Magnetochemistry, Volume 5, Issue 3 (September 2019) – 15 articles

Chiral surface formation was investigated in rotational magnetoelectrodeposition (RMED) of copper films, where an electrochemical cell was rotated in magnetic fields. The RMED was conducted with clockwise or anticlockwise rotation in the magnetic fields parallel or antiparallel to the ionic currents. The rotational frequencies were 0.5–6 Hz, and the magnetic fields were 2–5 T. The chiral behaviors are divided into four types: type I has chirality depending on the magnetic field polarity, type II has chirality depending on the rotational direction, and type III has chirality depending on both directions. Type IV represents chiral symmetry breaking, where the RMED films exhibit only L activity in any magnetic field polarity and rotational direction. Full article

The antibiotics known as bleomycins constitute a family of natural products clinically employed for the treatment of a wide spectrum of cancers. These antibiotics have the ability to chelate a metal center, most commonly Fe(II), and cause site-specific DNA cleavage upon oxidation. Bleomycin therapy is a successful course of treatment for some types of cancers. However, the risk of pulmonary fibrosis as an undesirable side effect, limits the use of the antibiotics in cancer chemotherapy. Bleomycins are differentiated by their C-terminal, or tail, regions, which have been shown to closely interact with DNA. Pulmonary toxicity has been correlated to the chemical structure of the bleomycin C-termini through biochemical studies performed in mice. In the present study, we examined the binding of Zn(II)Bleomycin-A₅ to a DNA hairpin of sequence 5′-CCAGTATTTTTACTGG-3′, containing the 5′-GT-3′ binding site. The results were compared to those from a previous study that examined the binding of Zn(II)Bleomycin-A₂ and Zn(II)Peplomycin to the same DNA hairpin. We provide evidence that, as shown for DNA hairpins containing the 5′-GC-3′ binding site, Zn(II)BLM-A₅ causes the most significant structural changes to the oligonucleotide. Full article

Advances of nanotechnology led to the development of nanoparticulate systems with many advantages due to their unique physicochemical properties. The use of iron-oxide magnetic nanoparticles (IOMNPs) in pharmaceutical areas increased in the last few decades. This article reviews the conceptual information about iron oxides, magnetic nanoparticles, methods of IOMNP synthesis, properties useful for pharmaceutical applications, advantages and disadvantages, strategies for nanoparticle assemblies, and uses in the production of drug delivery, hyperthermia, theranostics, photodynamic therapy, and as an antimicrobial. The encapsulation, coating, or dispersion of IOMNPs with biocompatible material(s) can avoid the aggregation, biodegradation, and alterations from the original state and also enable entrapping the bioactive agent on the particle via adsorption or covalent attachment. IOMNPs show great potential for target drug delivery, improving the therapy as a consequence of a higher drug effect using lower concentrations, thus reducing side effects and toxicity. Different methodologies allow IOMNP synthesis, resulting in different structures, sizes, dispersions, and surface modifications. These advantages support their utilization in pharmaceutical applications, and getting suitable drug release control on the target tissues could be beneficial in several clinical situations, such as infections, inflammations, and cancer. However, more toxicological clinical investigations about IOMNPs are necessary. Full article

Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need to be taken into account for a reliable description. Among the different contributions, the zero-point energy (ZPE) and the entropy play key roles. These quantities are usually calculated assuming a harmonic oscillator model for the molecular vibrations. We investigated the impact of including anharmonic corrections on the ZPE and the entropy and indirectly on the critical temperature of spin crossover. As test systems, we used a set of ten Fe(II) complexes and one Fe(III) complex, covering different coordination modes (mono-, bi-, and tri-dentate ligands), decreasing coordination number upon spin crossover, coordination by second- and third-row atoms, and changes in the oxidation state. The results show that the anharmonicity has a measurable effect, but it is in general rather small, and tendencies are not easily recognized. As a conclusion, we put forward that for high precision results, one should be aware of the anharmonic effects, but as long as computational chemistry is still struggling with other larger factors like the influence of the environment and the accurate determination of the electronic energy difference between HS and LS, the anharmonicity of the vibrational modes is a minor concern. Full article

First-order phase transitions (FOPT) and second-order phase transitions (SOPT) are commonly observed in Cu alloys containing lanthanide elements, due to their electronic configuration, and have an important effect on the optimization of their magnetocaloric effect (MCE). Alloys containing rare earths have the best magnetocaloric response; however, these elements are very expensive, due to their obtaining and processing methods. The present work reports the effect of using 3d transition elements and thermal treatments on the microstructure and MCE of Cu–11Al–9Zn alloys with 6.5 wt % Ni and 2.5 wt % Fe. It was found that thermal treatments of quenching and normalizing, as well as the use of Ni and Fe, have an important influence on both the resulting phases and MCE of the investigated alloy. MCE was calculated indirectly from the change in the magnetic entropy (–ΔS_m) under isothermal conditions, using Maxwell´s relation; it was found that samples subjected to normalizing presented a higher magnetocaloric effect than samples with quenching, which was related to the greater disorder in the alloy, due to the coexistence of β₁ + β phases. Full article

Magnetic Janus particles bring together the ability of Janus particles to perform two different functions at the same time in a single particle with magnetic properties enabling their remote manipulation, which allows headed movement and orientation. This article reviews the preparation procedures and applications in the (bio)sensing field of static and self-propelled magnetic Janus particles. The main progress in the fabrication procedures and the applicability of these particles are critically discussed, also giving some clues on challenges to be dealt with and future prospects. The promising characteristics of magnetic Janus particles in the (bio)sensing field, providing increased kinetics and sensitivity and decreased times of analysis derived from the use of external magnetic fields in their manipulation, allows foreseeing their great and exciting potential in the medical and environmental remediation fields. Full article

The mononuclear single-molecule magnet (SMM) [Dy(tta)₃(L)]⋅C₆H₁₄ (1) (where tta⁻ = 2-thenoyltrifluoroacetonate and L = 4,5-bis(propylthio)-tetrathiafulvalene-2-(2-pyridyl)benzimidazole-methyl-2-pyridine) was studied by spectro-electrochemistry. The resulting electronic spectra of the three oxidation states 1, 1⁺∙, and 1²⁺ were rationalized by time-dependent density functional theory (TD-DFT) calculations starting from the DFT optimized structures. The modulation of the magnetic anisotropy of the Dy^III center upon oxidation was also inspected at the Complete Active Space Self-Consistent Field (CASSCF) level of calculation. Full article

Magnetic iron oxide nanoclusters, which refers to a group of individual nanoparticles, have recently attracted much attention because of their distinctive behaviors compared to individual nanoparticles. In this review, we discuss preparation methods for creating iron oxide nanoclusters, focusing on synthetic procedures, formation mechanisms, and the quality of the products. Then, we discuss the emerging applications for iron oxide nanoclusters in various fields, covering traditional and novel applications in magnetic separation, bioimaging, drug delivery, and magnetically responsive photonic crystals. Full article

Using the structural and electronic tunability of molecules to control magnetism is a central challenge of inorganic chemistry. Herein, a ten-member family of the high-ordering temperature (T_c) molecule-based magnetic coordination networks of the form V[x-Cl_nPTCE]₂·yCH₂Cl₂ (PTCE = phenyltricyanoethylene, y < 0.5) were synthesized and characterized, where x is (are) the position(s) and n is the number of chlorine substitutions on the phenyl ring. These chlorophenyltricyanoethelenes are tunable analogs of the more commonly investigated tetracyanoethylene (TCNE). Varying the number and position of chlorine substitution around the phenyl ring engendered a family of network solids with significantly different magnetic ordering temperatures ranging from 146 to 285 K. The T_cs of these ferrimagnets were rationalized with the aid of cyclic voltammetry and Density Functional Theory (DFT) calculations. Full article

Two ligands, 2,4-di-2-pyridyl-2,4-pentanediol (rD and mD), were employed to synthesize two Mn₂ complexes, [Mn₂(rD)₂Br₂] (1) and [Mn₂(mD)₂(H₂O)₂]Br₂ (2). Compound 1 crystallized in a tetragonal space group, P4₁2₁2, with a novel hamburger shaped structure. A detailed study indicated that compound 1 did not contain a metal–metal bond, but antiferromagnetic coupling was observed between the Mn(III) ions. Compound 2 crystallized in a monoclinic space group, C2/c, with one Mn(II) and the other with Mn(IV). The two manganese ions were bridged by two alkoxide ligands, resulting in ferromagnetic coupling. Magnetic property studies confirm the above assignments. Full article

In recent years, magnetic nanoparticles (MNPs) have gained increasing attention as versatile carriers because of their unique magnetic properties, biocatalytic functionalities, and capabilities to work at the cellular and molecular level of biological interactions. Moreover, owing to their exceptional functional properties, such as large surface area, large surface-to-volume ratio, and mobility and high mass transference, MNPs have been employed in several applications in different sectors such as supporting matrices for enzymes immobilization and controlled release of drugs in biomedicine. Unlike non-magnetic carriers, MNPs can be easily separated and recovered using an external magnetic field. In addition to their biocompatible microenvironment, the application of MNPs represents a remarkable green chemistry approach. Herein, we focused on state-of-the-art two majorly studied perspectives of MNPs as versatile carriers for (1) matrices for enzymes immobilization, and (2) matrices for controlled drug delivery. Specifically, from the applied perspectives of magnetic nanoparticles, a series of different applications with suitable examples are discussed in detail. The second half is focused on different metal-based magnetic nanoparticles and their exploitation for biomedical purposes. Full article

Three coordination polymers of metal(II)-dicyanamido (dca) complexes with 4-methoxypyridine-N-oxide (4-MOP-NO); namely, catena-[Co(µ_1,5-dca)₂(4-MOP-NO)₂] (1), catena-[Mn(µ_1,5-dca)₂(4-MOP-NO)₂] (2), catena-[Cd(µ_1,5-dca)₂(4-MOP-NO)₂] (3), and the mononuclear [Cu(κ¹dca)₂(4-MOP-NO)₂] (4), were synthesized in this research. The complexes were analyzed by single crystal X-ray diffraction as well as spectroscopic methods (UV/vis, IR). The polymeric 1-D chains in complexes 1–3 were achieved by the doubly µ_1,5-bridging dca ligands and the O-donor atoms of two axial 4-MOP-NO molecules in trans configuration around the distorted M(II) octahedral. On the other hand, the two “trans-axial” pyridine-N-oxide molecules in complexes 2 and 3 display opposite orientation (s-trans). The DFT (density functional theory) computational studies on the complexes 1–3 were consistent with the experimentally observed crystal structures. Compounds 1 and 2 display weak antiferromagnetic coupling between metal ions (J = −10.8 for 1 and −0.35 for 2). Full article

We report herein on three zigzag one-dimensional coordination polymers of {[Ru₂(μ-NHOCR)₄](μ-SCN)}_n (R = o-Me-C₆H₄ (2), m-Me-C₆H₄ (3), p-Me-C₆H₄ (4)) formula. These new compounds have been obtained by reaction of the corresponding [Ru₂(μ-NHOR)₄(THF)₂](BF₄) complex with (NBu₄)(SCN) under different synthetic conditions. The crystal structure of [Ru₂(μ-NHOCC₆H₄-o-Me)₄(THF)₂](BF₄) (1), 2 and 3 are presented. A cis-(2,2) arrangement of the amidate ligands of the [Ru₂(μ-NHOCR)₄]⁺ units is observed in all cases. Interestingly, the structures of 2 and 3 show linkage isomerism in alternated tetraamidatodiruthenium units whose axial positions are occupied by the same type of donor atom of the SCN ligands. This results in zigzag chains with a Ru-S-C angle of 98.97° and Ru-N-C angle of 169.36° in the case of 2 and 97.99° and 159.26°, respectively, in the case of 3. The magnetic data obtained for 2–4 are indicative of a σ²π⁴δ²(π*δ*)³ ground state (S = 3/2) and a large zero-field splitting (ZFS) in all cases (D = 54.57, 62.72 and 43.00 cm⁻¹ for 2–4, respectively). Similar small antiferromagnetic interactions between diruthenium units (zJ = −0.93, −0.79 and −1.11 cm⁻¹ for 2–4, respectively) are estimated for all the polymers, suggesting an analogous zigzag arrangement of the chains for 4. Full article

Syntheses, crystal structures and characterization are reported for four new complexes [Cu₄Br₂(L)₄]Br₂ (1), [Ni₄(NO₃)₂(L)₄(H₂O)](NO₃)₂ (2), [Co₂(L)₃](ClO₄)₃ (3) and [Co(L)₂](ClO₄) (4), where L⁻ is the monoanion of the ditopic ligand N′-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide (LH) built on a picolinoyl hydrazone core fragment, and possessing a bidentate and a tridentate coordination pocket. The tetranuclear cation of 1·0.8H₂O·MeOH is a strictly planar, rectangular [2 × 2] grid. Two 2.21011 L⁻ ligands bridge adjacent Cu^II atoms on the short sides of the rectangle through their alkoxide oxygen atoms, and two 2.11111 ligands bridge adjacent Cu^II atoms on the long sides of the rectangle through their diazine groups; two metal ions are 5-coordinate and two are 6-coordinate. The tetranuclear cation of 2·0.2H₂O·3EtOH is a square [2 × 2] grid. The two 6-coordinate Ni^II atoms of each side of the square are bridged by the alkoxide O atom of one 2.21011 L⁻ ligand. The dinuclear cation of 3·0.8H₂O·1.3MeOH contains two low-spin octahedral Co^III ions bridged by three 2.01111 L⁻ ligands forming a pseudo triple helicate. In the mononuclear cation [Co(L)₂]⁺ of complex 4, the low-spin octahedral Co^III center is coordinated by two tridentate chelating, meridional 1.10011 ligands. The crystal structures of the complexes are stabilized by a variety of π–π stacking and/or H-bonding interactions. Compounds 2, 3 and 4 are the first structurally characterized nickel and cobalt complexes of any form (neutral or anionic) of LH. The 2.01111 and 1.10011 coordination modes of L⁻, observed in the structures of complexes 3 and 4, have been crystallographically established for the first time in coordination complexes containing this anionic ligand. Variable-temperature, solid-state dc magnetic susceptibility and variable-field magnetization studies at 1.8 K were carried out on complexes 1 and 2. Antiferromagnetic metal ion···metal ion exchange interactions are present in both complexes. The study reveals that the cation of 1 can be considered as a practically isolated pair of strongly antiferromagnetically coupled (through the diazine group of L⁻) dinulear units. The susceptibility data for 2 were fit to a single-J model for an S = 1 cyclic tetramer. The values of the J parameters have been rationalized in terms of known magnetostructural correlations. Spectral data (infrared (IR), ultraviolet/visible (UV/VIS), ¹H nuclear magnetic resonance (NMR) for the diamagnetic complexes) are also discussed in the light of the structural features of 1–4 and the coordination modes of the organic and inorganic ligands that are present in the complexes. The combined work demonstrates the ligating flexibility of L⁻, and its usefulness in the synthesis of complexes with interesting structures and properties. Full article