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

H-1 and H-2 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)(2)NH2, D2N(CH2)(2)ND2 and H2N(CD2)(2)NH2 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.