FeIII Ions Research Articles

Effect of Heteroatoms on Field-Induced Slow Magnetic Relaxation of Mononuclear FeIII ( S = 5/2) Ions within Polyoxometalates.

In this paper, the synthesis and magnetic properties of mononuclear FeIII-containing polyoxometalates (POMs) with different types of heteroatoms, TBA7H10[(A-α-XW9O34)2Fe] (IIX, X = Ge, Si; TBA = tetra- n-butylammonium), are reported. In these POMs, mononuclear highly distorted six-coordinate octahedral [FeO6]9- units are sandwiched by two trivacant lacunary units [A-α-XW9O34]10- (X = Ge, Si). These POMs exhibit field-induced slow magnetic relaxation based on the single high-spin FeIII magnetic center ( S = 5/2). Combining experiment and ab initio calculations, we investigated the effect of heteroatoms of the lacunary units on the field-induced slow magnetic relaxation of these POMs. By changing the heteroatoms from Si (IISi) to Ge (IIGe), the coordination geometry around the FeIII ion is mildly changed. Concretely, the axial Fe-O bond length in IIGe is shortened compared with that in IISi, and consequently the distortion of the [FeO6]9- unit in IIGe from the ideal octahedral coordination geometry becomes larger than that in IISi. The effective demagnetization barrier of IIGe (11.4 K) is slightly larger than that of IISi (9.2 K). Multireference ab initio calculations predict zero-field splitting parameters in good agreement with experiment. Although the differences in the coordination geometries and magnetic properties of IIGe and IISi are quite small, ab initio calculations indicate subtle changes in the magnetic anisotropy which are in line with the observed magnetic relaxation properties.

Synthesis, characterization and X-ray crystal structure of an iron(III) complex of a tripodal pyridoxal Schiff base ligand: effects of positional disorder on its magnetic properties

The synthesis and characterization of fac-{tris[(E)-5-(hydroxymethyl)-2-methyl-4-((methylimino-κN)methyl)pyridin-3-olato-κO]amine}iron(III) 7.5-hydrate is described, together with its crystal structure at 95 K. The FeIII ion is six-coordinated in a trigonally distorted octahedral configuration with the hexadentate tripodal pyridoxal Schiff base ligand. A positional disorder of the pyridoxal hydroxymethyl group is identified, which partly undergoes a cyclization forming a five-membered ring with the imine moiety. The two configurations occur in the ratio 79.5:20.5. In the crystal, the hydrogen bonds and π–π stacking interactions expand the mononuclear units into 2D sheets which are further stabilized by a system of hydrogen bonds to the 3D supramolecular network. The magnetic susceptibility data and EPR measurements indicate that the octahedral Fe(III) centers exist as a mixture of low- and high-spin forms within the temperature range 2–300 K. The presence of a mixture of the majority high-spin and the minority low-spin components showing a spin transition is proposed. The effect of zero-field splitting on magnetic properties is discussed. EPR spectra at X-band display signals of a high-spin Fe(III) complex of the rhombohedral symmetry with the zero-field splitting parameters E/D ratio approximately 1/3, along with the signals of a low-spin Fe(III) complex. Temperature dependence of the EPR spectra revealed a bend temperature T ≈ 88 K attributed to spin transition of the minority Fe(III) centers. The thermal stability of the compound was investigated by (TG, DTG, DTA) techniques. New iron(III) complex with tripodal pyridoxal Schiff base ligand was prepared. Single-crystal XRD data revealed a positional disorder of a side hydroxymethyl group. The magnetic data were analysed using the spin Hamiltonian including the ZFS term. EPR measurements at X-band confirmed magnetic anisotropy of the complex. Thermal stability of the complex was investigated by (TG, DTG, DTA) techniques.

A New Family of Heterometallic LnIII[12-MCFeIIIN(shi)-4] Complexes: Syntheses, Structures and Magnetic Properties

A new family of LnIII [12-Metallacrown-4] compounds of formulas (C5H6N) [LnFe4(shi)4(C6H5COO)4(Py)4]·3.5Py [Ln = EuIII (1); GdIII (2); TbIII (3); DyIII (4); and, H3shi = salicylhydroxamic acid] were obtained through one-pot reactions with H3shi, Fe(NO3)3·9H2O, and, Ln(NO3)3·6H2O as reagents. Single-crystal X-ray analyses show that they are isostructural and have the similar [12-MCFeIII N(shi)-4] core, with four benzoate molecules bridging the central LnIII ion to the ring FeIII ions. The negative charge of the 12-MC-4 metallacrown is balanced by one pyridinium cation, which forms the hydrogen bond with an adjacent solvent pyridine molecule. Magnetic measurements demonstrate antiferromagnetic coupling interactions and field-induced slow magnetic relaxation in complex 4.

Influence of the Substitution of the Ligand on MM′CT Properties of Mixed Valence Heterometallic Cyanido-Bridged Ru–Fe Complexes

We investigated how substitution of the ligand around the lower valent metal ion influences the electron transfer properties from the lower valent metal ion to the higher valent metal ion in heterometallic complexes. A series of new binuclear cyanido-bridged Ru/Fe complexes [TpmRu(L)(μ-CN)Fe(dppe)Cp][PF6]n (n = 2, 3) (Tpm = Tris(1-pyrazolyl)methane, dppe = bis(diphenylphosphino)ethane, L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4,4′-(CH3)2-bpy)) were synthesized and characterized. In the one-electron oxidized [TpmRuII(L)(μ-CN)FeIII(dppe)Cp][PF6]3 binuclear system, the cyanide bridge promotes the electron transfer from the RuII ion to the FeIII ion. As the substitution of L changes from 1,10-phenanthroline to 4,4′-dimethyl-2,2′-bipyridine, their molecular structure, cyclic voltammetry, IR and UV present obvious changing trends. Moreover, the assignment of MM′CT transition and the differences of electronic properties in the different mixed complexes with different ...

Use of the TCNQF4 2- Dianion in the Spontaneous Redox Formation of [FeIII (L- )2 ][TCNQF4 ⋅-

The reaction of [FeII (L. )2 ](BF4 )2 with Li2 TCNQF4 results in the formation of [FeIII (L- )2 ][TCNQF4 . - ] (1) where L. is the radical ligand, 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N-oxide and TCNQF4 is 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane. This has been characterised by X-ray diffraction, Raman and Fourier transform infrared (FTIR) spectroscopy, variable-temperature magnetic susceptibility, Mössbauer spectroscopy and electrochemistry. X-ray diffraction studies, magnetic susceptibility measurements and Raman and FTIR spectroscopy suggest the presence of low-spin FeIII ions, the anionic form (L- ) of the ligand and the anionic radical form of TCNQF4 ; viz. TCNQF4 . - . Li2 TCNQF4 reduces the [FeII (L. )2 ]2+ dication, which undergoes a reductively induced oxidation to form the [FeIII (L- )2 ]+ monocation resulting in the formation of [FeIII (L- )2 ][TCNQF4 . - ] (1), the electrochemistry of which revealed four well-separated, diffusion-controlled, one-electron, reversible processes. Mössbauer spectroscopy and electrochemical measurements suggest the presence of a minor second species, likely to be [FeII (L. )2 ][TCNQF4 2- ].

Experimental and Theoretical Identification of the Origin of Magnetic Anisotropy in Intermediate Spin Iron(III) Complexes.

The complexes [FeLN2S2X] [in which LN2S2=2,2′‐(2,2′‐bipryridine‐6,6′‐diyl)bis(1,1′‐diphenylethanethiolate) and X=Cl, Br and I], characterized crystallographically earlier and here (Fe(L)Br), reveal a square pyramidal coordinated FeIII ion. Unusually, all three complexes have intermediate spin ground states. Susceptibility measurements, powder cw X‐ and Q‐band EPR spectra, and zero‐field powder Mössbauer spectra show that all complexes display distinct magnetic anisotropy, which has been rationalized by DFT calculations.

Chemical assembly of the heteronuclear pivalate complex with the LiI and FeIII ions

The heteronuclear complex [Fe4Li2(O)2(Piv)10(H2O)2] (1, Piv is the pivalic acid anion) was obtained by refluxing FeIII pivalates with LiI pivalates in toluene and isolated as the 1•PhCH3 solvate with a toluene molecule. According to X-ray diffraction data, complex 1 contains the {Fe4Li2O2} core. The Mossbauer spectroscopy data indicate that the core comprises para magnetic FeIII ions in the high-spin state located in the symmetric octahedral environment of oxygen atoms. Thermolysis of 1 studied by simultaneous thermal analysis demonstrated thermal stability of the complex up to 225 °С. The main end product of thermolysis at 600 °С is the mixed oxide LiFe5O8.

On the Magnetic Coupling and Spin Crossover Behavior in Complexes Containing the Head-to-Tail [FeII2(μ-SCN)2] Bridging Unit: A Magnetostructural Experimental and Theoretical Study.

A new dinuclear complex [{Fe(tpc-OBn)(NCS)(μ-NCS)}2] (1) based on the tripodal tpc-OBn ligand (tpc-OBn = tris(2-pyridyl)benzyloxymethane), containing bridging μ-κN:κS-SCN and terminal κN-SCN thiocyanate ligands, has been prepared and characterized by single crystal X-ray diffraction, magnetic studies, and DFT theoretical calculations. This complex represents the first example of dinuclear FeII complex with double μ-κN:κS-SCN bridges in a head-to-tail configuration that exhibits ferromagnetic coupling between metal ions (JFeFe = +1.08 cm-1). Experimental and theoretical magnetostructural studies on this kind of infrequent FeII dinuclear complex containing a centrosymmetrically [Fe2(μ-SCN)2] bridging fragment show that the magnitude and sign of the magnetic coupling parameter, JFeFe, depend to a large extent on the Fe-N-C (α) angle, so that JFeFe decreases linearly when α decreases. The calculated crossover point below which the magnetic interactions change from ferromagnetic to antiferromagnetic is found at 162.3°. In addition, experimental results obtained in this work and those reported in the literature suggest that large Ntripodal-FeII distances and bent N-bound terminal κN-SCN ligands favor the high spin state of the FeII ions, while short Ntripodal-FeII distances and almost linear Fe-N-C angles favor a stronger ligand field, which enables the FeII ions to show spin crossover (SCO) behavior.

Modular construction, magnetic property, and luminescent sensing of 3D Mn(II) and Cd(II) coordination polymers based on p-terphenyl-2,2″,5″,5‴-tetracarboxylate acid

Two 3D modular designed coordination polymers, namely, {[H2N(CH3)2]2[Mn(TPT)]}n (1), and {[Cd(TPT)0.5(bib)]·0.5H2O}n (2) (H4TPT = p-terphenyl-2,2″,5″,5‴-tetracarboxylate acid, and bib = 1,3-bis((imidazol-1-yl) benzene) have been synthesized and structural characterized by EA, IR, TG, PXRD. Single-crystal X-ray diffraction analyses reveal that complex 1 is a 3D 4-connected {42.63.8}–sra net with the tiling modular being [42.62.82] = [4a.4b.62.8a.8b] (transitivity is 2451). While complex 2 is a 3D (4,4)-connected {64.82}{66}2–bbf net with tiling modular is [6.82]+[63.8] = [6 c.8a.8b]+[6a.6b.6 c.8a] (transitivity is 2352). The variable-temperature susceptibility of 1 has been investigated. Besides, complex 2 exhibits highly sensitive sensing of FeIII ions in DMF solution.

A new mononuclear neutral high-spin iron(III) complex with the different tridentate ligands 5-bromo-salicyl-aldehyde (pyridin-2-yl)hydrazone and 5-bromo-salicyl-aldehyde thio-semicarbazone.

The title neutral mononuclear complex, [1-(5-bromo-2-oxido-benzyl-idene)thio-semicarbazidato](4-bromo-2-{[2-(pyridin-2-yl)hydrazinyl-idene]meth-yl}pheno-lato)iron(III), [Fe(C8H6BrN3OS)(C12H9BrN3O)] (I), crystallizes in the monoclinic space group C2/c and has two different planar tridentate ligands. The central FeIII ion is coordinated to three N, two O and one S atom, forming a distorted octa-hedral FeN3O2S coordination geometry. In the crystal, the complex mol-ecules are linked by N-H⋯O and N-H⋯N hydrogen bonds and π-π inter-actions into layers parallel to (100). Magnetic measurements show that the central FeIII ion is in the high-spin state; this is also supported by the bond distances around the FeIII ion.

Modular [FeIII8MII6]n+ (MII = Pd, Co, Ni, Cu) Coordination Cages

The reaction of the simple metalloligand [FeIIIL3] [HL = 1-(4-pyridyl)butane-1,3-dione] with a variety of different MII salts results in the formation of a family of heterometallic cages of formulae [FeIII8PdII6L24]Cl12 (1), [FeIII8CuII6L24(H2O)4Br4]Br8 (2), [FeIII8CuII6L24(H2O)10](NO3)12 (3), [FeIII8NiII6L24(SCN)11Cl] (4), and [FeIII8CoII6L24(SCN)10(H2O)2]Cl2 (5). The metallic skeleton of each cage describes a cube in which the FeIII ions occupy the eight vertices and the MII ions lie at the center of the six faces. Direct-current magnetic susceptibility and magnetization measurements on 3-5 reveal the presence of weak antiferromagnetic exchange between the metal ions in all three cases. Computational techniques known in theoretical nuclear physics as statistical spectroscopy, which exploit the moments of the Hamiltonian to calculate relevant thermodynamic properties, determine JFe-Cu = 0.10 cm-1 for 3 and JFe-Ni = 0.025 cm-1 for 4. Q-band electron paramagnetic resonance spectra of 1 reveal a significantly wider spectral width in comparison to [FeL3], indicating that the magnitude of the FeIII zero-field splitting is larger in the heterometallic cage than in the monomer.

Synthesis, crystal structure, and properties of a tetrairon cluster based on 2-methyl-8-hydroxyquinoline

The synthesis, structure, and magnetic properties of a tetrairon(III) complex [Fe4(μ2-O)2Cl4(L)4]·0.5H2O (1, L = 2-methyl-8-hydroxyquinoline), which was prepared under solvothermal conditions and characterized by IR spectra, elemental analysis, TG, and single-crystal X-ray crystal diffraction, are presented. Each Fe center adopts a distorted trigonal bipyramid geometry and is coordinated with three oxygen atoms, one nitrogen atom, and one chlorine atom. Each 2-methyl-8-hydroxyquinoline is coordinated to two FeIII ions with μ2-η2:η1 coordination mode. The magnetic properties of the complex are dominated by antiferromagnetic exchange interactions.

Mapping the Assembly of Metal-Organic Cages into Complex Coordination Networks.

Structural transformations of supramolecular assemblies play an important role in the synthesis of complex metal-organic materials. Nonetheless, often little is known of the assembly pathways that lead to the final product. This work describes the conversion of cubic metal-organic polyhedra to connected-cage networks of varying topologies. The neutral cubic cage assembly of formula {Pd3 [PO(NiPr)3 ]}8 (PZDC)12 has been synthesized from {Pd3 [(NiPr)3 PO](OAc)2 (OH)}2 ⋅2 (CH3 )2 SO and 2,5-pyrazenedicarboxilic acid (PZDC-2H). This 42-component self-assembly is the largest known among the neutral cages with PdII ions. The cage contains twenty-four vacant carboxylate O-sites at the PZDC ligands that are available for further coordination. Post-assembly reactions of the cubic cage with FeII and ZnII ions produced cage-connected networks of dia and qtz topologies, respectively. During these reactions, the discrete cubic cage transforms into a network of tetrahedral cages that are bridged by the 3D metal ions. The robustness of the [Pd3 {[PO(NiPr)3 }]3+ molecular building units made it possible to map the post-assembly reactions in detail, which revealed a variety of intermediate 1D and 2D cage networks. Such step-by-step mapping of the transformation of discrete cages to cage-connected frameworks is unprecedented in the chemistry of coordination driven assemblies.

Isolable Borane-Based Diradical and Triradical Fused by a Diamagnetic Transition Metal Ion.

Complex Fe(bpyB)3 (1, bpyB = 5,5'-bis(dimesitylboranyl)-2,2'-bipyridine) and its reduced species [(18-c-6)K(THF)2]·[Fe(bpyB)3] (2) were synthesized. Their solid state and electronic structures were investigated by single crystal X-ray crystallography, electron paramagnetic resonance and UV-vis spectroscopy, and SQUID measurements. In 1 two bpyB radical anions are fused by a diamagnetic FeII ion, whereas in 2 all three bpyB ligands are in the radical state. Complex 1 possesses an open-shell singlet ground state with a singlet-triplet gap of 0.18 kcal mol-1 and 2 features an open-shell doublet ground state with a doublet-quartet gap of 1.4 kcal mol-1, as determined by SQUID measurements. The unpaired-electrons in 1 and 2 mainly delocalize over the boron atoms and the bipyrdine moieties with negligible spin density at the iron center. Complex 2 represents the first isolable example of boron-based triradicals.

Mixed-Valence Triferrocenium Complex with Electric Field Controllable Superexchange as a Molecular Implementation of Triple Quantum Dot

In this article, we propose molecular implementation of the quantum logic gate originally realized by the linear triple-quantum dot array accommodating two electrons. To reach this goal we propose to employ the mixed-valence triferrocenium complex exhibiting three isomeric forms with different oxidation degrees FeIII–FeII–FeIII, FeIII–FeIII–FeII, and FeII–FeIII–FeIII, which correspond to three instant localizations of the two holes over three iron ions. The long-range interaction between the terminal metal sites is considered in the framework of the Hubbard-like Hamiltonian which accounts for the electron transfer and inter- and intrasite Coulomb repulsion and takes into account differences in the orbital energies of FeIII and FeII ions. The interaction of the electrons with the applied electric field is also included in the Hamiltonian. It is shown that due to long-range superexchange between the two electronic spins the ground state of the triferrocenium complex is always a spin-singlet, and the first e...

Compensation behaviors in the diluted FeIIFeIII bimetallic oxalates

The compensation behaviors of FeIIFeIII bimetallic oxalates with defects were explored by constructing a diluted spin-2 and spin-5/2 ferrimagnetic Ising model. Within the effective-field theory based on Glauber-type stochastic dynamic, the effects of the concentration of FeII and FeIII ions on the compensation temperatures have been studied and the two-compensation points were found in FeIIFeIII bimetallic oxalates. The results showed that the compensation behaviors of the compounds were strongly affected by the presence of defects. In addition, the dilution enhanced the magnetization jumps of the compounds which have been found in earlier experimental and theoretical studies. In particular, the dynamic phase transition is absent in the nonequilibrium system with impurities in contrast to the corresponding equilibrium system.

Synthesis, Crystal Structure, and Electrochemistry of Iron and Cobalt Complexes Supported by a Pentadentate Amine‐bis(phenolate) Ligand

The pentadentate amine‐bis(phenolate) ligand 6,6′‐(dipyridin‐2‐ylmethylazanediyl)bis(methylene)bis(2,4‐dimethylphenol) (H2L) was prepared and characterized. This ligand readily coordinates with FeIII or CoIII ions, and the resulting complexes [FeIIILCl] (1) and [CoIIIL(H2O)]Cl (2) were characterized by elemental analysis. X‐ray structural studies show that the ligand in complexes 1 and 2 acts as a pentadentate ligand, leaving one coordination side of the transition metal available for exogenous ligands such as chloride ion (1) or water (2) ligand, and the central metal atoms are hexacoordinate in a similar distorted octahedral arrangement. Electrochemical studies reveal that each of the complexes exhibits multiple redox processes in the potential window investigated. Complex 1 shows one reversible oxidative event at 0.32 V and one quasi‐reversible reduction event at –1.03 V, while the complex 2 displays one reversible oxidative event at 0.18 V and one quasi‐reversible reduction at –0.64 V.

Self-Assembly of Monodisperse Carbon Dots into High-Brightness Nanoaggregates for Cellular Uptake Imaging and Iron(III) Sensing.

This study describes a bottom-up assembly route for monodisperse carbon dots (CDs) into different sizes of CD aggregates through the control of the concentration of fatty acids. The highly monodisperse CDs were prepared via solvent-thermal treatment of edible soybean oil, which generated glycerol-based polymer as a carbon source and fatty acid as a surface capping in the synthetic process. The as-synthesized CDs exhibited small particle size variation (2.7 ± 0.2 nm) and narrow emission bands (full width at half-maximum <20 nm). The monodisperse CDs can self-assemble into blue-, green-, yellow-, and red-emitting CD aggregates by tuning the concentration of fatty acids. Compared to commercially available organic dyes and semiconductor quantum dots, the CD aggregates provided a 10-7000-fold improvement in brightness. Additionally, their emission wavelength was tunable across the entire visible spectrum by tuning the excitation wavelength. Because of their high brightness, fluorescence imaging of a single carbon dot and CD aggregate was simply achieved using filter-free dark-field fluorescence microscopy (DFM). We also demonstrate the use of filter-free DFM to dynamically image cellular uptake of the monodisperse CDs in MCF-7 cells and Huh-7 liver cancer cells. Without the conjugation of the fluorophore to the CDs, the particle aggregation-induced red-shifted emission enables the development of the CD-based ratiometric sensor for FeIII ions and pyrophosphate based on FeIII-induced aggregation of the monodisperse CDs.

Rare examples of diphenoxido-bridged trinuclear NiII2FeIII complexes with a reduced salen type Schiff base ligand: Structures and magnetic properties

Three new trinuclear hetero-metallic complexes, [(NiLR)2Fe(N3)3] (1), [(NiLR(H2O))2Fe(C6H5CH2CO2)2]·(HSO4) (2) and [(NiLR(H2O))2Fe(C6H5CO2)2]·(HSO4)·(H2O)·(CH2Cl2) (3) have been synthesized using [NiLR] as a “metalloligand” (where H2LR=N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine). All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic study. In the angular trinuclear units of 1, the two terminals [NiLR] coordinate through double phenoxido bridges to the central FeIII ion which is penta-coordinated having terminally coordinated azide ion. The two terminal NiII centers are connected to each other and also to neighbouring units through μ1,3-azido bridges to form an alternating chain. On the other hand, complexes, 2 and 3 are linear discrete trinuclear species [NiII–FeIII–NiII] in which two terminal octahedral [NiLR] units coordinate to the central octahedral FeIII ion, located on a crystallographic centre of symmetry, through a μ2-phenoxido oxygen atom and a bridging carboxylato ion. Variable temperature magnetic susceptibility measurements show the presence of antiferromagnetic exchange interactions in 1 mediated through the phenoxido bridges (J1=−33.2cm−1,) and μ1,3-N3 single bridges (J2=−19.9cm−1 and J3=−16.7cm−1). On the other hand, compounds 2 and 3 show ferromagnetic coupling interactions mediated through the double phenoxido bridges with J values of +4.9 and +3.0cm−1 for 2 and 3, respectively.

Bimetallic metal-organic frameworks nanocages as multi-functional fillers for water-selective membranes

Although metal-organic frameworks (MOFs) with well-defined regular and porous structure have emerged as a family of nanoporous building blocks, the great potential of MOFs as multi-functional fillers for hybrid membranes deserves in-depth exploitation. In this study, bimetallic MOF nanocages, FeIII-HMOF-5, were prepared and incorporated into sodium alginate (SA) matrix to fabricate water-selective nanohybrid membranes. Introduction of FeIII ions into MOF-5 creates more coordinatively unsaturated sites, which leads to preferential dissolution of water molecules over ethanol molecules, thus elevating the solubility selectivity. The hollow structure of FeIII-HMOF-5 ensures the free diffusion of water molecules. The synergistic regulation of chemical composition and physical structure of MOFs endows the hybrid membranes with remarkably elevated separation factor and permeation flux. Taking dehydration of 90wt% ethanol aqueous solution as model system, the hybrid membrane containing FeIII-HMOF-5 exhibits the highest separation performance with separation factor of 3423 and permeation flux of 1540g/m2h, much higher than those for pure SA membrane and the hybrid membranes incorporating hollow MOF-5 (HMOF-5) and MOF-5. Moreover, the hybrid membranes containing FeIII-HMOF-5 display remarkably superior physicochemical stabilities and long-term operation stability. This study demonstrates a promising prospect of heterometallic hollow MOFs as multi-functional fillers in high-performance hybrid membranes.