Tzuoo-Tsair Luo

Self‐Assembled Arrays of Single‐Walled Metal–Organic Nanotubes

Many recent advances in the field of metal–organic framework (MOF) materials have been reported, not only from the standpoint of the potential applications, ranging from gas storage to catalysis and drug delivery, but also because of their intriguing architectures and framework topologies. 2] Conceptually, endless structures can be produced by assembling judiciously selected molecular building blocks. Just as the notable saying in crystal engineering goes “the limits are mainly in our imagination”, any conceivable MOF might be obtained in the future, although it is all currently imagination. Since the first discovery of carbon nanotubes (CNTs) by Iijima in 1991, discrete hollow tubular structures such as various CNTs and other synthetic nanotubes (SNTs) prepared from inorganic, organic, or biological precursors have been successfully developed, because they possess useful functionalities and can serve as molecular capillaries, sieves, and biological models. In theory, the curling-up or rollingup mechanism of topology transformations from 2D flat sheets to 1D hollow tubes is achievable. Thanks to effective design and synthesis strategies, many porous MOFs with various interesting network topologies have been reported over the past decade. Compared with the focus on CNTs and SNTs, it is surprising that significantly less effort has been directed to the preparation of metal–organic nanotubes (MONTs). In particular, discrete MONT structures are extremely rare to date. As part of our ongoing efforts in the design and synthesis of functional crystalline materials, 8d, 10] we wish to report herein on a unique type of MOF of [{[Cd(apab)2(H2O)]3(MOH)·G}n] (MAS-21–23, M I = Cs, K, Na, respectively; for MAS-22, G = 18 H2O·6C2H5OH·3C4H8O; apab = 4-amino-3[(pyridin-4-ylmethylene)amino]benzoate; MAS = materials of Academia Sinica), all of which consist of a large singlewalled metal–organic nanotube of [{Cd(apab)2(H2O)}3n] (MONT-A1) with an exterior wall diameter of up to 3.2 nm and an interior channel diameter of 1.4 nm. These MONTs are held together by alkaline cations to form 3D nanotubular supramolecular arrays (Figure 1). To the best of our knowledge, a single-walled MONT with such a large diameter is unprecedented. Compounds MAS-21–23 were synthesized by reaction of cadmium perchlorate, 4-amino-3-[(pyridin-4-ylmethylene)amino]benzoic acid (Hapab), and MOH (M = Cs, K, and Na, respectively) in an EtOH/THF/H2O solvent diffusion system at 4 8C through a single-step, self-organization process (Scheme 1). The appropriate choice of an organic ligand with specific functional groups and geometry is a major factor in achieving these large nanotube-based structures. The multifunctional Schiff base ligand of Hapab was designed deliberately and possesses a bending angle of 1208 between the pyridyl and carboxylate groups. Unlike similar bananashaped organic linkers, the use of the apab scaffold favors the formation of a tubular structure, rather than a spherical network.

A journey in search of single-walled metal–organic nanotubes

Single-walled metal–organic nanotubes (SWMONTs) represent a family of new, structured porous materials. Metal–organic nanotubes (MONTs) offer an attractive alternative to carbon nanotubes because cationic metal ions are incorporated into the backbones of MONTs. However, efforts regarding the preparation of metal–organic nanotubes have been few in number, compared with the focus on carbon nanotubes (CNTs) and synthetic nanotubes (SNTs). In particular, the preparation of single-walled metal–organic nanotubes (SWMONTs) remains largely unexplored. The goal of this feature article is to highlight synthetic strategies, the structural characteristics of this unique class of SWMONTs materials and explore possible applications.

Giant metal–organic frameworks with bulky scaffolds: from microporous to mesoporous functional materials

New concepts on the design and synthesis of crystalline metal-organic frameworks (MOFs) have made them a subject of considerable interest in the growing field of materials science. By creating larger cavity sizes by a nearly infinite combination of metal nodes and organic linkers, many innovative characteristics of microporous MOFs have been revealed. The primary goal of this perspective article is to highlight the frontiers in the development of giant MOFs that are deliberately constructed from metallated or metal-free bulky scaffolds. Incorporating these types of distinct bulky ligands into giant MOFs may lead to MOFs with a large cavity size, intriguing properties and new framework topology. Emerging applications of these materials in catalysis, adsorption, and sensors are also discussed.

Time‐Evolving Self‐Organization and Autonomous Structural Adaptation of Cobalt(II)–Organic Framework Materials with scu and pts Nets

Self-organization is a process, in which an internal system spontaneously opens a new route to increase system complexity without being guided by an external source. The concept of self-organization is central to the understanding of living organisms, biominerals, and new supramolecular materials. For chemistry, self-organizing equilibrium conditions can be controlled by changing a few critical factors (concentration, template, pH, temperature, solvent system, etc.) to generate desirable compounds. However, these explorations seem not to be completely applied in a few particular supramolecular systems. Inspired by biology, to construct a high-order architecture from individual building components, various driving forces may competitively predominate at certain stages of the self-assembly process. A subtle thermodynamic/kinetic balance may control and tune the materials growth delicately. Namely, self-organization processes can be operative if the building components are sufficient and in close proximity, under suitable conditions. If the supply of building units is depleted or reduced, the original equilibrium conditions will change, and a new self-organization process will take place. These intriguing phenomena of self-organization are triggered by an internal stimulus and seem to be easily understood in biology, but the phenomena has not been addressed in the synthesis system of metal–organic framework (MOF) materials. As part of our ongoing efforts in the design and synthesis of functional crystalline materials, we report herein on an intriguing supramolecular system that involves a distinct self-organization process, in which the product structures adapt to autonomous dynamic changes in the ratio of build-

Intrinsic low dielectric behaviour of a highly thermally stable Sr-based metal–organic framework for interlayer dielectric materials

A Sr-based metal–organic framework {[Sr2(1,3-bdc)2(H2O)2]·H2O}n (1) was synthesized under hydrothermal conditions by the reaction of Sr(NO3)2 and 1,3-bis(4,5-dihydro-2-oxazolyl)benzene. A single-crystal X-ray diffraction analysis revealed that compound 1 adopts a 2D layer structure with a monoclinic (C2/c) space group. The distance between the layers of the structure adjusts upon the removal of the water molecules from 95 °C to 330 °C. In addition, the dehydrated compound 1′ retains its crystalline morphology and shows a high thermal stability at temperatures of up to 420 °C. Significantly, the dehydrated compound 1′ has a very low dielectric constant (2.4), suggesting that it might be useful as an interlayer dielectric in integrated circuits. As indicated by impedance spectroscopy, such low dielectric constant behavior is due to the intrinsic nature of the bulk material. The preparation of a low dielectric constant Sr-based metal–organic framework with a high thermal stability opens new directions for research into its applications.

Impeller-like dodecameric water clusters in metal–organic nanotubes

A triazole ligand bearing carboxylate and amino groups has been incorporated into a nanotubular copper(II)–organic framework, in which the impeller-like (H2O)12 water clusters were trapped in the nanotubes and can be encapsulated reversibly and precisely.

An Unprecedentedly Huge Square-Grid Copper(II)-Organic Framework Material Built from a Bulky Pyrene-Derived Elongated Cross-Shaped Scaffold

A new bulky pyrene-derived elongated cross-shaped organic scaffold was successfully incorporated into a highly porous, noninterpenetrated square-grid copper(II)-organic framework material with the unprecedentedly huge dimensions of 25.5 x 25.5 A(2), while the layer-to-layer NH...N interaction leads to a unique hydrogen-bonded 6(4).8(2)-nbo net.

An unusual cobalt(II)-based single-walled metal–organic nanotube

Three rare Co(II)–organic frameworks were synthesized by tuning the relative reactant ratios of CoII : 2,4-H2pydc (2,4-H2pydc = 2,4-pyridinedicarboxylic acid) and introducing different structure-directing amines under hydrothermal conditions. Compound {[Co3(2,4-pydc)3(EtOH)(H2O)3]·EtOH}n (1), which was prepared using a 1 : 1 ratio of CoII : 2,4-H2pydc, consisted of a tricobalt(II) cluster that was employed to form a two-side-open box and these boxes were further self-assembled into a rare single-walled metal–organic nanotube (MONT). When the ratio was adjusted to 2 : 1 and accompanied with 4,4′-dipyridyl-piperazine (dpyp), the formation of zigzag chains of {[Co4(2,4-pydc)4(H2O)10]}n (2) with a tetracobalt(II) cluster unit occurred, finally these chains were linked into a 2D sheet with a 44-sql topology. However, compound {[Co(2,4-pydc)2(H2O)2]·[Co(dpyp)(H2O)4]}n (3) was synthesized under similar reaction conditions as for 2 except that triethylamine was added. 3 contained the polymeric chains of {[Co(dpyp)·(H2O)4]2+}n and the monocobalt complex [Co(2,4-pydc)2(H2O)2]2−, which were cooperatively connected via hydrogen bonding to form a 2D layer with a 44-sql topology. A pseudo-merohedral twinning law was applied to the twin case during the X-ray structural analysis of 2 that facilitated the R1 value to drop drastically.

Isorecticular Synthesis of Dissectible Molecular Bamboo Tubes of Hexarhenium(I) Benzene-1,2,3,4,5,6-hexaolate Complexes

A family of bamboo-like metal-organic nanotubes consisting of in situ synthesized macromolecular blocks (MB) is reported. The MBs are composed of six fac-(CO)3 Re cores, one benzene-1,2,3,4,5,6-hexaolate plate, and six pyridine-derivative pillar ligands, which have a doubly tri-legged geometry and can be mutually assembled, piece by piece. This entire system is characterized as a simple but precise supramolecular complexation of these macromolecular blocks and further introduces an archetypal approach to systematically constructing a tunable form of dissectible molecular bamboo tubes.

Guest dependent dielectric properties of nickel(II)-based supramolecular networks

Two nickel(II)-based low dielectric supramolecular compounds {[Ni2(bbim)(H2bbim)4]·2CH3COO·CH3CN}2 (1, H2bbim = bisbenzimidazole) and (±)-[Ni(H2bbim)3]·2Cl·2H2O (2) were synthesized and characterized by single-crystal X-ray crystallography. Compound 1 was found to have a dimeric structure with guest molecules such as acetate ions and acetonitrile in its environment, while compound 2 had a monomeric structure with chloride ions and water molecules associated with it. Both compounds were highly thermally stable, especially compound 1, which was stable at temperatures of up to 500 °C. More importantly, compound 1 adopted a sharp different frequency dependent dielectric behaviour when compared with 2. Compound 2 with highly polarizable guest molecules showed a significant higher value of dielectric constant (er′(ω) = 12.6 at 40 Hz) than that of 1 (er′(ω) = 4.76 at 40 Hz), indicating that solvent molecules and counterions play a crucial role in regulating the value of the dielectric constant. This study serves as a good example of the design of both high and low-κ materials with a judicious selection of guest molecules in the supramolecular networks.