[MIII(dmit)2]--Coordinated MnIII Salen-Type Dimers (MIII ) NiIII, AuIII; dmit2- ) 1,3-Dithiol-2-thione-4,5-dithiolate): Design of Single-Component Conducting Single-Molecule Magnet-Based Materials
Résumé
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 P¯1 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. Hu¨ckel 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]2 2- 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.