Conformation of 2-Aminomethylpyrrolidine and 2-Aminomethylpiperidine in Ternary Platinum(II) Complexes: Regulation of Conformation of the Diamine by the Coexisting Ligand

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Square-planar complexes with the formula [Pt(L₂)(L₁)](X)₂·nH₂O, where L₁ is S-2-aminomethylpyrrolidine (S-pyrda) or 2-aminomethylpiperidine (pipda) and L₂ is diammine (X=Cl), cyclobutane-1,1-dicarboxylato (cbdca) (X=none), 2,2′-bipyridine (bpy) (X=NO₃), or 1,10-phenanthroline (phen) (X=Cl), were prepared and the nature of the coordination of L₁ was examined by ¹H-NMR spectroscopy and X-ray crystallography. These 2-aminomethylazacycloalkane derivatives form five-membered chelate rings condensed with an azacycloalkane ring in cis- or trans-configurations. The ¹H-NMR spectrum of complexes with S-pyrda as L₁ were consistent with cis-condensed rings in an S(N) conformation with any of L₂ group. However, ¹H-NMR spectra of the complexes with pipda as L₁ indicated trans-fused successive rings for the diammine and cbdca as L₂, but spectra for bpy and phen as L₂ were consistent with a conformation having cis-fused successive rings. X-Ray crystallography data for the two complexes with pipda as L₁ and cbdca (1) and bpy (2) as L₂ confirms the different coordination behavior in the solid state.