No abstract

A fourfold interpenetrating diamondoid network, [{[Ni(cyclam)]2-(mtb)}(n)].8n H2O.4n DMF (1) (MTB=methanetetrabenzoate, DMF=dimethylformamide), has been assembled from [Ni(cyclam)][ClO4]2 (cyclam=1,4,8,11-tetraazacyclotetradecane) and methanetetrabenzoic acid (H4MTB) in DMF/H2O (7:3, v/v) in the presence of triethylamine (TEA). Despite the high-fold interpenetration, 1 generates 1D channels that are occupied by water and DMF guest molecules. Solid 1, after removal of guest molecules, exhibits selective gas adsorption behavior for H2, CO2, and O2 rather than N2 and CH4, suggesting possible applications in gas separation technologies. In addition, solid 1 can be applied in the fabrication of small Pd (2.0+/-0.6 nm) nanoparticles without any extra reducing or capping agent because a Ni II macrocyclic species incorporated in 1 reduces Pd II ions to Pd 0 on immersion of 1 in the solution of Pd(NO3)2.2H2O in MeCN at room temperature.

Various metal-organic frameworks (MOFs) have been prepared to obtain materials that show specific or multifunctional properties. Porous MOFs that contain free space where guest molecules can be accommodated are of particular interest because they can be applied in gas storage [1][2][3][4] and separation, [4][5][6] selective adsorption and separation of organic molecules, [1, 7] ion exchange, [8] catalysis, [9] sensor technology, [1,10] and for the fabrication of metal nanoparticles.[11]Secondary building units (SBUs) with a specific geometry have often been employed [12] for the modular construction of porous MOFs as they make the design and prediction of molecular architectures simple and easy. In particular, {M 2 -(CO 2 ) 4 }-type paddlewheel clusters that can be formed from the solvothermal reaction of M 2+ ions and the appropriate carboxylic acid are widely used for the construction of porous frameworks. Three-dimensional porous frameworks with various topologies (Pt 3 O 4 , boracites, NbO, and PtS nets) can be built from paddlewheel-type metal cluster SBUs and tri-or tetracarboxylates, [13][14][15][16] whereas pillared square-grid networks can be constructed from paddlewheel cluster SBUs and dicarboxylates in the presence of diamine ligands. [17] Porous MOFs with accessible metal sites (AMSs) should have a higher hydrogen storage capacity than those without AMSs, [14,18] although there are not yet enough experimental data to support this assumption. To determine the effect of AMSs in a MOF on H 2 adsorption, the H 2 uptakes should be compared for the same framework in the absence and presence of AMSs, or for two independent isostructural MOFs with and without AMSs. H 2 uptake has previously been measured under several different outgassing conditions. [13] Unfortunately, these experiments could not clearly demonstrate the effect of AMSs as the exact formula and structure at each stage were not known. Furthermore, even when coordinating solvent molecules are successfully removed with retention of the porous framework structure, the metal ion sometimes transforms its coordination geometry to the thermodynamically most stable form instead of keeping the AMSs. [4,19] Herein we report two porous MOFs with the same NbOtype net topology, namely [{Zn 2 (abtc)(dmf) 2 } 3 ]·4 H 2 O·10 dmf (1) and [{Cu 2 (abtc)(H 2 O) 2 } 3 ]·10 dmf·6 (1,4-dioxane) (2; H 4 abtc = 1,1'-azobenzene-3,3',5,5'-tetracarboxylic acid [20] ), and compare the gas adsorption data for the MOFs with and without AMSs.[21] Heating crystals of 1 and 2 under precisely controlled conditions allowed us to prepare [{Zn 2 -(abtc)(dmf) 2 } 3 ] (1 a; SNU-4) and [{Cu 2 (abtc)(dmf) 2 } 3 ] (2 a; SNU-5'), which have no AMSs, as well as [{Cu 2 (abtc)} 3 ] (2 b; SNU-5), which has AMSs. The framework structure of 1 a is the same as that of 1 and those of 2 a and 2 b are the same as that of 2, as evidenced by the PXRD patterns. Solid 1 a, 2 a, and 2 b exhibit higher adsorption capabilities for N 2 , CO 2 , CH 4 , and H 2 than other previously reported MOFs. In pa...

A porous metal-organic framework, [Co(II)(4)(micro-OH(2))(4)(MTB)(2) x (H(2)O)(4)](n) x 13nDMF x 11nH(2)O (SNU-15), has been prepared; the X-ray crystal structure reveals a CaF(2)-like structure that generates 3D channels and the desolvated solid [Co(II)(4) (micro-OH(2))(4)(MTB)(2)](n) (SNU-15') exhibits selective gas sorption properties for H(2) and O(2) gases over N(2) at 77 K, with exceptionally high O(2) density, as well as for CO(2) over CH(4) at 195 and 273 K, suggesting its potential application in gas separation processes.

The study of positive homotropic allosterism in supramolecular receptors is important for elucidating design strategies that can lead to increased sensitivity in various molecular recognition applications. In this work, the cooperative relationship between tetrathiafulvalene (TTF)-calix[4]pyrroles and several nitroaromatic guests is examined. The design and synthesis of new annulated TTF-calix[4]pyrrole receptors with the goal of rigidifying the system to accommodate better nitroaromatic guests is outlined. These new derivatives, which display significant improvement in terms of binding constants, also display a positive homotropic allosteric relationship, as borne out from the sigmoidal nature of the binding isotherms and analysis by using the Hill equation, Adair equation, and Scatchard plots. The host-guest complexes themselves have been characterized by single-crystal X-ray diffraction analyses and studied by means of UV-spectroscopic titrations. Investigations into the electronic nature of the receptors were made by using cyclic voltammetry; this revealed that the binding efficiency was not strictly related to the redox potential of the receptor. On the other hand, this work serves to illustrate how cooperative effects may be used to enhance the recognition ability of TTF-calix[4]pyrrole receptors. It has led to new allosteric systems that function as rudimentary colorimetric chemosensors for common nitroaromatic-based explosives, and which are effective even in the presence of potentially interfering anions.