Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

© 2015 AIP Publishing LLC. The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300K and has antiferromagnetic ordering below 10K. Mössbauer spectroscopy at 5K confirms the presence of magnetic ordering in the dendrimeric iron complex

Structural, magnetic and dynamic characterization of liquid crystalline iron(III) Schiff base complexes with asymmetric ligands

The iron(III) complexes that were formed by coordination of the Fe III ion with the asymmetric tridentate liquid crystalline Schiff base ligand (L), the water molecules and the different counterions [PF 6 - (1), NO3 - (2), and Cl- (3)] were studied by electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy demonstrated that each of the complexes investigated consists of two types of iron centers: S = 1/2 low-spin (LS) and S = 5/2 high-spin (HS). LS iron complexes 2, 3 and LS complex 1 in the temperature range 4.2-250 K have a (dxz,dyz)4(dxy)1 ground state. Interesting features werefound for the monocationic FeIII complex 1, [Fe(L)X(H2O)2]+X-, with X = PF6 - as the counterion. The LS and HS iron centers of 1 are coupled together antiferromagnetically and form a dimer structure by means of the water molecules and the PF6 - counterion. The second-type of LS and HS centers that are visible by means of EPR spectroscopy were best observed in the liquid crystalline (387-405 K) phase. The monitoring and the simulation of the EPR spectra enabled us to trace the dynamics of changing the number of the second-type of LS centers with respect to the first-type of LS centers. The observed dynamic process is characterized by the enthalpy value ΔH = 27.9 kJ/mol, which was caused by reorientation of the PF6 - counterion. Calculation of the observed g values for the second-type of LS complex 1 indicated that, in this case, the (d xy)2(dxz,dyz)3 ground state is stabilized. The conversion between the electron (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 configurations was found to be temperature dependent and was detected in the same material for the first time in iron complexes. We synthesized a novel compound, namely a liquid crystalline iron(III) Schiff base complex with the asymmetric ligand [Fe(L)X(H2O)2]+X-, where X = PF 6 - is the counterion. This compound has a labilelow-spin electron configuration that switches between the (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 ground states and is temperature-dependent. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

High-spin Fe(III) Schiff based complexes with photoactive ligands. Synthesis, EPR study and magnetic properties

© 2018 Elsevier Ltd A series of three novel Fe(III) compounds of the formula [FeL2]X (where X = Cl− (1), PF6− (2), NO3– (3), and L is a photoactive ligand, (4)-4-(((2-(ethylamino)ethyl)imino)methyl)-3-hydroxyphenyl 4-bromobenzoate) was synthesized and studied by means of electron paramagnetic resonance (EPR) and pulsed laser irradiation. The Fe3+ ions in these compounds are in a high-spin state. A thorough analysis of the EPR data suggests that compounds 1 and 2 undergo an order–disorder ferroelectric phase transition, and below the phase transition temperature (Tc = 100 and 200 K for compounds 1 and 2, respectively) a nonzero average electric dipole moment appears. To get an insight into molecular structure of Fe3+ ions and their supramolecular organization in low-temperature (LT) and high-temperature (HT) phases of compounds 1 and 2, a series of density functional theory calculations was performed. On the basis of our findings, the LT- and HT-phase structures were proposed for these compounds. It was also shown that, whereas the chloride and hexafluorophosphate anions are able to form a network of hydrogen bonds between the [FeL2]X units (ionic pairs), which enable an electric dipole ordering in the sample, the nitrate anions, in contrast, tend to form hydrogen bonds inside the ionic pair. This conclusion is evidenced by the observed EPR spectra, which are different for compound 3 and are not indicative of the existence of an order–disorder ferroelectric phase transition. The EPR data obtained upon irradiation of compound 1 show that photoexcitation in the UV region at 5 K destroys hydrogen bonds and converts cationic complexes into ligand-to-metal charge transfer (LMCT) states, in which the iron is ferrous, and the unpaired electron is located on the salicylidene moieties. The LMCT states decay back to the ferric one, and ferric complexes further form the most stable (LT) phase structure

STepwise Magnetic Behavior of the Liquid Crystal Iron(Iii) Complex

EPR and Mossbauer spectroscopy is used to study a new liquid crystal complex of iron(III) with a Schiff base: 4,4'S-dodecyloxybenzoyloxybenzoyl-4- oxysalicylidene-2-aminopyridine with a PF6'{ counterion. It is shown that Fe(III) ions exist only in the high-spin (HS, S = 5/2) state. It is found that under the influence of temperature the system demonstrates the stepwise behavior of the product of the integrated intensity of EPR lines (I ) and temperature (proportional to "where" is the magnetic susceptibility) with an inflection point at "80 K. Above 80 K a new EPR spectrum is detected due to the excited S = 2 state and the formation of dimeric molecules (through oxygen bridges) with a strong intramolecular antiferromagnetic exchange interaction J1 = 162.1 cm-V1. Below 80 K iron(III) complexes are organized in 1D chains where the exchange value J2 = 2.1 cm-V1. At 80 K there is a structural phase transition in the system: the transition from a 1D chain organization of HS Fe(III) centers to dimeric molecules. Based on quantum chemical calculations a model of the binuclear iron(III) complex is proposed. Copyright © 2013 by N. E. Domracheva, V. E. Vorob'eva, A. V. Pyataev, R. A. Manapov, E. M. Zueva, M. S. Gruzdev, U. V. Chervonova

Counterion effect on the spin-transition properties of the second generation iron(III) dendrimeric complexes

© 2017 Elsevier B.V.The magnetic properties and the influence of counterions on the spin crossover properties of two novel Fe(III) dendrimeric complexes of the second generation, namely [Fe(L)2]+X−, where L = 3,5-di(3,4,5-tris(tetradecyloxy)benzoyloxy)benzoyl-4-oxy-salicylidene-N’-ethyl-N-ethylenediamine X = Cl− (1), ClO4− (2), have been studied for the first time by magnetic susceptibility measurements and electron paramagnetic resonance (EPR) method in a wide (4.2–300 K) temperature range. EPR results showed that compound 1 contains about 98% of high-spin (HS, S = 5/2) and ∼2% of low-spin (LS, S = 1/2) Fe(III) centers, and undergoes an antiferromagnetic ordering below 7 K. The EPR integrated intensity of a broad line (g ≈ 2), corresponding to the HS iron(III) centers, passes through a broad maximum at Tmax ≈ 100 K, which is indicative of short-range correlation effects. The anomalous broadening of this EPR line at low temperatures with the critical exponent β = 1.5 upon approaching the long-range ordering transition (TNEPR = 7 K) from above indicates the quasi-two-dimensional antiferromagnetic nature of magnetism in complex 1. The spin-crossover effect is completely suppressed in compound 1. The complex with ClO4− counterion demonstrates a different magnetic behavior. EPR data showed that compound 2 contains about 77% of LS and ∼23% of HS Fe(III) centers at TNEPR = 10.2 K. It displays a partial spin crossover (S = 5/2 ↔ 1/2) above 150 K and undergoes the antiferromagnetic ordering below 10.2 K. The obtained results and the results of DFT calculations allowed us to conclude that a bilayered packing with a chain structure of Fe(III) centers in ionic bilayers is formed in compound 1, whereas a dimeric structure of Fe(III) centers is formed in compound 2. Thus, the ability of the counterion to form an effective network of hydrogen bonds and its size define the packing motif of the [Fe(L)2]+ complexes. Therefore, the replacing of the counterion has a significant impact on the magnetic properties of the compound

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

© 2015 Elsevier B.V. All rights reserved. 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 1/2) 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

Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

© 2015 AIP Publishing LLC. The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300K and has antiferromagnetic ordering below 10K. Mössbauer spectroscopy at 5K confirms the presence of magnetic ordering in the dendrimeric iron complex

Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

© 2015 AIP Publishing LLC. The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300K and has antiferromagnetic ordering below 10K. Mössbauer spectroscopy at 5K confirms the presence of magnetic ordering in the dendrimeric iron complex

Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

© 2015 AIP Publishing LLC. The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300K and has antiferromagnetic ordering below 10K. Mössbauer spectroscopy at 5K confirms the presence of magnetic ordering in the dendrimeric iron complex

Structural, magnetic and dynamic characterization of liquid crystalline iron(III) Schiff base complexes with asymmetric ligands

The iron(III) complexes that were formed by coordination of the Fe III ion with the asymmetric tridentate liquid crystalline Schiff base ligand (L), the water molecules and the different counterions [PF 6 - (1), NO3 - (2), and Cl- (3)] were studied by electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy demonstrated that each of the complexes investigated consists of two types of iron centers: S = 1/2 low-spin (LS) and S = 5/2 high-spin (HS). LS iron complexes 2, 3 and LS complex 1 in the temperature range 4.2-250 K have a (dxz,dyz)4(dxy)1 ground state. Interesting features werefound for the monocationic FeIII complex 1, [Fe(L)X(H2O)2]+X-, with X = PF6 - as the counterion. The LS and HS iron centers of 1 are coupled together antiferromagnetically and form a dimer structure by means of the water molecules and the PF6 - counterion. The second-type of LS and HS centers that are visible by means of EPR spectroscopy were best observed in the liquid crystalline (387-405 K) phase. The monitoring and the simulation of the EPR spectra enabled us to trace the dynamics of changing the number of the second-type of LS centers with respect to the first-type of LS centers. The observed dynamic process is characterized by the enthalpy value ΔH = 27.9 kJ/mol, which was caused by reorientation of the PF6 - counterion. Calculation of the observed g values for the second-type of LS complex 1 indicated that, in this case, the (d xy)2(dxz,dyz)3 ground state is stabilized. The conversion between the electron (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 configurations was found to be temperature dependent and was detected in the same material for the first time in iron complexes. We synthesized a novel compound, namely a liquid crystalline iron(III) Schiff base complex with the asymmetric ligand [Fe(L)X(H2O)2]+X-, where X = PF 6 - is the counterion. This compound has a labilelow-spin electron configuration that switches between the (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 ground states and is temperature-dependent. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim