Tien-Wen Tseng

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 flexible tris-phosphonate for the design of copper and cobalt coordination polymers: unusual cage array topology and magnetic properties

The reaction of the flexible tris-phosphonate precursor benzene-1,3,5-tris(methylenephosphonic acid) (H6btmp) with CuCl2·2H2O in H2O under hydrothermal conditions afforded the complex [Cu3(btmp)(H2O)3.6]·H2O (1·H2O). A similar reaction between 2,4,6-trimethylbenzene-1,3,5-tris(methylenephosphonic acid) (Me3-H6btmp) and Cu(NO3)2·3H2O or Co(NO3)2·6H2O gave the complex [Cu4(Me3-H2btmp)2(H2O)4] (2) or [Co6(Me3-btmp)2(H2O)4] (3), respectively. The cis,trans,trans-conformation of the flexible tris-phosphonate ligands resulted in the formation of 3D networks 1 and 3. Interestingly, the cis,cis,cis-conformation of the Me3-btmp ligand in 2 results in the formation of M4L2-type copper-based metalloprismatic cages, which can serve as building units for subsequent assemblies with phosphonate (P–O) linkages to afford a 2D array of nanocages. The magnetic study indicated that complexes 1·H2O, 2 and 3 all exhibit antiferromagnetic behaviors. Interestingly, results from alternating current (ac) magnetic susceptibility measurements revealed that complex 3 exhibits slow magnetic relaxation behavior at low temperatures.

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 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.

Ag4L2 Nanocage as a Building Unit toward the Construction of Silver Metal Strings

Self-assembly of AgNO 3 with the semirigid tetratopic ligands 1,2,4,5-tetrakis(benzoimidazol-1-ylmethyl)benzene (TBim) and 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (TDMBim) afforded compounds [Ag 4(mu 4-TBim) 2(mu 2-eta (2)-NO 3) 2](NO 3) 2. (1)/ 2CH 2Cl 2.2CH 3OH ( 1mu (1)/ 2CH 2Cl 2.2CH 3OH) and [(NO 3 (-)) subset{Ag 4(mu 4-TDMBim) 2}][Ag(NO 3) 2](NO 3) 2.CH 2Cl 2.CH 3OH.4H 2O ( 2.CH 2Cl 2.CH 3OH.4H 2O), respectively. The structures of 1 and 2 were characterized by single-crystal X-ray diffraction analysis. Both compounds adopt a M 4L 2-type tetragonal metalloprismatic cage structure, [Ag 4(mu 4-L) 2] (4+), with strong intramolecular silver-silver contacts. Compound 1 is a discrete species, while compound 2 is a novel infinite chainlike supramolecular array involving silver metal strings assembled from a [Ag 4(mu 4-L) 2] (4+) nanocage and silver linkages. Thermogravimetric analyses of 1. (1)/ 2CH 2Cl 2.2CH 3OH and 2.CH 3OH.4H 2O indicate that the Ag 4L 2-cage structures of 1 and 2 both are thermally stable up to 330 degrees C. Results from an in situ (1)H NMR study of AgNO 3 and TDMBim in different molar ratios unambiguously revealed the successive self-organization process, in which self-organization of the molecular cage takes place initially followed by crystallization of the corresponding supramolecular arrays with silver metal strings.

A huge diamondoid metal–organic framework with a neo-mode of tenfold interpenetration

A huge diamondoid metal–organic framework featuring a tenfold interpenetrating neo-mode, with an extra-framework volume of up to 48.7% despite its very high degree of interpenetration, is reported. The hydrogen bonding of the inter-networks directs the relative position of the frameworks and exhibits a self-catenated net with a point symbol of {(62.84)(64.8.10)2}.

Self-triggered conformations of disulfide ensembles in coordination polymers with multiple metal clusters

Five coordination polymers, {[Mn2(dtdn)2(4,4′-dmbpy)2(H2O)2]·DMF}n (1, dtdn = 6,6′-dithiodinicotinate), {[Mn6(dtdn)6(5,5′-dmbpy)4]·5DMF·2H2O}n (2), {[Mn3(dtdn)2(Hdtdn)2(phen)2]·H2O}n (3), {[Mn6(dtdn)6(H2O)4(DMF)4]·10DMF·10H2O}n (4), and {[Mn2(dtdn)2(H2O)2]·4MeOH·H2O}n (5) (4,4′-dmbpy = 4,4′-dimethyl-2,2′-bipyridine, 5,5′-dmbpy = 5,5′-dimethyl-2,2′-bipyridine, phen = 1,10-phenanthroline), were constructed under mild reaction conditions from Mn(II) ions and a twisted disulfide ligand, H2dtdn, in the presence of different ancillary N-donor coligands. These compounds show a variety of guest inclusion properties and interesting self-induced chirality. Compound 1 adopts 1D zigzag chains with mononuclear units that are mutually paired into a 1D ladder-like structure. Compound 2 consists of trinuclear clusters, and displays a 2D protuberant sheet with a (4,4)-sql topology. Compound 3 takes the form of a 1D double-stranded chain with rectangular loops comprised of trinuclear clusters, in which the Hdtdn− ligands dangle on both sides. Compound 4 adopts the form of a 2D network and exhibits a slightly undulating (44) topology that consists of trinuclear clusters, which are further hydrogen bonded into a 3D framework. Compound 5 features a 3D network consisting of 1D infinite metal oxide wires containing the [Mn2(dtdn)2(H2O)2] unit. Magnetic studies of compounds 2, 3, and 5 show that they have antiferromagnetic properties.

Structural Transformations of Amino-Acid-Based Polymers: Syntheses and Structural Characterization

A discrete complex [Zn(tpro)2(H2O)2] (1, Htpro = l-thioproline), and two structural isomers of coordination polymers, a 1D chain of [Zn(tpro)2]n (2) and a layered structure [Zn(tpro)2]n (3), were synthesized and characterized. The discrete complex 1 undergoes a temperature-driven structural transformation, leading to the formation of a 1D helical coordination polymer 2. Compound 3 is comprised of a 2D homochiral layer network with a (4,4) topology. These layers are mutually linked through hydrogen bonding interactions, resulting in the formation of a 3D network. When 1 is heated, it undergoes nearly complete conversion to the microcrystalline form, i.e., compound 2, which was confirmed by powder X-ray diffractions (PXRD). The carboxylate motifs could be activated after removing the coordinated water molecules by heating at temperatures of up to 150 °C, their orientations becoming distorted, after which, they attacked the activation sites of the Zn(II) centers, leading to the formation of a 1D helix. Moreover, a portion of the PXRD pattern of 1 was converted into the patterns corresponding to 2 and 3, and the ratio between 2 and 3 was precisely determined by the simulation study of in-situ synchrotron PXRD expriments. Consequently, such a 0D complex is capable of underdoing structural transformations and can be converted into 1D and/or 2D amino acid-based coordination polymers.