Yuh-Sheng Wen

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.

Synthesis and characterization of new fluorescent two-photon absorption chromophores

A series of dipolar and quadrupolar type two-photon absorption (TPA) compounds has been synthesized and TPA cross sections (σ) were measured by Ti∶sapphire femtosecond laser excitation fluorescence (λ = 800 nm). Among them, the compound [2,5-bis-[5-(4-diphenylaminophenylethynyl)thiophen-2-yl]-[1,3,4]oxadiazole], 12, has been structurally characterized by X-ray crystallography. The resulting data indicate that the structure of this compound possesses excellent coplanarity. The compounds have arylamines as the donor, and [1,3,4]oxadiazolyl, cyanovinyl or pyridazin-3,6-diyl moiety as the acceptor. Variation of arylamines and pendant alkyl groups was found to have a significant influence on σ values. By an appropriate combination of donor and acceptor, σ values of >103 GM (10−50 cm4s photon·molecule−1) can be achieved. One quadrupolar molecule (13) possessing an arylamine donor and a pyridazine acceptor has both a high σ value (1442 GM) and σ/MW (1.97 GM/g).

Substituted metal carbonylsXVIII. rhenium 1,1′-bis(diphenylphosphino)ferrocene (DPPF) complexes derived from [Re2(CO)9]. Crystal structures of two isomorphous pentametallic [M2(CO)9]2(μ-dppf) (M Mn, Re) and trimetallic Re2(CO)9(dppfO) complexes

Abstract Amine oxide-assisted decarbonylation of Re2(CO)10 in the presence of 1,1′-bis(diphenylphosphino)ferrocene (dppf) produces, under different conditions, [Re2(CO)9]2 (μ-dppf) (1), Re2(CO)9(1-dppf) (5) and its oxidation product Re2(CO)9(1-dppfO) (7). 1 undergoes an oxidative bridge-scission with Me3NO to give 7. X-ray crystallographic analysis of 1 and [Mn2(CO)9]2(μ-dppf) (2), included for comparison, revealed that the two molecules are isomorphous, each taking the form of an open and “linear” tetranuclear complex supported alternately by M M bonds and a “half eclipsed” dppf bridge. Complex 7, which is trimetallic, consists of dppf (mono)oxide coordinated to [Re2(CO)9] through the phosphine site. X-ray Photoelectron Spectra revealed the existence of the chemically inequivalent Re and P sites within the same molecule. The chemically distinct Re centres in 1, 5, 7 and Re2(CO)9(CH3CN) are differentiable by their Re(4f7/2) and Re(4f5/2) binding energies.

Crystal Engineering for π−π Stacking via Interaction between Electron-Rich and Electron-Deficient Heteroaromatics

New dipolar compounds containing alternating electron-rich thieno[3,2-b]thiophene units and electron deficient units have been synthesized. Compounds with 5-pyrimidinyl (compound 2) or benzothiazole (compound 5) as the electron-deficient unit were structurally characterized by the single-crystal X-ray diffraction method. The arrangement of the molecules is found to be one-dimensional slipped-pi-stack for 2. That of 5 is of slipped-pi-stack, albeit with a tilt angle between neighboring pi-stacks. The pi-pi interfacial distances of the molecules in the crystal lattice are 3.47 and 3.59 A for 2 and 5, respectively. On the basis of the crystal structure, compound 2, with negligible pi-pi slip along the short axis of the molecules, has a calculated electronic coupling value (0.153 eV) twice as large as that of the largest coupling of pentacene. Accordingly, the theoretically estimated hole mobility (mu(+)) for 2 (2.32 cm(2) s(-1) V(-1)) compares favorably with that of pentacene (1.93-5.43 cm(2) s(-1) V(-1)), despite of the larger reorganization energy for hole transport in 2. The symmetric intrastack S...C contacts found between the thieno[3,2-b]thiophene and pyrimidinyl units explain the unique features of the crystal structure of 2 and the resulting large electronic coupling.

Colorimetric and luminescent sensing of F− anion through strong anion–π interaction inside the π-acidic cavity of a pyridyl-triazine bridged trinuclear Re(I)–tricarbonyl diimine complex

A trinuclear star-shaped organometallic host with a pi-acidic interior cavity has been synthesized and this shows a strong anion-pi interaction with PF6-, as demonstrated in the crystal structure and colorimetric and luminescent responses with F- anion in solution.

Half-sandwich complexes with intramolecular amino group coordination: synthesis and structure of cationic molybdenum dienyl complexes

A half-sandwich cationic molybdenum dienyl complex with intramolecular amino group coordination was obtained from η5-C5H4CH2CH2N(CH3)2Mo(CO)2(η3-C6H9) via hydride abstraction followed by CO extrusion. It crystallized as an orange monoclinic compound with a = 10.4867(14), b = 14.843(3), c = 11.882(3) A, β = 94.057(15)°. The cyclohexadienyl ligand is shown as boat conformation. A second bidentate complex was isolated. Spectroscopic and elemental analysis data support the demethylation product of [η5-C5H4CH2CH2NH(CH3)Mo(CO)( η3-C6H8)]+ PF6−.

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-

Substituted metal carbonyls XV. Crystal and molecular structures of two isomorphous singly diphosphine-bridged complexes (OC)5M(μ-dppf)M(CO)5·CH2Cl2 (M = Cr, Mo; dppf = (Ph2PC5H4)2Fe)☆

Abstract The crystal structures of two dinuclear compounds (OC) 5 M(μ-dppf)M(CO) 5 ·CH 2 Cl 2 (M = Cr, Mo; dppf = (Ph 2 PC 5 H 4 ) 2 Fe), determined by single-crystal X-ray diffraction studies, were found to be isomorphous. (Crystal data: (OC) 5 Cr(μ-dppf)Cr(CO) 5 , space group C 2/ c , a 16.659(3), b 15.350(5), c 18.877(2) A, β 112.43(2)°, Final R 0.046 for 2999 observations. (OC) 5 Mo(μ-dppf)Mo(CO) 5 , space group C 2/ c , a 16.705(4), b 15.545(4), c 19.091(3) A, β 111.92(2)°, Final R 0.037 for 3332 observations). The diphosphine serves as a single bridge between two essentially unperturbed metal carbonyl spheres. The iron was located on a two-fold axis as required crystallographically. The relationship between the phosphinoferrocenyl geometry and the stability of this type of “open” complexes is described together with the solid-state decomposition data from Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) analyses.

Halide functionality dependent formation of molecular receptors and their ion recognition properties.

The halide functionality on N-bridged tripodal receptors has shown a distinct behavior on their self-assembly structures and binding ability toward HgCl(2) and ClO(4)(-) anions. The receptors containing fluoro, chloro, and iodo groups crystallized to form hemicarcerands in the solid state, whereas the receptor with a bromo group forms a molecular capsule via C-H...Br and C-H...pi interactions. The cavity of the molecular capsule is tunable and is capable of reversible encapsulating-releasing the guest molecules by pH modulation.

Electron transfer in mixed-valence 1,1,12,12-tetra-n-butyl[1,1]stannaferrocenophane: Electrochemical and near-IR spectroscopic studies

Abstract The physical properties of neutral and mixed-valence 1,1,12,12-tetra-n-butyl[1,1]stannaferrocenophanes are reported. The structure of the endo,endo-1,12-di-n-butyl-exo,exo-1,12-diiodo[1,1]stannaferrocenophane has been determined by X-ray diffraction. The compound crystallizes with monoclinic symmetry, space group P21/C, a 10.3282(14), b 10.7916(12), c 13.6772(18) A, β 94.080(12)°, V 1520.57 A3, and Z = 2. The structure was refined to give conventional discrepancy factors of RF = 0.036 and RWF = 0.031. The electron-transfer in the σ-bridged 1,1,12,12-tetra-n-butyl[1,1]stannaferrocenophane cation is attributed to the d-π overlap mechanism of tin atoms and the cyclopentadiene rings.