Possibility of Dielectric Material: Magnetic Resonance Study of Oxo-Bridged Dinuclear Ruthenium Mixed-Valence Complex

Solid-state broad line H-1-NMR (nuclear magnetic resonance) and ESR (electron spin resonance) were performed for an oxo-bridged dinuclear ruthenium [RuORu](5+) (Ru3.5+ORu3.5+) mixed-valence complex. The H-1-NMR spin-lattice relaxation rate T-1(-1) was significantly enhanced, to below 100 K with a peak at approximately 33 K. The T-1(-1) peak temperature was frequency-independent, indicating that this anomaly is a possible phase transition. Below approximately 40 K, an abrupt decrease of H-1-NMR spin-spin relaxation time T-2 provides evidence of the appearance of inequivalent H-1-sites (sudden decrease in symmetry). ESR spectra suddenly disappeared above 35 K. The electronic properties and possible charge ordering (Ru3+ORu4+) states in this mixed-valence compound are discussed from a microscopic point of view.