Blocking of Watson-Crick or Hoogsteen edges in purine nucleobases by a metal entity precludes involvement of these sites in interbase hydrogen bonding, thereby leaving the respective other edge or the sugar edge as potential H bonding sites. In mixed guanine, adenine complexes of trans-a(2)Pt(II) (a = NH3 or CH3NH2) of composition trans[(NH3)(2)Pt(9-EtA-N1)(9-MeGH-N](NO3)(2) (1a), trans-[(NH3)(2)Pt(9-EtA-N1)(9-MeGH-N](ClO4)(2) (1b), and trans,transI(CH3NH2)2(9-MeGH-N Pt(9-EtA-N1)Pt(9-MeGH-N7)](CH3NH2)(2)](ClO4)(4).2H(2)O (2) (with 9-EtA = 9-ethyladenine, 9-MeA= 9-methyladenine, 9-MeGH = 9-methylguanine), this aspect is studied. Thus, in 1b pairing of two adenine ligands via Hoogsteen edges and in 2 pairing of two guanine bases via sugar edges is realized. These situations are compared with those found in a series of related complexes.