The interaction of gaseous CO 2 with the surface of amine-modified nanoporous clays has been studied. CO 2 adsorption and adsorption microcalorimetry revealed high adsorption capacity and strong interaction with the surface at low pressures, due to the presence of amine groups. Considerable surface heterogeneity and high initial adsorption heat (125 kJ mol -1 ) have been observed, although the adsorption was reversible with hysteresis at low pressures and very slow desorption kinetics. Interaction between 13 CO 2 and the surface of the nanoporous clay materials has been investigated by 13 C and 15 N magic-angle spinning (MAS) NMR. 13 C NMR resonances at ca. 164 and 160 ppm have been assigned to, respectively, carbamate and carbamic acid, and the stability of these species have been studied. Peak areas and the amount of 13 CO 2 adsorbed allowed the determination of the concentration of carbamate and carbamic acid. To the best of our knowledge, this is the first time that solid-state NMR is used to clearly establish the formation of amine-CO 2 bonding at the surface of amine-modified nanoporous materials and to identify the nature of the species formed. The results presented here shed light on the mechanism of CO 2 activation, since the CO 2 adsorption on the surface of such materials is the activation step that allows further reactions to occur. The instability of the carbamate and carbamic acid species formed on the surface is important in explaining the reactivity of these intermediates and supports the possible application of these materials in CO 2 activation.

Two-dimensional (2D) solid-state nuclear magnetic resonance (SSNMR) experiments on samples loaded with C-labeled CO, "under controlled partial pressures", have been performed in this work, revealing unprecedented structural details about the formation of CO adducts from its reaction with various amine-functionalized SBA-15 containing amines having distinct steric hindrances (e.g., primary, secondary) and similar loadings. Three chemisorbed CO species were identified by NMR from distinct carbonyl environments resonating at δ ≈ 153, 160, and 164 ppm. The newly reported chemisorbed CO species at δ ≈ 153 ppm was found to be extremely moisture dependent. A comprehensive H-based SSNMR study [1DH and 2D H-X heteronuclear correlation (HETCOR, X =C, Si) experiments] was performed on samples subjected to different treatments. It was found that all chemisorbed CO species are involved in hydrogen bonds (HBs) with either surface silanols or neighboring alkylamines. H chemical shifts up to 11.8 ppm revealed that certain chemisorbed CO species are engaged in very strong HBs. We effectively demonstrate that NMR may help in discriminating among free and hydrogen-bonded functional groups. C{N} dipolar-recoupling NMR showed that the formation of carbonate or bicarbonate is excluded. Density functional theory calculations on models of alkylamines grafted into the silica surface assisted the H/C assignments and validated various HB arrangements that may occur upon formation of carbamic acid. This work extends the understanding of the chemisorbed CO structures that are formed upon bonding of CO with surface amines and readily released from the surface by pressure swing.

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct (13)C and (1)H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the (1)H and (13)C chemical shifts including weak interionic H-bonds, is quantified; (1)H chemical shift changes up to ∼-3.5 ppm for CH···π contacts and ∼+2 ppm (CH···O((-))); ∼+4.7 ppm (((+))NH···O((-))) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for (1)H and (13)C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates.

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Isostructural modular microporous Na2[Y(hedp)(H2O)0.67] and Na4[Ln2(hedp)2(H2O)2]‚nH2O (Ln ) La, Ce, Nd, Eu, Gd, Tb, Er) framework-type, and layered orthorhombic [Eu(H2hedp)(H2O)2]‚H2O and Na0.9[Nd0.9Ge0.10(Hhedp)(H2O)2], monoclinic [Ln(H2hedp)(H2O)]‚3H2O (Ln ) Y, Tb), and triclinic [Yb(H2-hedp)]‚H2O coordination polymers based on etidronic acid (H5hedp) have been prepared by hydrothermal synthesis and characterized structurally by (among others) single-crystal and powder X-ray diffraction and solid-state NMR. The structure of the framework materials comprises eight-membered ring channels filled with Na + and both free and lanthanide-coordinated water molecules, which are removed reversibly by calcination at 300°C (structural integrity is preserved up to ca. 475°C), denoting a clear zeolite-type behavior. Interesting photoluminescence properties, sensitive to the hydration degree, are reported for Na4[Eu2(hedp)2-(H2O)2]‚H2O and its fully dehydrated form. The 3D framework and layered materials are, to a certain extent, interconvertable during the hydrothermal synthesis stage via the addition of HCl or NaCl: of the 3D framework Na4[Tb2(hedp)2(H2O)2]‚nH2O, affords layered [Tb(H2hedp) (H2O)]‚3H2O, whereas layered [Tb(H2-hedp)(H2O)2]‚H2O reacts with sodium chloride yielding a material similar to Na4[Tb2(hedp)2(H2O)2]‚nH2O. In layered [Y(H2hedp)(H2O)]‚3H2O, noncoordinated water molecules are engaged in cooperative waterto-water hydrogen-bonding interactions, leading to the formation of a (H2O)13 cluster, which is the basis of an unprecedented two-dimensional water network present in the interlayer space.

This work discusses quantitatively the energy transfer mechanism that occurs in the white-light emission of sol−gel derived amine- and amide-functionalized hybrids. The white-light photoluminescence (PL) results from a convolution of the emission originated in the NH/CO groups of the organic/inorganic cross-links with electron-hole recombinations occurring in the siloxane nanoclusters, both emissions typical of donor−acceptor pairs. Two model compounds that reproduce separately the two hybrid's emissions were synthesized and characterized by X-ray diffraction, 29Si/H/13C magic-angle spinning NMR, diffuse reflectance, Fourier transform−IR, and photoluminescence spectroscopy to support their use as organic and inorganic structural models for the two counterparts of the hybrids. The comparison between the lifetimes of the two emissions of the inorganic and organic model compounds with those of the hybrids, the Arrhenius dependence with temperature of the siliceous-related lifetime in the hybrids, and the nonexponential behavior of the decay curve of the siliceous-related emission under lower excitation wavelengths are experimental evidence supporting the occurrence of energy transfer in the hybrids. This energy transfer rate is quantitatively estimated for d-U(600) (the diureasil host with smaller number of polymer repeat units) generalizing the ideas proposed recently for the intramolecular energy transfer between singlet and triplet ligand levels and ligand-to-metal charge transfer states in lanthanide coordination compounds. The dipole−dipole energy transfer rate between the two emitting centers is 1.3 × 109 s-1, larger than the value estimated for the transfer rate mediated by the exchange mechanism, 3.7 × 108 s-1. The predicted room-temperature emission quantum yield of that diureasil hybrid is comparable to the corresponding experimental value (7 ± 1 %), pointing out a strong dependence of the radiative component values of the two emissions with temperature, induced by the glass−rubber phase transition of the hybrid's polymer chains.

The difference in the crystal structure and growth kinetics of microtubes formed from l- and d-enantiomers of diphenylalanine dipeptide is investigated both experimentally and theoretically by computer simulation. The microtubes of l- and d-enantiomers grown simultaneously and under identical experimental conditions possess different crystallographic space groups, have essential difference in sizes, and demonstrate different growth kinetics. Computer simulation by molecular mechanics methods revealed a fundamental difference in the interaction between structural units of microtubes of different chiralities. A model describing chirality-dependent growth of microtubes is proposed.