Low-energy spin dynamics in the [YPc2]0 S=1/2 antiferromagnetic chain

1H nuclear magnetic resonance (NMR) measurements in [YPc2]0, an organic compound formed by radicals stacking along chains, are presented. The temperature dependence of the macroscopic susceptibility of the NMR shift and of the spin-lattice relaxation rate 1/T1 indicate that the unpaired electron spins are not delocalized but rather form a S=1/2 antiferromagnetic chain. The exchange couplings estimated from those measurements are all in quantitative agreement. The low-energy spin dynamics can be described in terms of diffusive processes and the temperature dependence of the corresponding diffusion constant suggests that a spin gap at ~1 K might be present in this compound.