PECULIARITIES OF THE ELECTRONIC-PROPERTIES OF THE KAPPA-PHASE STRUCTURES (BEDT-TTF)(2)CU(N(CN)(2))X WITH X=CL, BR, I

The structure of the title compounds is similar to other kappa-phase s tructures with respect to the checkerboard-like arrangement of the ET dimers (ET = BEDT-TTF) in the conducting planes, but different by the tilt alternation of these dimers in successive planes. The resulting i nequivalence of these planes tends to destabilize the metallic state w hich becomes extremely sensitive to changes in the S-S overlaps of nei ghbouring ET molecules. Such changes may result from anion substitutio n, lattice expansion, or also from ordering effects of the ethylene en d groups of the ET molecules. They lead to quite different electronic properties of the three isostructural compounds. We focus especially o n the strongly pressure-dependent properties of the Cl-compound, where a coexistence of magnetically ordered and superconducting states with rather spectacular superconducting reentrance effects is observed.