One-dimensional spin dynamics in a halogen-bridged mixed-valence palladium (II), (IV) complex studied by ¹H NMR

Abstract

The ¹H NMR spin—lattice relaxation time T₁ of [Pd(chxn)₂][PdBr₂(chxn) ₂]Br₄(chxn = 1R,2R-cyclohexanediamine) in the solid state was measured between 90 K and room temperature at Larmor frequencies of 10–60 MHz. The presence of thermally activated diffusive spins formed on paramagnetic Pd^III sites along the halogen-bridged 1D chain was revealed from the Larmor frequency dependence of T¹. The diffusion rates were estimated to be 2 × 10¹³, 9 × 10¹¹ and 6 × 10¹⁰ rad s⁻¹ at 303, 198 and 125 K, respectively. The rate observed around room temperature showed an Arrhenius-type temperature dependence with an activation energy of ≈1700 K. It is shown that the diffusive spin is delocalized over several Pd sites. The observed spin motion is attributable to the neutral soliton by referring to the electrical conductivity data.