Taking advantage of right angles in N1,N7-diplatinated purine nucleobases: Toward molecular squares, rectangles, and meanders

Di- and trinuclear complexes of trans-a(2)Pt(II) (a = NH3 or NH2CH3) and the purine model nucleobases 9-methyladenine (9-MeA), 9-ethyladenine (9-EtA), 9-methylguanine (9-MeGH), and 9-ethylguanine (9-EtGH) have been prepared and characterized. The following five compounds have been studied using X-ray crystallography: trans-[(NH3)(2)Pt(9-EtA-N7)(9-MeGH-N7)](NO3)(2). 1.4H(2)O (1b), trans, trans-{[Cl(NH2CH3)(2)Pt](2)-(9-EtA-N1,N7)}(ClO4)(2) (2), trans, trans-{[Cla(2)Pt](N1-9-MeA-N7)Pt(NH3)(2)(9-MeGH-N7)}(ClO4)(3). nH(2)O (a = NH2CH3, n = 1 (3a); a = NH3, n = 1.8 (3b)), and trans, trans, trans-{[Cl(NH3)(2)Pt](2)(N1-9-MeA-N7)(2)Pt(NH3)(2)}-(ClO4)(4). H2O (5). In all diplatinated adenine species (2, 3a, 3b, and 5) the Pt-N(1) and Pt-N(7) vectors are approximately at right angles, therefore making these complexes potential building blocks for molecular squares, rectangles, and meanders. Two open nucleobase quartets, 4 and 6, consisting of three trans-diamineplatinum(II) entities and four purine nucleobases (two bridging 9-MeA's and two terminal. 9-MeGH (4) and 9-EtGH (6), respectively) have been isolated and characterized by elemental analysis and H-1 and Pt-195 NMR spectroscopy.