On the Heterogeneous Nature of Cisplatin‐1‐Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH(3) Ligands as Likely Explanation

The conversion of the 1 : 1‐complex of Cisplatin with 1‐methyluracil (1MeUH), cis‐[Pt(NH(3))(2)(1MeU‐N3)Cl] (1 a) to the aqua species cis‐[Pt(NH(3))(2)(1MeU‐N3)(OH(2))](+) (1 b), achieved by reaction of 1 a with AgNO(3) in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH(3) ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis‐[(NH(3))(2)(1MeU‐N3)Pt(μ‐OH)Pt(1MeU‐N3)(NH(3))(2)](+)(3) as well as head‐tail cis‐[Pt(2)(NH(3))(4)(μ‐1MeU‐N3,O4)(2)](2+) (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of (1)H NMR and ESI‐MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ‐OH, μ‐1MeU, and μ‐NH(2) bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N(2) complex, [Pt(NH(3))(1MeU)(N(2))](+) appears to be formed in gas phase during the ESI‐MS experiment. In the presence of Na(+) ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non‐metalated uracil quartets found in tetrastranded RNA.