[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

Abstract

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-Rsaltmen(2-) = N,N '-(1,1,2,2-tetramethylethylene)-bis(5-Rsalicylideneiminate), dmit(2-) = 1,3-dithiol-2-thione-4,5-dithiolate). These compounds crystallize in the same triclinic P1 space group (Z = 1) and have a similar molecular structure with a bridging array of [M-(dmit)-Mn-(O(Ph))(2)-Mn-(dmit)-M] and a packing feature where the respective sets of 1a/1b and 2a/2b are isomorphous. Intermolecular pi-pi/S...S contacts are observed between the coordinating [M(dmit)(2)](-) moieties to form zigzag stair-like columns along the a axis direction. Huckel 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 sigma(r.t.) = 7 x 10(-4) S x cm(-1) and E(a) = 182 meV for 1a and sigma(r.t.) = 1 x 10(-4) S x cm(-1) and E(a) = 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 (J(Mn...Mn)/k(B) = -2.85 K), inducing a long-range antiferromagnetic order at T(N) = 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.

Ferromagnetic Exchange Coupling in a Family of MnIII Salen-Type Schiff-Base Out-of-Plane Dimers

“…The obtained Arrhenius parameters for the Type-A, -B, and -D compounds are summarized in Table . These parameters are similar across the series and comparable to that of previously reported dimers. ,− Therefore, the dimers in this report exhibit SMM behavior regardless of their ligand substituents.…”

“…All compounds form an out-of-plane dimeric structure self-bridged by two phenolate oxygen atoms of the 5-Rsaltmen 2– ligands, producing a di-μ 2 -phenolate bridging motif with an inversion center between Mn III ions. This basic structural feature is identical to that observed in the previously reported [Mn 2 (saltmen) 2 ] 2+ family. ,,− , Each Mn III site has an axially elongated octahedral geometry (quasi-tetragonal geometry) as typically seen in Mn III high-spin complexes with Jahn–Teller distortion, in which the equatorial coordination sites are occupied by a N 2 O 2 atom set of the 5-Rsaltmen 2– tetradentate ligand with average bond distances of ⟨Mn–N⟩ av = 1.987 Å and ⟨Mn–O⟩ av = 1.884 Å, and the two elongated axial (Jahn–Teller axis) positions are occupied by the dimer-forming phenolate oxygen O1* with Mn–O1* = 2.3471(13)–3.7218(5) Å and the apical ligand X with ⟨Mn–X⟩ av = 2.179 Å. This bridging motif, especially the Mn–O1* bond distance and relevant angles related to a parallelogram consisting of Mn–O1–Mn*–O1*, is very important to interpret the intradimer magnetic properties of these compounds; this relationship is the main subject of this work (vide infra).…”

“…D Mn2 can be roughly estimated by extrapolation of the linear region of the magnetization curve to its expected saturation value M sat = gS T (here, g = 2.0 and S T = 4) . The obtained D Mn2 values fell in the narrow range of −1.53 to −1.89 K, similar to those for FM coupled Mn III salen-type dimers reported previously. ,,− , Sigmoidal magnetization curves were observed for 1 , 6 , 9 , 11 , 16 , 19 , and 21 – 23 . This characteristic feature originates from spin flip from an AFM ordered state caused by interdimer AFM interactions.…”

“…With the development of superparamagnetic nanosized clusters, called single-molecule magnets (SMMs), − and superparamagnetic isolated chains, known as single-chain magnets (SCMs), − a class of Mn III salen-type out-of-plane dimer complexes (salen 2– is N , N ′-(ethylene)­bis­(salicylideneiminate)) have been attracting much attention. This is because superparamagnetic clusters not only have potential to be SMMs with a ferromagnetic (FM) S T = 4 ground state but also act as extendible uniaxial anisotropic building blocks for the design of SCMs, as well as their monomer forms. − In fact, the unverified knowledge of “the invariable S T = 4 magnetic nature of Mn III salen-type dimers” provided a strategy to produce the first FM-type SCMs, [Mn 2 (saltmen) 2 Ni­(pao) 2 (L 1 ) 2 ]­(A) 2 (saltmen 2– = N , N ′-(1,1,2,2-tetramethylethylene)­bis­(salicylideneiminate); pao – = pyridine-2-aldoximate; L 1 = 4-picoline, 4- t -butylpyridine, N -methylimidazole; A – = ClO 4 – , BF 4 – , PF 6 – , ReO 4 – ), and the related SCMs. − However, SMM behavior in [Mn 2 (saltmen) 2 ] 2+ dimers with strong uniaxial anisotropy was eventually proved in [Mn 2 (saltmen) 2 (ReO 4 ) 2 ] and a few derivatives. − Therefore, we decided to explore the variation of FM coupling in the dimers induced by changing the R substitution of the saltmen and axial X ligands on the Mn III center. The exchange coupling in the Mn III –(O ph ) 2 –Mn III bridge of linear tetranuclear complexes [Mn­(5-Rsaltmen)­Ni­(pao) (bpy) 2 ] 2 (ClO 4 ) 4 (5-Rsaltmen = N , N ′-(1,1,2,2-tetramethylethylene)­bis­(5-Rsalicylideneiminate); bpy = 2,2′-bipyridine) depended on the R substituent (R = H, Cl, Br, and MeO) .…”

Electroactive Benzothiazole Hydrazones and Their [Mo6O19]2− Derivatives: Promising Building Blocks for Conducting Molecular Materials

“…[11] Among these various materials, magnetic molecular conductors have been extensively studied. [5,12] Although a wide diversity of anions has been used to provide magnetic properties, the conducting component often relies on radical cations derived from the tetrachalcogenofulvalenes, and more scarcely on the relatively unstable dithiadiazafulvalene. [13] Inspired by the pioneering works of Hünig et al [14] and then Wheland, [15] some of us have started to explore the chemistry of 2,2'-azino-bis(N-alkylbenzothiazole) derivatives as an alternative donor.…”