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

The pi electron charge ordering in (DI-DCNQI)(2)Ag with a 1/4-filled 1-d ba nd and the d electron charge ordering in deuterated (DMe-DCNQI)(2)Cu with t he pi-d hybridization have been characterized by C-13 NMR. The profile of t he ordering is quite different between the two systems, reflecting the diff erent driving force. The intersite Coulomb interaction between the pi-elect rons is considered to be crucial in the former case while the perfect charg e ordering found in the latter salt seems to invoke cooperative mechanism i ncluding the rr electron-lattice (Peierls) instability, dxy level-lattice i nstability and strong correlation in the Cu site.