Intrachain Interactions Research Articles

Synthesis, structures and magnetic properties of two new hydrazine bridged 1D cobalt(II) coordination polymers

Two new hydrazine bridged 1D CoII coordination polymers formulated as [Co(N2H4)2F]Cl (1) and Co(N2H4)(H2O)2F2 (2) have been synthesized and magnetically characterized. Compound 1 consists of one-dimensional hydrazine-fluoride mixed bridged CoII chain, while compound 2 exhibits hydrazine bridged CoII chain with fluoride as terminal ligand. Magnetic susceptibility measurements reveal that compound 1 exhibits 1D antiferromagnetic characterization with a long-range ordering at 10.2 K, while compound 2 does not show long-range ordering above 2 K with antiferromagnetic intrachain interactions.

Self-assembled helical superstructures of polystyrene-b-poly(2-vinyl pyridine) with inversed helicity from induced chirality

This work aimed to examine the self-assembling behaviors of polystyrene-b-poly(2-vinyl pyridine) (PS-P2VP) complexed with chiral dopants, R-/S-mandelic acid (R-/S-MA). Induced vibrational circular dichroism (VCD) due to intra-chain chiral interaction suggests the formation of helical P2VP with preferred handedness by complexation with R-/S-MA, demonstrating the induced circular dichroism (ICD) behaviors for the C-C single bond without high-degree tacticity. Owing to the microphase separation, helical superstructures with controlled helicity could be formed from the self-assembly of PS-P2VP with ICD. Most interestingly, the self-assembled helical ribbon exhibits reversed helical sense to the helical P2VP, as evidenced by induced VCD through inter-chain chiral interaction and rationalized using cholesteric hard-core model due to a large value of P/d ratio.

Intrachain interaction topology can identify functionally similar intrinsically disordered proteins

Functionally similar IDPs (intrinsically disordered proteins) often have little sequence similarity. This is in stark contrast to folded proteins and poses a challenge for the inverse problem, functional classification of IDPs using sequence alignment. The problem is further compounded because of the lack of structure in IDPs, preventing structural alignment as an alternate tool for classification. Recent advances in heteropolymer theory unveiled a powerful set of sequence-patterning metrics bridging molecular interaction with chain conformation. Focusing only on charge patterning, these set of metrics yield a sequence charge decoration matrix (SCDM). SCDMs can potentially identify functionally similar IDPs not apparent from sequence alignment alone. Here, we illustrate how these information-rich “molecular blueprints” encoded in SCDMs can be used for functional classification of IDPs with specific application in three protein families—Ste50, PSC, and RAM—in which electrostatics is known to be important. For both the Ste50 and PSC protein family, the set of metrics appropriately classifies proteins in functional and nonfunctional groups in agreement with experiment. Furthermore, our algorithm groups synthetic variants of the disordered RAM region of the Notch receptor protein—important in gene expression—in reasonable accordance with classification based on experimentally measured binding constants of RAM and transcription factor. Taken together, the novel classification scheme reveals the critical role of a high-dimensional set of metrics—manifest in self-interaction maps and topology—in functional annotation of IDPs even when there is low sequence homology, providing the much-needed alternate to a traditional sequence alignment tool.

Roles of repeating-unit interactions in the stress relaxation process of bulk amorphous polymers

How the repeating-unit chemistry dominates polymer viscoelasticity remains as unclear. We employed four-set interaction parameters to represent thermodynamic and kinetic aspects of local intrachain and interchain interactions between monomers, which characterize polymer repeating-unit chemistry. We performed kinetic Monte Carlo simulations of Debye stress relaxation in stretched and parallel-aligned bulk amorphous polymers and evaluated the relative importance of each interactions in the diffusion energy derived from their Arrhenius fluid behaviors. The results demonstrated that, under the same strengths, the kinetic aspects of intrachain and interchain interactions raise much higher diffusion energies than their thermodynamic aspects. We discussed the example case of polyethylene. Our work paves the way towards the prediction of the structure-property relationship of the mechanical properties in bulk amorphous polymers.

Structural and magnetic properties of the quantum magnet BaCuTe2O6

We investigate the structural and magnetic properties of the new quantum magnet BaCuTe$_2$O$_6$. This compound is synthesized for the first time in powder and single crystal form. Synchrotron X-ray and neutron diffraction reveal a cubic crystal structure (P4$_1$32) where the magnetic Cu$^{2+}$ ions form a complex network. Physical properties measurements suggest the presence of antiferromagnetic interactions with a Curie-Weiss temperature of -33K, while long-range magnetic order occurs at the much lower temperature of ~6.3K. The magnetic structure, solved using neutron diffraction, reveals antiferromagnetic order along chains parallel to the a, b and c crystal axes. This is consistent with the magnetic excitations which resemble the multispinon continuum typical of the spin-1/2 Heisenberg antiferromagnetic chain. A consistent intrachain interaction value of ~34K is achieved from the various techniques. Finally the magnetic structure provides evidence that the chains are coupled together in a non-colinear arrangement by a much weaker antiferromagnetic, frustrated hyperkagome interaction.

Quasi-one-dimensional magnetic properties of NiNb2−xVxO6 compounds synthesized at high pressure in a nonstandard columbite-type structure

We report on the low-dimensional magnetic behavior of the series of compounds ${\mathrm{NiNb}}_{2\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{O}}_{6}$ ($0\ensuremath{\le}x\ensuremath{\le}2$), with a columbite-type crystal structure stabilized at high pressure and temperature. Based on susceptibility, magnetization, and specific-heat measurements, the system is characterized as presenting quasi-one-dimensional magnetism, with ${\mathrm{Ni}}^{2+}$ magnetic moments that can be modeled as Ising spins, placed along zigzag chains in the crystal structure. The low-temperature phase is found to consist of an antiferromagnetic arrangement of ferromagnetic chains, and a metamagnetic transition to uniform ferromagnetic order is observed under magnetic fields slightly above ${\ensuremath{\mu}}_{0}H=1\phantom{\rule{4pt}{0ex}}\mathrm{T}$. We discuss the effects of substituting vanadium for niobium, maintaining the same crystal structure along the whole series of samples. In particular, the long-range magnetic order, most clearly seen for $x=0$, tends to be suppressed as the vanadium content is increased. The exchange interactions are quantified, revealing that the ferromagnetic intrachain interactions vary from about $7\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for ${\mathrm{NiNb}}_{2}{\mathrm{O}}_{6}$ to $2\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for ${\mathrm{NiV}}_{2}{\mathrm{O}}_{6}$, remaining one order of magnitude larger than the mean antiferromagnetic interchain coupling.

Magnetic ground state of the one-dimensional ferromagnetic chain compoundsM(NCS)2(thiourea)2(M=Ni,Co)

The magnetic properties of the two isostructural molecule-based magnets, Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several techniques in order to rationalise their relationship with structural parameters and ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like ($D < 0$) single-ion anisotropy ($D_{\rm{Co}} \sim$ -100 K, $D_{\rm{Ni}} \sim$ -10 K). Crystal and electronic structure, combined with DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with ferromagnetic intrachain exchange interactions $J_{\rm{Co}}\approx+4$ K and $J_{\rm{Ni}}\sim+100$ K and weak antiferromagnetic interchain exchange, on the order of $J'$ $\sim-0.1$ K. Electron charge and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in $J$-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where DTN is know to harbour two magnetic field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic change in both the structural and magnetic properties.

Withanone from Withania somnifera Attenuates SARS-CoV-2 RBD and Host ACE2 Interactions to Rescue Spike Protein Induced Pathologies in Humanized Zebrafish Model.

PurposeSARS-CoV-2 engages human ACE2 through its spike (S) protein receptor binding domain (RBD) to enter the host cell. Recent computational studies have reported that withanone and withaferin A, phytochemicals found in Withania somnifera, target viral main protease (MPro) and host transmembrane TMPRSS2, and glucose related protein 78 (GRP78), respectively, implicating their potential as viral entry inhibitors. Absence of specific treatment against SARS-CoV-2 infection has encouraged exploration of phytochemicals as potential antivirals.AimThis study aimed at in silico exploration, along with in vitro and in vivo validation of antiviral efficacy of the phytochemical withanone.MethodsThrough molecular docking, molecular dynamic (MD) simulation and electrostatic energy calculation the plausible biochemical interactions between withanone and the ACE2-RBD complex were investigated. These in silico observations were biochemically validated by ELISA-based assays. Withanone-enriched extract from W. somnifera was tested for its ability to ameliorate clinically relevant pathological features, modelled in humanized zebrafish through SARS-CoV-2 recombinant spike (S) protein induction.ResultsWithanone bound efficiently at the interacting interface of the ACE2-RBD complex and destabilized it energetically. The electrostatic component of binding free energies of the complex was significantly decreased. The two intrachain salt bridge interactions (K31-E35) and the interchain long-range ion-pair (K31-E484), at the ACE2-RBD interface were completely abolished by withanone, in the 50 ns simulation. In vitro binding assay experimentally validated that withanone efficiently inhibited (IC50=0.33 ng/mL) the interaction between ACE2 and RBD, in a dose-dependent manner. A withanone-enriched extract, without any co-extracted withaferin A, was prepared from W. somnifera leaves. This enriched extract was found to be efficient in ameliorating human-like pathological responses induced in humanized zebrafish by SARS-CoV-2 recombinant spike (S) protein.ConclusionIn conclusion, this study provided experimental validation for computational insight into the potential of withanone as a potent inhibitor of SARS-CoV-2 coronavirus entry into the host cells.

Room temperature self-healing crosslinked elastomer constructed by dynamic urea bond and hydrogen bond

Designing a crosslinked polymer with autonomous self-healing at room temperature (RT) remains an arduous challenge because the topological network reconstructions are governed by crosslinking. Herein, a flexible strategy is described to develop intrinsically dynamic crosslinked elastomers with RT self-healing via a photo-initiated copolymerization to address these issues. The key is to incorporate a urea–urethane structure with dynamic urea bond into the polymer network as a flexible crosslinking unit. This strategy endows the crosslinked elastomer with superior properties, including autonomously rapid self-healing at RT, extreme stretchability of up to 1726%, high toughness (∼24.45 MJ m–3), extended stability, and recyclability. Upon damaged, the resultant elastomers instantly self-heal at RT and completely self-heal within 10 min without the assistance of external triggers. These amazing properties of the dynamic elastomer are attributed to the synergistic effect of the robustly dynamic urea bonds and inter- and intrachain hydrogen bond interactions. Notably, the self-healing and mechanical properties of the network can be optimized by tuning the dynamic crosslinker content. Dynamic reversibility occurs at RT evidenced by rheological tests. The facile fabrication method and multifunctional properties of the self-healable and stretchable crosslinked elastomer demonstrate that it shows great potential in smart protective coating and wearable electronics industry.

Synthesis, Crystallization, Structure Memory Effects, and Molecular Dynamics of Biobased and Renewable Poly(n-alkylene succinate)s with n from 2 to 10

In this article, we synthesize five poly(n-alkylene succinate)s, PnASs, with n = 2, 4, 6, 8, and 10 via multi-step polycondensation methods. Next, we comparatively investigate these renewable and biobased polyesters from the points of view of structure, crystallinity, and molecular mobility, employing 1H nuclear magnetic resonance spectroscopy, size-exclusion chromatography, viscometry, X-ray diffraction, differential scanning calorimetry (DSC, conventional and temperature modulation modes), polarized optical microscopy (POM), and broadband dielectric relaxation spectroscopy (BDS). Next to the successful synthesis of the materials, we evaluate the characteristics of crystallization (temperature and fraction); moreover, we explore for the first time, on the same type of succinic polyesters, the impact of n on the structure memory related to crystal nucleation as well as the changes in the semicrystalline morphology. We demonstrate that the structure/crystal memory is stronger for the lower n (shorter alkylene succinate monomers) because of more chain–chain associations, the result being independent from the overall length of the polymer chain (molar mass, Mn 13–80 kg/mass). The crystalline fraction (CF ∼ 12–34%) increases with n, also independently from Mn; however, the chain length affects directly the nucleation rate as Tc increases with Mn. The direct effects of n, in the inter-/intrachain interactions, as well as the indirect ones, on the CF and distribution of crystallites were found to be responsible for the alternations in the static glass transition temperature in DSC (lowering of Tg with n) and the dynamic glass transition (α, αc relaxations in BDS). For the sum of these PnASs, the molecular dynamics mapping is shown here, also for the first time. With increasing n, segmental dynamics accelerates, whereas, interestingly, the cooperativity drops (elimination for n = 10). Comparing these results with the recorded alternations in the semicrystalline morphology (POM), we conclude spatial confinement to be imposed on the mobile amorphous polymer by the tightly distributed crystallites when n increases. Overall, these data provide proofs for the potential for tuning of the final polymer properties connected with crystallization (mechanical performance and permeability), envisaging future biomedical, packaging, and other application for these PnASs.

Synthesis, structures and magnetic properties of copper(II) complexes with 1,2,3-triazole derivate as ligand: a single-crystal-to-single-crystal transformation from mononuclear to polymeric complex of copper(II)

A new mononuclear complex Cu(tdp)Br2·MeCN (1, tdp = 2,2′-(1H-1,2,3-triazole-1,4-diyl)dipyridine) has been synthesized, which can transform to a 1D coordination polymer [Cu(tdp)Br2]n (2) under ambient conditions through an irreversible single-crystal-to-single-crystal transformation process. The loss of lattice MeCN molecules in 1 was accompanied by the generation of new covalent bonds and an increase in dimensionality from 0 to 1D, leading to a change in magnetic exchange couplings between the adjacent Cu(II) ions. Magnetic susceptibility measurements indicate that 1 exhibits ferromagnetic interactions between the adjacent Cu(II) centers, while the intrachain magnetic interactions between Cu(II) ions are antiferromagnetic within 2.

Advances in the Multi-Orthogonal Folding of Single Polymer Chains into Single-Chain Nanoparticles.

The folding of certain proteins (e.g., enzymes) into perfectly defined 3D conformations via multi-orthogonal interactions is critical to their function. Concerning synthetic polymers chains, the “folding” of individual polymer chains at high dilution via intra-chain interactions leads to so-called single-chain nanoparticles (SCNPs). This review article describes the advances carried out in recent years in the folding of single polymer chains into discrete SCNPs via multi-orthogonal interactions using different reactive chemical species where intra-chain bonding only occurs between groups of the same species. First, we summarize results from computer simulations of multi-orthogonally folded SCNPs. Next, we comprehensively review multi-orthogonally folded SCNPs synthesized via either non-covalent bonds or covalent interactions. Finally, we conclude by summarizing recent research about multi-orthogonally folded SCNPs prepared through both reversible (dynamic) and permanent bonds.

Magnetic relaxation in dysprosium and terbium 1D-zigzag coordination chains having only 4,4′-bipyridine as connector

The coordination chain {[Dy(dbm)3bpy]·C7H8}n(1) having only 4,4′-bipyridine as connector has been prepared in high yield and its structural and magnetic properties have been investigated. It is isostructural with the terbium analogue {[Tb(dbm)3bpy]·C7H8}n(2) and features units repeating in a 1D-zigzag fashion, where the metal is octa-coordinated in a distorted square antiprism geometry. Despite the 1D structure, the absence of paramagnetic connectors prevents the direct magnetic intrachain interaction among the lanthanide ions. In zero magnetic field, only a small fraction of the magnetization of 1 displayed slow dynamics with no dependence on temperature. Upon application of a 1 kOe magnetic field, a relaxation process appears, compatible with a mixed Raman/Direct mechanisms. Magnetic dilution in the diamagnetic Y(III)-based analogue revealed that actually two distinct relaxation processes are active for 1, whose temperature dependence can be interpreted again with a mixed Raman/Direct relaxation model. Compound 2 displayed only in-field slow relaxation, compatible with the models employed for 1.

Tailoring Intrinsic Properties of Polyaniline by Functionalization with Phosphonic Groups.

Phosphonated polyanilines were synthesized by copolymerization of aniline (ANI) with both 2- and 4-aminophenylphosphonic acids (APPA). The material composition and the final properties of the copolymers can be easily tailored by controlling the monomers ANI/APPA molar feed ratio. An important influence on the reactivity of monomers has been found with the substituent position in the ring, leading to differences in the properties and size of blocks of each monomer in the polymer. As expected, while 2APPA shows more similarities to ANI, 4APPA is much less reactive. Phosphorus loading of ~5 at% was achieved in the poly(aniline-co-2-aminophenylphosphonic acid) (PANI2APPA) with a 50/50 molar feed ratio. All the resulting copolymers were characterized by different techniques. Experimental results and density functional theory (DFT) computational calculations suggest that the presence of phosphonic groups in the polymeric chain gives rise to inter- and intra-chain interactions, as well as important steric effects, which induce a slight twist in the substituted PANI structure. Therefore, the physicochemical, electrical, and electrochemical properties are modified and can be suitably controlled.

Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)3]3− Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]·1.5H2O}n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu3(bpy)3(CH3OH)(H2O)(C2O4)4][Cu(bpy)Cr(C2O4)3]·CH2Cl2·CH3OH·H2O}n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C2O4)]n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C2O4)3]nn− (Cr2–Cu4) with alternating [Cr(C2O4)3]3− and [Cu(bpy)]2+ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H2O)(µ-C2O4)Cu(bpy)(CH3OH)]2+ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}n (3) comprising three different metal centers (Ca2+, Cr3+ and Cu2+) oxalate-bridged, contains Ca2+ atoms as nodes connected with four Cr3+ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (66) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [CuIICrIII], whose mutual interaction could possibly originate through the spin polarization of Ca2+ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.

Static all-atom energetic mappings of the SARS-Cov-2 spike protein and dynamic stability analysis of "Up" versus "Down" protomer states.

The SARS-CoV-2 virion responsible for the current world-wide pandemic COVID-19 has a characteristic Spike protein (S) on its surface that embellishes both a prefusion state and fusion state. The prefusion Spike protein (S) is a large trimeric protein where each protomer may be in a so-called Up state or Down state, depending on the configuration of its receptor binding domain (RBD) within its distal, prefusion S1 domain. The Up state is believed to allow binding of the virion to ACE-2 receptors on human epithelial cells, whereas the Down state is believed to be relatively inactive or reduced in its binding behavior. We have performed detailed all-atom, dominant energy landscape mappings for noncovalent interactions (charge, partial charge, and van der Waals) of the SARS-CoV-2 Spike protein in its static prefusion state based on two recent and independent experimental structure publications. We included both interchain interactions and intrachain (domain) interactions in our mappings in order to determine any telling differences (different so-called “glue” points) between residues in the Up and Down state protomers. The S2 proximal, fusion domain demonstrated no appreciable energetic differences between Up and Down protomers, including interchain as well as each protomer’s intrachain, S1-S2 interactions. However, the S1 domain interactions across neighboring protomers, which include the RBD-NTD cross chain interactions, showed significant energetic differences between Up-Down and Down-Down neighboring protomers. This included, for example, a key RBD residue ARG357 in the Up-Down interaction and a three residue sequence ALA520-PRO521-ALA522, associated with a turn structure in the RBD of the Up state protomer, acting as a stabilizing interaction with the NTD of its neighbor protomer. Additionally, our intra chain dominant energy mappings within each protomer, identified a significant “glue” point or possible “latch” for the Down state protomer between the S1 subdomain, SD1, and the RBD domain of the same protomer that was completely missing in the Up state protomer analysis. Ironically, this dominant energetic interaction in the Down state protomer involved the backbone atoms of the same three residue sequence ALA520-PRO521-ALA522 of the RBD with the amino acid R-group of GLN564 in the SD1 domain. Thus, this same three residue sequence acts as a stabilizer of the RBD in the Up conformation through its interactions with its neighboring NTD chain and a kind of latch in the Down state conformation through its interactions with its own SD1 domain. The dominant interaction energy residues identified here are also conserved across reported variations of SARS-CoV-2, as well as the closely related virions SARS-Cov and the bat corona virus RatG13. We conducted preliminary molecular dynamics simulations across 0.1 μ seconds to see if this latch provided structural stability and indeed found that a single point mutation (Q564G) resulted in the latch releasing transforming the protomer from the Down to the Up state conformation. Full trimeric Spike protein studies of the same mutation across all protomers, however, did not exhibit latch release demonstrating the critical importance of interchain interactions across the S1 domain, including RBD-NTD neighboring chain interactions. Therapies aimed at disrupting these noncovalent interactions could be a viable route for the physico-chemical mitigation of this deadly virion.

New insights into the impact of graphene oxide incorporation on molecular ordering and photophysical properties of PTB7:C70 blends

Nano-fillers have been successfully incorporated in the active layer to enhance the performance of bulk heterojunction (BHJ)-based organic solar cells (OSCs). However, only little information is available on their impact on the molecular ordering of polymers in the BHJ blends. Here, we comprehensively analyze the absorption, photoluminescence (PL), and Raman spectra to understand the effect of incorporation of the graphene oxide (GO) nano-filler in PTB7:C70 blends on the molecular ordering of PTB7 polymer. Absorption spectroscopy unveils how the interplay between interchain and intrachain coupling modifies the molecular order and backbone characteristic of PTB7. The addition of C70 weakens both intrachain and interchain interaction of PTB7. Whereas, intrachain interaction gradually rises with increasing the GO concentration. PTB7 films show weakly interacting J-aggregate behavior; nevertheless, the interaction strength gradually improves with the increasing GO content. The PL analysis indicates well-segregated phase domains and enhanced molecular ordering for composite films with 1 wt% GO. The Raman spectra of PTB7:C70:GO composite films suggests the formation of highly ordered PTB7 aggregates. An in-depth understanding of how these properties of polymer blends change with the GO concentration has significant implications on exploiting them towards the development of electronic devices.

Magnetic properties and magnetic structure of the frustrated quasi-one-dimensional antiferromagnet SrCuTe2O6

Magnetization measurements on single-crystal cubic SrCuTe$_2$O$_6$ with an applied magnetic field of along three inequivalent high symmetry directions $[100]$, $[110]$, and $[111]$ reveal weak magnetic anisotropy. The fits of the magnetic susceptibility to the result from a quantum Monte Carlo simulation on the Heisenberg spin-chain model, where the chain is formed via the dominant third-nearest-neighbor exchange interaction $J_3$, yield the intra-chain interaction $(J_3/k_B)$ between 50.12(7) K for the applied field along $[110]$ and 52.5(2) K along $[100]$ with about the same $g$-factor of 2.2. Single-crystal neutron diffraction unveils the transition to the magnetic ordered state as evidenced by the onset of the magnetic Bragg intensity at $T_\textrm{N1}=5.25(9)$ K with no anomaly of the second transition at $T_\textrm{N2}$ reported previously. Based on irreducible representation theory and magnetic space group analysis of powder and single-crystal neutron diffraction data, the magnetic structure in the Shubnikov space group $P4_132$, where the Cu$^{2+}$~$S=1/2$ spins antiferromagnetically align in the direction perpendicular to the spin chain, is proposed. The measured ordered moment of $0.52(6)~\mu_B$, which represents 48% reduction from the expected value of $1~\mu_B$, suggests the remaining influence of frustration resulting from the $J_1$ and $J_2$ bonds.

Anisotropic properties, charge ordering, and ferrimagnetic structures in the strongly correlated β−V2PO5 single crystal

A combined study of transport, thermodynamic, neutron diffraction, nuclear magnetic resonance measurements and first principles calculation were performed for $\beta$-V$_2$PO$_5$ single crystal. It was shown to be a semiconductor with a band gap of 0.48 eV, undergoing a charge ordering (unusual V$^{2+}$ and V$^{3+}$) phase transition accompanied by a tetragonal to monoclinic structural distortion at 610 K and a paramagnetic to ferrimagnetic phase transition at 128 K with a propagation vector of $\textbf{k} = 0$. The easy axis is in the monoclinic $ac$ plane pointing 47(9)$^\circ$ away from the monoclinic $a$ axis. This collinear ferrimagnetic structure and anisotropic isothermal magnetization measurements suggest weak magnetic anisotropy in this compound. The first principles calculations indicate that the intra-chain interactions in the face-sharing VO$_6$ chains dominate the magnetic hamiltonian and identify the $\Gamma_5^+$ normal mode of the lattice vibration to be responsible for the charge ordering and thus the structural phase transition.

Uniform Spin-1/2-Chain System with a Weak Interchain Interaction.

A new hydroxyl sulfate-fluoride compound, Lu2Cu(SO4)2(OH)3F·H2O, was obtained using a hydrothermal method. This compound is found to crystallize in a monoclinic space group of P21/c, exhibiting a uniform chain structure along the b axis, in which the chains are composed of elongated CuO4+2 octahedra and further separated by SO4 tetrahedra and Lu3+ ions. The shortest Cu-Cu distance inside the chains is ∼3.394(1) Å, while that between neighboring chains is ∼7.878(1) Å. Magnetic and heat capacity measurements indicate that this compound does not possess long-range magnetic order until 2 K. The fitting of spin-chain models suggests a strong intrachain interaction J and a weak interchain interaction J' with a small value of |J'/J| < 3.20(2) × 10-3, indicating that Lu2Cu(SO4)2(OH)3F·H2O may be a nearly ideal one-dimensional spin-1/2-chain system.