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New [FeIII3] and [FeIII4] complexes with ligands formed in situ from pyCOMe transformations contain both square pyramidal and octahedral metal sites, and display distinct Mössbauer hyperfine parameters.

A new family of heterometallic [FeIII2Ln] (Ln = Gd, Tb, Dy, Ho) complexes, possessing an uncommon asymmetric “V-shaped” core and interesting magnetic properties is reported.

In a typical EPR experiment, the transitions require that the static magnetic field $$B_0$$ is oriented perpendicular to the microwave field $$B_1$$ (perpendicular mode). This is determined by the transition rules either in the classical or in the quantum mechanical description. However, there are cases where EPR transitions are observed when $$B_0$$ is oriented parallel to $$B_1$$ (parallel mode). Quite numerous studies can be found in the literature where EPR transitions in both modes (dual-mode EPR) are feasible. In the majority of cases, dual-mode EPR studies are typically applied in $$S>1/2$$ systems where non-zero transition probabilities for the parallel mode are the result of the state mixing provided by the zero-field splitting interaction. On the other hand, the observation of parallel-mode EPR signals in $$S=1/2$$ systems becomes feasible when strong hyperfine interaction between the electronic and nuclear spin is present, as has been theoretically predicted for the hydrogen atom having a hyperfine coupling constant of $$A_0=1420$$ MHz (Weil in Concepts Magn Reson Part A 28:331, 2006). Herein, we report the first dual-mode X-band EPR experiments of hydrogen atom (both isotopes $$^1$$ H and $$^2$$ H) encapsulated in polyhedral oligomeric silsesquioxane cages. We extend the theory to the case of deuterium and we extract analytical formulas for transition probabilities. For the forbidden transitions, this study revealed a first-order dependence of resonance fields on the nuclear g-factor, $$g_{\mathrm{n}}$$ , and the existence of a clock transition with $$f=307$$ MHz.

The high-spin S = 2 Mn(III) complex [Mn{(OPPh2)2N}3] (1Mn) exhibits field-induced slow relaxation of magnetization (Inorg. Chem.2013, 52, 12869). Magnetic susceptibility and dual-mode X-band electron paramagnetic resonance (EPR) studies revealed a negative value of the zero-field-splitting (zfs) parameter D. In order to explore the magnetic and electronic properties of 1Mn in detail, a combination of experimental and computational studies is presented herein. Alternating-current magnetometry on magnetically diluted samples (1Mn/1Ga) of 1Mn in the diamagnetic gallium analogue, [Ga{(OPPh2)2N}3], indicates that the slow relaxation behavior of 1Mn is due to the intrinsic properties of the individual molecules of 1Mn. Investigation of the single-crystal magnetization of both 1Mn and 1Mn/1Ga by a micro-SQUID device reveals hysteresis loops below 1 K. Closed hysteresis loops at a zero direct-current magnetic field are observed and attributed to fast quantum tunneling of magnetization. High-frequency and -field EPR (HFEPR) spectroscopic studies reveal that, apart from the second-order zfs terms (D and E), fourth-order terms (B4m) are required in order to appropriately describe the magnetic properties of 1Mn. These studies provide accurate spin-Hamiltonian (sH) parameters of 1Mn, i.e., zfs parameters |D| = 3.917(5) cm-1, |E| = 0.018(4) cm-1, B04 = B42 = 0, and B44 = (3.6 ± 1.7) × 10-3 cm-1 and g = [1.994(5), 1.996(4), 1.985(4)], and confirm the negative sign of D. Parallel-mode X-band EPR studies on 1Mn/1Ga and CH2Cl2 solutions of 1Mn probe the electronic-nuclear hyperfine interactions in the solid state and solution. The electronic structure of 1Mn is investigated by quantum-chemical calculations by employing recently developed computational protocols that are grounded on ab initio wave function theory. From computational analysis, the contributions of spin-spin and spin-orbit coupling to the magnitude of D are obtained. The calculations provide also computed values of the fourth-order zfs terms B4m, as well as those of the g and hyperfine interaction tensor components. In all cases, a very good agreement between the computed and experimentally determined sH parameters is observed. The magnetization relaxation properties of 1Mn are rationalized on the basis of the composition of the ground-state wave functions in the absence or presence of an external magnetic field.

Strain effects on g and metal hyperfine coupling tensors, A, are often manifested in Electron Paramagnetic Resonance (EPR) spectra of transition metal complexes, as a result of their intrinsic and/...

In this work, we reveal the coordination of copper ions absorbed by a series of covalent organic frameworks. The frameworks were synthesized through the nucleophilic substitution of either cyanuric chloride or phosphonitrilic chloride trimer by 4,4'-bipyridine, and they were utilized as absorbers for the removal of copper ions from aqueous solutions. The exfoliated counterpart of the layered network was compared to the bulk materials in terms of the copper retention capacity and efficiency. The ion absorption capacity of copper ranged from 100 to 290 mg/g depending on the morphology and chemical structure of the framework. As evidenced by the SEM and XRD analysis, the copper absorption induced certain morphological changes in the networks. EPR spectroscopy revealed the key finding of this study: the trigonal bipyramidal configuration of the copper ions in their divalent state, coordinated with the nitrogen of the core units, 4,4'-bipyridine, and chlorine ions. The analysis of the thoroughgoing experiments bridges the gap between coordination molecular chemistry and the field of covalent organic frameworks. EPR explores how the unique trigonal bipyramidal coordination could be suppressed in the end by the environment and, more specifically, by the addition of glycerol to the aqueous dispersions of the covalent organic frameworks.

Recent research has highlighted the key role played by the electron affinity of the active metal-nitrene/imido oxidant as the driving force in nitrene additions to olefins to afford valuable aziridines. The present work showcases a library of Co(II) reagents that, unlike the previously examined Mn(II) and Fe(II) analogues, demonstrate reactivity trends in olefin aziridinations that cannot be solely explained by the electron affinity criterion. A family of Co(II) catalysts (17 members) has been synthesized with the assistance of a trisphenylamido-amine scaffold decorated by various alkyl, aryl, and acyl groups attached to the equatorial amidos. Single-crystal X-ray diffraction analysis, cyclic voltammetry and EPR data reveal that the high-spin Co(II) sites (S = 3/2) feature a minimal [N(3)N] coordination and span a range of 1.4 V in redox potentials. Surprisingly, the Co(II)-mediated aziridination of styrene demonstrates reactivity patterns that deviate from those anticipated by the relevant electrophilicities of the putative metal nitrenes. The representative L(4)Co catalyst (−COCMe(3) arm) is operating faster than the L(8)Co analogue (−COCF(3) arm), in spite of diminished metal-nitrene electrophilicity. Mechanistic data (Hammett plots, KIE, stereocontrol studies) reveal that although both reagents follow a two-step reactivity path (turnover-limiting metal-nitrene addition to the C(b) atom of styrene, followed by product-determining ring-closure), the L(4)Co catalyst is associated with lower energy barriers in both steps. DFT calculations indicate that the putative [L(4)Co]NTs and [L(8)Co]NTs species are electronically distinct, inasmuch as the former exhibits a single-electron oxidized ligand arm. In addition, DFT calculations suggest that including London dispersion corrections for L(4)Co (due to the polarizability of the tert-Bu substituent) can provide significant stabilization of the turnover-limiting transition state. This study highlights how small ligand modifications can generate stereoelectronic variants that in certain cases are even capable of overriding the preponderance of the metal-nitrene electrophilicity as a driving force.

One the main research goals of bioinorganic chemists is the synthesis of novel coordination compounds possessing biological potency. Within this context, three novel iron(III) complexes with the non-steroidal anti-inflammatory drugs diflunisal and diclofenac in the presence or absence of the nitrogen donors 1,10-phenanthroline or pyridine were isolated and characterized by diverse techniques. The complexes were evaluated for their ability to scavenge in vitro free radicals such as hydroxyl, 1,1-diphenyl-2-picrylhydrazyl and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals, revealing their selective potency towards hydroxyl radicals. The in vitro inhibitory activity of the complexes towards the enzymes acetylcholinesterase and butyrylcholinesterase was evaluated, and their potential to achieve neuroprotection appeared promising. The interaction of the complexes with calf-thymus DNA was examined in vitro, revealing their ability to intercalate in-between DNA nucleobases. The affinity of the complexes for serum albumins was evaluated in vitro and revealed their tight and reversible binding.

The reaction of Ln(NO3)3∙6H2O (Ln = Gd, Tb, Dy) and Cu(O2CMe)2∙H2O with the polydentate Schiff base ligands OH-C10H6-CH NC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in Me2CO afforded the heptanuclear heterometallic complexes [Cu5Ln2(O2CMe)2(NO3)4(L1)2(HL1)2(Me2CO)2] (Ln = Gd (1), Tb (2), Dy (3)) and [Cu5Ln2(O2CMe)2(NO3)4(L2)2(HL2)2] (Ln = Gd (4), Tb (5), Dy (6)). Crystallographic studies revealed that complexes 1–3 and 4–6 consist of a central core {CuII5LnIII2(μ3-OR)6(μ3-O2CMe)2}8+ described as two distorted cubane subunits, {CuII3LnIII(μ3-OR)3(μ3-O2CMe)}5+, with a CuII ion in the common apex. Peripheral and bridging ligation is provided by two triply and two doubly deprotonated Schiff base ligands, two μ3-acetates and four chelating nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions in all complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was 16.3 J kg−1 K−1 at 2 K for ΔH = 5 T. Ac susceptibility measurements of 2, 3 and 6 revealed slow magnetic relaxation processes suggesting the presence of single-molecule magnet behavior.

The interaction of FeCl3 with the fenamate non-steroidal anti-inflammatory drugs has led to the formation and isolation of trinuclear iron(III) complexes, while in the presence of the nitrogen-donors 2,2′-bipyridine or pyridine tetranuclear iron(III) complexes were derived. The five resultant complexes were characterized by diverse techniques (including infrared, electronic and Mossbauer spectroscopy) and their crystal structures were determined by single-crystal X-ray crystallography. These complexes are the first structurally characterized Fe(III)-fenamato complexes. The complexes were evaluated for their ability to scavenge in vitro free radicals such as hydroxyl, 1,1-diphenyl-2-picrylhydrazyl and 2,2΄-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid). The in vitro binding affinity of the complexes to calf-thymus (CT) DNA was examined and their interaction with serum albumins was also investigated. In total, the complexes present promising activity against the radicals tested, and they may bind tightly to CT DNA possibly via intercalation and reversibly to serum albumins.

International audience; A 16-line pattern has been theoretically predicted, but hitherto not reported, for the Electron Paramagnetic Resonance (EPR) spectrum of antiferromagnetically coupled CuII triangles experiencing isotropic exchange of isosceles magnetic symmetry. Now, the crystallization of such a triangular species and its X-ray structure determination in a polar space group, R3 (No. 146), has enabled its single crystal EPR study. Its detailed magnetic susceptibility, and X- and Q-band, powder and single crystal EPR spectroscopic study reveals the effect of molecular structure and of Dzyaloshinskii–Moriya interactions (DMI) on the g‖, g⊥ and A‖ parameters of the spectrum; DMI is considered for the first time in such a context. Moreover, careful analysis of the spectrum allows the deconvolution of two slightly different cocrystallized magnetic species.

The high-spin

Among the intermediate catalytic steps of the water‐oxidizing Mn4CaO5 cluster of photosystem II (PSII), the final metastable S3 state is critically important because it binds one substrate and precedes O2 evolution. Herein, we combine X‐ and Q‐band EPR experiments on native and methanol‐treated PSII of Spinacia oleracea and show that methanol‐treated PSII preparations of the S3 state correspond to a previously uncharacterized high‐spin (S=6) species. This is confirmed as a major component also in intact photosynthetic membranes, coexisting with the previously known intermediate‐spin conformation (S=3). The high‐spin intermediate is assigned to a water‐unbound form, with a MnIV 3 subunit interacting ferromagnetically via anisotropic exchange with a coordinatively unsaturated MnIV ion. These results resolve and define the structural heterogeneity of the S3 state, providing constraints on the S3 to S4 transition, on substrate identity and delivery pathways, and on the mechanism of O−O bond formation., Electron paramagnetic resonance spectroscopy reveals that the final metastable catalytic state (S3) in biological water oxidation in higher plants is a mixture of a high‐spin and an intermediate‐spin form. These two forms represent distinct structural components related to water binding and activation on the path towards oxygen evolution.

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2·4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear NiII-LnIII-NiII moiety. The central LnIII ion is bridged to each of the terminal NiII ions through two deprotonated phenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands in distorted octahedral N2O4 environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1–4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave JNiGd = +0.42 cm−1, D = +2.95 cm−1 with gNi = gGd = 1.98. The ferromagnetic nature of the intramolecular Ni···Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (−ΔSm) reaches a maximum of 14.2 J kg−1 K−1 at 2 K. A brief literature survey of complexes containing the NiII-LnIII-NiII moiety is discussed in terms of their structural properties.

Strain effects on

Two new coordination polymers [Cu(btzx)2(MeOH)2](NO3)2 (1) and [Cu(btrcy)2(H2O)2](ClO4)2·btrcy (2) have been synthesized by reacting two bis-triazole/tetrazole-ligands namely m-xylylene-bis(tetrazole) (btzx) and bis(1,2,4-triazole)-trans-cyclohexane (btrcy) with Cu(NO3)2 and Cu(ClO4)2 respectively in a 1:3 metal/ligand ratio. These compounds are shown to form X-ray quality single-crystals under different conditions, and the crystal structures have been determined by single-crystal X-ray diffraction (SXRD). The SXRD data analysis revealed that 1 and 2 are 1D looped chain and 2D-square grid coordination polymers, respectively. More interestingly, the 2D-square grid architecture in 2 acts as an excellent host for the large guest ligand molecule btrcy, which is encapsulated within the voids of the 2D coordination polymer., info:eu-repo/semantics/published

The reactions of Mn(NO3)2·4H2O with the heterocyclic aromatic ligands 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz), 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) and 2,6-bis(pyrazol-1-yl)pyridine (bppy) in MeOH gave the cationic complexes [Mn(L)(NO3)(MeOH)2](NO3) (L = tppz (1), tptz (3), bppy (5)) and the neutral complexes [Mn(L)(NO3)2(S)] (L = tppz, S = H2O (2); L = tptz, S = MeOH (4); L = bppy, S = MeOH (6)), all of which contain the MnII ion in the rare seven-coordinate pentagonal bipyramidal geometry (the crystal structure of 6 contains also a MnII complex showing the rare eight-coordinate triangular dodecahedron geometry). The reactions of Mn(ClO4)2·6H2O with tptz and bppy in MeCN gave [Mn(tptz)(H2O)2(MeCN)](ClO4)2 (7) and [Mn(bppy)2](ClO4)2 (8), in which the MnII ion exhibits six-coordination. Electron Paramagnetic Resonance spectroscopy at X- and Q-band on powder samples was used in order to determine the zero field splitting (ZFS) parameters for 1–4 and 7, 8. All complexes exhibit ZFS parameter, |D| in the range 0.08–0.11 cm−1. The experimentally determined values are in agreement with theoretical calculations which reveal the contribution of each mechanism responsible for the ZFS interaction. The present results add further evidence that for seven-coordinated MnII complexes comprising N/O ligands ZFS is comparable to this found in six-coordinated MnII complexes.

The reaction of Ln(NO3)3·6H2O (Ln = Gd, Tb) and Cu(O2CMe)2·H2O with the polydentate Schiff base ligand OH C10H7 CH NC(C2H5)(CH2OH)2 (H3L) in Me2CO afforded the heptanuclear heterometallic complexes [Cu5Ln2(O2CMe)2(NO3)4(L)2(HL)2] (Ln = Gd (1), Tb (2)) which were characterized by single-crystal X-ray crystallography (1) and powder XRD measurements (2). Both complexes are isomorphous and consist of a central core {CuII5LnIII2(μ3-OR)6(μ3-O2CMe)2}8+ described as two distorted centrosymmetrically related cubane subunits, {CuII3LnIII(μ3-OR)3(μ3-O2CMe)}5+, with the common apex, Cu(1), residing on an inversion center. Peripheral ligation and bridging is provided by two triply and two doubly deprotonated Schiff base ligands, two μ3-acetates and four chelate nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions for both complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 15.7 J kg−1 K−1 at 2 K for ΔH = 5 T. Ac susceptibility measurements of 2 revealed slow magnetic relaxation process suggesting the presence of single-molecule magnet behavior.

Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mossbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol as a probe reaction. (C) 2017 Elsevier Inc. All rights reserved.

The syntheses, crystal and electronic structures are reported of three new mononuclear Mn(III) complexes with the formulae [Mn{(py)2C(OMe)(O)}2(MeOH)2](PF6) (1), [Mn{(py)2C(OMe)(O)}2](PF6) (2) and [Mn{(py)2C(OMe)(O)}2](ClO4) (3), where (py)2C(OMe)(O)− is the monoanion of the hemiacetal form of di-2-pyridyl ketone, (py)2CO. They were obtained from the reactions of (py)2CO with MnF3 in the presence of (NH4)PF6 (1, 2) or NaClO4 (3) in refluxing MeOH. The complex cations are centrosymmetric pseudo-octahedral with a rhombic arrangement of the donor atoms; the anion (py)2C(OMe)(O)− behaves as a N,O-bidentate chelating (η1:η1) ligand in 1 and as a N,O,N-tridentate chelating (η1:η1:η1) ligand in 2 and 3. The 3D architectures of 1–3 are characterized by hydrogen-bonded chains of the cations surrounded by columns of the counterions and are formed through an extensive network of cation–anion hydrogen bonds. The three compounds are the first structurally characterized Mn(III) complexes with (py)2CO-based ligation. Variable-temperature magnetic susceptibility, magnetization isotherms and X-band EPR spectra of 1 and 2 reveal high-spin MnIII atoms (S = 2), anisotropy effects and a positive value of ~ +4 cm−1 of the zero--field splitting parameter D; moreover, EPR spectroscopy indicates the contribution of rhombic and/or higher order terms.

The synthesis, structural characterization and magnetic studies of the 1D coordination polymer [MnIII2MnII(L)2(N3)2(MeOH)2]n (1) is presented. Compound 1 consists of MnIII-MnII-MnIII strictly linear trinuclear repeating units with bis(end-on azido/alkoxo) bridges between the central MnII ion and each one of the terminal MnIII ions, defining two rhombic units [MnIIIMnII(μ1,1-N3)(μ-OR)]. Each repeating unit is further linked to its neighboring ones through two μ-OR groups, defining rhombic units [MnIII2(μ-OR)2], thus promoting the chain structure of 1. The magnetic studies revealed that 1 displays single-chain magnet behavior (SCM) with energy barrier Δ = 53 ± 1 K. Compound 1 is the first example of SCM based on a mixed-valence linear trinuclear unit [MnIII2MnII(μ1,1-N3)2(μ-OR)2].

The Photosystem II (PSII) water oxidation to molecular oxygen process is catalyzed by an oxygen-bridged Mn4CaO5 cluster, known as Oxygen Evolving Complex (OEC) of PSII. The Mn4CaO5 cluster undergoes periodically four one-electron oxidation steps, S0 → S1, S1 → S2, S2 → S3, S3 → S0. The O2 release takes place during the S3-[S4]-S0 transition, S4 being a transient. The intermediates of the S-state transitions are known as metalloradical intermediate states (SiYz ) and involve the free radical of Tyrosine Z (Yz , TyrZ ). In most metalloradical states it was established that Yz interacts magnetically with the Mn4CaO5 cluster. However, in Ca2+- depleted PSII preparations the spin-spin interaction between the Mn4O5 and Yz , during the formation of the S2Yz intermediate state was not strongly supported experimentally. In our effort to investigate the existence of the aforementioned interaction, we took advantance of the NIR sensitivity of the S2 state of Mn4 and examined whether the S2Yz EPR spectrum can be modified. Our EPR experiments, combined with the simulation analysis of the spectra show that reversible modification of the S2 EPR spectrum by NIR irradiation results in a reversible change of the Yz EPR signal shape. These observations strongly support the idea of the magnetic interaction between the Mn4 and tyrosyl radical, upon the formation of the S2Yz metalloradical state in Ca2+- depleted PSII membranes.

Three new complexes namely [Cu(L1)H2O]·2H2O (1), [Cu2(L4)2(DMF)2(H2O)2](NO3)2 (4) and [{Cd2(L4)2Cl2(DMF)2}] (5), and two coordination polymers namely [Co(μ-L2)(DMF)2]·2H2O (2) and [Co(μ-L3)(DMF)2]·H2O (3) have been synthesized from a series of pyrazole-carboxylate ligands namely 1,1′-(ethane-1,2-diyl)bis(5-methyl-1H-pyrazole-3-carboxylic acid) (H2L1), 1,1′-(oxybis(ethane-2,1-diyl))bis(5-methyl-1H-pyrazole-3-carboxylic acid) (H2L2), 1,1′-(butane-1,4-diyl)bis(5-methyl-1H-pyrazole-3-carboxylic acid) (H2L3), and 2-(1′,5,5′-trimethyl-1H,1′H-[3,3′-bipyrazol]-1-yl)acetic acid (H2L4), and CuII/CdII/CoII ions. Single crystal structures of these compounds are discussed in the context of the effect of conformation of the ligands and supramolecular interactions observed within these edifices. Temperature-dependent magnetic data of 4 could be fitted best using two non-interacting CuII ions (S = 1/2) per molecule with giso = 2.28 and a temperature-independent paramagnetism, TIP = 1.75 × 10−5 cm3 mol−1.

The discovery of reactions utilizing previously considered inert functional groups opens up new paths towards the synthesis of desired products. Solutions of mononuclear ferric–pyrazole complexes react with diethyl ether cleaving a C–O bond to form chelating hemiaminals. Upon exposure to diffuse light, the latter react further to yield mononuclear ferrous products containing chelating aminals.

The synthesis and characterization of {[Co5(INA)3(HCOO)7(DMF)(H2O)]·2DMF·4H2O}∞ (INA– = the anion of isonicotinic acid) denoted as Co5‐INA·2DMF·4H2O is reported. The compound was isolated from the reaction of Co(NO3)2·6H2O with HINA in the presence of HCOOH in N,N‐dimethylformamide (DMF) at 100 °C. It exhibits a rigid 3‐D porous structure based on Co5 repeating units which are linked through carboxylate ligands (from HCOO– and INA–) to form an infinite rod‐shaped secondary building unit (SBU). The rods are connected through isonicotinate ligands to produce a unique (3,3,4,4,4‐coordinated) 5‐nodal 3D network with point symbol (4.5.6.72.9)(4.5.62.7.8)(4.5.7)2(5.62.73). Gas sorption studies revealed that Co5‐INA displays a microporous structure with BET area 264.5 m2 g–1 and CO2 uptake of 1.96/1.29 mmol·g–1 at 273/298 K (1 bar), respectively. Magnetism studies revealed that Co5‐INA displays spin canting behavior with a spin glass relaxation process at ca. 5.0 K.

Invited for the cover of this issue are Yann Garcia from Université catholique de Louvain, Belgium, and collaborators from partner universities and research centers. The cover image shows the square grid shape of an unprecedented Cu(II) coordination polymer with an “ancient temple architecture”.

The reaction of Gd(NO3)3·6H2O and [Cu2(piv)4(pivH)2] with the polydentate Schiff base ligands o-OH-C10H6-CH = NC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in MeOH afforded the enneanuclear heterometallic complexes [Cu7Gd2(L1)4(HL1)2(piv)4(H2O)(MeOH)3] (1) and [Cu7Gd2(L2)4(HL2)2(piv)4(MeOH)5] (2). Crystallographic studies revealed that both complexes are isostructural and consist of a central core {Cu7Gd2(μ3-Oalkoxo)6(μ2-Oalkoxo)4(μ2-Opivalato)2}8+. Peripheral ligation and bridging are provided by four triply and two doubly deprotonated Schiff base ligands, two μ3-pivalates, two chelate pivalates, and terminal aqua and/or MeOH molecules. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic intramolecular interactions in both complexes. The magnetocaloric effect of 1 and 2 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 13.3 and 12.1 Jkg-1K−1 for 1 and 2, respectively, at 2 K for ΔH = 5 T.

The mineralogy, morphology, and chemical composition of magnetic fractions separated from fly ashes (FAs) originating from Greek lignite-burning power plants was investigated. The oral bioaccessibility of potentially harmful elements (PHEs) from the fly ash magnetic fractions (FAMFs) was also assessed using in vitro gastrointestinal extraction (BARGE Unified Bioaccessibility Method, UBM). The FAMFs isolated were in the range 4.6-18.4%, and their mass specific magnetic susceptibility ranged from 1138 × 10-8 to 1682 × 10-8 m3/kg. XRD analysis and Mossbauer spectroscopy indicated that the dominant iron species were Fe-rich aluminosilicate glass along with magnetite, hematite, and maghemite (in decreasing order). The raw FAs exhibited differences in their chemical composition, indicating the particularity of every lignite basin. The elemental contents of FAMFs presented trends with fly ash type; thus, the FAMFs of high-Ca FAs were enriched in siderophile (Cr, Co, Ni) and lithophile (Cs, Li, Rb) elements and those separated from low-Ca FAs were presented depleted in chalcophile elements. Based on UBM extraction tests, the PHEs were more bioaccessible from the non-magnetic components of the FAs compared to the magnetic ones; however, the bioaccessible fractions estimated for the FAMFs were exceeding 40 % in many cases. Arsenic was found to be significantly bioaccessible (median ~ 80 %) from FAMFs despite the lower As contents in the magnetic fraction.

Reactions of FeIII sources with 2-pyridyl oxime ligands, pyC(R)NOH (R=H, Me, Ph), afforded the trinuclear oxo-centered complexes (NH4)[Fe3O(LH)6(H2O)3](ClO4)8 ⋅MeOH⋅1.14H2O (1⋅ MeOH⋅1.14H2O) and [Fe3O{pyC(H)NO)(PhCO2)6(H2O)]⋅MeCN (2⋅MeCN), the tetranuclear complex [Fe4(OH)4{pyC(Me)NO}4(H2O)4] (ClO4)4⋅3Me2CO⋅H2O (3⋅3Me2CO⋅H2O), and the hexanuclear complexes [Fe6(OH)6{pyC(Me)NO}6(H2O)6](ClO4)6⋅8Me2CO⋅2H2O (4⋅8Me2CO⋅2H2O), [Fe6(OH)6{pyC(Me)NO}6(MeCONH2)6](ClO4)6⋅2MeCN⋅H2O (5⋅2MeCN⋅H2O), [Fe6(OH)6 {pyC(Ph)NO}6(H2O)6](ClO4)6⋅4.4Me2CO ⋅1.6Et2O (6⋅4.4Me2CO ⋅1.6Et2O) and [Fe6(OH)6{pyC(Ph)NO}6(MeOH)6](ClO4)5.5(OH)0.5⋅MeOH⋅0.5H2O (7⋅MeOH ⋅0.5H2O), where LH is the zwitterion anionic form of 2-pyridinecarboxylic acid (picolinic acid). Complex 3 can be described as inverse 12-metallacrown-4, whereas 4–7 can be described as inverse 18-metallacrowns-6 and represent the first examples of iron(III) metallacyclic clusters with pyC(R)NOH (R=H, Me, Ph) ligands. Complexes 3 and 6 were characterized by Mossbauer spectroscopy and magnetic susceptibility measurements, while complex 2 was characterized by EPR spectroscopy.

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2∙4H2O and lanthanide nitrate salts in a 4 : 2 : 1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear NiII-LnIII-NiII moiety. The central LnIII ion is bridged to each of the terminal NiII ions through two deprotonated phenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands in distorted octahedral N2O4 environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1-4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave JNiGd = +0.42 cm&minus, 1, D = +2.95 cm&minus, 1 with gNi = gGd = 1.98. The ferromagnetic nature of the intramolecular Ni···Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (&minus, &Delta, Sm) reaches a maximum of 14.2 J kg&minus, 1 K&minus, 1 at 2 K. A brief literature survey of complexes containing the NiII-LnIII-NiII moiety is discussed in terms of their structural properties.

The magnetic properties of two trinuclear clusters of the type [CuII3(μ3-X)2X3] with X = Cl (1) and Br (2) are compared. Both clusters exhibit ferromagnetic interactions among the three Cu(II) ions yielding an S = 3/2 ground state. Although the clusters have similar structural features, namely a roughly trigonal bipyramidal geometry defined by the X ligands, they exhibit remarkably different anisotropic magnetic properties. This difference is reflected in the effective ZFS of the ground state: D3/2 = +0.088 cm−1 for 1 versus +1.038 cm−1 for 2 (both values at T ≤ 10 K), which values were determined by high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy in combination with dc magnetic susceptibility measurements; density functional theory (DFT) calculations are in agreement with the experimental results. The anisotropic parameters for 2, are more than ten-fold larger than those for 1, reflecting significant differences in the mixing of halogen (bromine vs. chloride) character into the Cu-3d orbitals. These differences have important consequences on the magnetic relaxation properties of the clusters, as measured by ac magnetic susceptibility. For 1, relaxation pathways within the S = 3/2 state, wherein the MS levels are close in energy, are negligible in the presence of a small external magnetic field, so that much slower relaxation via only the S = 1/2 excited states is operative. For cluster 2, in contrast, ZFS of the S = 3/2 ground state is relatively large and positive, which provides sufficient pathways for relaxation within the ground state and thus no slow relaxation is observed. The present results demonstrate that structurally similar clusters can have very different relaxation properties and the effect of seemingly “innocent” ligands, (i.e., halido ligands) on relaxation properties can be profound.

A comparative study of dielectric, specific heat, and magnetic properties has been carried out between bulk Y3Fe5O12 (YIG) samples which display different behavior regarding the dielectric and ac-susceptibility spectra. Experimental results are presented from two categories of YIG samples (called sample-A and sample-B). Sample-A exhibits zero imaginary part χ ″ ( T ) of the magnetic ac susceptibility whereas sample-B exhibits χ ″ ( T ) curves with two well defined broad maxima in the kHz region. These two maxima can be assigned to two different relaxation regimes. The frequency dependence of real ( e ′ ) and imaginary ( e ″ ) dielectric permittivity of sample-B reveals step-like transitions in e ′ and local maxima in e ″ at the kHz region, which are indicative for several relaxation processes. These processes are not observed in the electric permittivity of sample-A, indicating that dielectric and magnetic relaxation effects depend strongly on the preparation conditions of YIG. Such a completely different spectral behavior among YIG samples corresponds to a direct shape change of absorption sextets in Mossbauer spectra (MS). It was discovered that samples without dispersion in magnetic susceptibility and electric permittivity exhibit MS with distinct broadening of absorption lines in tetrahedral sites, as compared with samples that display dispersion. Moreover, Mossbauer spectroscopy for both categories of samples does not provide evidence for the presence of Fe2+.

The reaction of mixtures of Fe(O2CMe)2·2H2O and Ni(O2CMe)2·4H2O of various compositions with di-2-pyridyl ketone (py2CO, dpk) in MeCN under an inert atmosphere afforded a family of hetero-metallic enneanuclear clusters with general formula [Fe9−xNix(μ4-OH)2(O2CMe)8(py2CO2)4] (2,x= 1.00;3:x= 6.02;4,x= 7.46;5,x= 7.81). Clusters2–5are isomorphous to the homo-metallic [Fe9] cluster (1) previously reported by some of us, and also isostructural to the known homo-metallic [Ni9] cluster. All four clusters contain a central MIIion in an unusual 8-coordinate site and eight peripheral MIIions in distorted octahedral environments. The distribution of FeIIand NiIIions over these two distinct coordination sites in2–5can be established through a combination of X-ray fluorescence and Mössbauer spectroscopies, which show that FeIIpreferentially occupies the unique 8-coordinate metal site while NiIIaccumulates in the octahedral holes. Density functional theory indicates that the distribution of ions across the two sites arises not from any intrinsic preference of the FeIIions for the 8-coordinate sites, but rather because of the large ligand field stabilization energy available to NiIIin octahedral coordination.

A water-soluble octanuclear cluster, [Fe 8 ], was studied with regard to its properties as a potential contrast enhancing agent in magnetic resonance imaging (MRI) in magnetic fields of 1.3, 7.2 and 11.9 T and was shown to have transverse relaxivities r 2 = 4.01, 10.09 and 15.83 mM s −1 , respectively. A related hydrophobic [Fe 8 ] cluster conjugated with 5 kDa hyaluronic acid (HA) was characterized by 57 Fe-Mossbauer and MALDI-TOF mass spectroscopy, and was evaluated in aqueous solutions in vitro with regard to its contrast enhancing properties [r 2 = 3.65 mM s −1 (1.3 T), 26.20 mM s −1 (7.2 T) and 52.18 mM s −1 (11.9 T)], its in vitro cellular cytotoxicity towards A-549 cells and COS-7 cells and its in vivo enhancement of T 2 -weighted images (4.7 T) of a human breast cancer xenografted on a nude mouse. The physiologically compatible [Fe 8 ]-HA conjugate was i.v. injected to the tumor-bearing mouse, resulting in observable, heterogeneous signal change within the tumor, evident 15 min after injection and persisting for approximately 30 min. Both molecular [Fe 8 ] and its HA-conjugate show a strong magnetic field dependence on r 2 , rendering them promising platforms for the further development of T 2 MRI contrast agents in high and ultrahigh magnetic fields.

A two-dimensional network [Mn4(O2C-C6H4-CO2)4(dmf)4(H2O)2]n·2n(dmf) (1·2n(dmf)) is reported. The repeating units in 1 consist of linear tetranuclear subunits [Mn4(O2C-C6H4-CO2)4(dmf)4(H2O)2] linked through the carboxylato groups of the terephthalato ligands. The layers of 1 extend parallel to the bc crystallographic plane and are further associated to 3D supramolecular network through hydrogen bonding interactions. Magnetic susceptibility studies from powdered samples of 1 revealed very weak exchange coupling between the MnII ions within the tetranuclear repeating unit.

The reaction of mixtures of Fe(O

Nucleophilic attack by the carbanion −:CH2COCH3 at the carbonyl group of di-2-pyridyl ketone, (py)2CO, in the presence of CuII under moderately basic conditions has yielded the cationic mononuclear complex [Cu{(py)2C(CH2COCH3)(OH)}2](NO3)2·2H2O (1·2H2O) in ∼40% yield, where (py)2C(CH2COCH3)(OH) is the ligand bis(2-pyridine-2-yl)butane-1-ol-3-one. The CuII atom of the cation sits on a crystallographically imposed inversion center. The neutral molecule is coordinated to the metal ion as a tridentate fac chelating ligand through the hydroxyl oxygen atom and two 2-pyridyl nitrogen atoms. The pyridyl nitrogens are strongly coordinated to the metal ion, while the hydroxyl oxygen atoms form weak bonds with CuII. The coordination geometry at the CuII center is elongated octahedral. Various interactions build the crystal structure of the complex and Hirshfeld surface analysis was applied to evaluate the magnitude of interactions between the different chemical species in the crystal of 1·2H2O. IR, Raman and UV/VIS data of the solid complex are discussed in terms of the coordination mode of (py)2C(CH2COCH3)(OH), the ionic nature of nitrates and the stereochemistry at copper(II). The complex was studied in a frozen solution (MeOH–toluene, 1 : 1 v/v) by CW-EPR spectroscopy and advanced EPR methods such as ENDOR and HYSCORE. The results show that the low symmetry of the cation is retained in solution, with the four nitrogen atoms arranged in a square planar configuration and the unpaired electron residing in an orbital pointing towards them. The bonding parameters in the first coordination sphere and the spin density distribution have been fully analyzed based on the ligand hyperfine coupling constants.

Three novel copper(II) complexes of the antibacterial drug Levofloxacin (LVX), in the presence or absence of heterocyclic ligands such as 1,10-phenanthroline and 2,2-bipyridine, have been synthesized and fully characterized. The interaction of copper(II) with the deprotonated ligand LVX reveals that LVX coordinated to copper atom through the pyridone and one carboxylato oxygen. In case of the mixed ligand complexes the Cu atom is coordinated with two O atoms from LVX ligand and with two N atoms from the hetero-ligands. According to our results the formation of dimers is a typical characteristic for almost all of them. The presence of dimers in the crystal structure is also evident in the EPR spectra and this method can be used as a probe for the existence of such species. A significant characteristic of the structure is the intra- and inter-dimer π–π stacking interaction which governs the packing of complexes in the structure. The synthesized compounds were biologically evaluated. All the complexes show an increased biological activity in comparison with the free ligand.