Acenaphtho[1,2-d][1,2,3]triazole and Its Kuratowski Complex: A π-Extended Tecton for Supramolecular and Coordinative Self-Assembly.

π-Extended acenaphtho[1,2-d][1,2,3]triazoles, the unsubstituted Anta-H and its di-tert-butyl derivative Dibanta-H, as well as 5,6,7,8-tetrahydro-1H-naphtho[2,3-d][1,2,3]triazole Cybta-H were obtained in concise syntheses. In the solid state, Dibanta-H forms an unprecedented hydrogen-bonded cyclic tetrad, stabilized by dispersion interactions of the bulky tBu substituents, whereas a cyclic triad was found in the crystal structure of Anta-H. These cyclic assemblies form infinite slipped stacks in the crystals. Evidence for analogous hydrogen-bonded self-assembly in solution was provided by low-temperature NMR spectroscopy and computational analyses. Kuratowski-type pentanuclear complexes [Zn5 Cl4 (Dibanta)6 ] and [Zn5 Cl4 (Cybta)6 ] were prepared from the respective triazoles. In the Dibanta complexes, the π-aromatic surfaces of the ligands extend from the edges of the tetrahedral Zn5 core, yielding an enlarged structure with significant internal molecular free volume and red-shifted fluorescence.

Dynamic Studies on Kinetic H2 /D2 Quantum Sieving in a Narrow Pore Metal-Organic Framework Grown on a Sensor Chip.

The separation of deuterium from hydrogen still remains a challenging and industrially relevant task. Compared to traditional cryogenic methods for separation, based on different boiling points of H2 and D2 , the use of ultramicroporous materials offers a more efficient alternative method. Due to their rigid structures, permanently high porosity, tunable pore sizes and adjustable internal surface properties, metal-organic frameworks (MOFs), a class of porous materials built through the coordination between organic linkers and metal ions/clusters, are more suitable for this approach than zeolites or carbon-based materials. Herein, dynamic gas flow studies on H2 /D2 quantum sieving in MFU-4, a metal-organic framework with ultra-narrow pores of 2.5 Å, are presented. A specially designed sensor with a very fast response based on surface acoustic waves is used. On-chip measurements of diffusion rates in the temperature range 27-207 K reveal a quantum sieving effect, with D2 diffusing faster than H2 below 64 K and the opposite selectivity above this temperature. The experimental results obtained are confirmed by molecular dynamic simulation regarding quantum sieving of H2 and D2 on MOFs for which a flexible framework approach was used for the first time.

Tribenzotriquinacene receptors for C60 †fullerene rotors: towards C3 symmetrical chiral stators for unidirectionally operating nanoratchets.

The synthesis of a stereochemically pure concave tribenzotriquinacene receptor (7) for C60 fullerene, possessing C3 point group symmetry, by threefold condensation of C2 -symmetric 1,2-diketone synthons (5) and a hexaaminotribenzotriquinacene core (6) is described. The chiral diketone was synthesized in a five-step reaction sequence starting from C2h -symmetric 2,6-di-tert-butylanthracene. The highly diastereo-discriminating Diels-Alder reaction of 2,6-di-tert-butylanthracene with fumaric acid di(-)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by (1)H and (13)C NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7 % ee, based on the ee (99.9 %) of the chiral synthon (1). The absolute configuration of 7 could thus be established as all-S [(2S,7S,16S,21S,30S,35S)-(7)]. Spectroscopic titration experiments reveal that the host forms 1:1 complexes with either pure fullerene (C60) or fullerene derivatives, such as rotor 1'-(4-nitrophenyl)-3'-(4-N,N-dimethylaminophenyl)-pyrazolino[4',5':1,2][60]fullerene (R). The complex stability constants of the complexes dissolved in CHCl3/CS2 (1:1 vol. %) are K([C60 ⊂7]) = 319(±156) M(-1) and K([R⊂7]) = 110(±50) M(-1). With molecular dynamics simulations using a first-principles parameterized force field the asymmetry of the rotational potential for [R⊂7] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet.

Almost enclosed buckyball joints: synthesis, complex formation, and computational simulations of pentypticene-extended tribenzotriquinacene.

We report the synthesis of a tribenzotriquinacene-based (TBTQ) receptor (3) for C60 fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self-assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K1 =213±37 M(-1) for [C60 ⊂3], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C60 ⊂TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free-energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions.

CFA-18: a homochiral metal-organic framework (MOF) constructed from rigid enantiopure bistriazolate linker molecules.

In this work, we introduce the first enantiopure bistriazolate-based metal-organic framework, CFA-18 (Coordination Framework Augsburg-18), built from the R-enantiomer of 7,7,7',7'-tetramethyl-6,6',7,7'-tetrahydro-3H,3'H-5,5'-spirobi[indeno[5,6-d]-[1,2,3]triazole] (H2-spirta). The enantiopurity and absolute configuration of the new linker were confirmed by several chiroselective methods. Reacting H2-spirta in hot N,N-dimethylformamide (DMF) with manganese(ii) chloride gave CFA-18 as colorless crystals. The crystal structure with the composition [Mn2Cl2(spirta)(DMF)2] was solved using synchrotron single-crystal X-ray diffraction. CFA-18 shows a framework topology that is closely related to previously reported metal-azolate framework (MAF) structures in which the octahedrally coordinated manganese(ii) ions are triazolate moieties, and the chloride anions form crosslinked one-dimensional helical chains, giving rise to hexagonal channels. In contrast to MAFs crystallizing in the centrosymmetric space group R3[combining macron], the handedness of the helices found in CFA-18 is strictly uniform, leading to a homochiral framework that crystallizes in the trigonal crystal system within the chiral space group P3121 (no. 152).

Coordination frameworks assembled from Cu(II) ions and H2-1,3-bdpb ligands: X-ray and magneto structural investigations, and catalytic activity in the aerobic oxidation of tetralin.

The syntheses and crystal structures of H2-1,3-bdpb·MeOH, [Cu(II)2(1,3-bdpb)(OCH3)2] (CFA-5) and [Cu(I)Cl(H2-1,3-bdpb)] (H2-1,3-bdpb = 1,3-bis(3,5-dimethyl-1H-pyrazol-4-yl)benzene) are described. The copper(II) containing metal-organic framework (termed Coordination Framework Augsburg University-5, CFA-5) crystallizes in the trigonal crystal system, within the space group R3̄ (no. 148) and the unit cell parameters are as follows: a = 26.839(3), c = 15.8317(16) Å, V = 9876.2(19) Å(3). CFA-5 features a two-fold interpenetrated 3-D microporous framework structure of cross-linked wheel-shaped {Cu(II)(pz)(OMe)}12 fundamental building units, each containing twelve copper(II) ions, µ2-bridging MeO(-) groups and pyrazolate (pz(-)) ligands. Replacing copper(II) acetate by copper(II) chloride in the synthesis leads to compound [Cu(I)Cl(H2-1,3-bdpb)], which crystallizes in the orthorhombic crystal system, within the space group Pnma (no. 62) and the unit cell parameters are as follows: a = 6.1784(8), b = 6.1784(8), c = 6.1784(8) Å, V = 1583.8(4) Å(3). In contrast to the former compound, CuCl(H2-1,3-bdpb) is a non-porous compound consisting of Cu(I)-Cl zigzag chains expanding in the direction [100] and H2-1,3-bdpb ligands. CFA-5 is characterized by elemental and thermogravimetric analyses, variable temperature powder X-ray diffraction and IR-spectroscopy; and its porosity and magnetic properties are described in detail. CFA-5 shows a promising catalytic activity in the heterogeneously catalyzed aerobic oxidation of tetralin, which is compared with other catalytically active metal-organic frameworks.

CFA-2 and CFA-3 (Coordination Framework Augsburg University-2 and -3); novel MOFs assembled from trinuclear Cu(I)/Ag(I) secondary building units and 3,3',5,5'-tetraphenyl-bipyrazolate ligands.

The syntheses of H2-phbpz, [Cu2(phbpz)]·2DEF·MeOH (CFA-2) and [Ag2(phbpz)] (CFA-3) (H2-phbpz = 3,3',5,5'-tetraphenyl-1H,1'H-4,4'-bipyrazole) compounds and their crystal structures are described. The Cu(I) containing metal-organic framework CFA-2 crystallizes in the tetragonal crystal system, within space group I4(1)/a (no. 88) and the following unit cell parameters: a = 30.835(14), c = 29.306(7) Å, V = 27 865(19) Å(3). CFA-2 features a flexible 3-D three-connected two-fold interpenetrated porous structure constructed of triangular Cu(I) subunits. Upon exposure to different kinds of liquids (MeOH, EtOH, DMF, DEF) CFA-2 shows pronounced breathing effects. CFA-3 crystallizes in the monoclinic crystal system, within space group P2(1)/c (no. 14) and the following unit cell parameters: a = 16.3399(3), b = 32.7506(4), c = 16.2624(3) Å, ß = 107.382(2)°, V = 8305.3(2) Å(3). In contrast to the former compound, CFA-3 features a layered 2-D three-connected structure constructed from triangular Ag(i) subunits. Both compounds are characterized by elemental and thermogravimetric analyses, single crystal structure analysis and X-ray powder diffraction, FTIR- and fluorescence spectroscopy. Preliminary results on oxygen activation in CFA-2 are presented and potential improvements in terms of framework robustness and catalytic efficiency are discussed.

Advanced buckyball joints: synthesis, complex formation and computational simulations of centrohexaindane-extended tribenzotriquinacene receptors for C60 fullerene.

The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and π-π interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host.

Isolated and linear arrays of surfactant-encapsulated polyoxometalate clusters on graphite.

We report on the self-assembly of several surfactant-encapsulated clusters (SECs) on the basal plane of graphite consisting of the doughnut-shaped tungstophosphate anion [Na(H2O)P5W30O110] covered by a hydrophobic shell of surfactants. Well-ordered rodlike structures are observed using scanning force microscopy. No such ordering is observed if the surfactant methyltrioctadecylammonium is used for encapsulation, suggesting that the density of alkyl chains around the polyoxometalate cluster is an important factor in determining the order of SEC assemblies on graphite. Coadsorption of tetratetracontane (n-C44H90) and (DODA)14[Na(H2O)P5W30O110] results in single, isolated SECs on a buffer layer of tetratetracontane, as determined by scanning tunneling microscopy.

Nanosized ball joints constructed from C60 and tribenzotriquinacene sockets: synthesis, component self-assembly and structural investigations.

The formation of supramolecular host-guest complexes of fullerene (C(60)) and two novel tribenzotriquinacene based hosts (5 a and 5 b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, (1)H NMR) titration experiments. Association constants of K(1)=(2908+/-360) L mol(-1) and K(2)=(2076+/-300) L mol(-1) for C(60)/5 a, and K(1)=(5608+/-220) L mol(-1) and K(2)=(673+/-160) L mol(-1) for C(60)/5 b were obtained. Single crystal X-ray structural analysis of compound C(60) subset5 b3 toluene revealed that a molecule of C(60) was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit.

Two-dimensional metal-organic frameworks (MOFs) constructed from heterotrinuclear coordination units and 4,4'-biphenyldicarboxylate ligands.

Three novel metal-organic frameworks (MOFs) formulated as [Zn(2)M(BPDC)(3)(DMF)(2)].4DMF (M = Co(II), Ni(II) or Cd(II); BPDC = 4,4'-biphenyldicarboxylate; DMF = N,N'-dimethylformamide) have been prepared via solvothermal synthesis from mixtures of the corresponding transition metal salts and 4,4'-biphenyldicarboxylic acid (H(2)BPDC). The framework structures are characterized by single-crystal X-ray diffraction analysis, IR and UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis (TGA), and X-ray powder diffraction (XRPD). All three compounds possess essentially the same 2-D layered coordination framework consisting of linear heterotrinuclear secondary building units (SBUs) connected by rigid bridging BPDC ligands. Crystal data: for (C(60)H(66)CoN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.86, a = 20.463(4), b = 14.819(3), c = 23.023(5) A, beta = 111.75(3) degrees , V = 6484(2) A(3), Z = 4, D(c) = 1.382 Mg m(-3). For (C(60)H(66)N(6)NiO(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.64, a = 11.670(2), b = 14.742(3), c = 19.391(4) A, beta = 102.29(3) degrees , V = 3259.5(11) A(3), Z = 2, D(c) = 1.374 Mg m(-3). For (C(60)H(66)CdN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1402.33, a = 11.491(2), b = 14.837(3), c = 19.386(4) A, beta = 101.53(3) degrees , V = 3238.3(11) A(3), Z = 2, D(c) = 1.438 Mg m(-3).

Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.

Structure and properties of the dendron-encapsulated polyoxometalate (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], a first generation dendrizyme.

Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins.