From an S_T = 3 Single-Molecule Magnet to Diamagnetic Ground State Depending on the Molecular Packing of Mn^IIIsalen-type Dimers Decorated by N,N‘-Dicyano-1,4-naphthoquinonediiminate Radicals

Abstract

Two manganese(III) tetradentate Schiff-base dimers to which N,N'-dicyano-1,4-naphthoquinonediiminate (DCNNQI) radicals are attached have been selectively synthesized by varying the solvents used in the reactions: [Mn2(5-MeOsaltmen)2(DCNNQI)2].MeOH (1) and [Mn2(5-MeOsaltmen)(2)(DCNNQI)(2)] x 2CH2Cl2.2CH3CN (2) [5-MeOsaltmen2- = N,N'-(1,1,2,2-tetramethylethylene)bis(5-methoxysalicylideneiminate)]. These two complexes share the same molecular core, [(DCNNQI.-)-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)], where -(O)2- is a biphenolate bridge in the out-of-plane dimerized [Mn(2)(5-MeOsaltmen)2]2+ moiety. However, their packing arrangements are completely different. Whereas complex 1 is found to be relatively isolated, strong intermolecular dimerization of the DCNNQI moieties (with the nearest contact being approximately 3.0 A) is observed in 2, forming a one-dimensional chain of [-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)2-](infinity). The magnetic susceptibility of 1 can be modeled with an [S = 1/2, 2, 2, 1/2] four-spin system including strong antiferromagnetic Mn(III)/DCNNQI radical coupling (J(Mn/rad)/kB = -23 K) and ferromagnetic Mn(III)/Mn(III) coupling through the biphenolate bridge (J(Mn/Mn)/kB = +2.0 K). These interactions lead to an ST = 3 ground state that possesses significant uniaxial anisotropy (D(S=3)/kB = -2.1 K). Low-temperature ac and dc magnetic data of 1 reveal its single-molecule magnet behavior with quantum tunneling of the magnetization. By contrast, 2 possesses the diamagnetic ground state induced by dominating Mn(III)-Mn(III) antiferromagnetic interactions mediated by the diamagnetic DCNNQI dimers and/or pi-pi contact along the b axis.

Magnetic assemblies based on Mn(III) salen analogues

“…The compounds noted hereafter are not heterometal assemblies, but are closely related to the above tetranuclear compounds. The present compounds are [Mn III (5-MeOsaltmen)(DCNNQI)] 2 ·MeOH and [Mn III (5-MeOsaltmen)(DCNNQI)] 2 ·2CH 2 Cl 2 ·2CH 3 CN, which are decorated by a monoanionic organic radial DCNNQI molecule [133]. The bridging scheme is [Rad Mn III (O Ph ) 2 Mn III Rad] (Fig.…”

Two-dimensional grid structure based on dimeric manganese(III) tetradentate Schiff-base: Synthesis, structure and magnetic properties

“…Its out-of-plane dimeric form (S = 4) is an even better building block for the design of magnetic molecules or 1D assemblies. Approximately twenty dimeric manganese(III) compounds with salen type ligands have been reported up to date [3][4][5]. Several of them show slow relaxation of the magnetization due to the intrinsic property of individual molecules with the combined effect of uniaxial anisotropy (D) and the high-spin ground state (S T = 4) [3,4].…”

“…Approximately twenty dimeric manganese(III) compounds with salen type ligands have been reported up to date [3][4][5]. Several of them show slow relaxation of the magnetization due to the intrinsic property of individual molecules with the combined effect of uniaxial anisotropy (D) and the high-spin ground state (S T = 4) [3,4]. However, most of the reported dimeric Mn(III) salen type Schiff-base are simple dimeric units with various apical ligands [5].…”

“…Herein, we reported the synthesis, crystal structure, and magnetic properties of an unique 2D grid extended structure based on dimeric Mn(III) salen Schiff-base: {[Mn 4 (salen) 4 ClO 4 ) precursors adopt an out-of plane dimeric geometry. And each succinic acid bridged four dimers into a 2D network containing 30-membered cyclic centrosymmetrical polygonal grids.…”

Hetero-bimetallic yttrium(III)–rhenium(V)(salen) tetranuclear complex: Synthesis and crystal structure

“…Tetradentate bis(salicylidenamine) Rhenium compounds were also developed for catalytic applications like transfer reactions of oxygen atom [3,[8][9][10][11]. Recently, Schiff-base manganese complexes were used to obtain polynuclear molecules [12] and one-dimensional compounds which present a slow relaxation of the magnetization [13,14]. To our knowledge, no examples of Schiff-base technetium or rhenium complexes were reported to design such materials.…”