Spin solitons in halogen-bridged one-dimensional mixed-valence complexes, [M-II(en)(2)][(MBr2)-Br-IV(en)(2)](ClO4)(4) (M : Pt, Pd) studied by H-1 NMRand EPR

Temperature and Larmor frequency dependences of H-1 NMR spin-lattice relaxa tion time (T-1) in 1-D mixed-valence complexes [M(en)(2)][MBr2(en)(2)](ClO4 )(4) (M: Pt, Pd; en: ethylenediamine) were observed in the ranges 90-330 K and 15-60 MHz. EPR spectra observed for the Pd complex showed the presence of paramagnetic Pd-III sites of a temperature independent concentration of 10(-4) per Pd site, and a motional narrowing upon heating attributable to t hermally activated motions of these sites. The NMR T-1 data giving an omega (1/2) frequency dependence in the range 100-150 K were successfully analyse d by applying the Devreux's treatment of rapidly 1-D diffusing electron spi ns. Comparing the present results with the electrical conductivity data, th e diffusing paramagnetic spins could be explained by kink-type neutral soli tons analogous to the spin soliton model reported for trans-polyacetylene. Diffusion rates of 10(12)-10(13) and 10(13)-10(14) rad s(-1) were estimated in Pt and Pd complexes, respectively, below ca. 150 K. This diffusion in t he present 1-D structure complexes was shown to be much easier than that in [Pd(chxn)(2)][PdBr2(chxn)(2)]Br-4 (chxn: 1R,2R-cyclohexanediamine) with 2- D hydrogen bond networks.