Properties of the Platinum—Pyrimidine Blues

Reaction of a solution of the diaqua cation, c/5 [Pt(NH3)2(H20)2 formed in situ by the reaction of cw-[PtCl2(NH3)2] with silver nitrate, with a 2,4-dihydroxopyrimidine, or its sugar derivative, over a period of days at approximately neutral pH allows isolation of the dark blue products as salts of stoichiometry [Pt(NH3)2(pyrimidine)] (N03)i 2 [4]. Few blue complexes are obtained with other amines although a purple complex from cyclopropylamine with apparent stoichiometry of Pt/amine/pyrimidine = 3/2/3 (independent of any charge neutralisation) has been reported [5]. A blue species from [PtCl2(en)] has also been reported [6], and its structure 

The results cited above indicated the platinum—pyrimidine blues to be oligomeric, mixed-valent cations with metal—metal bonding, in line with opinions on the original platinblau , first described in 1908 from the reaction of platinum salts in the presence of amides [10]. The bridging, and thus chain extension, occurs through the pyrimidines and the remarkable propensity of platinum—ammine complexes to stack in species such as [Pt(NH3)2Br2Pt(NH3)2Br4] [11] undoubtedly contributes to the chain extension and indeed, the platinum—pyrimidine blues are another example of this tendency. 

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