Hydrolytically stable adsorbents, with notable water uptake, are of prime importance and offer great potential for many water-adsorption-related applications. Nevertheless, deliberate construction of tunable porous solids with high porosity and high stability remains challenging. Here, we present the successful deployment of reticular chemistry to address this demand: we constructed Cr-soc-MOF-1, a chemically and hydrolytically stable chromium-based metal-organic framework (MOF) with underlying soc topology. Prominently, Cr-soc-MOF-1 offers the requisite thermal and chemical stability concomitant with unique adsorption properties, namely extraordinary high porosity (apparent surface area of 4,549 m 2 /g) affording a water vapor uptake of 1.95 g/g at 70% relative humidity. This exceptional water uptake is maintained over more than 100 adsorption-desorption cycles. Markedly, the adsorbed water can be fully desorbed by just the simple reduction of the relative humidity at 25 C. Cr-soc-MOF-1 offers great potential for use in applications pertaining to water vapor control in enclosed and confined spaces and dehumidification.

The development of practical solutions for the energy-efficient capture of carbon dioxide is of prime importance and continues to attract intensive research interest. Conceivably, the implementation of adsorption-based processes using different cycling modes, e.g., pressure-swing adsorption or temperature-swing adsorption, offers great prospects to address this challenge. Practically, the successful deployment of practical adsorption-based technologies depends on the development of made-to-order adsorbents expressing mutually two compulsory requisites: i) high selectivity/affinity for CO and ii) excellent chemical stability in the presence of impurities. This study presents a new comprehensive experimental protocol apposite for assessing the prospects of a given physical adsorbent for carbon capture under flue gas stream conditions. The protocol permits: i) the baseline performance of commercial adsorbents such as zeolite 13X, activated carbon versus liquid amine scrubbing to be ascertained, and ii) a standardized evaluation of the best reported metal-organic framework (MOF) materials for carbon dioxide capture from flue gas to be undertaken. This extensive study corroborates the exceptional CO capture performance of the recently isolated second-generation fluorinated MOF material, NbOFFIVE-1-Ni, concomitant with an impressive chemical stability and a low energy for regeneration. Essentially, the NbOFFIVE-1-Ni adsorbent presents the best compromise by satisfying all the required metrics for efficient CO scrubbing.

An unprecedented single crystal-to-single crystal transformation occurs when a binuclear oxovanadium(V) compound [V(V)(2)O(2)(L)(2)] 1 involving 2,6-bis(hydroxymethyl)-p-cresol (H(3)L) as a bridging ligand is exposed simultaneously to white light and aerial oxygen to generate an oligomeric compound [V(IV)(2)O(2)(L*)(2)] 2 (H(2)L* is 3-hydroxymethyl-5-methylsalicylaldehyde). Each vanadium(V) center in 1 is reduced to vanadium(IV) in 2 at the expense of a two-electron alcohol-to-aldehyde oxidation in the coordinated ligand. The additional electron being released is possibly consumed by molecular oxygen to generate hydrogen peroxide.

The protonated form [H(2)(L)](CF(3)SO(3))(2) (1) of a new redox-active bis-bidentate nitrogenous heterocyclic ligand, viz., 3,3'-dipyridin-2-yl[1,1']bi[imidazo[1,5-a]pyridinyl] (L), and its zinc(II) and cadmium(II) complexes (2 and 3) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, both 2 and 3 have triple-stranded helical structures involving ligands that experience twisting and bending to the extent needed by the stereoelectronic demand of the central metal ion. The metal centers in the zinc(II) complex [Zn(2)(L)(3)](ClO(4))(4) (2) are equivalent, each having a distorted octahedral geometry, flattened along the C(3) axis with a Zn1···Zn1# separation of 4.8655(13) Å. The cadmium complex [Cd(2)(L)(3)(H(2)O)](ClO(4))(4) (3), on the other hand, has a rare type of helical structure, showing coordination asymmetry around the metal centers with a drastically reduced Cd1···Cd2 separation of 4.070 Å. The coordination environment around Cd1 is a distorted pentagonal bipyramid involving a N(6)O donor set with the oxygen atom coming from a coordinated water, leaving the remaining metal center Cd2 with a distorted octahedral geometry. The structures of 2 and 3 also involve anion-π- and CH-π-type noncovalent interactions that play dominant roles in shaping the extended structures of these molecules in the solid state. In solution, these compounds exhibit strong fluxional behavior, making the individual ligand strands indistinguishable from one another, as revealed from their (1)H NMR spectra, which also provide indications about these molecules retaining their helical structures in solution. Electrochemically, these compounds are quite interesting, undergoing ligand-based oxidations in two successive one-electron steps at E(1/2) of ca. 0.65 and 0.90 V versus a Ag/AgCl (3 M NaCl) reference. These molecules are all efficient emitters in the red and blue regions because of ligand-based π*-π fluorescent emissions, tuned appropriately by the attached Lewis acid centers.

Four multiring heterocyclic ligands with benzimidazole (L 1 and L 3 ) and benzothiazole nuclei (L 2 and L 4 ) are reported. Their silver(I) complexes involving a variety of anions (both organic and inorganic) have been prepared by the process of self-assembly and structurally characterized by single-crystal X-ray diffraction analyses. Discrete metallocyclic complexes) have been formed with the ligands L 3 and L 4 , respectively, where the pyridine nitrogen atom N1 is in the 3-position as against the coordination polymers, and [Ag(L 2 ) 2 (cis-HOOCCHdCHCOO)] n , 2b, with the ligands L 1 and L 2 , respectively, in which the N1 atom occupies the 4-position in the pyridine ring. In addition to the primary ligands (L 1 -L 4 ), the counteranions also have a dominant influence on the overall structures of these compounds. Secondary bonding interactions, namely, hydrogen bonding, π 3 3 3 π-stacking, and C-H 3 3 3 π interactions, are also proven effective in shaping the dimensionalities of the solid state structures. Thus, a zigzag chain structure of 1a mediated by a nitrate anion generates a more complicated double layer structure in 1b where trifluoroacetate has replaced nitrate as the counterion. Discrete 12-membered metallocycles in 3a-3c generate 2-D arrays of flat (3a) and undulating topologies (3b and 3c), depending upon the type of their associated anions. Metallocycles 4a and 4b have less complicated structures compared to those of 3a-3c because of the replacement of NH by S in the heterocyclic ring, thereby reducing the hydrogen-bonding potential in the primary ligand in going from L 3 to L 4 . In the solid state, the complexes show enhanced phosphorescence at 77 K with triplet lifetime in the range of 0.5-0.8 s, much shorter than those for the free ligands (2.3 -3.3 s) because of increased spin-orbit coupling introduced by the coordinated Ag þ ion. This heavy-atom effect also has a causative influence in shortening the fluorescence lifetimes of these compounds.