Electronic state of the organic salt (DI-DCNQI)2Ag, where DI-DCNQI is 2,5-diiodo-N,N'-dicyanoquinonediimine.

Abstract

${(\mathrm{D}\mathrm{I}\ensuremath{-}\mathrm{D}\mathrm{C}\mathrm{N}\mathrm{Q}\mathrm{I})}_{2}$Ag where DI-DCNQI is 2,5-diiodo-$N$, ${N}^{\ensuremath{'}}$-dicyanoquinonediimine has been investigated by electrical resistance, magnetic susceptibility, and $^{1}\mathrm{H}$ NMR measurements, and found to be nonmetallic with a charge gap of \ensuremath{\sim}490 K and with spin susceptibility showing localization of the $\ensuremath{\pi}$-electron spins. Antiferromagnetic ordering is evidenced at a low temperature. This is a first case of the electron antiferromagnet among the DCNQI-metal family in which the $\ensuremath{\pi}$ electrons on the DCNQI columns have an antiferromagnetic state. The nature of a Mott insulator demonstrates the importance of electronic correlation in the $\ensuremath{\pi}$ electrons in the DCNQI systems.