Synthesis and Magnetic Properties of New Mono- and Binuclear Iron Complexes with Salicyloylhydrazono Dithiolane Ligand

Abstract

We report here experimental evidence for the formation in the solid state of a new binuclear Fe (III) 2(mu-OMe) 2(HL) 4 complex (H 2L is 2-salicyloylhydrazono-1,3-dithiolane). The isostructural Mn (III) 2(mu-OMe) 2(HL) 4 complex has provided the strongest ferromagnetic interaction value (J approximately 20 cm (-1)) between Mn (III) ions to date. The new iron binuclear compound presented in this study shows antiferromagnetic intramolecular coupling, which agrees with the theoretical study that we previously proposed. During our synthetic work, we also observed an unexpected spontaneous reduction of the new Fe (III)(HL) 2Cl,S complex to the new Fe (II)(H 2L) 2Cl 2 high-spin mononuclear complex. This process has been checked by cyclo-voltammetry as well as pseudosteady voltammetry.

Spontaneous Reduction of High‐Spin FeIII Complexes Supported by Benzoic Hydrazide Derivative Ligands

“…Nevertheless, a closely related phenomenon has recently been described by us, and this color change corresponds to a spontaneous reduction of Fe III to Fe II , as was unambiguously confirmed by electrochemical measurements as well as EPR studies (see below). [6] On this basis, it is very likely that the present color change arises from the conversion of complex 1a (Fe III , dark blue) to 1b, a Fe II light-yellow compound in DMF solution. Interestingly, this reduction appears to be reversible, as 1b may be rapidly converted back 1a by exposure to air.…”

“…The ligands HL (5) , HL (6) , and H 2 L (7) were prepared according to literature procedures. [10,11] …”

“…Complex 2a was prepared by direct reaction of HL (6) and FeCl 3 in DMF. Unfortunately, no suitable single crystals of 2a could be grown thus far despite numerous attempts; nevertheless, electrochemical measurements as well as EPR studies are strongly consistent with 2a consisting of a mononuclear Fe III complex with chelating L (6)-ligands, DMF and/or Cl in the direct coordination sphere of iron ion (vide infra and Experimental Section).…”

“…The solid-state molecular structure of compound 2b (Figure 2) was thus established by X-ray crystallographic studies, identifying 2b as a Fe II mononuclear species. In the latter complex, the metal center (Fe II located on the crystallographic inversion center) is surrounded by two neutral HL (6) ligands and two chloride atoms in a trans position to one another ( Figure 2). The overall structure of 2b appears to be very similar to that recently published by our group.…”

“…[6] This unexpected reduction was fully investigated by electrochemistry, EPR studies, magnetic measurements and solid-state molecular structure determination. Considering that closely related dinuclear compounds [7] can exhibit strong ferromagnetic coupling, such a spontaneous reduction phenomenon opens up new research opportunities, as recently pointed out by Wernsdorfer et al [8] Thus, provided this reduction process is understood and well controlled, such molecular complexes may offer the possibility to tune the magnetic coupling exchange by changing the spin state, especially if this can be induced by external stimuli.…”