Cationic tetrakis(nucleobase)complexes of PtII as metalloligands and potential building blocks for molecular architectures

Abstract

Three cationic tetrakis(nucleobase) complexes of Pt^II have been synthesized: [Pt(Hmhyp-N⁷)₄](NO₃)₂·H₂O 1, [Pt(Hegua-N⁷)₄](NO₃)₂·2KNO₃·5H₂O 2 and trans-[Pt(Hmcyt-N³)₂(Hegua-N⁷)₂](NO₃)₂3 (Hmhyp = 9-methylhypoxanthine, Hegua = 9-ethylguanine, Hmcyt = 1-methylcytosine). The X-ray crystal structure of 1 has been determined. All three cationic compounds rapidly react with Hg^II, but gel formation prevented an adequate characterization of the products formed. However, a Cu^II adduct of 1 was isolated in crystalline form and characterized crystallographically. [{(H₂O)Cu(Hmhyp)₄Pt}₂Cu(ClO₄)₄](ClO₄)₂(NO₃)₄·6H₂O 4 crystallizes in a centrosymmetric Cu–Pt–Cu–Pt–Cu chain structure with Cu–Pt separations of 2.791(1) Å (outside) and 3.8980(9) Å (inside). Two of the three Cu^II ions are bound via exocyclic O⁶ sites of the Hmhyp nucleobases. At neutral and moderate alkaline pH both 1 and 2 form virtually insoluble precipitates, which redissolve at strongly alkaline pH to give eventually anionic [Pt(L)₄]²⁻ species (L = mhyp, egua). Finally, 2 interacts with complementary Hmcyt to give Watson–Crick associates, as demonstrated by ¹H NMR spectroscopy in DMSO-d₆.