Magnetic properties of novel dendrimeric spin crossover iron(III) complex

Highlight•Dynamical spin clusters (nano-regions with antiferromagnetically correlated spins) have been found in the paramagnetic phase.•25% of the Fe(III) molecules are involved in the partial spin crossover (S=5/2⇔1/2S=5/2⇔1/2) above 160 K.•Antiferromagnetic ordering in the compound is observed below 10 K.

The synthesis and magnetic properties of novel dendrimeric spin crossover Fe(III) complex of formula [Fe(L)2]+PF6−, where L = 3,5-di(3,4,5-tris(tetradecyloxy)benzoyloxy)benzoyl-4-oxy-salicylidene-N′-ethyl-N-ethylenediamine have been studied for the first time by magnetic susceptibility, Electron Paramagnetic Resonance (EPR) and Mössbauer spectroscopy in the wide (2–300 K) temperature range. EPR showed that the compound is magnetically inhomogeneous, consists of two magnetic sub-lattices, displays a partial spin crossover (S=5/2⇔1/2S=5/2⇔1/2) of ∼25% of the Fe(III) molecules above 160 K and undergoes the antiferromagnetic (AF) ordering below 10 K. High-spin (HS, S = 5/2) Fe(III) centers with weakly distorted octahedral environment most probably form chains in layers. The dimeric molecules, formed from low-spin (LS, S = 1/2) centers and HS centers with strongly distorted octahedral environment are likely located between the layers and are involved in the spin crossover. EPR has shown the presence of AF dynamical spin clusters in the high temperature (70–300 K) range, which are visible in the short time scale (10−10 s) and could not be registered in the static magnetic measurements. Mössbauer spectra demonstrated in a paramagnetic state of the compound a quadrupole doublet with average isomer shift of 0.35 mm/s and splitting 0.72 mm/s corresponding to HS Fe(III) centers. Below 60 K, the spectra displayed the appearance of magnetic hyperfine structure, whose relaxation nature testifies the collective spin flips of small clusters in the material. Mössbauer spectroscopy confirmed the existence of AF ordering in the Fe(III) dendrimeric complex at 5 K.

Graphical abstractThe new spin-crossover dendrimeric iron(III) complex exhibiting mesogenic properties was studied by EPR, DC magnetic susceptibility and Mössbauer spectroscopy. EPR showed that the compound is magnetically inhomogeneous, consists of two magnetic sub-lattices, displays a partial spin crossover (S=5/2⇔1/2S=5/2⇔1/2) of ∼25% of the Fe(III) molecules above 160 K and undergoes the antiferromagnetic (AF) ordering below 10 K. EPR also found the presence of the dynamical spin clusters (nano-regions with antiferromagnetically correlated spins) in the paramagnetic phase. Mössbauer spectroscopy is fully confirmed the EPR results. Below 60 K, the Mössbauer spectra displayed the appearance of magnetic hyperfine structure, whose relaxation nature testifies the collective spin flips of small clusters in the material. The existence of AF ordering in the Fe(III) dendrimeric complex found at 5 K.Figure optionsDownload full-size imageDownload as PowerPoint slide