ESR observation of averaged-valence and charge-density-wave states in quasi-one-dimensional halogen-bridged binuclear metal complexes

Abstract Electron spin resonance (ESR) measurements have been performed on quasi-one-dimensional iodo-bridged binuclear metal complexes (MMX-chain compounds) A 4 [Pt 2 (pop) 4 I]· n H 2 O (A=Li, Na, K, Rb, Cs; pop=P 2 O 5 H 2 2− ). ESR signals show a clear distinction between averaged-valence (AV) and charge-density-wave (CDW) states predicted from optical studies in these complexes. While spin susceptibility χ of the CDW states shows Curie-like behavior, χ of the AV states shows a crossover from Curie to weakly temperature-dependent behavior at high temperatures, characteristic of the Heisenberg antiferromagnetic chains. The Na ( n =2) and Cs ( n =0) compounds are typical ones exhibiting the characters of the AV and CDW states, respectively. Furthermore, a signal around g =4 is observed, which is more remarkable in the CDW states, suggesting the formation of the state with S =1 or higher spin values as a defect state with a continuous fine-structure parameter distribution.