Rare-Earth Elements in Molecular Conductors: Crystal and Electronic Structures

Novel molecular metal salts comprising an organic donor 2,5-bis(1, 3-dithiol-2-ylidene)1,3,4,6- tetrathiapentalene (BDT-TTP) and lanthanide nitrato complex anions [M(NO3)y]-(y-3) were synthesized as the composition (BDT-TTP)x[M(NO3)y]. Attempts on X-ray crystal structure analyses gave rise to a detection of two polymorphs. One of the polymorph, which had a composition of (BDT-TTP)5[M(NO3)5] for M= Nd, Sm, Eu and Gd, was analyzed in detail. Five crystallographically independent BDT-TTP molecules were stacked face-to-face to form a pentad, which was jointed one after another by crystallographic inversion centers into a one-dimensional column. The calculated overlap integrals of the highest occupied molecular orbitals revealed that not only intracolumnar orbital overlaps but also transverse intermolecular interactions were important in the electronic band formation. Consequently, the system has two-dimensional Fermi surfaces that explain the stable metallic states. Magnetic measurements on the four salts, with M= Nd, Sm, Eu and Gd, showed Curie paramagnetic moments on rare-earth ions which were superimposed on the Pauli paramagnetism of metallic pielectrons. Especially, the magnetic susceptibility of the isolated Eu3+ ion was written using Curie term and extremely large Van Vleck term.