Synthesis and Platinum (II) Complexes of Different Polyazacyclophane Receptors

During the last years, research on coordination chemistry of platinum has aroused great interest due to their potential biological applications. Herein, we report the interaction of PtCI₄^2- with different polyazacyclophanes containing a pyridine unit as aromatic spacer. Formation of complexes has been studied by ¹H and ¹⁹⁵Pt NMR spectroscopy. Analysis of the recorded spectra of D₂O solutions containing L and PtCl₄^2- in a 1:1 molar ratio at acidic pH shows the evolution with time of the ¹H and ¹⁹⁵Pt signals. Different crystal structures have been solved by X-ray diffraction analysis. At acidic pHs, the metal ion is coordinated by the central amino group of the macrocyclic cavity and three chloride or bromide atoms, in a square planar geometry. Formation of [Pt(H₂L1)Br₃]Br (1) and [Pt(H₂L2)Br₃]Br (2) reveals the rapid substitution of chloride ligands in PtCl₄^2- by bromide ligands. However, as reveals the crystal structure obtained for [Pt^IVL3Br₂](PtBr₄)(H₂O) (4), at slightly higher pH values, the metal ion is coordinated through all nitrogen atoms of the macrocyclic cavity and an oxidation to Pt(IV) occurs.