Neighboring Chains Research Articles

Investigation of (001), (010), and (100) surface termination and surface energies of the Zintl Ca5Ga2Sb6

Zintl Phases are a class of intermetallic compounds that combine ionic and covalent bonding to form charge-balanced structures, leading to semiconducting properties. The Ca5M2Sb6 family of Zintl compounds, (M =Al, Ga, In), have demonstrated promising thermoelectric efficiency, meaning they can be used to convert a temperature gradient into useful electrical energy. Ca5M2Sb6 compounds crystallize in a highly anisotropic structure comprised of chains of corner-linked MSb4 tetrahedra, in which each neighboring chain is joined via Sb-Sb covalent bonds, forming an infinite polyanionic “ladder”. In the present study, we used first principles calculations to study various surface terminations of the Ca5Ga2Sb6 structure as a mechanism to understand its crystal growth morphology. Our results indicate that the calcium stoichiometry of the crystal surface plays an important role in surface reconstruction, specifically leading to the formation or breaking of covalent bonds. Our results suggest that surface energy as a function of stoichiometry and crystallographic orientation is only one piece of the puzzle in understanding the growth habits of Ca5Ga2Sb6 crystals.

Tracking the Amide I and αCOO- Terminal ν(C=O) Raman Bands in a Family of l-Glutamic Acid-Containing Peptide Fragments: A Raman and DFT Study.

The E-hook of β-tubulin plays instrumental roles in cytoskeletal regulation and function. The last six C-terminal residues of the βII isotype, a peptide of amino acid sequence EGEDEA, extend from the microtubule surface and have eluded characterization with classic X-ray crystallographic techniques. The band position of the characteristic amide I vibration of small peptide fragments is heavily dependent on the length of the peptide chain, the extent of intramolecular hydrogen bonding, and the overall polarity of the fragment. The dependence of the E residue’s amide I ν(C=O) and the αCOO− terminal ν(C=O) bands on the neighboring side chain, the length of the peptide fragment, and the extent of intramolecular hydrogen bonding in the structure are investigated here via the EGEDEA peptide. The hexapeptide is broken down into fragments increasing in size from dipeptides to hexapeptides, including EG, ED, EA, EGE, EDE, DEA, EGED, EDEA, EGEDE, GEDEA, and, finally, EGEDEA, which are investigated with experimental Raman spectroscopy and density functional theory (DFT) computations to model the zwitterionic crystalline solids (in vacuo). The molecular geometries and Boltzmann sum of the simulated Raman spectra for a set of energetic minima corresponding to each peptide fragment are computed with full geometry optimizations and corresponding harmonic vibrational frequency computations at the B3LYP/6-311++G(2df,2pd) level of theory. In absence of the crystal structure, geometry sampling is performed to approximate solid phase behavior. Natural bond order (NBO) analyses are performed on each energetic minimum to quantify the magnitude of the intramolecular hydrogen bonds. The extent of the intramolecular charge transfer is dependent on the overall polarity of the fragment considered, with larger and more polar fragments exhibiting the greatest extent of intramolecular charge transfer. A steady blue shift arises when considering the amide I band position moving linearly from ED to EDE to EDEA to GEDEA and, finally, to EGEDEA. However, little variation is observed in the αCOO− ν(C=O) band position in this family of fragments.

HJ-aggregates of donor-acceptor-donor oligomers and polymers.

A vibronic exciton model is developed to account for the spectral signatures of HJ-aggregates of oligomers and polymers containing donor-acceptor-donor (DAD) repeat units. In (DAD)N π-stacks, J-aggregate-promoting intrachain interactions compete with H-aggregate-promoting interchain interactions. The latter includes Coulombic coupling, which arises from "side-by-side" fragment transition dipole moments as well as intermolecular charge transfer (ICT), which is enhanced in geometries with substantial overlap between donors on one chain and acceptors on a neighboring chain. J-behavior is dominant in single (DAD)N chains with enhanced intrachain order as evidenced by an increased red-shift in the low-energy absorption band along with a heightened A1/A2 peak ratio, where A1 and A2 are the oscillator strengths of the first two vibronic peaks in the progression sourced by the symmetric quinoidal-aromatic vibration. By contrast, the positive H-promoting interchain Coulomb interactions operative in aggregates cause the vibronic ratio to attenuate, similar to what has been established in H-aggregates of homopolymers such as P3HT. An attenuated A1/A2 ratio can also be caused by H-promoting ICT which occurs when the electron and hole transfer integrals are out-of-phase. In this case, the A1 peak is red-shifted, in contrast to conventional Kasha H-aggregates. With slight modifications, the ratio formula derived previously for P3HT aggregates is shown to apply to (DAD)N aggregates as well, allowing one to determine the effective free-exciton interchain coupling from the A1/A2 ratio. Applications are made to polymers based on 2T-DPP-2T and 2T-BT-2T repeat units, where the importance of the admixture of the excited acceptor state in the lowest energy band is emphasized.

Molecular and Crystal Structure of a Chitosan-Zinc Chloride Complex.

We determined the molecular and packing structure of a chitosan–ZnCl2 complex by X-ray diffraction and linked-atom least-squares. Eight D-glucosamine residues—composed of four chitosan chains with two-fold helical symmetry, and four ZnCl2 molecules—were packed in a rectangular unit cell with dimensions a = 1.1677 nm, b = 1.7991 nm, and c = 1.0307 nm (where c is the fiber axis). We performed exhaustive structure searches by examining all of the possible chain packing modes. We also comprehensively searched the positions and spatial orientations of the ZnCl2 molecules. Chitosan chains of antiparallel polarity formed zigzag-shaped chain sheets, where N2···O6, N2···N2, and O6···O6 intermolecular hydrogen bonds connected the neighboring chains. We further refined the packing positions of the ZnCl2 molecules by theoretical calculations of the crystal models, which suggested a possible coordination scheme of Zn(II) with an O6 atom.

Adaptable Reversibly Interlocked Networks from Immiscible Polymers Enhanced by Hierarchy-Induced Multilevel Energy Consumption Mechanisms

The present work proposes a novel strategy to prepare reversibly interlocked networks with enhanced mechanical properties through hierarchy-induced multilevel energy consumption mechanisms. The core issue lies in the introduction of in situ inter-macromolecular ionic interactions among the component networks regardless of their miscibility, which is hard to be implemented in other materials. Traditional small-molecule contra-ions are no longer necessary accordingly. As revealed by the proof-of-concept transparent interlocked networks composed of immiscible cross-linked styrene–butadiene rubber (SBR) and polyethylenimine (PEI), the interlocking architecture and the inter-macromolecular ionic interactions are mutually promoted. The latter pulls the immiscible polymer chains together, favoring the formation of the former, while the former prevents the neighboring chains from separation and helps the complexation among the counterpart functional groups. Eventually, multilevel energy consumption mechanisms can be triggered under the applied force and the conventionally conflicting properties including strength, toughness, and creep resistance of the interlocked networks are remarkably increased at the same time. Moreover, the moisture sensitivity that used to accompany ionic interactions disappears, which broadens the application scope of the materials in practice. Owing to the included reversible Diels–Alder bonds and Schiff base, the SBR and PEI-based interlocked networks are self-healable and reprocessable and can even be unlocked producing the original single networks. It is anticipated that a versatile and facile platform technique may thus be developed for creating new polymeric materials with advanced multifunctionality.

Function Trumps Form in Two Sugar Symporters, LacY and vSGLT.

Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H3O+) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.

Constructing Anhydrous Proton Conductive Aramid Membranes through Grafting Kevlar Micro-fibrils with Phosphoric Acid

Polyparaphenylene terephthalamide (PPTA) is a para-aramid polymer and it has been widely used as the ultra-light functional material in the fields of energy storage and transformation, military and aviation owing to some merits of strength, stability and lightweight, etc. The aim of this work is to propose a facile strategy of constructing anhydrous proton conductive aramid membranes through grafting Kevlar micro-fibrils with phosphoric acid (PA). In the prepared Kevlar-PA structure, PA molecules functioned as bridges to link the neighboring molecular chains through the formed intermolecular hydrogen bonds. More PA molecules were doped while Kevlar-PA membranes were immersed into (100−50) wt.% PA solutions with the formation of (Kevlar-PA)/(100%−50%)PA membranes. Successful construction of Kevlar-PA structure could guarantee fine performance on proton conduction in (Kevlar-PA)/(100%−50%)PA membranes. Specifically, (Kevlar-PA)/100%PA membranes showed the anhydrous proton conductivity of 2.68×10−1 S/cm at 160 °C and the stable value of 2.25×10−1 S/cm at 120 °C in a 300-hour non-stop test. The similar proton conduction resistance could be revealed from the invariable activation energy (Ea) values. Higher proton conductivity thus signified more proton conduction carriers participating the proton conduction processes. The introduction of PA molecules in Kevlar micro-fibrils that was substantially more effective at constructing conductive aramid membranes comparing to the strategies of treating the surface of Kevlar fibers. This research is expected to provide a facile and promising strategy to construct anhydrous proton conductive aramid membranes through grafting micro-fibrils of aramid nanofibers (ANFs), showing a great promise in the preparation of membrane electrolytes from ANFs.

Correlation Functions for a Chain of Short Range Oscillators

We consider a system of harmonic oscillators with short range interactions and we study their correlation functions when the initial data is sampled with respect to the Gibbs measure. Such correlation functions display rapid oscillations that travel through the chain. We show that the correlation functions always have two fastest peaks which move in opposite directions and decay at rate t^{-frac{1}{3}} for position and momentum correlations and as t^{-frac{2}{3}} for energy correlations. The shape of these peaks is asymptotically described by the Airy function. Furthermore, the correlation functions have some non generic peaks with lower decay rates. In particular, there are peaks which decay at rate t^{-frac{1}{4}} for position and momentum correlators and with rate t^{-frac{1}{2}} for energy correlators. The shape of these peaks is described by the Pearcey integral. Crucial for our analysis is an appropriate generalisation of spacings, i.e. differences of the positions of neighbouring particles, that are used as spatial variables in the case of nearest neighbour interactions. Using the theory of circulant matrices we are able to introduce a quantity that retains both localisation and analytic viability. This also allows us to define and analyse some additional quantities used for nearest neighbour chains. Finally, we study numerically the evolution of the correlation functions after adding nonlinear perturbations to our model. Within the time range of our numerical simulations the asymptotic description of the linear case seems to persist for small nonlinear perturbations while stronger nonlinearities change shape and decay rates of the peaks significantly.

Short- and long-range structure correlations with ionic transport near the glass transition for lithium-ion polyacrylonitrile-based electrolytes using DMSO plasticizer

Here, we report a joint experimental and theoretical study using molecular dynamics calculations focusing on short- and long-range structure correlations with ionic transport near the glass transition for lithium-ion polyacrylonitrile-based electrolytes using DMSO as plasticizer. The presence of subtle modifications of the polymeric structural features near the glass transition (Tg) is rarely reported in the literature and could be relevant to study free volume in polymer-based electrolytes. Our in-situ small angle X-ray scattering (SAXS) analysis at different temperatures evidence an increment of free volume and partial loss of long-range coherence between polyacrylonitrile neighbor chains just above Tg in strong correlation with an Arrhenius behavior crossover observed for the ionic transport in these polyacrylonitrile-based electrolytes. Advancing the understanding of lithium-ion conductivity Arrhenius behavior for polymeric electrolytes with Tg slightly above room temperature could be of great relevance due to the overlap with the operating temperature range of lithium-ion batteries.

Anion-driven supramolecular modulation of spin-crossover properties in mononuclear iron(III) Schiff-base complexes.

A series of Fe(III) complexes [Fe(5-F-sal-N-1,4,7,10)]Y (Y = PF6- for 1, Y = ClO4- for 2, Y = I- for 3 and Y = NO3- for 4) have been prepared. Single-crystal X-ray crystallographic studies show that complex 1 crystallizes in the orthorhombic Pna21 space group and complexes 2-4 have an isomorphous structure and crystallize in the same monoclinic space group, P21/n. Complexes 2-4 have two independent molecules (Fe1 and Fe2) in the unit cell. Magnetic susceptibility measurements demonstrated that complexes 1 and 3 showed a gradual one-step SCO behavior (T1/2 for 1 = 177 K and for 3 = 227 K) without thermal hysteresis. The magnetic behavior of 2 shows an incomplete two-step SCO process at T1/2 = 114 K and 170 K, respectively, while 4 is in a high-spin state at all measured temperatures. A careful evaluation of the supramolecular structures of these complexes revealed correlation between the supramolecular packing forces and their SCO behavior. The crystal structure of 1 consists of a three-dimensional (3D) extended network constructed from N-H⋯F and C-H⋯F hydrogen bonds, and C-H⋯π and C⋯C short contacts. In compounds 2-4, the crystal packing is governed by C⋯C, C-H⋯π and p-π interactions for the Fe1 centers and by C-H⋯π/O interactions for the Fe2 centers, which form 1D chains. Additional interactions (C-H⋯F and N-H⋯O/I) connect the neighboring chains and planes to form a complex supramolecular network. The anion⋯π interactions in 4 provide a means for preventing SCO occurring at low temperatures. This suggests that the supramolecular connectivity of the anions influences the magnetic properties.

Self-Poling Polyvinylidene Fluoride-Based Piezoelectric Energy Harvester Featuring Highly Oriented β-Phase Structured at Multiple Scales

Self-poling poly(vinylidene fluoride) (PVDF) featuring uniformly aligned dipoles can convert mechanical vibrations into electrical energy without post-poling treatment, which is a topic of intense interest in self-powered flexible electronics. However, the current strategies to align PVDF rich in β-crystals have some limitations, such as complex processing, low productivity, and so on. Herein, a self-poling flexible PVDF generator structured with a highly oriented β-phase was prepared via a normal melt processing pathway, by combining flow-induced crystallization with the stabilizing effect of dopamine-functionalized carbon nanotubes (P-CNTs) on the oriented molecules. In this case, the intense flow field exerted by microinjection facilitated the gauche–trans transition and uniform orientation, while with the help of strong interaction between O–H groups of P-CNTs and F–C groups of PVDF, P-CNTs recruited and immobilized the neighboring short chains onto the surface, suppressing the molecular relaxation. As a result, rich electroactive β-phases with preferential alignment characteristics were cultivated in situ, resulting in intrinsic self-oriented dipoles. The extraordinary piezoelectric properties of the PVDF were fully utilized even without polarization treatment, and the open-circuit voltage density reached ∼11 V/cm2, with over 4-fold improvement as compared to that of the randomly oriented sample fabricated by conventional cast method. Finally, the potential application as a robust energy harvester was explored by converting irregular mechanical energy from finger movements into utilizable electric energy, lighting green light-emitting diodes. This multi-scale control from crystalline composition to morphology based on flow-induced crystallization is achieved by simple melt-processing and thus can be suitable for large-scale continuous fabrication of self-poling piezoelectric PVDF energy harvesting devices.

Efficient Organic Solar Cells from Molecular Orientation Control of M-Series Acceptors

<h2>Summary</h2> A "face-on" molecular orientation is essential for photovoltaic materials with efficient vertical carrier transport, but understanding how the molecular structures control their orientations remains challenging. Based on a ladder-type fused-ring core without <i>sp</i>³-hybridized bridging atoms, novel acceptor-donor-acceptor (A-D-A or ADA)-type nonfullerene acceptors (M3 and M32) are developed, and their molecular orientation behaviors are successfully controlled by the neighboring side chains. With linear n-cetyl chains on the nitrogen atoms, the acceptor (M32) tends to adopt an "edge-on" molecular orientation, whereas with bulky branched 2-hexyldecyl chains, the acceptor (M3) has a preferred "face-on" orientation. Blended with a donor polymer of PM6, M3 shows optimal phase separation and dramatically improved electron transport, consequently leading to a much higher device performance than M32. Further optimization of the M3-based devices yields an outstanding efficiency of 16.66%. The strategy of molecular orientation control proposed here will inspire many other innovative designs and syntheses of high-performance nonfullerene acceptors.

Synthesis, molecular and crystal structure of a heterometallic Cu(II)–Ge(IV) complex with 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetracetic acid and 2,2'-bipyridine

A novel synthesis method was developed which allows isolating a new coordination compound with polymeric structure {[Ge2(OH)2(3-hpdta)2Cu2(bipy)2]2Н2О}n (І) (where hpdta5– – anion of 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetracetic acid, bipy – 2,2'-bipyridine) in solid state. Elemental composition, features of thermal decomposition, and molecular and crystalline structure of the synthesized complex were established. According to the data of X-ray diffraction analysis, complex I is a coordination polymer. The polymer chain is formed due to the bridging function of deprotonated ligands hpdta5–, which are simultaneously coordinated with germanium and copper atoms. Ge(1) and Ge(2) atoms have the same coordination environment and distorted octahedral polyhedrons. The coordination polyhedron of Ge(2) is formed due to the coordination of oxygen atoms of two carboxylate and one deprotonated hydroxyl groups of one ligand hpdta5–_1 and carboxylate group of the second ligand hpdta5–_2 in the equatorial direction. In the axial direction, the Ge atom coordinates with the nitrogen atom of the ligand hpdta5–_1 and the hydroxo-ligand. The coordination polyhedrons of Cu(1) and Cu(2) are square pyramids, in which molecules of bipy are coordinated with Cu2+ by two nitrogen atoms. One nitrogen atom and one oxygen atom of the carboxylate group of the hpdta5– ligand are located in the base of a square pyramid. In the apical direction, copper coordinates with deprotonated hydroxyl group of the same hpdta5– ligand. A –-stacking interaction was detected in the crystal between the -systems of bipyridines of two neighboring coordination polymer chains directed along the crystallographic axis a that form double chains with the cavities of 623.04 Å3.

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.

Steady-state temperature distribution under near-field radiative heat transfer inside a linear chain of polaritonic nanoparticles

Thermal transport mediated by near-field interactions is superdiffusive in an ordered network of nanoparticles, such as linear chains. Based on such nanostructures, here we study a classical thermal-nonequilibrium problem, that is, the steady-state temperature distribution inside the chain of equally spaced polaritonic nanoparticles. The existence of the linear temperature profile and anomalous temperature variations in the inner region and near the boundary of a dense chain embedded in vacuum, respectively, is demonstrated by analyzing the effective radiative thermal conductivity within the system. Such temperature distributions are closely relevant to the strength of propagating surface modes sensitive to the chain density and dielectric material. We also demonstrate that, the presence of a homogeneous nonabsorbing background medium renders the steady-state temperature profile of the dense chain nonlinear, as well as enhancing drastically the long-distance heat exchange by two orders of magnitude relative to the vacuum case. This enhancement is a result of the high density of propagating waves in the medium, and is further confirmed by analyzing the energy density distribution over the chain. Furthermore, in a complex system consisting of many parallel chains, we show that, in steady state, temperatures of the thermal drive chain are allowed to tailor by its neighboring chains due to many-body interactions. This work opens ways to qualitatively assess and manipulate the stationary temperature field in advanced nanostructures, such as topological plasmonic chains and nanoparticle arrays.

Across dimensions: Two- and three-dimensional phase transitions from the iterative renormalization-group theory of chains.

Sharp two- and three-dimensional phase transitional magnetization curves are obtained by an iterative renormalization-group coupling of Ising chains, which are solved exactly. The chains by themselves do not have a phase transition or nonzero magnetization, but the method reflects crossover from temperaturelike to fieldlike renormalization-group flows as the mechanism for the higher-dimensional phase transitions. The magnetization of each chain acts, via the interaction constant, as a magnetic field on its neighboring chains, thus entering its renormalization-group calculation. The method is highly flexible for wide application.

Exploring the effect of silicene monolayer on the structure and function of villin headpiece and amyloid fibrils by molecular dynamics simulations.

With the development of various nanomaterial expected to be used in biomedical fields, it is more important to evaluate and understand their potential effects on biological system. In this work, two proteins with different structure, Villin Headpiece (HP35) with α-helix structure and protofibrils Aβ1-42 with five β-strand chains, were selected and their interactions with silicene were studied by means of molecular dynamics (MD) simulation to reveal the potential effect of silicene on the structure and function of biomolecules. The obtained results indicated that silicene could rapidly attract HP35 and Aβ1-42 fibrils onto the surface to form a stable binding. The adsorption strength was moderate and no significant structural distortion of HP35 and Aβ1-42 fibrils was observed. Moreover, the strength of calculated the H-bonds in neighbor chain of Aβ1-42 fibrils indicated that the mild interactions between silicene and fibrils could regularize the structure of Aβ1-42 fibrils and stabilize the interactions between five chains of fibrils protein, which might enhance the aggregation of Aβ1-42 fibrils. This study provides a new insight for understanding the interaction between nanomaterials and biomolecules and moves forward the development of silicene into biomedical fields.

Spin Crossover in Iron(III) Quinolylsalicylaldiminates: The Curious Case of [Fe(qsal-F)2](Anion).

A family of iron(III) spin crossover complexes with different counteranions, [Fe(qsal-F)2]A (qsal-F = 4-fluoro-2-[(8-quinolylimino)methyl]phenolate; A = PF6- 1, OTf- 2, NO3- 3, ClO4- 4, BF4- 5, or NCS- 6) have been prepared. All compounds are isostructural and crystallize (triclinic P1̅ space group) with two independent iron(III) centers (Fe1 and Fe2) in the asymmetric unit. No solvent molecules are found in the crystal lattice, allowing us to directly probe the relative influence of anion variation on the spin crossover characteristics. The crystal packing is governed by three types of π-π interactions (type A, type B, and type C), which form undulating 1D chains. Additional interactions (π-F, C-H···O/F, and P4AE) connect the neighboring chains to form a complex supramolecular network. Hirshfeld surface analysis supports these findings. The anions are located between the cationic [Fe(qsal-F)2]+ chains; hence, similar interchain distances (dchain) are observed irrespective of the anion. However, the interplane distances (dplane) are influenced by the crystal packing and increase proportionally with the anion size. Magnetic studies reveal that smaller anions tend to stabilize the low-spin state (NO3- 3, ClO4- 4, and BF4- 5), while larger anions (PF6- 1 and OTf- 2) exhibit lower transition temperatures (Tonset for 1 = 200 K and T for 2 = 190 K) and gradual spin crossovers. The anomaly is 6, where, despite having the smallest anion, it exhibits the lowest transition temperature with magnetic hysteresis in the first step (T1/2↑ = 170 K and T1/2↓ = 157 K). This suggests the size, shape, and supramolecular connectivity of the anion all influence the magnetic properties.

Influence of the Architecture of Soft Polymer-Functionalized Polymer Nanoparticles on Their Dynamics in Suspension.

The behavior of nanogels in suspension can be dramatically affected by the grafting of a canopy of end-tethered polymer chains. The architecture of the interfacial layer, defined by the grafting density and length of the polymer chains, is a crucial parameter in defining the conformation and influencing the dynamics of the grafted chains. However, the influence of this architecture when the core substrate is itself soft and mobile is complex; the dynamics of the core influences the dynamics of the tethered chains, and, conversely, the dynamics of the tethered chains can influence the dynamics of the core. Here, poly(styrene) (PS) particles were functionalized with poly(methyl acrylate) (PMA) chains and swollen in a common solvent. NMR relaxation reveals that the confinement influences the mobility of the grafted chain more prominently for densely grafted short chains. The correlation time associated with the relaxation of the PMA increased by more than 20% when the grafting density increased for short chains, but for less than 10% for long chains. This phenomenon is likely due to the steric hindrance created by the close proximity to the rigid core and of the neighboring chains. More interestingly, a thick layer of a densely grafted PMA canopy efficiently increases the local mobility of the PS cores, with a reduction of the correlation time of more than 30%. These results suggest an interplay between the dynamics of the core and the dynamics of the canopy.

Synthesis, crystal structure and magnetic properties of a heterometallic framework based on Ni4Gd nodes and 2,2′-phosphinico-dibenzoate ligand

A 4s-3d-4f heterometallic compound with the formula: [KNi4GdL4(H2O)8]·14·5H2O (1) was obtained by self-assembly of nickel nitrate and gadolinium nitrate with 2,2′-phosphinico-dibenzoic acid (H3L) under hydrothermal condition. Meanwhile, the molecular structure was confirmed by single-crystal X-ray diffraction analysis, IR and EA. The compound composes of a 3D framework based on Ni4Gd nodes and 2,2′-phosphinico-dibenzoate ligand. Interestingly, the {Ni4Gd} node exhibits a metal tetrahedron with Gd(III) ion locked in it. The pentanuclear {Ni4Gd} tetrahedra are further connected by double carboxylate groups resulting a zig-zag chain along b-axis. Moreover, the neighboring chains are bridged by potassium ions with water molecules to form a 3D framework. Variable-temperature magnetic susceptibility studies indicate that ferromagnetic interactions occur between the Ni(II) and Gd(III) ions.