Intrachain Interactions Research Articles

Theoretical investigation of the behavior of CuSe2O5 compound in high magnetic fields

Based on the analytical and numerical approaches, we investigate thermodynamic properties of CuSe2O5 compound at high magnetic fields which is a candidate for the strong intra-chain interaction in quasi one-dimensional (1D) quantum magnets. Magnetic behavior of the system can be described by the 1D spin-1/2 XXZ model in the presence of the Dzyaloshinskii–Moriya (DM) interaction. Under these circumstances, there is one quantum critical field in this compound. Below the quantum critical field the spin chain system is in the gapless Luttinger liquid (LL) regime, whereas above it one observes a crossover to the gapped saturation magnetic phase. Indications on the thermodynamic curves confirm the occurrence of such a phase transition. The main characteristics of the LL phase are gapless and spin–spin correlation functions decay algebraic. The effects of zero-temperature quantum phase transition are observed even at rather high temperatures in comparison with the counterpart compounds. In addition, we calculate the Wilson ratio in the model. The Wilson ratio at a fixed temperature remains almost independent of the field in the LL region. In the vicinity of the quantum critical field, the Wilson ratio increases and exhibits anomalous enhancement.

Responsive Stabilization of Nanoparticles for Extreme Salinity and High-Temperature Reservoir Applications.

Colloidal stabilization of nanoparticles under extreme salinity and high temperature conditions is a key challenge in the development of next generation technologies for subsurface reservoir characterization and oil recovery. Polyelectrolytes have been investigated as nanoparticle stabilizers, but typically fail at high ionic strengths and elevated temperatures due to excessive charge screening and dehydration. We report an approach to nanoparticle stabilization that overcomes these limitations, and exploits the antipolyelectrolyte phenomenon, in which screening of intrachain electrostatic interactions causes a polyzwitterion chain to undergo a structural transition from a collapsed globule to a more open coil-like regime with increases in ionic strength and temperature. Small-angle neutron scattering on a model zwitterionic polymer in solution indicated an increase in both radius of gyration and excluded volume parameter of the polymer with increases in ionic strength and temperature. The model zwitterion was subsequently incorporated within a polymeric stabilizer for nanoparticles under harsh reservoir conditions, and used to functionalize hydrophilic (silica) as well as hydrophobic (polystyrene) nanoparticles. Long-term colloidal stability was achieved at salt concentrations up to 120,000 mg/dm3 at 90 °C, approximately twice the stability limit previously reported in the literature. The approach can be broadly generalized to a large class of synthetic polyzwitterions, and can be adapted to a wide variety of other colloidal systems in which demands placed by extreme salinity and temperature conditions must be met.

Interplay of Intramolecular Noncovalent Coulomb Interactions for Semicrystalline Photovoltaic Polymers

Four different kinds of photovoltaic polymers were synthesized by controlling the intrachain noncovalent coulomb interactions through the incorporation of alkoxy- or alkylthio-substituted phenylene, 4,7-di(furan-2-yl)benzothiadiazole, and 4,7-di(thiophen-2-yl)benzothiadiazole as a building block. Fine modulation of the interplay of dipole–dipole, H-bond, and chalcogen–chalcogen interactions (O···S, O···H, S···S, S···F, etc.) along the polymeric backbone influenced the chain planarity, interchain organization, film morphology, and electrical and photovoltaic properties significantly. By replacing the alkoxy substituents with alkylthio groups, the torsional angle increased (136–168°) due to the absence of an O···S attractive coulomb interaction (and/or increased S···S steric hindrance), enhancing the amorphous nature with hindered interchain packing. The alkoxy-substituted polymers exhibited nanofibrillar structures, showing strong interlamellar scattering peaks up to (300) with tight face-on π–π stacking i...

Synthesis, structure and magnetic properties of [CrCyclam(C[tbnd]C-6-methoxynaphthalene)2](TCNQ)n(1,2-dichloroethane) (n = 1, 2)

New chromium-acetylide-based magnetic materials, [CrCyclam(CC-NaphOMe)2](TCNQ)n(1,2-dichloroethane) (Cyclam=1,4,8,11-tetraaza cyclotetradecane, TCNQ=7,7,8,8-tetracyanoquinodimethane, NaphOMe=6-methoxynaphthalene, n=1, 2) were prepared. The crystal structures are characterized by uniform ferrimagnetic chains of [CrCyclam(CC-NaphOMe)2]+ (S=3/2) and (TCNQ)n− (S=1/2), where π–π-stacking between NaphOMe ligands and (TCNQ)n− units mediates intermolecular exchange interactions. The strengths of the intrachain exchange interactions were estimated to be 2J/kB=−19.5 and −4.6K for n=1 and 2, respectively. The observed strengths of the interactions, especially in the case of n=1, suggest that π-conjugated acetylide ligands can play an important role in constructing molecule-based magnetic materials.

A Nearly Ideal One-Dimensional S = 5/2 Antiferromagnet FeF3(4,4'-bpy) (4,4'-bpy =4,4'-bipyridyl) with Strong Intrachain Interactions.

An ideal one-dimensional (1D) magnet is expected to show exotic quantum phenomena. For compounds with larger S (S = 3/2, 2, 5/2, ...), however, a small interchain interaction J' tends to drive a conventional long-range ordered (LRO) state. Here, a new layered structure of FeF3(4,4'-bpy) (4,4'-bpy = 4,4'-bipyridyl) with novel S = 5/2 (Fe(3+)) chains has been hydrothermally synthesized by using 4,4'-bpy to separate chains. The temperature-dependent susceptibility exhibits a broad maximum at high as 164 K, suggesting a fairly strong Fe-F-Fe intrachain interaction J. However, no anomaly associated with a LRO is seen in both magnetic susceptibility and specific heat even down to 2 K. This indicates an extremely small J' with J'/J < 3.2 × 10(-5), making this new material a nearly ideal 1D antiferromagnet. Mössbauer spectroscopy at 2.7 K reveals a critical slowing down of the 1D fluctuations toward a possible LRO at lower temperatures.

Spin-Liquid Ground State in the Spin 1/2 Distorted Diamond Chain Compound K3Cu3AlO2(SO4)4

The new compound K3Cu3AlO2(SO4)4, representing a spin 1/2 distorted diamond chain system, was synthesized and its magnetic properties were studied by magnetic susceptibility, specific heat, and high-field magnetization measurements. Magnetic Cu2+ ions were found to form a highly one-dimensional distorted diamond chain with strong intrachain interactions. Short-range magnetic correlations were observed to develop in a two-stage process without magnetic long-range ordering by magnetic susceptibility and specific heat measurements. The exchange constant ratio J2/J1, where J2 is the magnetic interaction of the diamond backbone and J1 is the magnetic interaction of the monomers along the chain, was estimated to be 2.5, demonstrating that the magnetic ground state is composed of an alternating dimer–monomer spin-liquid phase. The absence of an M = 0 plateau in the high-field magnetization curve is also consistent with an alternating dimer–monomer model. These results strongly suggest that K3Cu3AlO2(SO4)4 is the first material exhibiting an alternating dimer–monomer spin-liquid ground state.

Quantum phases of hardcore bosons in two coupled chains: A density matrix renormalization group study

We consider hardcore bosons in two coupled chains of one dimensional lattices at half filling with repulsive intrachain interaction and interchain attraction. This can be mapped onto a coupled chain of spin-1/2 $XXZ$ model with interchain ferromagnetic coupling. We investigate various phases of hardcore bosons (and related spin model) at zero temperature by a density matrix renormalization group method. Apart from the usual superfluid and density wave phases, pairing of interchain bosons leads to the formation of phases like pair superfluid and density wave of strongly bound pairs. We discuss the possible experimental realization of such correlated phases in the context of cold dipolar gas.

Synthesis and Characterization of Polyurethane/Clay Nanocomposites

This paper describes synthesis of a series of polyurethane (PU)/clay nanocomposites by using two different chain extenders ethylenediamine (ED) and 1,3-diamino-2-propanol (DAP). By using DAP as a chain extender, PU/clay nanocomposites show not only the stronger inter-and intrachain interactions through hydrogen bonding, but also exhibit enhanced clay exfoliation as evidenced by the disappearance of clay diffraction at 2θ = 2.5-10°.

Consequences of critical interchain couplings and anisotropy on a Haldane chain

Effects of interchain couplings and anisotropy on a Haldane chain have been investigated by single crystal inelastic neutron scattering and density functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$. Significant effects on low energy excitation spectra are found where the Haldane gap ($\Delta_0 \approx 0.41J$; where $J$ is the intrachain exchange interaction) is replaced by three energy minima at different antiferromagnetic zone centers due to the complex interchain couplings. Further, the triplet states are split into two branches by single-ion anisotropy. Quantitative information on the intrachain and interchain interactions as well as on the single-ion anisotropy are obtained from the analyses of the neutron scattering spectra by the random phase approximation (RPA) method. The presence of multiple competing interchain interactions is found from the analysis of the experimental spectra and is also confirmed by the DFT calculations. The interchain interactions are two orders of magnitude weaker than the nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations reveal that the dominant intrachain nearest-neighbor interaction occurs via nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty $d$ orbital of V ions. The present single crystal study also allows us to correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where it lies within the spin-liquid phase.

Ferromagnetic Coupling Through the End-to-End Thiocyanate Bridge in Cobalt(II) and Nickel(II) Chains

The preparation, spectroscopic characterization, and X-ray crystal structure of two novel one-dimensional compounds of formula [MII(tppz)(NCS)(μ-1,3-NCS)]n [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and M = Co(1) and Ni (2)] are reported. 1 and 2 are isomorphous compounds, and they crystallize in the P21/n space group. Their structures are made up of zigzag chains of cobalt(II) (1) and nickel(II) ions (2) bridged by single end-to-end thiocyanate groups with a tridentate tppz molecule and a terminally bound thiocyanate-N ligand achieving distorted MN5S octahedral surroundings around each metal center. The main source of the distortion of the ideal octahedron is due to the geometrical constraints issued from the occurrence of two fused five-member chelate rings of the tridentate tppz ligand, the values of the N–M–N bond angles covering the range 75.58(9)–78.66(9)°. The M–N bond lengths vary in the range 2.025(3)–2.116(29 (1) and 2.001(2)–2.079(2) Å (2), and they are shorter than the M–S bond distance [2.6395(10) (1) and 2.5225(9) Å (2)]. The values of the intrachain metal–metal separation are 6.4197(7) (1) and 6.3257(5) Å (2). The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. Both compounds exhibit intrachain ferromagnetic interactions with values of the magnetic coupling (J) of +4.60 (1) and +7.82 cm–1 (2) [the spin Hamiltonian being defined as Ĥ = −JΣi = 1n–1ŜiŜi+1].

Anion-specific effects on the behavior of pH-sensitive polybasic brushes.

The anion-specific solvation and conformational behavior of weakly basic poly(2-dimethylamino)ethyl methacrylate (poly(DMA)), poly(2-diethylamino)ethyl methacrylate (poly(DEA)), and poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brushes, with correspondingly increasing inherent hydrophobicity, have been investigated using in situ ellipsometric and quartz crystal microbalance with dissipation (QCM-D) measurements. In the osmotic brush regime, as the initial low concentration of salt is increased, the brushes osmotically swell by the uptake of solvent as they become charged and the attractive hydrophobic inter- and intrachain interactions are overcome. With increased ionic strength, the brushes move into the salted brush regime where they desolvate and collapse as their electrostatic charge is screened. Here, as the brushes collapse, they transition to more uniform and rigid conformations, which dissipate less energy, than similarly solvated brushes at lower ionic strength. Significantly, in these distinct regimes brush behavior is not only ionic strength dependent but is also influenced by the nature of the added salt based on its position in the well-known Hofmeister or lyotropic series, with potassium acetate, nitrate, and thiocyanate investigated. The strongly kosmotropic acetate anions display low affinity for the hydrophobic polymers, and largely unscreened electrosteric repulsions allow the brushes to remain highly solvated at higher acetate concentrations. The mildly chaotropic nitrate and strongly chaotropic thiocyanate anions exhibit a polymer hydrophobicity-dependent affinity for the brushes. Increasing thiocyanate concentration causes the brushes to collapse at lower ionic strength than for the other two anions. This study of weak polybasic brushes demonstrates the importance of all ion, solvent, and polymer interactions.

Synthesis, characterization, and use as emissive layer of white organic light emitting diodes of the highly isotactic poly(N‐pentenyl‐carbazole)

The synthesis and the microstructural characterization of isotactic poly (N‐pentenyl‐carbazole) (i‐PPK) are reported. The achieved polymer is semicrystalline, the melting temperature is 138°C. i‐PPK Fourier transform infrared spectroscopy (FTIR) spectrum and X‐ray diffraction pattern are compared with those of polyvinylcarbazole. The observed differences are tentatively associated to higher flexibility of the i‐PPK chains due to the alkylene group connecting the carbazole group to the main chain. The presence of intrachain and interchain interactions between carbazole units, which bring these groups to stack each other, is assumed. i‐PPK optical properties are investigated and an electroluminescent behaviour of polymer is observed. Organic light emitting diodes based on i‐PPK layers are founded to emit white light. POLYM. COMPOS., 36:1110–1117, 2015. © 2015 Society of Plastics Engineers

Fastener Effect on Uniaxial Chemical Pressure for One-Dimensional Spin-Crossover System, [FeII(NH2-trz)3](CnH2n+1SO3)2·xH2O: Magnetostructural Correlation and Ligand Field Analysis

Abstract One-dimensional spin-crossover (SCO) polymers of formula [FeII(NH2-trz)3](CnH2n+1SO3)2·xH2O (trz: 4-substituted-1,2,4-triazole; n = 1–9) have been synthesized. They displayed hysteretic SCO transition around 280–350 K. The spin transition temperatures (T1/2) in the heating and cooling processes increased, and the hysteresis width became narrower with increasing alkyl chain length (n). From the analysis of EXAFS, the nearest-neighbor Fe–Fe distance decreased with increasing n, and it had a close relationship with T1/2. This is highly indicative of the increase of intrachain interaction of [FeII(NH2-trz)3] with n being attributed to the uniaxial chemical pressure effect induced by van der Waals force between alkyl chains, so-called “fastener effect.” To elucidate the physicochemical effect on T1/2, the ligand field and Racah parameter (B) were estimated by analysing the pre-edge region in Fe-K edge XANES spectra based on the ligand-field theory. B decreased with increasing n, which was closely consistent with the behavior of T1/2 and 57Fe Mössbauer isomer shift (IS). Judging from these results, a covalency between FeII 3d and ligand π* orbital is enhanced by the fastener effect, leading to the expansion of the 3d orbital, i.e. the remarkable decrease of B and IS, which is the dominating factor on T1/2 in our system.

Diazopyridine–Ni(ii) complexes exhibiting intra-chain ferromagnetic interaction after irradiation: formation of magnetic gel

The gel of a diazopyridine–Ni(ii) complex in EtOH–20% CH2Cl2 solution showed the magnetic behavior of a ferromagnetic chain with the correlation length of 5–6 units after irradiation, suggesting the formation of magnetic gel.

Spin dynamics of Mn pyrochlore lattice in YMn2Zn20-xInx

It is shown in a new class of pyrochlore compound YMn2Zn20-xInx (with x = 2.36) that the spin fluctuation rate (v) is proportional to temperature (v ∝ T) below T0 ~10 K where heavy-fermion(HF)-like behavior is observed. Such a linear T dependence, commonly found in Y(Sc)Mn2 and LiV2O4, is expected for intersecting quasi-1D Hubbard chains, suggesting that the quasi-1D character of the t2g band associated with the pyrochlore lattice plays an important role in the emergence of the HF-like state, where T0 may correspond to intra-chain antiferromagnetic interaction energy between Mn spins.

Unusual magnetic behaviors and electronic configurations driven by diverse Co(II) or Mn(II) MOF architectures.

Five novel metal organic frameworks were obtained by hydro-solvothermal reactions using the hexafluorisopropylidenebis(benzoic) acid (H2hfipbb) as linker and Co(II) or Mn(II) ions as connectors. [Co2(Hhfipbb)(TEA)], compound 1 (TEA = triethanolamine trianion) with a three-dimensional (3D) framework, and a tpu net; [Co1.5(hfipbb)2]·HN(CH2CH3)3 and [Co3(hfipbb)2]·2{HN(CH2CH3)3}, compounds 2 and 2-a, respectively, both with two-dimensional structure, sql topologies, and different layer packings. Compounds 3 and 4, having the general formula [M2(hfipbb)2]·C7H8, where M = Co (3) or Mn (4), have 3D frameworks with an sqc topology. A deep analysis of the magnetic measurements reveals different striking magnetic behaviors resulting from diverse secondary building unit and framework architectures. Compound 1 presents canted antiferromagnetic chains, compound 2 contains ferromagnetic linear trimeric clusters, and compound 3 exhibits ferromagnetic chains. For the three compounds, a 3D canted antiferromagnetic structure takes place at ∼8 K by means of weak magnetic interactions between the mentioned magnetic units. Such long-range magnetic order is precluded with the application of a high enough magnetic field. Compound 4 evidenced intrachain antiferromagnetic interactions.

H- and J-aggregation of fluorene-based chromophores.

Understanding of H- and J-aggregation behaviors in fluorene-based polymers is significant both for determining the origin of various red-shifted emissions occurring in blue-emitting polyfluorenes and for developing polyfluorene-based device performance. In this contribution, we demonstrate a new theory of the H- and J-aggregation of polyfluorenes and oligofluorenes, and understand the influence of chromosphere aggregation on their photoluminescent properties. H- and J-aggregates are induced by a continuous increasing concentration of the oligofluorene or polyfluorene solution. A relaxed molecular configuration is simulated to illustrate the spatial arrangement of the bonding of fluorenes. It is indicated that the relaxed state adopts a 21 helical backbone conformation with a torsion angle of 18° between two connected repeat units. This configuration makes the formation of H- and J-aggregates through the strong π-π interaction between the backbone rings. A critical aggregation concentration is observed to form H- and J-aggregates for both polyfluorenes and oligofluorenes. These aggregates show large spectral shifts and distinct shape changes in photoluminescent excitation (PLE) and emission (PL) spectroscopy. Compared with "isolated" chromophores, H-aggregates induce absorption spectral blue-shift and fluorescence spectral red-shift but largely reduce fluorescence efficiency. "Isolated" chromophores not only refer to "isolated molecules" but also include those associated molecules if their conjugated backbones are not compact enough to exhibit perturbed absorption and emission. J-aggregates induce absorption spectral red-shift and fluorescence spectral red-shift but largely enhance fluorescence efficiency. The PLE and PL spectra also show that J-aggregates dominate in concentrated solutions. Different from the excimers, the H- and J-aggregate formation changes the ground-state absorption of fluorene-based chromophores. H- and J-aggregates show changeable absorption and emission derived from various interchain interactions, unlike the β phase, which has relatively fixed absorption and emission derived from an intrachain interaction.

Unexpected Strong Antiferromagnetic Interaction in [CuCyclam][Ni(1,2‐benzenedithiolate)2]2

AbstractTwo new molecule‐based magnetic materials were prepared, namely, [CuCyclam(CH3CN)2][Ni(bdt)2]2 and [CuCyclam][Ni(bdt)2]2 (bdt = 1,2‐benzenedithiolate). The former compound is characterized by a two‐dimensional layer structure, in which axially coordinated acetonitrile molecules prevent cation–anion stacking. The weak antiferromagnetic interaction of 2J/kB = –6.2 K between the adjacent [CuCyclam(CH3CN)2]+ (S = 1/2) and [Ni(bdt)2]– (S = 1/2) moieties leads to a ferrimagnetic transition at 2.6 K. In contrast to the structure of [CuCyclam(CH3CN)2][Ni(bdt)2]2, the crystal structure of [CuCyclam][Ni(bdt)2]2 is characterized by alternately stacked [CuCyclam]2+ and [Ni(bdt)2]– units, and another [Ni(bdt)2]– anion bridges the chain to form a two‐dimensional ferrimagnetic layer. The magnetic susceptibility of [CuCyclam][Ni(bdt)2]2 reveals a quite strong intrachain antiferromagnetic interaction of 2J/kB = –66 K between the [CuCyclam]2+ and [Ni(bdt)2]– ions. The weak interchain and interlayer interactions make the crystals antiferromagnetic below 3.2 K.

Calorimetry of Low-Dimensional Metal-Assembled Complexes

A kind of molecule-based magnets, metal-assembled complexes tend to possess low-dimensionalities for their magnetic lattices. Heat capacity calorimetry is a powerful tool for elucidation of the magnetic properties of metal-assembled complexes. Heat capacity measurements were carried out for the one-dimensional metal-assembled complexes MnIICuII(obbz).nH2O (obbz = oxamidobis(benzoato), n = 1, 5) and two-dimensional metal-assembled complexes NBu4[MIICrIII(ox)3] (Bu = n-butyl; M = Cu, Fe; ox = oxalato) and PPh4[MnIICrIII(ox)3] (Ph = phenyl). MnIICuII(obbz).5H2O undergoes an antiferromagnetic phase transition at TN = 2.18 K and have a heat capacity hump above TN, which can be reproduced well by the spin quantum number S = 2 one-dimensional ferromagnetic Heisenberg model with the intrachain exchange interaction J/kB = 0.75 K, where kB is the Boltzmann constant. Partially dehydrated MnIICuII(obbz)H2O exhibits a ferrimagnetic phase transition at Tc = 17 K and shows a heat capacity tail above Tc, which can be reproduced rather by the S = 2 two-dimensional ferromagnetic Heisenberg models. NBu4[CuIICrIII(ox)3], NBu4[FeIICrIII(ox)3], and PPh4[MnCr(ox)3] indicate ferromagnetic phase transitions at TC = 6.98 K, 12.0 K, and 5.85 K, respectively, and heat capacity tails above TC, which can be reproduced well by the two-dimensional ferromagnetic Heisenberg models of honeycomb lattice with the intralayer exchange interactions J/kB = 5.0 K, 2.5 K, and 0.95 K, respectively. Keywords: Heat capacity, high-temperature series expansion, magnetic entropy, magnetic phase transition, metal-assembled complex, molecule-based magnet, low dimensionality, spin wave.

Influence of Copper(II) and Nickel(II) Ions in the Topology of Systems Based on a Flexible Bis-Oxamate and Bipyridine Building Blocks

Single crystals of the mononuclear bis-oxamate nickel(II) complex [Ni(bipy)(H2edpba)]·dmso (1) are obtained by reacting [Ni(bipy)Cl2]·H2O and the flexible K2(H2edpba) ligand [bipy = 2,2′-bipyridine; H4edpba = N,N′-2,2′-ethylenediphenylenebis(oxamic acid)]. The reaction of 1 with copper(II) ions resulted in two products in which the replacement of the nickel(II) ion by copper(II) took place: the chain compound [Cu(bipy)(H2edpba)]n·3nH2O·ndmso [dmso = dimethyl sulfoxide] (2) and the analogous chain compound without dmso crystallization molecules [Cu(bipy)(H2edpba)]n·1.5nH2O (3a) in its polycrystalline form. The reaction of [Cu(bipy)Cl2] and K2(H2edpba) yielded single crystals of [Cu(bipy)(H2edpba)]n·1.5nH2O (3b). The H2edpba2– ligand exhibits the anti conformation in 1, 2, and 3b, but it adopts different coordination modes: terminal bis-bidentate (1) and bridging bis-bidentate (2 and 3b) through the two pairs of carbonyl-oxygen atoms of the two oxamate arms. Magnetic susceptibility measurements carried out on a polycrystalline sample of 3b in the temperature range 1.9–295 K showed the occurrence of very weak intrachain antiferromagnetic interactions [J = −0.40 cm–1, the Hamiltonian being defined as H = −J ∑iSi·Si+1], in agreement with the large values of the copper–copper separation [8.308(3) Å].