Honeycomb Network Research Articles

An unusual 3D coordination polymer assembled through parallel interpenetrating and polycatenating of (6,3) nets

Reaction of AgClO4 with a bulky semi-flexible tripodal ligand 2,4,6-tris(4-((pyridin-4-ylthio)methyl)phenyl)-1,3,5-triazine (tppt) affords highly undulating (6,3) honeycomb networks [Ag3(tppt)2](ClO4)3·8DMSO which display unusual net entanglement. Three (6,3) nets interweave in parallel to give rise to a 3-fold interpenetrating basic layer (2D → 2D parallel). In addition, every such layer interlocks four other layers, two above and two below (2D → 3D parallel). Therefore, totally fifteen (6,3) nets are involved in entanglement with respect to each basic layer, in which each single (6,3) net shows 11-fold interpenetration and 5-fold catenation, thus resulting in a novel 3D coordination polymer containing both interpenetration and polycatenation.

The first crystallographic observation of up to the third hydration layer of Cu(II) ion in an unusual ‘water-cation layer’ templated by an Anderson polyoxometallate

This constitutes the first crystallographic observation of hydrated Cu(II) ion retaining up to its third hydration layer which, along with the chair form water hexamer, builds up a unique water-cation layer. Moreover, an unprecedented supramolecular honeycomb network of [Cu(phen)3]2+ units templated by Anderson polyoxometallate units occupy the intervening spaces between successive water layers. Complex 1 is a rare example of parallel interpenetration of a 2D π–π network and a 3D pillar-layered hydrogen bonded network.

Control of Charge Transfer Phase Transition and Ferromagnetism by Photoisomerization of Spiropyran for an Organic−Inorganic Hybrid System, (SP)[FeIIFeIII(dto)3] (SP = spiropyran, dto = C2O2S2)

Iron mixed-valence complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)](dto = C(2)O(2)S(2)), shows a spin entropy-driven phase transition called charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) around 120 K and a ferromagnetic transition at 7 K. These phase transitions remarkably depend on the hexagonal ring size in the two-dimensional honeycomb network structure of [Fe(II)Fe(III)(dto)(3)](-)(infinity). In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photoirradiation, we have synthesized a photosensitive organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)(3)](SP = spiropyran), and investigated the photoinduced effect on the magnetic properties. Upon UV irradiation at 350 nm, a broad absorption band between 500 and 600 nm appears and continuously increases with the photoirradiation time, which implies that the UV irradiation changes the structure of spiropyran from the closed form to the open one in solid state. The photochromism in spiropyran changes the ferromagnetic transition temperature from 5 to 22 K and the coercive force from 1400 to 6000 Oe at 2 K. In this process, the concerted phenomenon coupled with the charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) and the photoisomerization of spiropyran is realized.

Design of Cocrystals via New and Robust Supramolecular Synthon between Carboxylic Acid and Secondary Amide: Honeycomb Network with Jailed Aromatics

A new synthon involving carboxylic acid and a secondary amide with anti geometry has been identified and used as a designing element to engineer the cocrystals of symmetrically substituted triamides, tricarboxylic acids, and aromatic guest molecules. The robustness of the synthon has been explored by considering the pyridine functional groups in the amide molecules.

The structure of mixed H2O–OH monolayer films on Ru(0001)

Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations, whereby a fraction of the water molecules partially dissociate and form mixed H(2)O-OH structures. X-ray photoelectron spectroscopy and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H(2)O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H(2)O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for density functional theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.

Underpotential deposition of hydrogen on Pt(111): a combined direct molecular dynamics/density functional theory study

A combined direct molecular dynamics/density functional theoretical study of the electro-oxidation of molecular hydrogen at the Pt(111)/water interface has been carried out to provide insights into the adsorbed underpotential deposition (UPD) states of hydrogen at submonolayer coverages of bridging hydrogen atoms Hads(bridge). As in our previous study, H2 oxidation proceeds via the Heyrovsky process, forming a hydrated H+ ion and an UPD hydrogen atom, which is strongly adsorbed and is lying nearly flat in a bridging position on the Pt(111) surface. At submonolayer coverage, the UPD Hads(bridge) atoms spontaneously self-assemble to form a hexagonal 2D honeycomb network on the Pt(111) surface, a signature that could be considered to be characteristic of UPD states of hydrogen.

Self-Assembly of Chiral Molecular Honeycomb Networks on Au(111)

Self-assembly of the specifically designed 3-fold symmetric 1,3,5-trikis(4'-carboxylphenyl)-2,4,6-trikis(4'-tert-butylphenyl)-benzene molecule on a Au(111) surface is investigated by means of in situ ultrahigh vacuum scanning tunneling microscopy. A variety of chiral honeycomb networks with increasing interpore distance is observed. Experiments and force field calculations reveal that the formation of the two-dimensional hexagonal porous networks is driven by a balance of molecular close-packing within half-unit cells and cyclic hydrogen bonding dimerization between half-unit cells. The honeycomb networks are shown to be chiral owing to asymmetric molecular close-packing within the half-unit cells.

Detection of Corneal Fibrosis by Imaging Second Harmonic–Generated Signals in Rabbit Corneas Treated with Mitomycin C after Excimer Laser Surface Ablation

Recent studies have shown that confocal imaging of second harmonic-generated (SHG) signals can detect corneal collagen organization. The purpose of this study was to assess whether SHG signals can detect differences in corneal fibrosis after excimer laser surface ablation (photorefractive keratectomy [PRK]). Rabbits received 9-D PRK in one eye followed by treatment with either mitomycin C (MMC) or vehicle. Corneal haze was measured by in vivo confocal microscopy before and 2, 4, 8, and 12 weeks after surgery. Animals were then killed and corneas were evaluated by visible and nonlinear confocal microscopy. PRK induced significant haze in vehicle-treated corneas that peaked at 2 weeks and remained elevated at 12 weeks after surgery. MMC treatment significantly (P < 0.05) reduced corneal haze at 2 weeks and was essentially normal by 12 weeks. Imaging of SHG signals in vehicle-treated eyes showed an anterior layer of collagen forming a honeycomb network blending into a dense mat of irregularly arranged collagen fibers that overlaid normal orthogonally arranged collagen lamellae. MMC treatment showed normal collagen organization at the surface. Fibrotic tissue was associated with a high cell density and alignment of intracellular actin filaments with collagen fiber bundles. In MMC-treated eyes, an anterior acellular zone overlaid a sparsely populated stroma containing isolated and enlarged keratocytes. Imaging of SHG signals provides a sensitive means for detection of corneal fibrosis after surface ablation and can be used to assess the effects of antifibrotic therapy on corneal healing after refractive surgery.

Solvent Effects on Supramolecular Networks Formed by Racemic Star-Shaped Oligofluorene Studied by Scanning Tunneling Microscopy

Two-dimensional networks of star-shaped oligofluorene end-capped with carboxylic groups (StOF-COOH3) are investigated using scanning tunneling microscopy (STM) in solvents with different polarities and functionality on graphite surface. The high-resolution STM images show that the assembly of StOF-COOH3 is strongly solvent dependent. Well-ordered porous honeycomb networks are revealed at the octanoic acid/graphite and 1,2,4-tricholrobenzene/graphite interfaces, while an irregular and densely packed structure is observed at the 1-phenyloctane/graphite interface. In n-tetradecane, an intermediate state of the coexistence of a disordered and honeycomb structure is identified on the surface. High resolution STM images revealed two different hydrogen-bonded networks for StOF-COOH3 molecules with 1-octanoic acid as the solvent, including homochiral domains and heterochiral domains. The stabilization of the networks consisting of chiral species at the graphite surface is suggested to be possibly associated with ...

A Fluorescent and Phosphorescent Nanoporous Solid: Crystalline Calix[4]arene

Calix[4]arene forms elongated nanoporous microcrystals. The pores are linear nano-channels (1.7 nm diameter) arranged in a honeycomb network. The crystals luminesce at room temperature according to a variety of processes that include monomer fluorescence (lifetime of ca. 1.1 ns), dimer fluorescence (lifetime of ca. 5.4 ns), and monomer phosphorescence (lifetime of ca. 2 s). The dimers result from pi-orbital overlap of adjacent phenol groups from neighboring nano-channels, with C-C distances of ca. 4 A.

Role of Interaction Anisotropy in the Formation and Stability of Molecular Templates

Surface templating via self-assembly of hydrogen-bonded molecular networks is a rapidly developing bottom-up approach in nanotechnology. Using the melamine-PTCDI molecular system as an example we show theoretically that the network stability in the parameter space of temperature versus molecular coupling anisotropy is highly restricted. Our kinetic Monte Carlo simulations predict a structural stability diagram that contains domains of stability of an open honeycomb network, a compact phase, and a high-temperature disordered phase. The results are in agreement with recent experiments, and reveal a relationship between the molecular size and the network stability, which may be used to predict an upper limit on pore-cavity sizes.

Poly[diaqua-μ2-oxalato-di-μ2-pyrimidine-2-carboxylato-dimanganese(II)

In the title compound, [Mn2(C2O4)(C5H3N2O2)2(H2O)2]n, the MnII atom exhibits a distorted octa­hedral coordination geometry, with the centrosymmetric oxalate anion and the monoanionic pyrimidine-2-carboxyl­ate ligands generating a two-dimensional honeycomb network with a (6,3)-topology.

Periodic flux jump in superconducting Pb networks as consequence of the extended Little–Parks effect

The extended Little–Parks effect of superconducting network is known as a periodic Tc variation as a function of magnetic field. Superconducting Pb honeycomb networks of matching field 0.106G and triangular microhole lattice of Pb of matching field 0.425G have been fabricated by the combination of electron-beam lithography and a lift-off process of evaporated Pb films. The application of magnetic field corresponds to the vortex filling into superconducting networks. We measured the magnetization of the networks systematically by using a SQUID magnetometer. We found that flux jump appears rather periodically as a function of magnetic field. Flux jumps may be induced by a periodic decrease of the critical current density of the network. To the authors’ knowledge, this is for the first time to observe the regular flux jumps due to the critical current modification coming from the extended Little–Parks effect of the superconducting networks.

Two new 2D μ-azido, μ-oxalato manganese(II) complexes. Synthesis, structure and magnetic properties

By using the oxalate (ox) and azide bridging ligands, the compounds of formulae [Mn 2(N 3) 2(ox)(4-OHpy) 2] n ( 1) (4-OHpy = 4-hydroxypyridine) and [NaMn(ox)(N 3)(H 2O) 4] ( 2) can be prepared. The oxalate ligand is generated by the slow decomposition of l-ascorbic acid. The X-ray diffraction analysis reveals two-dimensional systems: in ( 1), zigzag Mn(II) chains with alternating di-EO-azides (EO = end-on) and di- O, O-pyridone (tautomeric keto-form) bridges are bridged in turn by oxalato anions to form unprecedented two-dimensional honeycomb networks. In ( 2), zigzag Mn(II) chains with oxalate bridges are bridged in turn by double μ 1 , 1 - N 3 - anions to form also unprecedented 2D honeycomb layers. In the structure of 2, the azide group and water molecules are partially disordered. The magnetic susceptibility measurements indicate bulk antiferromagnetic coupling for 1 and 2.

The Use of 2,1,3‐Benzoselenadiazole as an Auxiliary Ligand for the Construction of New 2D Silver(I)/Benzene‐ or Cyclohexane‐1,3,5‐tricarboxylate Honeycomb Networks

AbstractThe reaction of freshly synthesized [Ag(NH3)2](OH), 2,1,3‐benzoselenadiazole (bsd) and benzene‐ or cyclohexane‐1,3,5‐tricarboxylic acid (H3btc/H3ctc) results in two new coordination polymers containing 2D Ag3(btc) and Ag3(ctc) hexagonal motifs, namely [Ag3(btc)(bsd)6]·0.5H2O (1) and [Ag3(ctc)(bsd)3]·1.5bsd·3.5H2O (2). Complex 1 is a 3D supramolecular framework extended by deformed 2D Ag3(btc) honeycomb nets via Se···N synthons formed between the dangling monodentate bsd groups, whereas 2 is a 3D metal–organic framework of nanoscale cages made up from ideal Ag3(ctc) honeycomb layers and μ2‐bridging bsd ligands.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Fabrication of porous carbon nanotube network

We used the spin-coating method combined with ultrasonic atomization as a continuous, one-step process to generate a two-dimensional honeycomb network that was constructed from pure multi-walled carbon nanotubes.

Molecular networks. Design and serendipity

The supramolecular assembly of a 2D honeycomb network viacarboxylic acid–pyrimidinone-dimer synthon and the unexpected occurrence of 3D diamondoid net in the crystal structure of a dipyridyl urea hydrate illustrate the title theme.

A manganese(ii) coordination polymer with mixed pyrimidine-2-carboxylate and oxalate bridges: synthesis, structure, and magnetism

A new two-dimensional (2D) coordination polymer with mixed pyrimidine-2-carboxylate (pymca) and oxalate (ox) bridges, [Mn(2)(pymca)(2)(ox)(H(2)O)(2)](n) (1), was synthesized by a hydrothermal reaction involving the in situ formation of the pymca and ox ligands from 2-cyanopyrimidine (pymCN), and its structure and magnetic properties were characterized. The dianionic ox and monoanionic pymca ligands are both potentially bis(chelating) and have been used to construct anionic and cationic 2D honeycomb networks [(6,3) net], respectively. In the present compound, ox assumes the usual bis(chelating) bridging mode, but pymca serves as a tridentate bridge with one of the pyrimidyl nitrogens uncoordinated. The two different bridges collaborate to generate a highly undulated 2D layer with the (6,3) net topology, and the layers are closely packed in parallel through pi-pi interactions between pyrimidyl rings and hydrogen bonds involving coordinated water molecules, oxalate oxygens, and uncoordinated pyrimidyl nitrogens. Magnetic measurements reveal that the compound is a spin-canted antiferromagnet with weak ferromagnetic transition below T(c) = 2.4 K.

Pairs and heptamers of C70 molecules ordered via PTCDI-melamine supramolecular networks

In this paper, we report on the use of two PTCDI-melamine supramolecular networks on Au(111) to trap C70 molecules. The different supramolecular networks were formed by changing the postannealing temperature after molecular deposition. We observed, using scanning tunneling microscopy, that the deposition of C70 onto a PTCDI melamine network with parallelogram cavities results in the long-range ordering of paired C70, whereas the deposition of C70 molecules onto a PTCDI-melamine honeycomb network results in the trapping of C70 heptamers.

Phonons in conventional and auxetic honeycomb lattices

The modes of vibrations in honeycomb and auxetic structures are studied, with models in which the lattice is represented by a planar network where sites are connected by strings and rigid rods. The auxetic network is obtained modifying a model proposed by Evans et al. in 1991, and used to explain the negative Poisson's ratio of auxetic materials. This relevant property means that the materials have a lateral extension, instead to shrink, when they are stretched. For what concerns the acoustic properties of these structures, they absorb noise and vibrations more efficiently than non-auxetic equivalents. The acoustic and optical dispersions obtained in the case of the auxetic model are compared with the dispersions displayed by a conventional honeycomb network. It is possible to see that the phonon dispersions of the auxetic model possess a complete bandgap and that the Goldstone mode group velocity is strongly dependent on the direction of propagation. The presence of a complete bandgap can explain some experimental observations on the sound propagation properties of the auxetic materials.