Recent Advances in Various Metal–Organic Channels for Photochemistry beyond Confined Spaces

Abstract

Tailor-made molecular channel architectures are a hot issue in the fields of nanotechnology, molecular sieves, ion sensors, recognition, confined space reactors, and fluidic transport systems. Carbon nanotubes have been a particular focus, though they cannot easily be synthesized to predefined structures and sizes. Rational design and construction of molecular channel structures based on coordination chemistry has been recognized as a useful approach. Metal-organic channel (MOC) structures can be generated by utilizing, at least in principle, molecular self-assembly of metal ions as angular units with designed ligands as spacers. Recent developments in molecular channel chemistry include exciting advances in photochemical applications and supramolecular material functionality, in addition to general applications such as transport, diffusion and exchange, separation, gas storage, catalysis, and simple encapsulation. In order to carry out the diverse channel functionalities, a large number of studies have been conducted on the synthesis of robust and stable 3D coordination polymers, which show permanent porosity without any guest molecules within the channels, in that the robustness of the channel structures after removal of the solvate/guest molecules is of interest because the structural integrity of the extended structures must be maintained during the reactions. These compounds can be regarded as analogous to zeolites. This Account highlights advances in the construction, from metal cations and multidentate pyridyl ligands, of various MOCs and useful molecular materials as photoreaction platforms. We begin by discussing the fact that detailed proof-of-concept construction of various systematic MOC structures has been introduced mainly in terms of the metal ions as angular components and the pyridyl ligands as spacers. This approach leads to structural complexity of assembled MOC motifs such as metallamacrocycles, helical and cylindrical coordination polymers, vertical arrays of 1D coordination polymers, interweaving and eclipsed stacking of 2D coordination polymers, and typical 3D coordination polymers. Notwithstanding the diversity of their skeletal structures, confined spaces of the channels are suitable for the study of photochemical performances including radical trapping, photocyclopropanation, dye inclusion and energy transfer, and guest-to-host structural transmission. The key aspect of their utility is not only the preparation of photoresistant MOCs but also channel tuning for inclusion of photoactive guests. Guest molecules, which are compatible with the size, shape, and polarity of the channels, can be incorporated into the crystals, instead of simple organic solvents, thus giving rise to host-guest complexes in the solid state. Such MOC studies could facilitate the development of chemical sensors, new photocatalytic systems, and useful molecular photochemical reactors.

Molybdenum Dioxide in Carbon Nanoreactors as a Catalytic Nanosponge for the Efficient Desulfurization of Liquid Fuels

“…In addition, the performance of molybdenum-based nanocatalysts can be optimized using support materials, which are known to both stabilize nanoparticles against sintering and promote further activity by facilitating charge transfer between the catalysts and the support material. [24,25] Hollow graphitized nanofibers (GNFs) with an internal diameter of 60 nm-structural analogues to carbon nanotubes, but possessing nanoscale step-edges on the inside-are particularly attractive as their corrugated interior surfaces promote the formation and enhance the stability of catalytic centers, [26][27][28] while increasing the concentration of reactants around the catalyst, without restricting the transport of reactants to and products from the internal cavity (the critical dimensions of most small molecules are typically at least two orders of magnitude smaller than the internal diameter of GNFs). [20][21][22][23] Among catalyst supports, hollow carbon nanostructures, such as carbon nanotubes, may offer several potential benefits for ODS catalysts.…”

“…[20][21][22][23] Among catalyst supports, hollow carbon nanostructures, such as carbon nanotubes, may offer several potential benefits for ODS catalysts. [24,25] Hollow graphitized nanofibers (GNFs) with an internal diameter of 60 nm-structural analogues to carbon nanotubes, but possessing nanoscale step-edges on the inside-are particularly attractive as their corrugated interior surfaces promote the formation and enhance the stability of catalytic centers, [26][27][28] while increasing the concentration of reactants around the catalyst, without restricting the transport of reactants to and products from the internal cavity (the critical dimensions of most small molecules are typically at least two orders of magnitude smaller than the internal diameter of GNFs). [29,30] Furthermore, as porous activated carbons have shown promise in the desulfurization of fuels via ADS, [31,32] we anticipated that GNFs, possessing the high internal surface area of nanotubes and maximal π-π stacking interactions between guest and host at the graphitic step-edges, may offer enhanced extraction of aromatic organosulfur contaminants, promoting simultaneous desulfurization via both the ADS and ODS mechanisms.…”

Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds

“…In all of the previous 87 structures described in this review, the original parent structure, which is often aggregated [25], has been disrupted by the addition of base. In 88, the thermodynamically favoured dimeric structure, as opposed to the initially formed one-dimensional coordination polymer [93,94], is retained but, with the addition of base in the form of 3-pyald to increase the normally observed S 5 donor set to NS 5 . These four structures, again, point to the unpredictability of this chemistry and substantiate the need of systematic studies.…”

“…While these were initially in the realm of materials science with applications relating to energy and gas storage, photo-responsive materials, catalysis, etc. [3][4][5][6][7], there are increasing applications of coordination polymers relevant to bioinorganic chemists. Examples include coordination polymers functioning as carriers for drug In this bibliographic review, the structural chemistry of zinc and cadmium 1,1-dithiolates and bipyridyl-type ligands is surveyed.…”

Synthesis and Structural Diversity of Main Group Metal Coordination Complexes Constructed from V‐Shape Bis(3‐methyl‐1H‐pyrazole‐4‐carboxylic acid)alkane Ligands

“…Coordination polymers (CPs) composed of metallic centers connected by organic O-and/or N-donor ligands continue to grow extremely rapidly for their fascinating structural diversities and potential applications in heterogeneous catalysis, gas storage, gas separation, luminescence, chemical sensing, magnetism, drug delivery, and so forth. [1][2][3][4][5][6][7][8] Up to now, many transition metal and lanthanide metal CPs have been designed and constructed, however, main group metal CPs have not been well explored. In fact, the main group metals having low polarizability and various coordination modes, can be used to generate CPs featuring variable robust structures and interesting properties.…”