules of ammonia and four chlorides, in an alternating manner. It is a semi-conductor.

History
The salt was discovered by Heinrich Gustav Magnus in the early 1830's. It was one of the first examples of a metal complex of ammonia. Ammonia species are very common now - they were after all the basis of Alfred Werner's discoveries. MGS has the same empirical formula as cis-PtCl2(NH3)2 ("Peyrone chloride") and trans-PtCl2(NH3)2. These cis and trans compounds are molecules, whereas Magnus' green salt is a polymer.

Preparation
One mixes aqueous solutions of [Pt(NH3)4]2+ and [PtCl4]2-. A deep green precipitate appears. In recent years, it has been possible to generate soluble polymers by replacing the ammonia with ethylhexylamine.