The crystal structure of a high-pressure superconductor [(CH3)(2)(C2H5)(2)N] [Pd(dmit)(2)](2) at 10 kbar was determined by diamond-anvil cell to clarify the origin of unique P-T phase diagram of this system, The doubling of lattice spacing along the Pd(dmit)(2) stack was observed, The novel neutral nickel complex with the extended TTF dithiolato ligand, trimethylenedithiotetra-thiafulvalenedithiolate[tmdt(2-) = (S6C9H6)(2-)], have been synthesized, The single crystal of [Ni(tmdt)(2)] was metallic down to 0.6 K. The crystal structure and electronic band structure calculation showed [Ni(tmdt)(2)] is the first single-component molecular metal with three-dimensional Fermi surfaces.