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.