Delocalization of Spin Projection in Weak Exchange Linear Chains, Evidenced by Multi-Frequency Hf-Epr Spectroscopy.

High-field electron paramagnetic resonance (HF-EPR) spectroscopy was used to investigate the unusual temperature and frequency dependence of the powder spectrum of the Gd(HBPz(3))(2) tropolonate complex (GdTrp). A new type of H/T effect is evidenced. This effect is interpreted in terms of the formation of spin projection states delocalized and quasi delocalized along linear chains of Gd 31 ions in high magnetic fields due to the competition between the weak dipole and exchange spin-spin interaction and the particular structure of the molecular complex. The number of ions in the chain depends strongly on the orientation of the magnetic field and on the relaxation processes.