The compounds cis-[(TMED)Pt(9-MeG) 2](PF 6) 2· 2H 2O (1), cis-[(TMED)Pt(9-EtG) 2](ClO 4) 2·2H 2O(2). cis-[(TMED)Pt(DMX) 2](PF 6) 2·4H 2O (3) and cis-[(TMED)Pt(TMX) 2](PF 6) 2· xH 2O ( x ≈ 4) (4), where TMED = N,N,N′,N′-tetramethylethylenediamine, 9-MeG = 9-methylguanine, 9-EtG = 9-ethylguanine, DMX = 1,3-dimethylxanthine and TMX = 1,3,9-trimethylxanthine, have been prepared and structurally characterized by X-ray methods. Compound 1 crystallises in space group Pn, with a = 10.675(1), b = 12.970(1), c = 12.016(1) Å, β = 97.05(1)°, Z = 2. Compound 2 crystallizes in space group Pbca, with a = 13.886(1), b = 31.742(4), c = 14.958(2) Å, Z = 8. Compound 3 crystallizes in space group C2/ c, with a = 37.557(4), b = 12.215(2), c = 15.823(3) Å, β = 90.47(1)°, Z = 8. Compound 4 cyrstallises in the space group C2/ c, with a = 38.516(5), b = 12.078(2), c = 16.219(2) Å, β = 97.88(1)°, Z = 8. Compounds 3 and 4 are structurally similar. Each [(TMED)Pt(Base) 2] 2+ cation shows square-planar coordination to Pt with the two independent purine ligands coordinated through N7 and arranged in a head-to-tail conformation. The structures are compared with each other and with related compounds in terms of their base/base and base/coordination plane dihedral angles, and their different crystalline environments.