Two-dimensional Polymeric Network Research Articles

Single crystals of purely organic free-standing two-dimensional woven polymer networks

The aesthetic and practicality of macroscopic fabrics continue to encourage chemists to weave molecules into interlaced patterns with the aim of providing emergent physical and chemical properties when compared with their starting materials. Weaving purely organic molecular threads into flawless two-dimensional patterns remains a formidable challenge, even though its feasibility has been proposed on several occasions. Herein we describe the synthesis of a flawless, purely organic, free-standing two-dimensional woven polymer network driven by dative B−N bonds. Single crystals of this woven polymer network were obtained and its well-defined woven topology was revealed by X-ray diffraction analysis. Free-standing two-dimensional monolayer nanosheets of the woven polymer network were exfoliated from the layered crystals using Scotch Magic Tape. The surface features of the nanosheets were investigated by integrated low-dose and cryogenic electron microscopy imaging techniques. These findings demonstrate the precise construction of purely organic woven polymer networks and highlight the unique opportunities for the application of woven topologies in two-dimensional organic materials.

Coexistence of Crumpling and Flat Sheet Conformations in Two-Dimensional Polymer Networks: An Understanding of Aggrecan Self-Assembly.

We investigate the conformational properties of self-avoiding two-dimensional (2D) ideal polymer networks with tunable mesh sizes as a model of self-assembled structures formed by aggrecan. Polymer networks having few branching points and large enough mesh tend to crumple, resulting in a fractal dimension of d_{f}≈2.7. The flat sheet behavior (d_{f}=2) emerges in 2D polymer networks having more branching points at large length scales; however, it coexists with crumpling conformations at intermediate length scales, a feature found in scattering profiles of aggrecan solutions. Our findings bridge the long-standing gap between theories and simulations of polymer sheets.

Thermoresponsive and antibacterial two-dimensional polyglycerol-interlocked-polynipam for targeted drug delivery.

Two-dimensional polymeric networks are a new class of polymers with interesting physicochemical and biological properties. They promise a wide range of future biomedical applications including pathogen interactions, drug delivery, bioimaging, photothermal, and photodynamic therapy, owing to their unique features, such as high surface area and multivalent interactions at nano-biointerfaces. In this work, a thermosensitive two-dimensional polymeric network consisting poly(N-isopropylacrylamide) (pNIPAM) chains that are mechanically interlocked by a polyglycerol platform was synthesized and used for bacteria incapacitation. Two-dimensional hyperbranched polyglycerol (2D-hPG) was synthesized by a graphene-assisted strategy and used for encapsulation of azobisisobutyronitrile (AIBN). Radical polymerization of N-isopropylacrylamide by encapsulated AIBN resulted in thermoresponsive platforms with ~ 500 nm lateral size and 20–50 nm thickness. Due to its porous structure, 2D-PNPG was able to efficiently load antibiotics, such as tetracycline (TC) and amoxicillin (AMX). The rate of release of antibiotics from 2D-PNPG and the antibacterial activity of the system correlated with the variation of temperature as a result of the thermosensitivity of 2D-PNPG. This study shows that two-dimensional polymers are efficient platforms for future biomedical applications including drug delivery and bacteria incapacitation.Graphical abstract Thermoresponsive two-dimensional nanomaterials with the ability of loading therapeutic agents and antibacterial activity are synthesized and characterized.

Electronic structure evolution induced by the charge redistribution during the construction of two-dimensional polymer networks from monomers to crystal frameworks.

Two-dimensional covalent organic frameworks (COFs) are a new type of porous crystalline material constructed by the linkage of organic building units through covalent bonds to produce predetermined structures. Here, the electronic structure evolution induced by the charge redistribution during the construction of two-dimensional polymer networks (sp2c-COF-2 and COF-66) from building units to crystal frameworks is examined theoretically. The calculated results demonstrate that the electronic structure of the framework is controlled by the relative energy level between the frontier orbitals of organic building core and linker units as well as the charge transfer amount between them during the construction of the framework. Moreover, it is observed that a noncoplanar framework becomes more conjugated because the charge transfer amount between core and linker units becomes larger during the construction of 2D frameworks, which leads to a larger charge carrier mobility within the 2D structure of COFs. The charge carrier mobility along the z-direction of the COF crystal is dominated by the interface interaction between COF layers. Thereby, we believed reasonable design or selection of organic building units plays a key role in improving the electronic and optoelectronic properties of such 2D organic frameworks.

Acidic triggering of reversible electrochemical activity in a pyrenetetraone-based 2D polymer

In this communication, a novel two-dimensional polymer network (DAPT-TFP) has been synthesized based on pyrenetetraone moieties connected through robust enamine functional groups. Results show that DAPT-TFP exhibit high thermal and chemical stability, even after subjecting the material to a basic or acidic media for certain time (1 M H2SO4 or 1 M NaOH, respectively). An application to conductive additive-free electrode is detailed, as a proof of the ideal interaction between the ions of the neutral aqueous electrolyte and the molecular polymer nanostructure activated by simple acidic treatment. Thus, the study indicates that the redox properties of new organic electrode materials exhibiting limited electroactive properties can be boosted by a straightforward acidic treatment.

Dialkyldithiocarbamate platinum(II) complexes of [Pt(S2CNR2)2] (R = iso-C3H7, iso-C4H9): Preparation, 13C CP-MAS NMR, molecular structure, supramolecular self-assembly and thermal behaviour

Two new dialkyldithiocarbamato platinum(II) complexes of [Pt(S2CNR)2], R = iso-C3H7 (1) and iso-C4H9 (2), have been prepared and characterised using 13C CP-MAS NMR. The crystal and molecular structures of the isolated compounds were established by single-crystal X-ray diffraction. The unit cell of 1 contains four centrosymmetric discrete molecules of [Pt{S2CN(iso-C3H7)2}2], of which the pairs are structurally inequivalent to each other (hereafter denoted as molecules 1a and 1b). At the supramolecular level, due to numerous intermolecular CH⋯S hydrogen bonds, the 1a molecules form linear polymeric ribbons, whose interaction with the 1b molecules results in a two-dimensional polymeric network. In the structure of 2, the construction of supramolecular zigzag chains by non-centrosymmetric molecules of [Pt{S2CN(iso-C4H9)2}2] is determined by intermolecular CH⋯Pt anagostic interactions. The thermal behaviour of crystalline compounds 1 and 2 was studied by simultaneous thermal analysis (STA), a combination of the TG and DSC techniques, under an argon atmosphere. In both cases, platinum(II) sulfide (PtS) was identified as the main end-product upon thermal decomposition of the complexes at 600 °C.

Electronic Structure of Two-Dimensional π-Conjugated Covalent Organic Frameworks

Increasing attention is being given to the development of covalent organic frameworks (COFs) that are based on monolayers of fully π-conjugated structures. At first glance, such two-dimensional (2D) polymer networks could simply be viewed as a mere extension into a second dimension of the quasi-one-dimensional (1D) conjugated polymers at the origin of the field of organic electronics. However, such a view misses essential characteristics coming specifically from 2D lattice symmetry. Our aims in this Perspective are twofold. We seek (i) to provide a conceptual, chemistry-oriented theoretical description of the impact on the electronic structure of this extension from 1D to 2D and (ii) to establish chemical structure–symmetry–electronic property relationships for this class of 2D π-conjugated COFs.

Effects of substituent groups on the crystal structures and luminescence properties of zero-/two-dimensional Zn(II) complexes

The 3-position substituted imidazo[1,2-a]pyridine ligands L1 and HL2 were facilely synthesized, and used for construction of two novel luminescent Zn(II) complexes, namely [ZnCl2(L1)2] (1) and [Zn(L2)2]n (2). Single-crystal X-ray diffraction analysis shows that 1 is zero-dimensional structure, whereas, 2 possesses two-dimensional polymeric network with rhombic grid motifs. The structural differences between 1 and 2 should be determined by the different substituent groups adjacent to carbonyl groups of the 3-position substituted imidazo[1,2-a]pyridine ligands. Complex 1 reveals the red-shifted emission band, compared to free L1 ligand, whereas, 2 displays similar emission spectrum to free HL2 ligand. Such results are also ascribed to substituent group effects and corresponding structural differences.

Relative contributions of chain density and topology to the elasticity of two-dimensional polymer networks.

Understanding the relationships between the structure of polymer networks and their mechanical properties is important for the design of advanced soft materials with optimal properties. However, classical rubber elasticity theories often fall short in their description of the network structure, while simulation techniques at molecular scale remain impractical at that length scale. Here we develop a computational approach based on random discrete networks, in which the polymer network is represented as an assembly of non-linear springs connected at crosslinking points. The density of elastically-effective chains, average network coordination and chain contour lengths are varied independently in order to identify their respective contributions to the network elasticity. Numerical results suggest scaling relations between network parameters and elastic properties that are markedly different from the predictions of classical rubber elasticity theories. In particular, the elastic modulus of 2D random networks is found to be independent of density at constant topology, and proportional to the average coordination at constant density. The discrepancy is due to the pre-straining of the chains in the discrete network, which is not accounted for in classical models of rubber elasticity. Our results have implications for the interpretation of experimental data for ideal network gels that are formed by the cross-coupling of macromolecular building blocks in solution.

Quantifying reconnective activity in braided vector fields.

We introduce a technique for evaluating the changing connectivity of a vector field whose integral curves (field lines) form tangled tubular bundles. Applications of such fields include magnetic flux ropes, relativistic plasma jets, stirred two-dimensional fluids, superfluid vortices, and polymer networks. The technique is based on maps of the field line winding-the average entanglement of a given field line with all other field lines. Previously this had been developed for divergence-free vector fields. By extending some previous theoretical results, we show how it can be applied to any vector field that forms a tubular bundle. We demonstrate the efficacy of this technique on data from laboratory plasma experiments with two interacting magnetic flux ropes. Performed in the UCLA Large Plasma Device, the plasma's magnetic field structure is too complex to identify a single dominant current sheet as an expected site of magnetic reconnection. Previously, this complex structure had restricted the ability to analyze the evolving magnetic connectivity, but this is no such restriction to our method. We demonstrate that the plasma establishes a periodically oscillating cycle of magnetic field structure variation which, while triggered by an ideal instability, is dominated by magnetic reconnection. This reconnection leads to periodically varying coherence of a merged central flux rope, a conclusion supported by analysis of the writhing structure of the magnetic field.

Vapor-Phase Growth and Structural Characterization of Single Crystals of Magnesium Doped Two-Dimensional Fullerene Polymer Mg2C60

Single crystals of magnesium doped fullerene polymer Mg2C60 can be directly grown via a binary vapor-phase mixture of Mg and C60, in sealed glass tubes at elevated temperatures. This is the first single crystal, in metal-doped two-dimensional fullerene polymers, which enables precise X-ray structural refinement. The Mg2C60 crystallizes in a monoclinic space group, I2/m, with lattice parameters of a = 9.324(2) A, b = 9.041(2) A, c = 14.817(3) A, and β = 91.699(10)°. A Mg atom is located at each tetrahedral fullerene ball interstice, where the shortest Mg–C distance is 2.341(2) A, suggesting that the Mg cation is in van der Waals contact with carbon p orbitals. The precise structure of the two-dimensional fullerene polymer network is characterized by comparison with structural data reported previously on powder samples.

Mechanical Response of Two-Dimensional Polymer Networks: Role of Topology, Rate Dependence, and Damage Accumulation

The skeleton of many natural and artificial soft materials can be abstracted as networks of fibers/polymers interacting in a nonlinear fashion. Here, we present a numerical model for networks of nonlinear, elastic polymer chains with rate-dependent crosslinkers similar to what is found in gels. The model combines the worm-like chain (WLC) at the polymer level with the transition state theory for crosslinker bond dynamics. We study the damage evolution and the force—displacement response of these networks under uniaxial stretching for different loading rates, network topology, and crosslinking density. Our results suggest a complex nonmonotonic response as the loading rate or the crosslinking density increases. We discuss this in terms of the microscopic deformation mechanisms and suggest a novel framework for increasing toughness and ductility of polymer networks using a bio-inspired sacrificial bonds and hidden length (SBHL) mechanism. This work highlights the role of local network characteristics on macroscopic mechanical observables and opens new pathways for designing tough polymer networks.

Sequence-specific fluorometric recognition of HIV-1 ds-DNA with zwitterionic zinc(II)-carboxylate polymers

Four water-stable zwitterionic zinc-carboxylate polymers are prepared by reacting N-carboxymethyl-(3,5-dicarboxy)-pyridinium bromide (H3CmdcpBr) with zinc(II) nitrate in the presence of NaOH, through adjusting the solvents and ancillary ligands. With H2O as the solvent and the absence of an ancillary ligand, a two-dimensional (2D) polymer network [Zn(Cmdcp)(H2O)]n (1) is formed. In a mixed H2O/DMF solvent and with the presence of chelating ligands 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and 2-(4-pyridyl)benzimidazole (pbz), a one-dimensional (1D) polymer of {[Zn2(Cmdcp)(bipy)2(H2O)5](NO3)2·3H2O}n (2), a mononuclear ionic species of [Zn(phen)(H2O)4][Cmdcp] (3), and a 2D polymer of {[Zn(Cmdcp)(pbz)][pbz]·7H2O}n (4) are accordingly formed. Compounds 1–4 are characterized by IR, elemental analyses and single crystal X-ray crystallography. Compound 2 strongly adsorbs single-stranded DNA (ss-DNA) probe (denoted as P-DNA) labeled with carboxyfluorescein (FAM) and quenches its fluorescence via a photo-induced electron transfer process. If, however, a double-stranded DNA (ds-DNA) of the human immunodeficiency virus 1 (HIV-1 ds-DNA) is further present, the P-DNA interacts with the major groove in HIV-1 ds-DNA via Hoogsteen hydrogen bonding to form a rigid triplex structure. This results in partial or complete fluorescence recovery depending on the concentration of HIV-1 ds-DNA. The findings are applied in fluorometric sensing of HIV-1 ds-DNA. The calibration plot is linear in the 0–60nM target DNA concentration range, with a 7.4nM detection limit (at a signal-to-noise ratio of 3). The assay is highly specific and not interfered by one base pair mutated for complementary target HIV-1 ds-DNA, complementary ss-DNA, single-base pair mutated for complementary ss-DNA, non-specific ss-DNA sequences, and higher-order dimeric G-quadruplexes.

Physical and mechanical properties of composite materials on the basis of an ice matrix

The technique for the preparation of composite materials in which ice serves as the matrix and polymer fillers (the reinforcement) with various chemical compositions and morphologies and chemical ice modifiers serve as the tool for affecting its structure and properties is proposed in this work. The physical and mechanical properties of the composites (bending strength) are studied, and the character of the effect of two-dimensional and three-dimensional polymer networks, their amount, assembling, and concentration of modifiers are revealed. Also, the simultaneous action of polymer fillers and modifiers is considered. It is shown that the proposed technique makes it possible to control the physical and mechanical properties of composites on the basis of ice and create substantially stronger materials when compared to natural ice.

Synthesis, Single Crystal Structure, and Magnetic Properties of 3-D Cu(NITpPy)2[Cu(CN)3].2CH3OH.2H2O Complexes

A new Cu(II) complexes containing nitroxide radicals Cu(NITpPy)2[Cu(CN)3]. 2CH3OH.2H2O has been successfully synthesized. The single crystal X-ray analysis revealed that the compound belongs to monoclinic crystal system (C2/c (#15)). The existence of the C≡N radical and water molecules are observed by using infra-red within the range of 4000-500 cm-1 and 3500-3000 cm-1, respectively. The Cu(NITpPy)22+ units are connected through N(CN)2− bridging ligands in 2 coordination developing, respectively, into one-dimensional and two-dimensional polymeric networks. Paramagnetic interactions in the compound appear in the vicinity of room temperature. As the temperature decreased, low dimensional antiferromagnetic interactions established and Cu(II)-radicals antiferromagnetic interactions dominates down to 2 K with μeff = 0.8129 μB

Unusual 4-arsonoanilinium cationic species in the hydrochloride salt of (4-aminophenyl)arsonic acid and formed in the reaction of the acid with copper(II) sulfate, copper(II) chloride and cadmium chloride.

Structures having the unusual protonated 4-arsonoanilinium species, namely in the hydrochloride salt, C6H9AsNO3+·Cl-, (I), and the complex salts formed from the reaction of (4-aminophenyl)arsonic acid (p-arsanilic acid) with copper(II) sulfate, i.e. hexaaquacopper(II) bis(4-arsonoanilinium) disulfate dihydrate, (C6H9AsNO3)2[Cu(H2O)6](SO4)2·2H2O, (II), with copper(II) chloride, i.e. poly[bis(4-arsonoanilinium) [tetra-μ-chlorido-cuprate(II)]], {(C6H9AsNO3)2[CuCl4]}n, (III), and with cadmium chloride, i.e. poly[bis(4-arsonoanilinium) [tetra-μ-chlorido-cadmate(II)]], {(C6H9AsNO3)2[CdCl4]}n, (IV), have been determined. In (II), the two 4-arsonoanilinium cations are accompanied by [Cu(H2O)6]2+ cations with sulfate anions. In the isotypic complex salts (III) and (IV), they act as counter-cations to the {[CuCl4]2-}n or {[CdCl4]2-}n anionic polymer sheets, respectively. In (II), the [Cu(H2O)6]2+ ion sits on a crystallographic centre of symmetry and displays a slightly distorted octahedral coordination geometry. The asymmetric unit for (II) contains, in addition to half the [Cu(H2O)6]2+ ion, one 4-arsonoanilinium cation, a sulfate dianion and a solvent water molecule. Extensive O-H...O and N-H...O hydrogen bonds link all the species, giving an overall three-dimensional structure. In (III), four of the chloride ligands are related by inversion [Cu-Cl = 2.2826 (8) and 2.2990 (9) Å], with the other two sites of the tetragonally distorted octahedral CuCl6 unit occupied by symmetry-generated Cl-atom donors [Cu-Cl = 2.9833 (9) Å], forming a two-dimensional coordination polymer network substructure lying parallel to (001). In the crystal, the polymer layers are linked across [001] by a number of bridging hydrogen bonds involving N-H...Cl interactions from head-to-head-linked As-O-H...O 4-arsonoanilinium cations. A three-dimensional network structure is formed. CdII compound (IV) is isotypic with CuII complex (III), but with the central CdCl6 complex repeat unit having a more regular M-Cl bond-length range [2.5232 (12)-2.6931 (10) Å] compared to that in (III). This series of compounds represents the first reported crystal structures having the protonated 4-arsonoanilinium species.

Unprecedented layered coordination polymers of dithiolene group 10 metals: magnetic and electrical properties.

One-pot reactions between Ni(ii), Pd(ii) or Pt(ii) salts and 3,6-dichloro-1,2-benzenedithiol (HSC6H2Cl2SH) in KOH medium under argon lead to a series of bis-dithiolene coordination polymers. X-ray analysis shows the presence of a common square planar complex [M(SC6H2Cl2S)2](2-) linked to potassium cations forming either a two-dimensional coordination polymer network for {[K2(μ-H2O)2(μ-thf)(thf)2][M(SC6H2Cl2S)2]}n [M = Ni () and Pd ()] or a one-dimensional coordination polymer for {[K2(μ-H2O)2(thf)6][Pt(SC6H2Cl2S)2]}n (). In the coordination environment of the potassium ions may slightly change leading to the two-dimensional coordination polymer {[K2(μ-H2O)(μ-thf)2][Pt(SC6H2Cl2S)2]}n () that crystallizes together with . The physical characterization of compounds show similar trends, they are diamagnetic and behave as semiconductors.

Curvature-induced crosshatched order in two-dimensional semiflexible polymer networks.

A recurring motif in the organization of biological tissues are networks of long, fibrillar protein strands effectively confined to cylindrical surfaces. Often, the fibers in such curved, quasi-two-dimensional (2D) geometries adopt a characteristic order: the fibers wrap around the central axis at an angle which varies with radius and, in several cases, is strongly bimodally distributed. In this Rapid Communication, we investigate the general problem of a 2D crosslinked network of semiflexible fibers confined to a cylindrical substrate, and demonstrate that in such systems the trade-off between bending and stretching energies, very generically, gives rise to crosshatched order. We discuss its general dependency on the radius of the confining cylinder, and present an intuitive model that illustrates the basic physical principle of curvature-induced order. Our findings shed new light on the potential origin of some curiously universal fiber orientational distributions in tissue biology, and suggests novel ways in which synthetic polymeric soft materials may be instructed or programmed to exhibit preselected macromolecular ordering.

Synthesis, Crystal Structure, and Luminescent Properties of a Two-Dimensional Mn(II) Coordination Polymer: Catena-(diaqua-tetrakis(µ2-cinnamato-o,o′)-manganese(II))

A new manganese(II) complex: Catena-(diaqua-tetrakis(µ2-cinnamato-o,o′)-manganese(II) was prepared by the method of solvothermal synthesis, and its two-dimensional coordination polymeric network was determined by X-ray diffraction. It crystallized in monoclinic, space group C2/c, with a = 36.934(14) Å, b = 6.468(2) Å, c = 7.435(3) Å, ß = 91.733(7)°, Z = 4, Dc = 1.441 Mg/m3, V = 1775.2(11) Å3. Under ultraviolet radiation of 338 nm the emissions of the title complex mainly result from its ligand: cinnamic acid.

Crystal structure of 3,4-di-chloro-anilinium hydrogen phthalate.

In the title salt, C6H6Cl2N+·C8H5O4 −, the carb­oxy­lic acid and carboxyl­ate groups of the anion form dihedral angles of 20.79 (19) and 74.76 (14)°, respectively, with the plane of the benzene ring. In the crystal, mol­ecules are assembled into a two-dimensional polymeric network parallel to (100) via N—H⋯O and O—H⋯O hydrogen bonds. In addition, within the layer, there are π–π stacking inter­actions between the benzene rings of the cation and the anion [centroid–centroid distance = 3.6794 (17) Å]. A weak C—H⋯O interaction is also observed.