Magnetochemistry, Volume 6, Issue 2 (June 2020) – 12 articles

A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, N_ap(CH₂CH ₂NH₂)₃ (tren), and a few closely related tripodal amines with Cr(II), Mn(III) (d⁴), Mn(II), Fe(III) (d⁵), Fe(II) (d⁶), and Co(II) (d⁷) is provided. Attention is focused on examination of key structural features, the M-N_imine, M-N_amine, or M-O and M-N_ap bond distances and N_imine-M-N(O) bite and C-N_ap-C angles and how these values correlate with spin state selection and spin crossover (SCO) behavior. A comparison of these experimental values with density functional theory calculated values is also given. The greatest number, 132, of complexes is observed with cationic mononuclear iron(II) in a N₆ donor set, Fe(II)N₆. The dominance of two spin states, high spin (HS) and low spin (LS), in these systems is indicated by the bimodal distribution of histogram plots of Fe(II)-N_imine and Fe(II)-N_{azole/pyridine} bond distances and of N_imine–Fe(II)-N_{azole/pyridine} and C-N_ap-C bond angles. The values of the two maxima, corresponding to LS and HS states, in each of these histograms agree closely with the theoretical values. The iron(II)-N_imine and iron(II)-N_{azole/pyridine} bond distances correlate well for these complexes. Examples of SCO complexes of this type are tabulated and a few of the 20 examples are discussed that exhibit interesting features. There are only a few mononuclear iron(III) cationic complexes and one is SCO. In addition, a significant number of supramolecular complexes of these ligands that exhibit SCO, intervalence, and chiral recognition are discussed. A summary is made regarding the current state of this area of research and possible new avenues to explore based on analysis of the present data. Full article

Spintronics is one of the most exciting applications of graphene-based devices. In this work Density Functional Theory is used to study a nanojunction consisting of two semi-infinite graphene electrodes contacted with an iron-porphyrin (FeP) molecule, which plays the role of spin filter for the incoming unpolarized electrons. The graphene-FeP contact closely resembles the recently synthesized porphyrin-decorated graphene [He et al., Nat. Chem. 2017, 9, 33–38]. The analysis of the spectral properties of the system shows a variation of the orbital occupancy with respect to the isolated FeP molecule and an hybridization with the delocalized states of the substrate, while the overall magnetic moment remains unchanged. Doping the electrodes with boron or nitrogen atoms induces a relevant rearrangement in the electronic structure of the junction. Upon B doping the current becomes significantly spin polarized, while N doping induces a marked Negative Differential Resistivity effect. We have also investigated the possible exploitation of the FeP junction as a gas sensor device. We demonstrate that the interaction of CO and O₂ molecules with the Fe atom, while being strong enough to be stable at room temperature (2.0 eV and 1.1 eV, respectively), induces only minor effects on the electronic properties of the junction. Interestingly, a quenching of the spin polarization of the current is observed in the B-doped system. Full article

Reactions of Fe(II) with the tripodal chelating ligand 1,1,1-tris(2-pyridyl)ethoxymethane (py₃C-OEt) and (NCE)⁻ co-ligands (E = S, Se, BH₃) give a series of mononuclear complexes formulated as [Fe(py₃C-OEt)₂][Fe(py₃C-OEt)(NCE)₃]₂·2CH₃CN, with E = S (1) and BH₃ (2). These compounds are the first Fe(II) spin cross-over (SCO) complexes based on the tripodal ligand tris(2-pyridyl)ethoxymethane and on the versatile co-ligands (NCS)⁻ and (NCBH₃)⁻. The crystal structure reveals discrete monomeric isomorph structures formed by a cationic [Fe(py₃C-OEt)₂]²⁺ complex and by two equivalent anionic [Fe(py₃C-OEt)(NCE)₃]⁻ complexes. In the cations the Fe(II) is facially coordinated by two py₃C-OEt tripodal ligands whereas in the anion the three nitrogen atoms of the tripodal ligand are facially coordinated and the N-donor atoms of the three (NCE)⁻ co-ligands occupy the remaining three positions to complete the distorted octahedral environment of the Fe(II) centre. The magnetic studies show the presence of gradual SCO for both complexes: A one-step transition around 205 K for 1 and a two-step transition for compound 2, centered around 245 K and 380 K. Full article

Magnetic nanoparticles have been largely applied to increase the efficacy of antibiotics due to passive accumulation provided by enhancing permeability and retention, which is essential for the treatment of lung infections. Recurring lung infections such as in the life-shortening genetic disease cystic fibrosis (CF) are a major problem. The recent advent of the CF modulator drug ivacaftor, alone or in combination with lumacaftor or tezacaftor, has enabled systemic treatment of the majority of patients. Magnetic nanoparticles (MNPs) show unique properties such as biocompatibility and biodegradability as well as magnetic and heat-medicated characteristics. These properties make them suitable to be used as drug carriers and hyperthermia-based agents. Hyperthermia is a promising approach for the thermal activation therapy of several diseases, including pulmonary diseases. The benefits of delivering CF drugs via inhalation using MNPs as drug carriers afford application of sufficient therapeutic dosages directly to the primary target site, while avoiding potential suboptimal pharmacokinetics/pharmacodynamics and minimizing the risks of systemic toxicity. This review explores the multidisciplinary approach of using MNPs as vehicles of drug delivery. Additionally, we highlight advantages such as increased drug concentration at disease site, minimized drug loss and the possibility of specific cell targeting, while addressing major challenges for this emerging field. Full article

The article describes the interaction of nanocomposites based on the Fe_mO_n–SiO₂ system with an electromagnetic field (radiation) in an ultra-wide frequency range 0–10²¹ Hz. The development of the technique based on the sol–gel method for producing nanocomposites is described, which made it possible to achieve superparamagnetic properties in combination with low toxicity when used in vivo and in vitro and a high microwave absorption coefficient, which makes it possible to use the obtained nanocomposites in solving a wide range of practical problems. The most effective methods of exposure and threshold levels of the electromagnetic field, the corresponding modifications of the magnetic structure, crystalline structure and microstructure of nanocomposites are determined. Full article

Spinel ferrite nanoparticles represent a class of magnetic nanoparticles (MNPs) with enormous potential in magnetic hyperthermia. In this study, we investigated the magnetic and heating properties of spinel soft NiFe₂O₄, MnFe₂O₄, and hard CoFe₂O₄ MNPs of comparable sizes (12–14 nm) synthesized by the polyol method. Similar to the hard ferrite, which predominantly is ferromagnetic at room temperature, the soft ferrite MNPs display a non-negligible coercivity (9–11 kA/m) arising from the strong interparticle interactions. The heating capabilities of ferrite MNPs were evaluated in aqueous media at concentrations between 4 and 1 mg/mL under alternating magnetic fields (AMF) amplitude from 5 to 65 kA/m at a constant frequency of 355 kHz. The hyperthermia data revealed that the SAR values deviate from the quadratic dependence on the AMF amplitude in all three cases in disagreement with the Linear Response Theory. Instead, the SAR values display a sigmoidal dependence on the AMF amplitude, with a maximum heating performance measured for the cobalt ferrites (1780 W/g_Fe+Co), followed by the manganese ferrites (835 W/g_Fe+Mn), while the nickel ferrites (540 W/g_Fe+Ni) present the lowest values of SAR. The heating performances of the ferrites are in agreement with their values of coercivity and saturation magnetization. Full article

Magnetite nanoparticles (Fe₃O₄), average particle size of 12.9 nm, were synthesized de novo from ferrous and ferric iron salt solutions (total iron salt concentration of 3.8 mM) using steady-state headspace NH_3(g), 3.3% v/v, at room temperature and pressure, without mechanical agitation, resulting in >99.9% yield. Nanoparticles size distributions were based on enumeration of TEM images and chemical compositions analyzed by: XRD, EDXRF, and FT-IR; super-paramagnetic properties were analyzed by magnetization saturation (74 emu/g). Studies included varying headspace [NH_3(g)] (1.6, 3.3, 8.4% v/v), and total iron concentrations (1.0 mM, 3.8 mM, 10.0 mM, and >>10 mM). An application of the unmodified synthesized magnetite nanoparticles included analyses of tetracycline’s (50, 100, 200, 300, and 400 ppb) in aqueous, which was compared to the same tetracycline concentrations prepared in aqueous synthesis suspension with >97% extraction, analyzed with LC-MS/MS. Full article

Paintings are complex multi-layered systems made of organic and inorganic materials. Several factors can affect the degradation of paintings, such as environmental conditions, past restoration works and, finally, the type of painting technique and the art materials used over the centuries. The chemical–physical characterization of paintings is a constant challenge that requires research into and the development of novel analytical methodologies and processes. In recent years, solvents and water-related issues in paintings are attracting more attention, and several studies have been focused on analyzing the interaction between water molecules and the constitutive materials. In this study, recent applications applying different NMR methodologies were shown, highlighting the weakness and the strength of the techniques in analyzing paintings. In particular, the study of water and its diffusive interactions within wall and oil paintings was performed to prove how the portable NMR can be used directly in museums for planning restoration work and to monitor the degradation processes. Furthermore, some preliminary results on the analysis of varnishes and binders, such us linseed oil, shellac, sandarac and colophony resins, were obtained by ¹H HR-MAS NMR spectroscopy, highlighting the weakness and strengths of this technique in the field of conservation science. Full article

Two mononuclear Re^IV complexes of general formula (PPh₄)₂[ReX₆] [PPh₄⁺ = tetraphenylphosphonium cation, X = Br (1) and I (2)] have been prepared and structurally and magnetically characterised. Both compounds crystallise in the triclinic system with space group Pī. Their structures are made up of hexahalorhenate(IV), [ReX₆]²⁻, anions, and bulky PPh₄⁺ cations. Each Re^IV ion in 1 and 2 is six-coordinate and bonded to six halide ions in a quasi regular octahedral geometry. In their crystal packing, the [ReX₆]²⁻ anions are well separated from each other through the organic cations, generating alternated anionic and cationic layers, and no intermolecular Re−X···X−Re interactions are present. Variable-temperature dc magnetic susceptibility measurements performed on microcrystalline samples of 1 and 2 show a very similar magnetic behaviour, which is typical of noninteracting mononuclear Re^IV complexes with S = 3/2. Ac magnetic susceptibility measurements reveal the slow relaxation of the magnetisation in the presence of external dc fields for 1 and 2, hence indicating the occurrence of the field-induced single-ion magnet (SIM) phenomenon in these hexabromo- and hexaiodorhenate(IV) complexes. Full article

The two mononuclear complexes of the formula [Dy(tta)₃(L)] (1) and [Dy(hfac)₃(L)] (2) (where tta^- = 2-thenoytrifluoroacetylacetonate and hfac^- = 1,1,1,5,5,5-hexafluoroacetylacetonate) were obtained from the coordination reaction of the Dy(tta)₃·2H₂O or Dy(hfac)₃·2H₂O units with the 1,10-phenantroline-5,6-dione ligand (L). Their structures have been determined by X-ray diffraction studies on single crystals, and they revealed a supramolecular assembly of tetramers through σ-π interactions. Both complexes displayed a Single-Molecule Magnet (SMM) behavior without an external applied magnetic field. Magnetic relaxation happened through Orbach, Raman and Quantum Tunneling of the Magnetization (QTM). Wavefunction theory calculations were realized to rationalize the magnetic properties. Full article

Magnetic resonance spectroscopy of biomolecules has recently gained attention for clinical diagnosis. Its combination with saliva collection and analysis can promote early disease detection and monitoring, by identifying biomarkers of specific underlying pathology or disease as detected in saliva. With this novel, non-invasive technique, certain salivary biomarkers have been linked to dental and periodontal tissues pathology, as well as to specific head and neck cancer malignancies. At present, diagnostic biomarkers are still in need for further identification (e.g., diagnosis and monitoring of Sjögren’s syndrome), and nuclear magnetic resonance spectroscopy has been found to be a promising technique to compliment the current analytic methodology. Moreover, this article reports on the various data collection and analysis parameters used in the literature. Protocol standardization is yet to be established not only for the laboratory procedures, but also for the clinical sample collection. Herein, we review the current status of utilizing nuclear magnetic resonance in order to further support data on health associated biomarkers, and we also propose a saliva sampling scheduling protocol with the potential to be used in the clinical and experimental setting for standardization of the testing methodology. Full article