Syntheses, Structures, and Physical Properties of Nickel Bis(dithiolene) Complexes Containing Tetrathiafulvalene (TTF) Units

To contribute to the development of single-component molecular metals, several nickel complexes with cyclohexeno-condensed or ethylenedioxy-substituted TTF (tetrathiafulvalene) dithiolate ligands, (R4N)n[Ni(chdt)2] [R = Me, n =
2 (1); R = nBu, n = 1 (2); n = 0 (3)] and (R4N)n[Ni(eodt)2] [R = Me, n = 2 (4); R = nBu, n = 1 (5); n = 0 (6)],
were prepared. X-ray structures were determined on the monoanionic species 2 and 5. The tetra-n-butylammonium
complex of the monoanionic [Ni(chdt)2] (2) with a 1:1 composition revealed that its magnetic susceptibility gave a
good agreement with the Bonner−Fisher model (J/kB = −28 K), which was derived from the one-dimensional
chains of anions with a regular interval. On the other hand, the magnetic susceptibility of the tetra-n-butylammonium
complex of the monoanionic [Ni(eodt)2] (5) showed the Curie−Weiss behavior (C = 0.376 K·emu·mol-1 and ϑ =
−4.6 K). Both of the monoanionic species 2 and 5 indicate that they belong to the S = 1/2 magnetic system and
have relatively large and anisotropic g-values, suggesting the contribution of the nickel 3d orbital. Electrical resistivity
measurements were performed on the compressed pellets of the neutral species 3 and 6. Fairly large conductivities
were obtained (σrt = 1−10 S·cm-1). In addition, despite the measurements on the compressed pellets of powder
samples, the neutral species 6 showed metallic behavior down to ca. 120 K and retained high conductivity even
at 0.6 K [σ(0.6 K)/σrt ≈ 1/30], suggesting the crystal to be essentially metallic down to very low temperature. The
electrical behavior and Pauli paramagnetism of 6 indicate the system to be a new single-component metal.