Temperature and Larmor frequency dependences of 1H NMR spin-lattice relaxation time (T1) 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 PdIII sites of a temperature independent concentration of 10-4 per Pd site, and a motional narrowing upon heating attributable to thermally activated motions of these sites. The NMR T1 data giving an ω1/2 frequency dependence in the range 100-150 K were successfully analysed by applying the Devreux's treatment of rapidly 1-D diffusing electron spins. Comparing the present results with the electrical conductivity data, the diffusing paramagnetic spins could be explained by kink-type neutral solitons analogous to the spin soliton model reported for trans-polyacetylene. Diffusion rates of 1012-1013 and 1013-1014 rad s-1 were estimated in Pt and Pd complexes, respectively, below ca. 150 K. This diffusion in the present 1-D structure complexes was shown to be much easier than that in [Pd(chxn)2][PdBr2(chxn)2]Br4 (chxn: 1R,2R-cyclohexanediamine) with 2-D hydrogen bond networks.
|Number of pages||5|
|Journal||Journal of the Chemical Society - Faraday Transactions|
|Publication status||Published - 1998 Jan 1|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry