A series of complexes containing the purine model nucleobases 9-methyladenine (9-MeA), 9-methylhypoxanthine (9-MeHxH), and 9-methylguanine (9-MeGH) have been prepared and in part (2, 3a, 4b) X-ray structurally characterized: trans-[(NH 3 ) 2 Pt(9-MeA-N7)(9-MeHxH-N7)](ClO 4 ) 2 (2), trans,trans-[a 2 (9-MeGH-N7)Pt(9-MeA-N7,N1)Pta 2 (9-MeGH-N7)](ClO 4 ) 4 ·nH 2 O (a=NH 3 , n=2 (3a); a=CH 3 NH 2 , n=2 (3b)), trans,trans-[a 2 (9-MeHxH-N7)Pt(9-MeA-N7,N1)Pta 2 (9-MeHxH-N7)]X 3.4 Y 0.6 ·nH 2 O (a=NH 3 , X=Y=ClO 4 − , n=3 (4a); a=NH 3 , X=ClO 4 − , Y=Cl − , n=2.5 (4b); a=CH 3 NH 2 , X=Y=ClO 4 − , n=2 (4c)). In addition, a helical coordination polymer derived from 2 and AgNO 3 , trans-[{(NH 3 ) 2 (9-MeHxH-N7)(9-MeA-N7)}Ag(NO 3 )(H 2 O)](ClO 4 )(NO 3 ) (5), has been obtained and studied by X-ray analysis. The two bases in 2 are oriented head–head and display a donor (D), acceptor (A) sequence for H bonding of DADA, making it thus self-complementary and causing it to crystallize as a dimer, hence as a dimetalated base quartet. Both 3a and 4b associate through pairs of O(6)⋯N(1) intermolecular H bonds between 9-MeHxH and 9-MeGH ligands, respectively, into metalated base sextets. Ag + coordination in 5 takes place in a bridging fashion through N(1) and N(3) of 9-MeA, leading to a helical [AgNCN] ∞ backbone with 9-MeA acting as a tridentate ligand.