The adsorption/desorption of up to 0.75 g of water vapour per g of the porous MOFs 3D-{M 3 O(X)(H 2 O) 2 [btc] 2 $nH 2 O}, MIL-100 (M ¼ Al, Fe; X ¼ OH, F, btc ¼ benzene-1,3,5-tricarboxylate, trimesate), occurs at small relative pressures of p/p 0 < 0.4 and a comparatively small hysteresis. Together with very good cycle stability, these properties render both MIL-100(Al and Fe) very suitable candidates for thermally driven heat pumps or adsorption chillers.More than 50% of the energy consumption and, simultaneously, the CO 2 emissions of modern buildings originate from air conditioning processes. These are traditionally based on electrically driven, mechanical compression chillers and heat pumps or classical burner systems, respectively. This demand is expected to rise in the future because of increased living standards and global climate change. 1 However, with alternative technologies, less exergetic (that is, closer to equilibrium) forms of energy, even low-temperature waste heat from industrial processes, can be employed for both heating and cooling. Solar heat as driving energy is especially interesting due to the high coincidence of cooling demand and solar irradiation. While multiple working principles for thermally driven heat-pumps can be realised, the evaporation-adsorption method has proven most feasible for this purpose and is briefly described in Fig. 1 and Table 1.The presented process renders cooling applications independent of precious electrical energy. If it is used for heating, the incorporation of environmental heat allows for considerable fuel savings. The coefficient of performance (i.e. the relation between useful and driving heat), power density, cost and operating lifetime of the complete machine are governed by the sorption material and its figures of merit, i.e. porosity, water sorption capacity, hydrophilicity and hydrothermal stability. 2,3 The achievable loading lift and also the required desorption temperature directly depend on the hydrophilicity of the material, i.e., the p/p 0 value at which adsorption occurs

ABSTRACT:The water loading capacity and water cycle stability (40 adsorption/ desorption cycles) of four nitro-or amino-functionalized MIL-101Cr materials (1−4) is assessed for heat transformation applications. Amino-or nitro-functionalized (1, 3) and partially amino-or nitro-functionalized MIL-101Cr (2, 4) have been synthesized through time-controlled postsynthetic modification of MIL-101Cr. The partially functionalized materials (2, 4) contain about 78 mol % amino-or nitro-functionalized terephthalate linker. Hydrophilic nitro or amino functionalities were introduced into MIL-101Cr in order to achieve water loading at lower p/p 0 values for possible use in thermally driven adsorption chillers or heat pumps. Among the four materials studied, fully aminated MIL-101Cr-NH 2 , 1, and partially aminated MIL-101Cr-pNH 2 , 2, showed the best water loadings (about 1.0 gH 2 O/gMIL) as well as water stability over 40 adsorption−desorption cycles. After 40 cycles, the X-ray powder diffractogram and Brunauer−Emmett−Teller (BET) surface determination of amino-functionalized materials indicated structural integrity with Δ BET = −6.3% after 40 cycles, while the nitro-functionalized MIL-101Cr exhibited a decrease in their BET surface of Δ BET = −25% and −20% for 3 and 4, respectively.

The protocols of the crystalline sponge method, particularly those in the soaking, data collection and refinement processes, are considerably improved to give reliable structural information.

Porous chromium(III) 2-nitro-, 2-amino-, and nonfunctionalized terephthalate (MIL-101Cr) metal organic frameworks are heterogeneous catalysts for diacetal formation from benzaldehyde and methanol (B-M reaction) as well as other aldehydes and alcohols. MIL-101Cr-NO2 obtained by direct reaction between CrO3 and 2-nitro-terephthalate showed the highest activity with 99% conversion in the B-M reaction in 90 min and turnover numbers of 114. The activity decreased in the order MIL-101Cr-NO2 > MIL-101Cr > MIL-101Cr-NH2. Within different samples of nonfunctionalized MIL-101Cr the activity increased with surface area. Methanol gas sorption of the different MIL materials correlates with the BET surface area and pore volume but not with the diacetalization activity. Benzaldehyde adsorption from heptane showed no significant difference for the different MILs. Gas sorption studies of CD3CN to probe for a higher Lewis acidity in MIL-101Cr-NO2 remained inconclusive. A high B-M catalytic activity of wet MIL-101Cr-NO2 excluded significant contributions from coordinatively unsaturated Lewis-acid sites. pH measurements of methanol dispersions of the MIL materials gave the most acidic pH (as low as 1.9) for MIL-101Cr-NO2, which significantly increased over MIL-101Cr (3.0) to MIL-101Cr-NH2 (3.3). The increase in acidity is of short range or a surface effect to the heterogeneous MIL particles as protons dissociating from the polarized aqua ligands (Cr-OH2) have to stay near the insoluble counteranionic framework. The variation in Brønsted acidity of MIL-101Cr-NO2 > MIL-101Cr ≈ MIL-101Cr-NH2 correlates with the withdrawing effect of NO2 and the diacetalization activity. The catalytic B-M activity of soluble, substitution-inert, and acidic Cr(NO3)3·9H2O supports the Brønsted-acid effect of the MIL materials. Filtration and centrifugation experiments with MIL-101Cr-NO2 revealed that about 2/3 of the catalytic activity comes from nano-MOF particles with a diameter below 200 nm. The MIL-101Cr-NO2 catalysts can be recycled five times with very little loss in activity. The diacetalization activity of MIL-101Cr-NO2 decreases with the alcohol chain length from methanol over ethanol, n-propanol, n-butanol, to almost inactive n-pentanol, while conversions for benzaldehyde, paratolylaldehyde, 4-chlorobenzaldehyde, and cyclohexanone all reach 90% or more after 90 min.

Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg(2+) in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg(2+) has been shown among 11 M(2+) ions, viz., Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ca(2+), and Mg(2+) studied, including those of the mercury group and none of these ions impede the recognition of Hg(2+) by L. Role of the solvent on the recognition of Hg(2+) has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg(2+) by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg(2+) with L has been further established based on (1)H and (13)C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg(2+) have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg(2+) toward L have been established based on the DFT computational calculations.

Crystalline sponges (CS) used under a set of standard conditions have often failed to give viable N-containing nucleophilic compounds. Despite the high affinity of these nucleophiles to the binding sites of the CS, N-containing compounds considerably harm the coordination framework of the CS during the guest-soaking step. Herein, it is disclosed that these compounds are efficiently absorbed into the CS, without harming the host, under mild conditions (<4 °C, <2 μg) that normally do not work for common organic guests. Moreover, the use of ZnCl as the metal component of CS significantly improved the tolerance and robustness of the host framework toward N-containing compounds. Out of 22 drug (or drug-like) N-containing compounds chosen from the WHO model list of essential medicines, we succeeded in analyzing 17 analytes with the modified protocols and/or by using the ZnCl -noded CS. This demonstrates that the CS method is now a practical tool for drug-discovery research in pharmaceutical industries.

Pyrimidine (pym) ligands with their two endocyclic N-donor atoms provide 120° angles for molecular constructs, which, with the 90° angle metal fragments cis-a(2)M(II) (M=Pt, Pd; a=NH(3) or a(2)=diamine), form cyclic complexes known as metallacalix[n]arenes (with n=3, 4, 6, 8, …). The number of possible isomers of these species depends on the symmetry of the pym ligand. Although highly symmetrical (C(2v)) pym ligands form a single linkage isomer for any n and can adopt different conformations (e.g., cone, partial cone, 1,3-alternate, and 1,2-alternate in the case of n=4), low-symmetry pym ligands (C(s)) can produce a higher number of linkage isomers (e.g., four in the case of n=4) and a large number of different conformers. In the absence of any self-sorting bias, the number of possible species derived from a self-assembly process between cis-a(2)M(II) and a C(s)-symmetrical pym ligand can thus be very high. By using the C(s)-symmetric pym nucleobase cytosine, we have demonstrated that the number of feasible isomers for n=4 can be reduced to one by applying preformed building blocks such as cis-[a(2)M(cytosine-N3)(2)](n+) or cis-[a(2)M(cytosinate-N1)(2)] (for the latter, see the accompanying paper: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2011, 17, DOI: 10.1002/chem.2010002723) and treating them with additional cis-a(2)M(II) . Moreover, intramolecular hydrogen-bonding interactions between the O2 and N4H(2) sites of the cytosine ligands reduce the number of possible rotamers to one. This approach of the "directed" assembly of a defined metallacalix[4]arene is demonstrated.

MIL-101Cr fully or partially (p) postsynthetically modified with nitro (-NO2) or amino (-NH2) groups was shown to be a robust, water stable, selective and enhanced carbon dioxide (CO2) adsorption material with the amine-functionality. The highly microporous amine-modified frameworks (up to 1.6 cm(3) g(-1) total pore volume) exhibit excellent thermal stability (>300 °C) with BET surface areas up to 2680 m(2) g(-1). At 1 bar (at 273 K) the gases CO2, CH4 and N2 are adsorbed up to 22.2 wt%, 1.67 wt% and 2.27 wt%, respectively. The two amine-modified MIL-101Cr-NH2 (4) and MIL-101Cr-pNH2 (5) showed the highest gas uptake capacities in the series with high ratios for the CO2 : N2 and CO2 : CH4 selectivities (up to 119 : 1 and 75 : 1, respectively, at 273 K). Comparison with non-modified MIL-101Cr traces the favorable CO2 adsorption properties of MIL-101Cr-NH2 (4) and MIL-101Cr-pNH2 (5) to the presence of the Lewis-basic amine groups. MIL-101Cr-NH2 (4) has a high isosteric heat of adsorption of 43 kJ mol(-1) at zero surface coverage and also >23 kJ mol(-1) over the entire adsorption range, which is well above the heat of liquefaction of bulk CO2. Large CO2 uptake capacities of amine-functionalized 4 and 5, coupled with high adsorption enthalpy, high selectivities and proven long-term water stability, make them suitable candidates for capturing CO2 at low pressure from gas mixtures including the use as a CO2 sorbent from moist air.