Two types of charge ordering in DCNQI-metal complexes studied by 13C-NMR

The π electron charge ordering in (DI-DCNQI)2Ag with a 1/4-filled l-d band and the d electron charge ordering in deuterated (DMe-DCNQI)2Cu with the π-d hybridization have been characterized by 13C NMR. The profile of the ordering is quite different between the two systems, reflecting the different driving force. The intersite Coulomb interaction between the π-electrons is considered to be crucial in the former case while the perfect charge ordering found in the latter salt seems to invoke cooperative mechanism including the π electron-lattice (Peierls) instability, dry level-lattice instability and strong correlation in the Cu site.