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 contains a linear chain of alternating [PtCl4]2− anions and [Pt(NH3)4]2+ cations, in which the platinum atoms are separated by 3.25 Å. It is a semi-conductor. The compound may be prepared by mixing aqueous solutions of [Pt(NH3)4]2+ and [PtCl4]2−, to obtain a deep green precipitate. This salt was discovered by Heinrich Gustav Magnus in the early 1830s. The corresponding palladium compound ([Pd(NH3)4PdCl4] is known as "Vauquelin’s salt".
Soluble analogues of the salt can be prepared by replacing the ammonia with ethylhexylamine.
Magnus' green salt was one of the first examples of a metal ammine complex. Ammonia species are very common now; they were, after all, the basis of Alfred Werner's discoveries. Magnus' green salt 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.
^Bremi, J.; Caseri, W. and Smith, P. (2001). "A new compound derived from Magnus' green salt: solid state structure and evidence for platinum chains in solution". J. Mater. Chem.11 (10): 2593–2596. doi:10.1039/b104675f.