Molecular motions and phase transitions in halogen-bridged one-dimensional complexes [Pt(en)2][PtX2(en)2](ClO4)4 (X: I, Br)

Abstract

¹H and ²H NMR and thermal measurements were performed on crystalline [Pt(en)₂][PtI₂(en)₂](ClO₄)₄ in which protonated and partially deuterated ethylenediamines H₂N(CH₂)₂NH₂, D₂N(CH₂)₂ND₂ and H₂N(CD₂)₂NH₂ were used as the ligand “en”. A metastable crystalline phase of [Pt(en)₂][PtBr₂(en)₂](ClO₄)₄ with conformational disorder of the en chelate rings was shown to have a different phase transition at ca. 380 K to the stable crystalline form of the ordered structure. NMR spectra and relaxation times showed that the distribution of the en conformation is not static but dynamic in both I and Br complexes where a puckering motion of en chelate rings was shown to take place between asymmetric potential wells.