Strong Antiferromagnetic Interactions Research Articles

Pressure control of magnetic order and excitations in the pyrochlore antiferromagnet MgCr2O4

MgCr2O4 is one of the best-known realizations of the pyrochlore-lattice Heisenberg antiferromagnet. The strong antiferromagnetic exchange interactions are perturbed by small further-neighbor exchanges such that this compound may in principle realize a spiral spin liquid (SSL) phase in the zero-temperature limit. However, a spin Jahn-Teller transition below TN≈13 K yields a complicated long-range magnetic order with multiple coexisting propagation vectors. We present neutron scattering and thermomagnetic measurements of MgCr2O4 samples under applied hydrostatic pressure up to P=1.7 GPa demonstrating the existence of multiple close-lying nearly degenerate magnetic ground states. We show that the application of hydrostatic pressure increases the ordering temperature by around 0.8 K per GPa and increases the bandwidth of the magnetic excitations by around 0.5 meV per GPa. We also evidence a strong tendency for the preferential occupation of a subset of magnetic domains under pressure. In particular, we show that the k=(0,0,1) magnetic phase, which is almost negligible at ambient pressure, dramatically increases in spectral weight under pressure. This modifies the spectrum of magnetic excitations, which we interpret unambiguously as spin waves from multiple magnetic domains. Moreover, we report that the application of pressure reveals a feature in the magnetic susceptibility above the magnetostructural transition. We interpret this as the onset of a short-range ordered phase associated with k=(0,0,1), previously not observed in magnetometry measurements. Published by the American Physical Society 2024

Spin–spin interaction in a highly stable neutral diradical: σ-boned dimer of trioxotriangulene

Abstract A σ-bonded dimer of 4,8,10-trioxotriangulene (TOT) was newly synthesized and its electronic spin structure was characterized. The neutral diradical had a singlet ground state due to the strong antiferromagnetic interaction through the σ-bond. The strong intramolecular interaction within the σ-dimer caused a near-infrared photoabsorption of around 700–1,000 nm, which is close to that of the π-stacked dimer of TOT monoradical.

Cobalt(II) Paddle-Wheel Complex with 3,5-Di(tert-butyl)-4-hydroxybenzoate Bridges: DFT and ab initio Calculations, Magnetic Dilution, and Magnetic Properties

A new binuclear "paddle-wheel" complex, [Co2(bhbz)4(EtOH)2]·4EtOH (1, Hbhbz-3,5-di(tert-butyl)-4-hydroxybenzoic acid); an isostructural zinc complex (2); a and magnetically diluted sample of [Zn1.93Co0.07(bhbz)4(EtOH)2]·4EtOH (3) were obtained. Molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. DFT calculations for 1 indicate strong Co-Co antiferromagnetic exchange interactions in the binuclear fragment. It was shown that when one paramagnetic ion in the binuclear molecule is replaced by a diamagnetic zinc(II) ion, the remaining cobalt(II) ion can be considered as an isolated center with magnetic anisotropy, the parameters of which are determined by ab initio calculations. Magnetic properties for samples 1 and 3 were investigated and analyzed in detail.

Morphology dependent negative dielectric permittivity in spinel ferrite nanostructures

Metamaterials with negative dielectric permittivity has become a research hotspot due to their potential efficacy in various electromagnetic utilizations, such as, filter and antenna design, novel capacitance and inductor design, electromagnetic absorber etc. This study unfurls immense possibilities of inducing metamaterial properties such as negative dielectric permittivity in Magnesium Ferrite, a naturally occurring compound, just by restructuring the morphology. Herein, we report the correlation between structural, dielectric, and magnetic properties of the system in the same chemical composition but different morphologies, namely, nano solid spheres (NSSs) and nano hollow spheres (NHSs). Strikingly, only NHSs show negative dielectric permittivity owing to the Lorentz dielectric resonance in the vicinity of a metamagnetic transition. Further investigations show that the hollow cores and greater number of interfaces in NHSs, in comparison to NSSs, cause the uncompensated charges to accumulate within them and release at some frequencies and temperatures, leading to the backscattering of dipoles, which in turn induces the resonance. NSSs with stronger anti-ferromagnetic interaction and impermeable morphology do not show any sign of negative dielectric permittivity.

Tunable inversion degree of MnIn2S4 thiospinels prepared by high-pressure synthesis, and its implication in the optical and magnetic properties

Indium thiospinels (AIn2S4, A= transition metals) have attracted significant attention due to their potential for manipulating magnetic and optoelectronic properties through changes in chemical composition. Defined in the cubic space group Fd-3 m (No. 227), the crystal structure consists of a framework of edge-sharing InS6 octahedra (Oh symmetry), with A cations coordinated tetrahedrally (Td symmetry) to sulfur. In this study, we describe a rapid high-pressure synthetic method (3.5 GPa) to prepare MnIn2S4 polycrystalline samples, with tunable degree of inversion (λ) or Mn-In antisite, meaning that some Mn occupy the octahedral sites and some In atoms are located at the tetrahedral positions. We found that λ closely depends on the synthesis temperature. Notably, the refinement of the crystal structure from X-ray diffraction data reveals positive correlations between the inversion degree and different properties such as the band gap, expanding its spectral coverage, and the magnetic behavior, depending on the occupancy rate of the octahedral or tetrahedral sites by the strongly magnetic Mn2+ ions. Whereas the paramagnetic behavior is not affected by the inversion degree, for higher λ values (30%<λ < 38%), achieved at synthesis temperatures as high of 800ºC, the random distribution of Mn2+ ions between Td and Oh sites accounts for a spin-glass state with a clear cusp in the magnetic susceptibility (ac and dc), based on the strong short-range antiferromagnetic interactions.

Magnetic properties of an oxo-bridged dinuclear iron(III) complex resulting from the oxidation of mononuclear iron metallacycles with a flexible ethylenediphenylenebis(oxamate) ligand

Transition metal ions such as copper(II), nickel(II), cobalt(II), and manganese(II) are widely used in the formation of mono- or oligonuclear metallacyclic complexes with the flexible N,N’-2,2′-ethylenediphenylenebis(oxamate) ligand (H4edpba); however similar supramolecular complexes with iron(II) and iron(III) are rarely obtained. In this work, we synthesized for the first time a new air-stable oxo-bridged diiron(III) complex of formula {[Fe(H2edpba)(dmso)]2(μ-O)}·dmso·H2O (2) from dioxygen oxidation of the putative mononuclear iron(II) complex precursor of formula [Fe(H2edpba)(H2O)2]Cl (1) in dimethylsulfoxide (dmso). Compound 2 crystallizes in the monoclinic system and contains one oxo group bridging two cationic mononuclear metallacyclic moieties, [Fe(H2edpba)(dmso)]+. The iron(III) ions are also coordinated to four oxygen atoms from the dianionic H2edpba2− ligands in a tetradentate fashion, while an oxygen atom from the coordinated dmso molecules. Mössbauer spectroscopy confirms the presence of high-spin (HS) Fe3+ ions (2). The magnetic properties of 2 reveal a strong antiferromagnetic interaction between the two HS Fe3+ ions (J = −226.46 cm−1), in agreement with the DFT calculations (J = −207.99 cm−1).

Exploring electrochemical and magnetic properties of Fe(III) coordination cluster: An efficient electrocatalyst for water oxidation

In the present study, we investigated the electrochemical, water oxidation and magnetic properties of iron complex, [Fe6III(µ3-O)2(piv)6(edteH)2(N3)2] (1), (where = piv: pivalic acid and edteH4; N,N,N′,N′-Tetrakis(2-hydroxyethyl)ethylenediamine). To investigate the electrocatalytic activity of 1 for water splitting, linear sweep voltammetry (LSV) was executed to acquire the polarization curve at a scan rate of 5 mVs−1. Electrochemical Impedance Spectroscopy (EIS) was measured to obtain resistance values. The electrochemical investigation indicates about the high efficiency of the complex for the oxidation of water and overpotential 210 mV with 10 mA.cm−2 inclusive of Tafel slope of 88 m.V.dec−1. The high value of current density confirms about the proof of oxygen evolution behavior for the complex. In EIS study, the low value of charge transfer resistance indicates the fast kinetics in water-splitting process (OER) which complies with the LSV results and tafel slopes. In chronopotentiometry test, there was no significant catalytic degradation and no observable change in potential over 24 h that is confirmation about excellent stability of the compound. Magnetic study reveals the existence of strong antiferromagnetic interactions in this complex. Moreover, magnetization indicates a value of 10.02 at 70 kOe which is a good Brillouin fitting with S = 5.0 and g = 2.0.

Effects of Difluorophenyl Substituents on Structural, Redox, and Magnetic Properties of Blatter Radicals

Blatter radicals 1-(3,4-difluorophenyl)-(1a) and 1-(2,4-difluorophenyl)-3-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (1b) were prepared in good yields through oxidation of the corresponding amidrazones using MnO2 in dry CH2Cl2. Cyclic voltammetry showed that both radicals are oxidized and reduced chemically and electrochemically reversibly in accordance with −1/0 and 0/+1 processes. EPR spectroscopy indicated that spin density is mainly delocalized on the triazinyl moiety of the heterocycle. The structure of all paramagnets was unambiguously confirmed by single-crystal X-ray diffraction, and two different 1D chains of alternating radicals were identified. 3,4-difluorophenyl-derivatives 1a are packed into columns composed of two kinds of alternating centrosymmetric dimers, having comparatively short intermolecular distances. In crystals of 2,4-difluorophenyl-derivative 1b, the parallel arrangement of bicyclic moieties and phenyl rings favors the formation of 1D regular chains wherein the radicals are related by translation parallel to the crystallographic stacking axis. Magnetic susceptibility measurements in the 2–300 K region showed that in crystals of the radicals, strong antiferromagnetic interactions are dominant. Subsequent fitting of the dependence of χT on T with 12-membered looped stacks gave the following best-fit parameters: for 1a, g = 2.01 ± 0.05, J1/kB = −292 ± 10 K (according to BS-DFT calculations J2 = 0.12 × J1 and J3 = 0.61 × J1); for 1b, g = 2.04 ± 0.01 J1/kB = −222 ± 17 K. For comparison, in a nonfluorinated related radical, there are only very weak intermolecular interactions along the columns (J/kB = −2.2 ± 0.2 K). These results illustrate the magnitude of the influence of the difluorophenyl substituents introduced into Blatter radicals on their structure and magnetic properties.

Magnetic Anisotropy in a Verdazyl-Based Complex with Cobalt(II)

A verdazyl-based complex with Co2+ ion, (p-Py-V-p-Br)2[Co(hfac)2], was successfully synthesized. The molecular arrangement indicates that spins on the radical and Co form a one-dimensional (1D) spin chain, where the intermolecular interaction between the radicals and the intramolecular interaction between the radical and Co exhibit threefold periodicity. The strong antiferromagnetic interaction between radical spins forms a nonmagnetic singlet dimer, yielding paramagnetic behavior associated with the residual spins on the Co2+ ion in the low-temperature region. We evaluated the anisotropic g values by analyzing the electron spin resonance powder patterns. Furthermore, we considered the spin–orbit coupling and distorted crystal fields of the Co2+ ion and explained the triaxial anisotropic behavior. We also evaluated the anisotropy of the expected effective exchange interaction between the fictitious spins on the Co2+ ions, indicating the existence of an Ising-like exchange interaction. These results demonstrate that the strong spin–orbit coupling of the Co2+ ion in the present verdazyl-based compound yields an effective spin-1/2 with anisotropic g values and Ising-like exchange interactions.

Synthesis of copper(II) halide dimers with 2-amino-5-methylpyridine and serendipitous copper catalyzed synthesis of 3-bromo-2-ethyl-5-methyl-1H-pyrrolo[2,3-b]pyridine

Reaction of CuX2·nH2O (X = Cl, n = 2; X = Br, n = 0) with 2-amino-5-methylpyridine (5MAP) in acetonitrile yielded [(5MAP)2CuX2]2 (1, Cl; 2, Br). The compounds are isomorphous and crystallize in the monoclinic space group P21 /n as bihalide bridged dimers. Variable temperature magnetic measurements show very weak exchange in the two compounds (-2.1(1) K) which may correlate with previously proposed magnetostructural correlations for bihalide bridged Cu(II) dimers. In attempts to prepare 2 in 2-butanone as solvent, [(3-Br-2-Et-5-Mepyrpy)(CH3CO2)4Cu2] (3) was serendipitously isolated (3-Br-2-Et-5-Mepyrpy = 3-bromo-2-ethyl-5-methyl-7H-pyrrolido[2,3-b]pyridinium). The bicyclic ligand was synthesized in situ by condensation of 5MAP with the solvent; the acetate ions were generated by copper(II) catalyzed Baeyer-Villiger oxidation of the solvent. A mechanism for the synthesis is proposed. The resulting Cu-paddlewheel compound exhibits strong (-400 K) antiferromagnetic interactions.

A family of methoxide-bridged Cu(II) compounds with N-heterocyclic ligands: dimers and chains

Three new methoxide-bridged Cu(II) dimers are reported: tetrakis(2-methylpyrazine)di(μ-methoxy)diperchloratodicopper(II) (1), tetrakis(2-amino-5-iodopyridine)dibromide-di-μ-methoxydicopper(II) tetramethanol (2) and catena[(2-amino-5-methylpyridine)μ-bromido-μ-methoxycopper(II) (3). The compounds were characterized by single-crystal X-ray diffraction and variable temperature magnetic measurements. All three compounds crystallize in the triclinic space group P-1, and the dimers lie across a crystallographic inversion center. The dimers in 3 are further bridged into an alternating chain motif via semi-coordinated Cu(II)/Br interactions. All three compounds exhibit strong antiferromagnetic interactions with J/kB = −348(8) K for 1, and the exchange in 2 and 3 being too strong to estimate from the available data. The magnetic data for 1-3 are dominated by trace paramagnetic impurities at temperatures below 200 K. Correlation of the structures with the observed magnetic behavior is proposed.

New Dinuclear Macrocyclic Copper(II) Complexes as Potentially Fluorescent and Magnetic Materials.

Two dinuclear copper(II) complexes with macrocyclic Schiff bases K1 and K2 were prepared by the template reaction of (R)-(+)-1,1'-binaphthalene-2,2'-diamine and 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde K1, or 4-tert-butyl-2,6-diformylphenol K2 with copper(II) chloride dihydrate. The compounds were characterized by spectroscopic methods. X-ray crystal structure determination and DFT calculations confirmed their geometry in solution and in the solid phase. Moreover, intermolecular interactions in the crystal structure of K2 were analyzed using 3D Hirshfeld surfaces and the related 2D fingerprint plots. The magnetic study revealed very strong antiferromagnetic CuII-CuII exchange interactions, which were supported by magneto-structural correlation and DFT calculations conducted within a broken symmetry (BS) framework. Complexes K1 and K2 exhibited luminescent properties that may be of great importance in the search for new OLEDs. Both K1 and K2 complexes showed emissions in the range of 392-424 nm in solutions at various polarities. Thin materials of the studied compounds were deposited on Si(111) by the spin-coating method or by thermal vapor deposition and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The thermally deposited K1 and K2 materials showed high fluorescence intensity in the range of 318-531 nm for K1/Si and 326-472 nm for the K2/Si material, indicating that they could be used in optical devices.

Structural Diversity, XAS and Magnetism of Copper(II)-Nickel(II) Heterometallic Complexes Based on the [Ni(NCS)6]4- Unit.

The new heterometallic compounds, [{Cu(pn)2}2Ni(NCS)6]n·2nH2O (1), [{CuII(trien)}2Ni(NCS)6CuI(NCS)]n (2) and [Cu(tren)(NCS)]4[Ni(NCS)6] (3) (pn = 1,2-diaminopropane, trien = triethylenetetramine and tren = tris(2-aminoethylo)amine), were obtained and characterized by X-ray analysis, IR spectra, XAS and magnetic measurements. Compounds 1, 2 and 3 show the structural diversity of 2D, 1D and 0D compounds, respectively. Depending on the polyamine used, different coordination polyhedron for Cu(II) was found, i.e., distorted octahedral (1), square pyramidal (2) and trigonal bipyramidal (3), whereas coordination polyhedron for nickel(II) was always octahedral. It provides an approach for tailoring magnetic properties by proper selection of auxiliary ligands determining the topology. In 1, thiocyanate ligands form bridges between the copper and nickel ions, creating 2D layers of sql topology with weak ferromagnetic interactions. Compound 2 is a mixed-valence copper coordination polymer and shows the rare ladder topology of 1D chains decorated with [CuII(tren)]2+ antennas as the side chains attached to nickel(II). The ladder rails are formed by alternately arranged Ni(II) and Cu(I) ions connected by N2 thiocyanate anions and rungs made by N3 thiocyanate. For the Cu(I) ions, the tetrahedral thiocyanate environment mixed N/S donor atoms was found, confirming significant coordination spheres rearrangement occurring at the copper precursor together with the reduction in some Cu(II) to Cu(I). Such topology enables significant simplification of the magnetic properties modeling by assuming magnetic coupling inside {NiIICuII2} trinuclear units separated by diamagnetic [Cu(NCS)(SCN)3]3- linkers. Compound 3 shows three discrete mononuclear units connected by N-H…N and N-H…S hydrogen bonds. Analysis of XAS proves that the average ligand character and the covalency of the unoccupied metal d-based orbitals for copper(II) and nickel(II) increase in the following order: 1 → 2 → 3. In 1 and 2, a weak ferromagnetic coupling between copper(II) and nickel(II) was found, but in 2, additional and stronger antiferromagnetic interaction between copper(II) ions prevailed. Compound 3, as an ionic pair, shows, as expected, a spin-only magnetic moment.

Stoichiometry driven tuning of physical properties in epitaxial Fe3-xCrxO4 thin films

Tuning magnetic and electronic transport properties in spinel oxides requires a faithful description between chemical composition and cation site-occupation. Here this challenge is addressed using Fe3-xCrxO4 thin films grown by oxygen-assisted molecular-beam epitaxy within a wide range of composition (0.0 ≤ x ≤ 1.2). Spectroscopic measurements (e.g., X-ray magnetic circular dichroism), refined by theoretical simulations (e.g., crystal field multiplet), are performed to establish a quantitative link between chromium content, Fe2+/Fe3+ site-occupation and macroscopic physical properties of the layers. It is found that Fe3-xCrxO4 thin films (i) delay the transition from inverse to normal spinel configuration with increasing chromium content and (ii) promote collinear spin structure, at odds with bulk material. As a result, strong antiferromagnetic interactions are preserved between spins in tetrahedral and octahedral spinel sublattices, so that chromium-rich thin films exhibit Curie temperatures above room temperature and higher magnetization. Electron hopping is also favored by this singular cation distribution and electronic band gap is smaller than expected for these thin films. The cation site-occupation is therefore a key feature to consider for applications of Fe3-xCrxO4 thin films in spintronics and photocatalysis, as it enables manipulation of magnetic properties (Curie temperature and magnetization) and band gap engineering.

СИНТЕЗ, СТРОЕНИЕ И МАГНИТНЫЕ СВОЙСТВА КОМПЛЕКСОВ Cu(II) НА ОСНОВЕ 4,6-ДИМЕТИЛПИРИМИДИЛГИДРАЗОНА ДИАЦЕТИЛМОНОКСИМА: ЭКСПЕРИМЕНТАЛЬНОЕ И ТЕОРЕТИЧЕСКОЕ ИССЛЕДОВАНИЕ

In order to study the effect of the dimethylpyrimine fragment nature on the structure and magnetic properties of coordination compounds, new binuclear Cu(II) metallochelates were synthesized. The coordination compounds are [Cu2(HL)2(CH3OH)2](ClO4)2 (1) and [Cu2(HL)2(NO3)2] (2), where HL – the monodeprotonated form of 2-hydrazino-4,6-dimethylpyrimidine and diacetylmonoxime condensation product. The structure and properties of complexes were established using elemental analysis, 1H NMR, IR-spectroscopy, magnetochemistry. It was shown that the coordination compounds are diamagnetic at room temperature due to the strong antiferromagnetic exchange interaction between paramagnetic Cu(II) ions: −2J &gt; 1000 cm−1. The data obtained are in a good agreement with the results of quantum chemical calculations (theory level B3LYP/6 311G(d)).

A bis-calix[4]arene-supported [CuII16] cage.

Reaction of 2,2'-bis-p-tBu-calix[4]arene (H8L) with Cu(NO3)2·3H2O and N-methyldiethanolamine (Me-deaH2) in a basic dmf/MeOH mixture affords [CuII16(L)2(Me-dea)4(μ4-NO3)2(μ-OH)4(dmf)3.5(MeOH)0.5(H2O)2](H6L)·16dmf·4H2O (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu12], in which the four capping metal ions are the CuII ions housed in the calix[4]arene polyphenolic pockets. The [CuII8] square prism is held together "internally" by a combination of hydroxide and nitrate anions, with the N-methyldiethanolamine co-ligands forming dimeric [CuII2] units which edge-cap above and below the upper and lower square faces of the prism. Charge balance is maintained through the presence of one doubly deprotonated H6L2- ligand per [Cu16] cluster. Magnetic susceptibility measurements reveal the predominance of strong antiferromagnetic exchange interactions and an S = 1 ground state, while EPR is consistent with a large zero-field splitting.

Thermally induced dimensionality changes in derivatives of a "super stable" Blatter radical.

Two derivatives of a "super stable" Blatter radical (1,3-diphenyl-7-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl) with N(1)-Ar = 2-CF3C6H4 and 2-MeOC6H4 were obtained and investigated using XRD and SQUID magnetometry methods. The investigation revealed strong antiferromagnetic interactions in both radicals, which are described using the Hatfield model. For the latter radical, an abrupt and reversible change in the χ(T) plot was observed at 29 K. It was ascribed to a structural transition, consistent with a two-dimensional to one-dimensional thermally activated crossover, as supported by specific heat measurements (CvHvs. T). It is suggested that the transition is related to an order-disorder transition of the CF3 group, which is corroborated using XRD structural analysis.

Syntheses and magnetic properties of a bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine and its metal complexes.

A novel bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine, NIT-2-TrzPm (NIT-2-TrzPm = (2-(2'-triazolopyrimidine)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)) and six new transition metal complexes of this ligand, namely [M(hfac)2(NIT-2-TrzPm)]·CH2Cl2 (M = Mn (1Mn) and Co (2Co)), [M(hfac)2]2(NIT-2-TrzPm) (M = Mn (3Mn) and Co (4Co)), [Mn(NIT-2-TrzPm)2(MeOH)2](ClO4)2·MeOH (5Mn), and [Co(NIT-2-TrzPm)2(MeOH)2]2(ClO4)4·4MeOH (6Co) were prepared and characterized structurally and magnetically. These complexes can be selectively synthesized by controlling the reaction ratio of M(hfac)2·2H2O to the radical ligand (for 1Mn to 4Co) or using metal perchlorates as the starting materials (for 5Mn and 6Co). Single crystal X-ray crystallographic analyses confirmed that 1Mn and 2Co are isostructural 3d-2p MII-radical complexes, in which the NIT-2-TrzPm radical acts as a terminal bidentate ligand chelating to one 3d ion, while 3Mn and 4Co are isostructural 3d-2p-3d MII-radical-MII complexes with the NIT-2-TrzPm radical acting as a bridging ligand between two 3d ions. For complexes 5Mn and 6Co, two NIT-2-TrzPm ligands from the equatorial positions coordinate with the metal center to form the 2p-3d-2p structures with the axial positions occupied by two methanol molecules. Magnetic analysis on the MnII complexes revealed the existence of a strong antiferromagnetic interaction between the MnII and the NIT radical spin, while weak ferromagnetic coupling for Mn⋯Mn and Rad⋯Rad in the Mn-NIT-Mn and Rad-Mn-Rad spins was confirmed. Interestingly, although the NIT-bridged complexes 3Mn and 4Co possess significantly different magnetic anisotropy, field-induced slow magnetic relaxation can be observed in both complexes, which was assigned to the phonon bottleneck effect for 3Mn and field-induced SMM behavior for 4Co. To the best of our knowledge, 3Mn is the first example of the NIT-bridged binuclear MnII complex undergoing slow magnetic relaxation.

New CuSO4‐related high‐temperature polymorph of AgIISO4**

AbstractSilver(II) compounds exhibit powerful oxidizing properties and strong magnetic superexchange, but most of them comprise fluoride ligands. AgSO4 is a rare fluorine‐free salt of Ag(II) which found some application in organic chemistry. Here, we report a discovery of a new AgSO4 polymorph (β). The distinct nature of the two polytypes of AgSO4 is established using powder X‐ray diffraction, vibrational spectroscopy and theoretical calculations. The β polymorph crystallizes in the monoclinic system (P21/n) and shows structural similarities with CuSO4. DFT calculations indicate very small differences in the energy of the two AgSO4 polymorphs and that the relative stability of the β polymorph should increase with temperature. The monoclinic distortion of the orthorhombic CuSO4 prototype originates from an unprecedented strong antiferromagnetic interaction between Ag sites along the unit cell diagonal.

Linker Redox Mediated Control of Morphology and Properties in Semiconducting Iron-Semiquinoid Coordination Polymers.

The emergence of conductive 2D and less commonly 3D coordination polymers (CPs) and metal-organic frameworks (MOFs) promises novel applications in many fields. However, the synthetic parameters for these electronically complex materials are not thoroughly understood. Here we report a new 3D semiconducting CP Fe5 (C6 O6 )3 , which is a fusion of 2D Fe-semiquinoid materials and 3D cubic Fex (C6 O6 )y materials, by using a different initial redox-state of the C6 O6 linker. The material displays high electrical conductivity (0.02 S cm-1 ), broad electronic transitions, promising thermoelectric behavior (S2 σ=7.0×10-9 W m-1 K-2 ), and strong antiferromagnetic interactions at room temperature. This material illustrates how controlling the oxidation states of redox-active components in conducting CPs/MOFs can be a "pre-synthetic" strategy to carefully tune material topologies and properties in contrast to more commonly encountered post-synthetic modifications.