[M^III(dmit)₂]⁻-Coordinated Mn^III Salen-Type Dimers (M^III = Ni^III, Au^III; dmit²⁻ = 1,3-Dithiol-2-thione-4,5-dithiolate): Design of Single-Component Conducting Single-Molecule Magnet-Based Materials

Four linear-type tetranuclear complexes, [Mn(5-Rsaltmen){M(dmit)2}]2 (R = MeO, M = Ni, 1a; M = Au, 1b; R = Me, M = Ni, 2a; M = Au, 2b), were synthesized and structurally characterized (5-Rsaltmen2− = N,N ′-(1,1,2,2-tetramethylethylene)-bis(5-Rsalicylideneiminate), dmit2− = 1,3-dithiol-2-thione-4,5-dithiolate). These compounds crystallize in the same triclinic P1̅ space group (Z = 1) and have a similar molecular structure with a bridging array of [M−(dmit)−Mn−(OPh)2−Mn−(dmit)−M] and a packing feature where the respective sets of 1a/1b and 2a/2b are isomorphous. Intermolecular π−π/S···S contacts are observed between the coordinating [M(dmit)2]− moieties to form zigzag stair-like columns along the a axis direction. Hückel calculations revealed a strong intermolecular dimerization within the [Ni(dmit)2]− column that makes them magnetically silent even at room temperature. Nevertheless, 1a and 2a with M = Ni behave as semiconductors with σr.t. = 7 × 10−4 S·cm−1 and Ea = 182 meV for 1a and σr.t. = 1 × 10−4 S·cm−1 and Ea = 292 meV for 2a, while 1b and 2b with M = Au are insulators. As a result of the strong dimerization of the [Ni(dmit)2]− anions, the magnetic properties of 1a are essentially identical to those of 1b and 2b, which can be described as isolated Mn(III) dimers, acting as single-molecule magnets (SMM). Meanwhile, the magnetic properties of 2a are dominated by the intermolecular Mn···Mn antiferromagnetic interactions via the singlet [Ni(dmit)2]22− dimer (JMn···Mn/kB = −2.85 K), inducing a long-range antiferromagnetic order at TN = 6.4 K. The present systems are unique materials made of neutral single-component complexes that exhibit two major solid-state properties, that is, electrical conductivity and magnetism, varied as semiconductor/SMM for 1a, insulator/SMM for 1b and 2b, and semiconductor/antiferromagnet for 2a by tuning metal center and partial structural modification.