Covalent organic frameworks and organic cage structures

The last 20 years have seen an enormous interest in research on the topic of crystalline porous framework materials, especially metal–organic frameworks (MOFs). MOFs exploit reversible metal–coordination chemistry to create extended, crystalline solids.1 However, a similar set of porous ordered covalent networks based on the reversible and modular connection of a vast array of rigid and symmetrical building blocks through covalent bonds has also emerged during this time. These materials, coined as “Covalent Organic Frameworks (COFs)”, have summoned considerable attention in the last decade, starting with a significant contribution from the Yaghi group,2 owing to their unique designing features as well as enormous potential.3 Like COFs, porous molecular crystals that are not interconnected by covalent bonding have also picked up significant research interest. Although these materials do resemble COFs, unlike COFs, they can be solution processable.4 For any structural chemists, these materials are excellent tools that can lead to more informed design processes and create a deeper understanding of how targeted porous extended structures should be made

Effects of pore modification on the templating of guest molecules in a 2D honeycomb network

This work was supported by the UK Engineering Physical Sciences Research Council (EPRSC) and the EU.1,7-Diadamantanethioperylene-3,4:9,10-tetracarboxylic diimide, (Ad-S)(2)-PTCDI, adsorbed on Au (111) from solution was investigated by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). (Ad-S)(2)-PTCDI forms a well-ordered monolayer whose structure is described by a (2 root 63 x root 19) R19.1 degrees chiral unit cell containing four molecules. Codeposition of (Ad-S)(2)-PTCDI with 1,3,5-triazine-2,4,6-triamine (melamine) yields a honeycomb network whose (7 root 3 x 7 root 3)R30 degrees unit cell is identical to the unsubstituted PTCDI/melamine analogue. The effect of the adamantyl thioether moieties on the adsorption of guest molecules is investigated using adamantane thiol and C-60. While the thioether units do not affect the packing of adamantane thiol molecules a pronounced influence is seen in the case of fullerene. Pore modification involving different combinations of enantiomers of (Ad-S)(2)-PTCDI give rise to distinctly different arrangements of C-60 molecules. The diversity of patterns is further increased by the presence of unsubstituted PTCDI molecules.PostprintPeer reviewe

Per-alkoxy-pillar[5]arenes as electron donors: Electrochemical properties of dimethoxy-pillar[5]arene and its corresponding rotaxane

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 1,4-dimethoxypillar[5]arene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in [2]rotaxanes, suggesting that pillar[5]arenes can be employed as viable, yet unreported, electron donors

Nickel(II) metal-organic frameworks with N,N’-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide ligands: influence of secondary building unit geometry on dimensionality and framework dimensions

When Ni(NO3)2∙6H2O and N,N’-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNDI) are reacted, a one-dimensional coordination polymer (1) is formed. However, reaction with either terephthalic acid (2) or 2,6-naphthalenedicarboxylic acid (3) affords two-dimensional, pillared metal-organic frameworks. 2 and 3 containing rectangular voids of different dimensions which are dictated by the carboxylate ligand and the arrangement of the [M(k2-O2NO)]2(μ2-O2CR)2] secondary building unit (SBU) that forms the nodes of the framework. The role of SBU geometry, intermolecular face-to-face π–π and lone pair–π interactions involving the DPNDI ligands are discussed

Restricting shuttling in bis(imidazolium)…pillar[5]arene rotaxanes using metal coordination

Metal coordination to a series of bis(imidazolium)…pillar[5]arene [2]rotaxanes through the formation of metal-carbene bonds facilitates a new strategy to restrict the shuttling motion in [2]rotaxanes. Whereas the pillar[5]arene macrocycle rapidly shuttles along the full length of the bis(imidazolium) rod for the parent [2]rotaxane, Ag(I) coordination to the imidazolium groups through the formation of N-heterocyclic carbenes leads to restricted motion, effectively confining the shuttling motion of the [2]rotaxane. The Ag(I) coordinated [2]rotaxanes can be reacted further, either removing the Agcarbene species to recreate the parent [2]rotaxane, or reaction with more bulky Pd(II) species to further restrict the shuttling motion through steric inhibition

Ullmann coupling reactions on Ag(111) and Ag(110); substrate influence on the formation of covalently coupled products and intermediate metal-organic structures Metal-Organic Structures

On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometalic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required

Thin film synthesis of hybrid ultramicroporous materials (HUMs)- a comparative approach

© 2020 The thin-film synthesis of the hybrid ultramicroporous material (HUM) TIFSIX-3-Ni on glass substrates are reported for the first time. Several methods of film formation are employed including dip-coating, seeding and secondary growth, vapour-assisted conversion, rapid thermal deposition and in-situ coating. Using the in-situ approach with dimethylformamide as solvent, we were able to grow homogeneous TIFSIX-3-Ni films at relatively low temperatures (85 °C) and short times (5 h) without substrate modification. During this study, we also significantly reduced the TIFSIX powder synthesis time to 15 h

Synthesis of MIL-53 thin films by vapour-assisted conversion

A simple method for the preparation of MIL-53 thin films is reported. By employing a vapour-assisted conversion (VAC) approach we were able to prepare homogeneous MIL-53 films on a variety of glass, silicon or alumina substrates. Our strategy uses a vessel that allows film growth in an environment with a solvent-saturated atmosphere, in this case DMF. The VAC preparative conditions lead to the formation of a homogeneous film of the MOF and avoids the formation of alternative aggregates, such as starting materials. The effect of reaction temperature and time are investigated allowing identification of the optimum conditions to produce good film quality

Measuring the mechanical properties of molecular conformers

Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules

Simulated structure and imaging of NTCDI on Si(1 1 1)-7 × 7 : a combined STM, NC-AFM and DFT study

The adsorption of naphthalene tetracarboxylic diimide (NTCDI) on Si(1 1 1)-7 × 7 is investigated through a combination of scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM) and density functional theory (DFT) calculations. We show that NTCDI adopts multiple planar adsorption geometries on the Si(1 1 1)-7 × 7 surface which can be imaged with intramolecular bond resolution using NC-AFM. DFT calculations reveal adsorption is dominated by covalent bond formation between the molecular oxygen atoms and the surface silicon adatoms. The chemisorption of the molecule is found to induce subtle distortions to the molecular structure, which are observed in NC-AFM images