Molecular Braid Research Articles

Near-infrared phosphorescence emission of three-fold interpenetrated MOF based on 1,4-bis(imidazole-1-ylmethyl)benzene: Syntheses, structure and photoelectron performance

One new Zn(II) based 3D metal-organic framework (MOF) [Zn(IPA) (TBMIM)] (1) (IPA ​= ​isophthalic acid, TBMIM ​= ​1,4-bis(imidazole-1-ylmethyl)benzene) has been synthesized under hydrothermal conditions. X-ray single-crystal diffraction analysis indicates that the title MOF exhibits a 3-fold interpenetrated diamond network with new type of molecular braid. Time-resolved measurements reveal that 1 emissions rare example of near-infrared phosphorescence at room temperature. The density functional theoretical (DFT) calculations indicate complete separation of molecular orbits between IPA and TBMIM ligands, which is in favor of the generation of triplet state excitons. This MOF also shows well photoelectron responds performance owing to the abundant π···π stacking in the entanglement molecular braids, which afford long-range π electrons delocalization for efficient electron transport.

From Au-Thiolate Chains to Thioether Sierpiński Triangles: The Versatile Surface Chemistry of 1,3,5-Tris(4-mercaptophenyl)benzene on Au(111).

Self-assembly of 1,3,5-tris(4-mercaptophenyl)benzene (TMB), a 3-fold symmetric, thiol-functionalized aromatic molecule, was studied on Au(111) with the aim of realizing extended Au-thiolate-linked molecular architectures. The focus lay on resolving thermally activated structural and chemical changes by a combination of microscopy and spectroscopy. Thus, scanning tunneling microscopy (STM) provided submolecularly resolved structural information, while the chemical state of sulfur was assessed by X-ray photoelectron spectroscopy (XPS). Directly after room-temperature deposition, only less well ordered structures were observed. Mild annealing promoted the first structural transition into ordered molecular chains, partly organized in homochiral molecular braids. Further annealing led to self-similar Sierpiński triangles, while annealing at even higher temperatures again resulted in mostly disordered structures. Both the irregular aggregates observed at room temperature and the chains were identified as metal-organic assemblies, whereby two out of the three intermolecular binding motifs are energetically equivalent according to density functional theory (DFT) simulations. The emergence of Sierpiński triangles is driven by a chemical transformation, i.e., the conversion of coordinative Au-thiolate to covalent thioether linkages, and can be further understood by Monte Carlo simulations. The great structural variance of TMB on Au(111) can on one hand be explained by the energetic equivalence of two binding motifs. On the other hand, the unexpected chemical transition even enhances the structural variance and results in thiol-derived covalent molecular architectures.

Four novel coordination frameworks with high degree of diamondoid interpenetration containing scarce quadruple-stranded homo-axis helices and quintuple-stranded molecular braids

Four novel interpenetrated diamondoid (dia) networks, namely [Zn(1,4-bdc)(bibp)] (1), [Mn(bqdc)(bibp)] (2), [Cd(bqdc)(bibp)] (3), [Co4(bqdc)4(bibp)4] (4). (bibp=1,4-bis(4-(imidazole-1-yl)benzyl)piperazine, 1,4-bdc=1,4-benzenedicarboxylate, bqdc=2,2′-biquinoline-4,4′-dicarboxylate), have been synthesized by using mixed spacer ligands with significantly different lengths. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra and TG analyses. Compound 1 is an unusual 8-fold [4+4] interpenetrated dia network containing the unique quadruple-stranded braid (i.e. quadruple-stranded homo-axis helices), which is further entangled by another quadruple-stranded braid to produce an unprecedented octuple-stranded braid derived from eight individual dia nets. Compounds 2 and 3 are isostructural, while compound 4 is isoreticular to them. They all exhibit 5-fold interpenetrating dia networks containing an exceptional quintuple-stranded molecular braid. In addition, the photoluminescence properties of compounds 1 and 3, and the magnetic property of compound 4 were studied.

Collapse and coexistence for a molecular braid with an attractive interaction component subject to mechanical forces

Dual mechanical braiding experiments provide a useful tool with which to investigate the nature of interactions between rod-like molecules, for instance actin and DNA. In conditions close to molecular condensation, one would expect an appearance of a local minimum in the interaction potential between the two molecules. We investigate this situation, introducing an attractive component into the interaction potential, using a model developed for describing such experiments. We consider both attractive interactions that do not depend on molecular structure and those which depend on a DNA-like helix structure. In braiding experiments, an attractive term may lead to certain effects. A local minimum may cause molecules to collapse from a loosely braided configuration into a tight one, occurring at a critical value of the moment applied about the axis of the braid. For a fixed number of braid pitches, this may lead to coexistence between the two braiding states, tight and loose. Coexistence implies certain proportions of the braid are in each state, their relative size depending on the number of braid pitches. This manifests itself as a linear dependence in numerically calculated quantities as functions of the number of braid pitches. Also, in the collapsed state, the braid radius stays roughly constant. Furthermore, if the attractive interaction is helix dependent, the left-right handed braid symmetry is broken. For a DNA like charge distribution, using the Kornyshev–Leikin interaction model, our results suggest that significant braid collapse and coexistence only occurs for left handed braids. Regardless of the interaction model, the study highlights the possible qualitative physics of braid collapse and coexistence; and the role helix specific forces might play, if important. The model could be used to connect other microscopic theories of interaction with braiding experiments.

Undulations in a weakly interacting mechanically generated molecular braid under tension

We consider mechanically generated molecular braids composed of two molecules where long range interactions between them can be considered to be very weak. We describe a model that takes account of the thermal fluctuations of the braid, steric interactions between the molecules, and external mechanical forces. In this model, both sets of ends, of the two molecules, are considered to be separated by a fixed distance much larger than the radius of the braid. One set of ends is rotated to generate a braid of a certain number of pitches (or turns), while the other set remains fixed. This model may describe the situation in which the ends of each molecule are attached to a substrate and a magnetic bead; to the latter a pulling force and rotational torque can be applied. We discuss various aspects of our model. Most importantly, an expression for the free energy is given, from which equations, determining the various geometric parameters of the braid, can be obtained. By numerically solving these equations, we give predictions from the model for the external torque needed to produce a braid with a certain number of turns per bending persistence length, as well as the end to end extension of the two molecules for a given pulling force. Other geometric parameters, as well as the lateral force required to keep the ends of the two molecules apart, are also calculated.

ChemInform Abstract: Molecular Braids in Metal—Organic Frameworks

AbstractReview: ca. 50 refs.

Triple-meso helices as alcohol reservoirs and discriminators: structural properties and thermal behaviors of silver(i) coordination molecular braids containing diethylbis(4-pyridyl)silanes

Self-assembly of silver triflate with L in alcohol solvent produces characteristic triple-meso helices [Ag3(L)3(ROH)](CF3SO3)3 (L = diethylbis(4-pyridyl)silane; R = Me, Et, n-Pr, and n-Bu) with six units in each turn. Their unit cell volumes are sensitive to the size of the coordinated alcohol molecules. An unusual "alcohol molecules at triple-meso helices" system is a characteristic reversible alcohol container and discriminator via appropriate association/dissociation. The meso helical solids are favored in the order MeOH > EtOH > n-PrOH > n-BuOH via an interaction between the silver(I) ion and the alcohol molecule. The crystals evaporate the coordinated alcohol molecules at low temperatures, and finally calcination at 600 °C produces micro-sized chaotic surface materials consisting of silver(0) without silicon(IV) oxide.

Molecular braids in metal–organic frameworks

Molecular braids represent one of the most fascinating topological networks in the fields of supramolecular chemistry and crystal engineering. In this Tutorial Review we provide an overview of the sustainable exploration of those metal-organic frameworks (MOFs) with the topology of molecular braid. Since the first example of the triple-stranded molecular braid in MOFs was reported by our group in 2005, another five attractive molecular braids in MOFs have already been prepared through several different pathways by us and other groups. Indeed, these known examples include the triple-, quintuple- and sextuple-stranded molecular braids. Besides the molecular braids found in MOFs, this type of unique topological network was also observed in organic co-crystals, and the only example of this is discussed in context as well.

A new type of entangled coordination network: coexistence of polythreading and polyknotting involved molecular braids

A fascinating polythreaded coordination network formed by 1D crankshaft shaped chains threading into a 2D undulated sheet in a one-over/one-under interweaving fashion was reported, in which the 2D layer exhibits an unusual polyknotted entanglement containing triple-stranded molecular braids.

Solvent-Controlled Rare Case of a Triple Helical Molecular Braid Assembled from Proton-Transferred Sebacic Acid

A novel triple helix based on proton-transferred sebacic acid was observed in a 1:1 organic salt of [(Hambtz)+(Hsba)−·2H2O] (1, ambtz = 2-amino-6-methoxybenzothiazole, H2sba = sebacic acid) incorporating a zigzag water chain. Changing the solvent system, another simple 1D zigzag chain, cocrystal [(ambtz)2(H2sba)] (2), was obtained. The structural dissimilarity between them was dependent on different conformations of ambtz and H2sba modulated by solvent systems. The photoluminescence behaviors of 1 and 2 were also discussed.

New topology observed in highly rare interlaced triple-stranded molecular braid

In this work, we present one novel metal–organic compound, namely Co3(L)6(4,4′-bpy)3(1), where HL and 4,4′-bpy are salicylaldehyde and 4,4′-bipyridine, respectively. The single-crystal X-ray diffraction shows that compound 1 crystallizes in the C2/c space group, the Co(II) ions are six-coordinated to bear the CoO4N2 octahedral geometry, and the overall structural feature is the intriguing topological building of interlaced triple-stranded molecular braid. A further investigation reveals that the present topology of triple-stranded molecular braid is very different from the reported cases and presents a new topology that is never developed, so far.

Rare Case of a Triple-Stranded Molecular Braid in an Organic Cocrystal

We describe the use of two bent molecules, tetrabromobisphcnol-S (2) and 1,3-bis(4-pyridyl)-propane (3), to build an interesting organic cocrystal [(C 6 H 2 OBr 2 ) 2 SO 2 ]·[(C 5 H 4 N) 2 (CH 2 ) 3 ]·MeOH (4). In the structure ot cocrystal 4, the cocrystallizing components (coformers) 2 and 3 assemble into a 1:1 supramolecular adduct featuring unprecedented triple-stranded entanglement, called a molecular braid. via O-H···N interactions, which is the first example of such one-dimensional entanglement in the realm of organic cocrystals.

A novel self-penetrating metal–organic open framework containing unusual triple-stranded molecular braid and septuple helices

Self-assembly of a long V-shaped 4,4′-oxydiphthalate (odpa) ligand and copper salt in the presence of a linear bidentate ligand affords a unique self-penetrating metal–organic open framework [Cu 2(odpa)(bpy) 2] ( 1) (bpy = 4,4′-bipyridine), exhibiting an unprecedented binodal four-connected (6 4.8 2) 2(6 2.8 4) topology. Its structure was determined by single-crystal X-ray diffraction analysis and further characterized by elemental analyses, IR spectrum, X-ray powder diffraction, and TG analysis. Compound 1 is a novel three-dimensional (3D) guest-free porous framework containing molecular braids and septuple helices, which are particularly rare in metal–organic coordination polymers.

A New Lanthanide Coordination Polymer of Pyrazine-2,6-dicarboxylic Acid: Synthesis, Crystal Structure and Thermal Property

A new rare earth coordination polymer, [Er2(PZDC)3(H2O)4]n· 5nH2O (1) (H2PZDC = pyrazine -2,6-dicarboxylic acid) has been solvothermally synthesized and characterized by single crystal X-ray diffraction, elemental analyses, IR spectra and TG analysis. Single crystal X-ray diffraction shows that the complex has a 2D metal-organic framework that contains double-stranded molecular braid structure. Furthermore, the 2D MOFs are assembled into 3D supramolecular network via various hydrogen bonds interactions.

Exceptional Self-Penetrating Networks Containing Unprecedented Quintuple-Stranded Molecular Braid, 9-Fold Meso Helices, and 17-Fold Interwoven Helices

Self-assembly of long V-shaped ligands and d10 metal salts in the presence of a linear bidentate ligand affords two unprecedented self-penetrating coordination networks {[Zn4(bptc)2(bpy)4].(C5H3N).4H2O}n (1) and {[Cd2(sdba)2(bpy)(H2O)2].2H2O}n (2) (bptc = 3,3',4,4'-benzophenonetetracarboxylate, sdba = 4,4'-sulfonyldibenzoate, bpy = 4,4'-bipyridine). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, X-ray powder diffraction, and TG analyses. 1 adopts a novel 3D framework containing three types of molecular braids, among which the quintuple-stranded molecular braid represents the highest-stranded molecular braid presently known for entangled systems. 2 is an uncommon self-penetrating 2D network containing pseudo-Borromean links and double-stranded helices. More interestingly, when the strong hydrogen bonds between layers are taken into account, the resulting net of 2 becomes an eight-connected 3D self-penetrating network with an unprecedented (421.67) topology, which represents the highest connected topology presently known in self-penetrating systems. Furthermore, the photoluminescent properties of 1 and 2 were studied.

An Investigation of the Self‐Assembly of Neutral, Interlaced, Triple‐Stranded Molecular Braids

The synthesis and structures of six compounds prepared in two different systems have been explored with the purpose of isolating coordination polymers with interlaced triple-stranded molecular braid architectures. The dinuclear paddle-wheel units of [Cu(2)(maa)(4)2 H(2)O] can be rationally tuned to form three classes of isomorphous compounds, namely [Cu(2)(maa)(4)(bpp)] (1) (bpp=1,3-bis(4-pyridyl)propane, Hmaa=2-methylacrylic acid), [Cu(3)(maa)(6)(bpp)(2)] (2), and[Cu(4)(maa)(8)(bpp)(4)(H(2)O)(2)]2 H(2)O (3), with a bridging bpp ligand, at controlled ligand-to-metal molar ratios, and lead to three coordination polymers having similar one-dimensional characteristics but different mono- and dinuclear nodes. Compound 1, with a bpp:[Cu(2)(maa)(4)2 H(2)O] stoichiometry of 1:1, contains a zigzag chain containing dinuclear nodes, whereas polymer 2, with a bpp:[Cu(2)(maa)(4)2 H(2)O] stoichiometry of 1.5:1, also adopts the topology of a zigzag chain but with both mono- and dinuclear nodes. Compound 3, with a bpp:[Cu(2)(maa)(4)2 H(2)O] stoichiometry of 2:1, contains a neutral, interlaced, triple-stranded molecular braid, which is interwoven by three single-stranded meso-helical chains that contain only a mononuclear node. With the three aromatic chelating terminal ligands 2,2':6',2''-terpyridine (tpy), 1,10-phenanthroline (phen), and di(2-pyridyl)amine (dpa) we have also prepared three neutral complexes containing the linear, rigid bridging ligand biphenyl-4,4'-dicarboxylate (bpdc), namely [Cd(bpdc)(tpy)]H(2)O (4), [Cu(bpdc)(phen)(2)]4.25 H(2)O (5), and [Cu(bpdc)(dpa)] (6). An infinite meso-helix is formed initially in 4, and then three of these chains assemble into a triple-stranded braid similar to that of 3. Complexes 5 and 6 have a mononuclear and a looped dinuclear structure, respectively. Compounds 3 and 4 are unusual examples of triple-stranded molecular braid coordination frameworks based on different types of co-ligands.

Self‐Assembly of an Interlaced Triple‐Stranded Molecular Braid with an Unprecedented Topology through Hydrogen‐Bonding Interactions

Molekulares Weben: Beim Mischen eines CuII-Komplexes mit Schaufelrad-Struktur mit einem hochflexiblen, neutralen 1,3-Bis(4-pyridyl)propan-Liganden im Verhältnis 1:2 entsteht ein verkettetes Gebilde, das genau wie ein Haarzopf aussieht (siehe Strukturbild). Die drei Stränge werden durch Wasserstoffbrücken zusammengehalten.

Self‐Assembly of an Interlaced Triple‐Stranded Molecular Braid with an Unprecedented Topology through Hydrogen‐Bonding Interactions

Self‐Assembly of an Interlaced Triple‐Stranded Molecular Braid with an Unprecedented Topology through Hydrogen‐Bonding Interactions

Molecular braids: quintuple helical hydrogen bonded molecular network†

The synthesis of 1, characterized by a calix[4]arene backbone in 1,3-alternate conformation bearing four pyridines acting as hydrogen bond acceptors, was achieved and its solid state structure studied by X-ray diffraction on a single crystal; in the presence of 4,4′-biphenol 6 acting as a dihydrogen bond donor, compound 1 formed infinite single strand helical 1-D molecular networks which upon lateral association were packed in the crystalline phase as quintuple helices.

Design and synthesis of macromolecular structures from self‐assembling building blocks

AbstractThe self‐assembling properties of a variety of building‐blocks are used to generate different types of nanostructures, e.g. molecular golfballs, molecular tubes, and molecular braids.