Novel carboplatin analogs containing flexible and potentially intercalating ligands: Preparation and X-ray crystal structures of di-2-pyridyl ketone cyclobutanedicarboxylate platinum(II) and of 2,3-bis(2-pyridyl)pyrazine cyclobutane dicarboxylate platinum(II)

The crystal structures of the cyclobutanedicarboxylate (cbdc) platinum(II) complexes of di-2-pyridyl ketone (dpk) 1, [Pt(dpk)(cbdc)] and of 2,3-bis(2-pyridyl)pyrazine (bpp) 2, [Pt(bpp)(cbdc)] · 2CH₂Cl₂ have been determined by X-ray crystallography. Crystal data are: 1, orthorhombic space group Pbcn, a = 16.164(3), b = 10.749(2), c = 18.601 (3) Å, V = 3232(1) ų and Z = 8; 2, triclinic space group P1̄, a = 9.437(2), b = 15.424(3), c = 9.342(2) Å, α = 107.45(2), β = 91.92(1), γ = 82.68(1), V = 1287(1) ų and Z = 2. In the former structure, the dpk ligand did not undergo the metal promoted hydration reaction to yield a facial tridentate ligand. It binds the platinum in a bidentate fashion retaining the sp² hybridization around the carbonyl carbon. The conformational strain is relieved by distortion of the planar ligand through rotation of the pyridyl rings around the bonds connecting them to the carbonyl group to yield a non-planar ligand. In the second structure (bpp complex), the chelating pyrazine and pyridyl rings are coplanar and the non-ligating pyridyl ring is nearly perpendicular to them.