Conductive copper salts of 2,5-disubstituted N,N′-dicyanobenzoquinonediimines (DCNQIs):: Structural and physical properties

Structural and physical properties of the Cu salts of a series of pi-acceptors N,N'-dicyanobenzoquinonediimines (DCNQIs) are described. The most notable feature of this system is that 3d electrons in Cu interact with p pi electrons in DCNQI near the Fermi level. This unique feature has provided a lot of interesting solid state properties: the Mott transition triggered by the Peierls transition, the pressure-induced metal-insulator transition, the metal-insulator-metal (reentrant) transition, the three-dimensional Fermi surface, the anomalous isotope effects, the antiferromagnetic transition, the weak ferromagnetism, and the electron mass enhancement. The aim of this account is to give an overview of this unique p pi-d system.