BIS(PURINE) COMPLEXES OF TRANS-A2PTII : PREPARATION AND X-RAY STRUCTURES OF BIS(9-METHYLADENINE) AND MIXED 9-METHYLADENINE, 9-METHYLGUANINE COMPLEXES AND CHEMISTRY RELEVANT TO METAL-MODIFIED NUCLEOBASE TRIPLES AND QUARTETS

Mononuclear bis(purine) complexes of trans-a2PtII, trans-[(NH3)2Pt(9-MeA-N7) (9-MeGH-N7)](NO3)2·H2O (1b) and trans-[(NH3)2Pt(9-MeA-N7)2](ClO4)2·H2O (3c), have been prepared and their structures determined by X-ray crystallography. 1b:  Space group P1, a = 7.245 (5) A, b = 7.715(6) A, c = 10.907(8) A, α = 82.36(6)°, β = 86.62(6)°, γ = 70.15(6)°, V = 568.3(7) A3, Z = 1. 3c:  Space group P21/c, a = 8.312(2) A, b = 15.386(3) A, c = 12.365(2) A, β = 94.83(3)°, V = 1575.72(55) A, Z = 2. The cation of 3c is centrosymmetric. In the cation of 1b, the two purines adopt a head−head orientation with an intramolecular H bond of 2.94(3) A between the exocyclic amino group of 9-MeA and the exocyclic carbonyl group of 9-MeGH. Di- and trinuclear derivatives of 1b and 3c have been synthesized and/or studied in solution. They include compounds of types Cl•N1-A-N7•GH (2a), T•N1-A-N7•GH (2b), GH•N1-A-N7•T (2c), and GH•N7-A-N1•N1-A-N7•GH (2d) as well as X•N1-A-N7•N7-A-N1•X (X = Cl (4), GH (5a), T (5b)) with • representing tran...