Intrachain Interactions Research Articles

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.

Coordination polymers containing a pyrazole-based ligand and 4,4′-bipyridine as a spacer: enhancing the family of nonzero-dimensional compounds featuring single-ion magnetic behavior

Two coordination polymers with molecular formula 1∞[M(L)2(4,4′-bipy)(H2O)2], where M stands for CoII (1) or CuII, (2), and L = 5-amino-1-phenyl-1H-pyrazole-4-carboxylate ligand were obtained by slow solvent diffusion and characterized by spectroscopic techniques, single crystal and powder X-ray diffraction, magnetic measurements, and DFT calculations. Magnetic studies carried out for complex 1 showed the key role played by the zero-field splitting and the experimental fit parameters were correlated to CASSCF calculations. Moreover, AC magnetic measurements for 1 revealed a field-induced slow relaxation of the magnetization and a single-ion magnet behavior. For the copper-containing polymer, two kinds of magnetic interactions were observed in the magnetic data and confirmed by using broken-symmetry DFT calculations: (i) ferromagnetic interchain coupling mediated by the hydrogen-bonds and (ii) antiferromagnetic intrachain interaction through the 4,4′-bipy ligand.

Unraveling the nature of Fe-doping mediated inter- and intra-chain interactions in Ca3Co2O6

The structural and magnetic properties of quasi-one-dimensional (1D) spin-chain compounds Ca3Co2-xFexO6 (x = 0, 0.1, 0.2 and 0.3) synthesized by a sol-gel method have been systematically studied by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), neutron powder diffraction (NPD), dc and ac magnetization measurements. The samples adopt a rhombohedral crystal structure with the space group R-3c in a temperature range of 5–100 K. Fe ions are found to locate at the trigonal prism Co2 crystallographic sites. Fe doping converts some of low-spin Co3+ ions at Co1 octahedral sites into Co2+ ions. For the high-temperature paramagnetic phase, the Curie paramagnetic temperature θp changes its sign from positive to negative at x = 0.2, implying that the dominant magnetic interaction is driven from ferromagnetic (FM) to antiferromagnetic (AFM) upon Fe substitution. A partial low-spin to high-spin state crossover of the Co1 ions is observed at high Fe-doping level x = 0.3. All the samples exhibit a long-range spin-density wave (SDW) AFM ordering below TN, followed by a spin-glass-like transition at Tf. These low-temperature magnetic phases were significantly suppressed upon Fe doping. The Fe substitution in Ca3Co2-xFexO6 weakened both intrachain and interchain magnetic interactions, caused by enhanced magnetic disorder due to the different magnetic characters of Ising Co and Heisenberg Fe spins.

Generalized Circuit Topology of Folded Linear Chains.

SummaryA wide range of physical systems can be formally mapped to a linear chain of sorted objects. Upon introduction of intrachain interactions, such a chain can “fold” to elaborate topological structures, analogous to folded linear polymer systems. Two distinct chain-topology theories, knot theory and circuit topology, have separately provided insight into the structure, dynamics, and evolution of folded linear polymers such as proteins and genomic DNA. Knot theory, however, ignores intrachain interactions (contacts), whereas chain crossings are ignored in circuit topology. Thus, there is a need for a universal approach that can provide topological description of any folded linear chain. Here, we generalize circuit topology in order to grasp particularities typically addressed by knot theory. We develop a generic approach that is simple, mathematically rigorous, and practically useful for structural classification, analysis of structural dynamics, and engineering applications.

Collective Spin Manipulation in Antiferroelastic Spin-Crossover Metallo-Supramolecular Chains.

Coupled spin-crossover complexes in supramolecular systems feature rich spin phases that can exhibit collective behaviors. Here, we report on a molecular-level exploration of the spin phase and collective spin-crossover dynamics in metallo-supramolecular chains. Using scanning tunneling microscopy, spectroscopy, and density functional theory calculations, we identify an antiferroelastic phase in the metal-organic chains, where the Ni atoms coordinated by deprotonated tetrahydroxybenzene linkers on Au(111) are at a low-spin (S = 0) or a high-spin (S = 1) state alternately along the chains. We demonstrate that the spin phase is stabilized by the combined effects of intrachain interactions and substrate commensurability. The stability of the antiferroelastic structure drives the collective spin-state switching of multiple Ni atoms in the same chain in response to electron/hole tunneling to a Ni atom via a domino-like magnetostructural relaxation process. These results provide insights into the magnetostructural dynamics of the supramolecular structures, offering a route toward their spintronic manipulations.

Knot theory for proteins: Gauss codes, quandles and bondles

Proteins are linear molecular chains that often fold to function. The topology of folding is widely believed to define its properties and function, and knot theory has been applied to study protein structure and its implications. More that 97% of proteins are, however, classified as unknots when intra-chain interactions are ignored. This raises the question as to whether knot theory can be extended to include intra-chain interactions and thus be able to categorize topology of the proteins that are otherwise classified as unknotted. Here, we develop knot theory for folded linear molecular chains and apply it to proteins. For this purpose, proteins will be thought of as an embedding of a linear segment into three dimensions, with additional structure coming from self-bonding. We then project to a two-dimensional diagram and consider the basic rules of equivalence between two diagrams. We further consider the representation of projections of proteins using Gauss codes, or strings of numbers and letters, and how we can equate these codes with changes allowed in the diagrams. Finally, we explore the possibility of applying the algebraic structure of quandles to distinguish the topologies of proteins. Because of the presence of bonds, we extend the theory to define bondles, a type of quandle particularly adapted to distinguishing the topological types of proteins.

Large magnetic anisotropy in a quasi-1D ferromagnetic complex Co(sba)(H2O)2·H2O (sba = 4-sulfobenzoate)

We have determined the crystal structures of new Co(II) polynuclear complex Co(sba)(H2O)2·H2O (sba ​= ​4-sulfobenzoate) (1) by X-ray crystallography. The crystal structure of 1 shows Co(II) uniform chains in which octahedral Co(II) centers are connected through double μ-OH2 single syn-syn μ-carboxylato bridging ligands, and these uniform chains are well separated by the sba ligands. Magnetization and magnetic susceptibility data of a single crystal of 1 taken along the different crystallographic axes suggest a large uniaxial magnetic anisotropy, the so-called Ising anisotropy, possessing large c∗-axis magnetic moments. Magnetic susceptibility data of 1 is explained by an 1D Ising ferromagnet with intra-chain exchange interaction of Jz/kB ​= ​39.6 ​K.

Multifunctional Ni(II)-Based Metamagnetic Coordination Polymers for Electronic Device Fabrication.

The combination of two 8-aminoquinoline-based Schiff base ligands (L1 and L2) with SCN- and Ni(II) has led to the synthesis of two new one-dimensional thiocyanato-bridged coordination polymers: [Ni(L1)(NCS)2]n (1) and [Ni(L2)(NCS)2]n (2). Both compounds are isostructural and consists of regular zigzag thiocyanato-bridged chains with very weak S···S interchain interactions. The measured room-temperature conductivities of compounds 1 and 2 (7.0 × 10-5 and 2.0 × 10-5 S m-1, respectively) are indicative of semiconductor behavior which increases in the presence of photoillumination (3.5 × 10-4 and 4.9 × 10-4 S m-1, respectively). The measured I-V characteristics of compound 1 and 2 based thin film metal-semiconductor (MS) junction devices under irradiation and nonirradiation conditions show a nonlinear rectifying behavior, typical of a Schottky diode (SD). The rectification ratios (Ion/Ioff) of the SDs in the dark at ±2 V (26.96 and 31.96 for 1- and 2-based devices, respectively) increase to 44.19 and 79.42, respectively, upon light irradiation. The photoinduced behavior has been analyzed by thermionic emission theory, and to determine the diode parameters, the Cheung's method has been employed. These diode parameters indicate that compound 2 has a better performance in comparison to compound 1 and that these materials are good candidates for applications in electrochemical devices. Magnetic measurements show that both compounds present ferromagnetic Ni-Ni intrachain and weak antiferromagnetic interchain interactions. The isothermal magnetizations at 2 K show that both compounds are metamagnets with critical fields of ca. 130 mT in 1 and 90 mT in 2 at 2 K. In the ferromagnetic phase (above the critical field), both compounds exhibit a long-range ferromagnetic order with critical temperatures of around 3.5 K in 1 and 3.0 K in 2. DC and AC measurements with different applied DC fields confirm the metamagnetic behaviors and have allowed the determination of the magnetic phase diagram in both compounds.

Fragility of 1D Floppy Materials

The fragility works as a fundamental concept characterizing glass‐forming liquids, whereas its atomic structural interpretation remains a challenge. Herein, viscosity behaviors in polyethylene (PE), S, Se, and Te are examined, which consist of distorted chain molecules with varied interchain strength, in comparison with that in SiO2, a typical strong material. Among the 1D materials, S and PE appear to be fairly strong. Such results suggest that the viscosity exhibits Arrhenius‐type behaviourif it is governed by single microscopic mechanisms such as SiO bond scission or interchain slippages. In contrast, Se and Te appear fragile with non‐Arrhenius variations, which could be ascribable to mixed inter‐ and intrachain interactions. Among these floppy materials, it is known that Se is the best glass former, the reason being discussed.

Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4

Comprehensive studies of magnetic properties of GdCr3(BO3)4 single crystal have been carried out. The integrals of intrachain (J/k = 4 ± 1 K) and interchain (J΄/k ≈ −0.7 K) exchange interactions in the Cr subsystem have been determined and the strength of Cr-Gd exchange interaction (JCr-Gd/k ~ −0.2 K) has been estimated. The values of the exchange field 2HE ≈ 17 T and the effective magnetic anisotropy field HA ≈ 0.05 T of GdCr3(BO3)4 have been estimated. The electric polarization ΔPa along the a axis in the longitudinal geometry of the experiment has been detected. Correlations between the electric polarization and the magnetization of the studied compound have been found. The spin-reorientation phase transition in the magnetically ordered state has been found. This transition exists for the external magnetic field applied along any crystallographic direction and the transition field depends weakly on the direction of the field. Nature of the spin-reorientation phase transition has been discussed. Magnetic phase diagram has been constructed and spin configurations for the low-field and high-field phases have been proposed.

Wet and dry internal friction can be measured with the Jarzynski equality

The existence of two types of internal friction wet and dry is revisited, and a simple protocol is proposed for distinguishing between the two types and extracting the appropriate internal friction coefficient. The scheme requires repeatedly stretching a polymer molecule, and measuring the average work dissipated in the process by applying the Jarzynski equality. The internal friction coefficient is then estimated from the average dissipated work in the extrapolated limit of zero solvent viscosity. The validity of the protocol is established through analytical calculations on a one-dimensional free-draining Hookean spring-dashpot model for a polymer, and Brownian dynamics simulations of: (a) a single-mode nonlinear spring-dashpot model for a polymer, and (b) a finitely extensible bead-spring chain with cohesive intra-chain interactions, both of which incorporate fluctuating hydrodynamic interactions. Well-established single-molecule manipulation techniques, such as optical tweezer-based pulling, can be used to implement the suggested protocol experimentally.

Synthesis, crystal and magnetic structure of the spin-chain compound Ag2RuO4

We report synthesis and crystal structure refinement of $\mathrm{A}{\mathrm{g}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$, followed by combined analysis of its physical properties through bulk experimental tools (magnetic susceptibility, electron transport, and heat capacity measurements), a microscopic experimental tool (temperature dependent neutron diffraction), and ab initio first-principles calculations. We observe a rather unique ${(\mathrm{Ru}{\mathrm{O}}_{3/1}{\mathrm{O}}_{2/2})}_{\mathrm{n}}$ polyoxoanion, where Ru is in a distorted trigonal bipyramidal coordination by oxygen. The $\mathrm{Ru}{\mathrm{O}}_{5}$ polyhedra are linked via the apical oxygen atoms to form chains extending along the crystallographic $a$ axis. Crystal structure, magnetization, and ab initio calculations indicate that Ru is in the $+6$ oxidation state with a nominal valence electron configuration of $4{d}^{2}$. Bulk magnetization, specific-heat, and neutron-diffraction measurements provide clear indication of an antiferromagnetic transition around 75 K with moderate spin canting in the order of ${30}^{\ensuremath{\circ}}$ with respect to the $c$ axis. The neutron-diffraction results as well as the density functional theory based first-principles calculations of exchange interactions revealed that the strong intrachain interaction is predominantly of ferromagnetic (FM) type, and that this spin order along the chains couples with the neighboring chains through comparatively weak FM and antiferromagnetic interactions. Notably, the Land\'e $g$ factor is found to be 1.8 (with an infinite chain model and even a simple Curie-Weiss approach), away from the ideal value of 2, due to the low dimensionality of the Ru/O substructure.

Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties.

Two different isomers of [Co(NCS)2(4-chloropyridine)2]n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)2(4-chloropyridine)2(H2O)2 (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)2(L)2]n compounds with linear chains.

All-acceptor polymers with noncovalent interactions for efficient ambipolar transistors

By invoking intrachain noncovalent interactions (NCIs) in diazine-based mA-wA polymers, high and balanced hole and electron mobilities were achieved.

Two azido-bridged homospin Fe(ii)/Co(ii) coordination polymers featuring single-chain magnet behavior.

Two azido-bridged homospin Fe(ii)/Co(ii) coordination polymers [Fe2(Bzp)2(N3)4]n (1) and [Co4(Bzp)4(N3)8·(MeOH)2]n (2) (bzp = 2-benzoylpyridine) are prepared, which consist of one-dimensional neutral chains with pure EO-azido (μ2-1,1-N3) bridges. Magnetically, both 1 and 2 exhibit considerable intrachain ferromagnetic interactions which benefit from the EO-azido bridging mode, leading to typical single-chain magnet (SCM) behavior under both the "infinite-size" and "finite-size" regime and pronounced hysteresis loops. As far as the bridging network is concerned, complex 1 represents not only a rare example of homospin Fe(ii)-based SCMs but also the first Fe(ii) chain compound with pure EO-azido bridges.

End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N3O2] Ligand: Synthesis, Structure, and Magnetism.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N3)C2H5OH]C2H5OH}n where H2DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N3O2] ligand and Ln = Dy (1), Y0.930Dy0.070 (2), Er (3), Y0.923Er0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N5O3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N3- bridges connecting the metal centers into infinite chain. The [LnN5O3] coordination polyhedron can be regarded as a distorted dodecahedron (D2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers Ueff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln3+ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln3+ ions.

Self‐Consistent Four‐Particle Cluster Model of Fe3+ Heisenberg Chains: Spectral and Magnetic Properties of YFe3(BO3)4 Crystals

The magnetic properties of antiferromagnetic quasi‐1D YFe3(BO3)4 crystals are studied based on the analysis of the measured optical spectra of the Fe3+ ions in different rare‐earth (RE) iron borates and a self‐consistent four‐particle cluster approach to helical iron chains. The parameters of crystal fields affecting the Fe3+ ions are calculated in the framework of the exchange charge model. The parameters of the isotropic intrachain and interchain exchange interactions between the Fe3+ ions are determined from modeling the temperature dependences of magnetic susceptibilities, the phase transition temperature, and spontaneous magnetic moments. The magnetic easy‐plane anisotropy is explained as the result of dipolar interactions between the Fe3+ ions in the trigonal crystal lattice. The developed model can be used to analyze and predict the properties of multiferroic multifunctional RE iron borates and highlight contributions of the iron subsystem into the magnetoelectric and magnetoelastic effects in these compounds.

Effect of segmental compatibility imposed over metal based polybutadiene polyurethane

Series of metal based polyurethanes (PUs) have been synthesized from hydroxyl terminated polybutadiene (HTPB) with combination of a potential energetic material, 2,4-dinitrobenzene (DNB) and burn rate (BR) enhancer, ferrocene with two objectives: (1) exerting flexibility into otherwise brittle PU film and (2) increasing BR of composite solid propellant (CSP). HTPB was first functionalized with DNB at the terminal carbons and then ferrocene was grafted radically as poly (vinyl ferrocene) (PVF) chain onto the pendant vinyl bond of HTPB. The degree of PVF grafting was altered by appropriate reaction recipes to find out the effect of Fe content on various physical properties including fluidity of the HTPB. Density function theory (DFT) calculation showed that the dominating intra-chain interactions over inter-chain owing to the strong interactions between NO2 of DNB and cyclopentadiene of ferrocene are the driving force for improvement in various physical properties of PVF-grafted-HTPB-DNB. Cyclic voltammetry (CV) measurement showed one electron reversible redox behavior of the grafted PVF polymer chain with slow electron transfer process. Further the mechanical stability, thermal stability and properties of PUs have been studied thoroughly; the results indicated a strong influence of DNB and ferrocene in the chains on the physical properties. All the DNB modified PU membranes displayed exceptionally enhanced flexibility along with much lower Tg value compared to neat PVF-g-HTPB-PU. The presence of DNB at the chain end of soft segment (SS) causes strong segmental mixing between SS and hard segment (HS) domains which helps in enhancing the elasticity of SS chain by increasing the inter polymer chain distance. Morphology of the hard segment domains formation has been probed by small angle X-ray scattering (SAXS) and further confirmed by FESEM. Burn rate of composite solid propellant made from the HTPB-DNB-g-PVF binder is found to be ~18% larger than the HTPB-DNB.

Intrinsically distinct hole and electron transport in conjugated polymers controlled by intra and intermolecular interactions

It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole transport within the same film microstructure of a model copolymer semiconductor. Relatively, holes predominantly bleach inter-chain interactions with H-type electronic coupling character, while electrons’ relaxation more strongly involves intra-chain interactions with J-type character. Holes and electrons mobility correlates with the presence of a charge transfer state, while their ratio is a function of the relative content of intra- and inter-molecular interactions. Such fundamental observation, revealing the specific role of the ground-state intra- and inter-molecular coupling in selectively assisting charge transport, allows predicting a more favorable hole or electron transport already from screening the polymer film ground state optical properties.

Universal features of complex n-block copolymers

We study the conformational properties of complex polymer macromolecules, consisting in general of n subsequently connected chains (blocks) of different lengths and distinct chemical structure. Depending on the solvent conditions, the inter- or intra-chain interactions of some blocks may vanish, causing rich conformational behavior. Our main attention is focused on the universal conformational properties of such molecules. Applying the direct polymer renormalization group approach, we derive the analytical expressions for the scaling exponent , governing the number of possible conformations of n-block copolymer, and analyze the effective linear size measures of individual blocks. In particular, the degree of extension of the block sizes as functions of n and position of blocks in sequence is quantitatively estimated. The numerical simulations of the simplest n = 2-block copolymer chain on a cubic lattice are also performed to give an illustration of the conformational behavior of such molecules.