Dynamics of bound states of dihydrogen at Cu(I) and Cu(II) species coordinated near one and two zeolite framework aluminium atoms: A combined sorption, INS, IR and DFT study

Abstract Ambient conditions sorption isotherms of dihydrogen in a series of various levels of Cu-exchanged ZSM-5 zeolites, with two different Si/Al ratios, namely 11.5 and 25, show the presence of different amount of Cu centres able to strongly bind H2. Although the isosteric heats of adsorption derived from these isotherms are rather similar, of the order of 30 kJ/mol H2, Inelastic Neutron Scattering (INS) of adsorbed dihydrogen and Fourier-Transformed Infra-Red (FTIR) spectroscopy measurements of adsorbed CO and NO reveal that copper is encountered in two oxidation states. At least two types of Cu(I) ions are clearly detected as well as some heterogeneity of the Cu(II) species. The number of these Cu species is different in the two investigated ZSM-5 materials and depends on the Cu exchange level. With the aid of DFT model cluster calculations we find that under different coordination environments, determined by the Al distribution, both mono- and divalent Cu ions could bind H2 with a different strength. Unprecedentedly, we found that Cu-ions compensating two Al atoms, i.e. formally Cu(II) species, relatively far apart from each other, may behave very similarly to the monovalent Cu-species or alternatively viewed – as Cu(I) species that compensate for two framework Al-atoms. Such Cu-species also form stable η2 dihydrogen complexes

Crystal growth of coordination polymers by gel diffusion

The use of gels or viscous materials as growth media for a wide range of compounds, including proteins, inorganic and organic compounds has already been reported in the literature. In the presence of a gel, sedimentation and convection currents are greatly suppressed and the mass transport of the molecules occurs mainly by diffusion. As a result, a lower nucleation density and a better crystal quality are usually observed.[1a] We report, here, new interesting phenomena observed in crystallization experiments ofcoordination compounds by using gels as diffusion media.[1b]. We have tested a variety of gel and resin-like systems as dispersion matrixes to crystallize a special class of polymeric and porous inorganic compound: the \u201ccoordination polymers\u201d. We have used the gel technique to increase the size and quality of the crystals and as a mean to modify the crystal habit and get new crystalline species. [1b] In our experiments, we have observed some new phenomena of gel inclusion and morphological alteration of crystal surfaces. Diffraction, optical observations and interferometric measurements have been used for in situ monitoring the mass transport in the gelled/fluid phase during the crystallization process and for studying the crystallization kinetic. Funding from the Cariplo Foundation grant \u2018\u20182012\u20100921\u201d is gratefully acknowledged. [1] a) K.H. Henisch, Crystals in Gels and Liesegang Rings, Cambridge University Press, Cambridge, 1998; b) L. Carlucci, G. Ciani, J. M. Garc\ueca-Ruiz, M. Moret, D. M. Proserpio and S. Rizzato Cryst. Growth Des., 2009, 9(12), 5024-5034. [2] S.Rizzato et al., unpublished results

High H2 Sorption Energetics in Zeolitic Imidazolate Frameworks

A combined experimental and theoretical study of H2 sorption was carried out on two isostructural zeolitic imidazolate frameworks ZIFs , namely ZIF 68 and ZIF 69. The former consists of Zn2 ions that are coordinated to two 2 nitroimidazolate and two benzimidazolate linkers in a tetrahedral fashion, while 5 chlorobenzimidazolate is used in place of benzimidazolate in the latter compound. H2 sorption measurements showed that the two ZIFs display similar isotherms and isosteric heats of adsorption Qst . The experimental initial H2 Qst value for both ZIFs was determined to be 8.1 kJ mol 1, which is quite high for materials that do not contain exposed metal centers. Molecular simulations of H2 sorption in ZIF 68 and ZIF 69 confirmed the similar H2 sorption properties between the two ZIFs, but also suggest that H2 sorption is slightly favored in ZIF 68 with regards to uptake at 77 K 1.0 atm. This work also presents inelastic neutron scattering INS spectra for H2 sorbed in ZIFs for the first time. The spectra for ZIF 68 and ZIF 69 show a broad range of intensities starting from about 4 meV. The most favorable H2 sorption site in both ZIFs corresponds to a confined region between two adjacent 2 nitroimidazolate linkers. Two dimensional quantum rotation calculations for H2 sorbed at this site in ZIF 68 and ZIF 69 produced rotational transitions that are in accord with the lowest energy peak observed in the INS spectrum for the respective ZIFs. We found that the primary binding site for H2 in the two ZIFs generates high barriers to rotation for the adsorbed H2, which are greater than those in several metal organic frameworks MOFs which possess open metal sites. H2 sorption was also observed for both ZIFs in the vicinity of the nitro groups of the 2 nitroimidazolate linkers. This study highlights the constructive interplay of experiment and theory to elucidate critical details of the H2 sorption mechanism in these two isostructural ZIF

4-Benzyl­piperazin-1-ium chloride chloro­form solvate

The ions of the title chloro­form-solvated salt, C11H17N2 +·Cl−·CHCl3, are linked by a strong N—H⋯Cl hydrogen bond; the solvent mol­ecule also inter­acts with the chloride ion through a C—H⋯Cl hydrogen bond. Additionally, neighboring cations form weak hydrogen bonds to the anion, resulting in a supra­molecular ribbon that runs along the a axis

Crystal growth in gelled solution : applications to coordination polymers

Some critical issues concerning the complex synthesis and crystallization of designed coordination polymers are highlighted by using gels as diffusion media. The systematic use of gel methods in a variety of different crystallization configurations has been proven useful in revealing the field of existence and the stability hierarchy of competitive and concomitant crystalline phases, and also in discovering some important effects due to gel matrices. The most interesting phenomena observed are the modification and alteration of the macro- and microscopic morphology of crystals due to gel incorporation, which are responsible for changes in many properties and functionalities of these materials, opening up new possibilities for their applications in a variety of technological fields. In addition, a kinetic study of a gel grown polymeric system has also been conducted, demonstrating the continuous evolution of crystal morphology and its connection with the crystal growth process and growth mechanism

Structures of furanosides : geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha -D-arabinofuranoside (1), methyl beta -D-arabinofuranoside (2), methyl alpha -D-lyxofuranoside (3), methyl beta -D-ribofuranoside (4) and methyl alpha -D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate. unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C-1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations

Synthesis, characterization and biological activity of novel Cu(II) complexes of 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehy de-4N-substituted thiosemicarbazones

Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (1, -NH2; 2, -NHMe; 3, -NHEt) have been prepared and characterized. In both the X-ray structures of 1 and 3, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in 1a and nitrate in 1b) or in the co-ligand (water in 3a and methanol in 3b). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes 1 and 3 confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes 2 and 3 exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes 2 and 3 also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained

An ant colony-based semi-supervised approach for learning classification rules

Semi-supervised learning methods create models from a few labeled instances and a great number of unlabeled instances. They appear as a good option in scenarios where there is a lot of unlabeled data and the process of labeling instances is expensive, such as those where most Web applications stand. This paper proposes a semi-supervised self-training algorithm called Ant-Labeler. Self-training algorithms take advantage of supervised learning algorithms to iteratively learn a model from the labeled instances and then use this model to classify unlabeled instances. The instances that receive labels with high confidence are moved from the unlabeled to the labeled set, and this process is repeated until a stopping criteria is met, such as labeling all unlabeled instances. Ant-Labeler uses an ACO algorithm as the supervised learning method in the self-training procedure to generate interpretable rule-based models—used as an ensemble to ensure accurate predictions. The pheromone matrix is reused across different executions of the ACO algorithm to avoid rebuilding the models from scratch every time the labeled set is updated. Results showed that the proposed algorithm obtains better predictive accuracy than three state-of-the-art algorithms in roughly half of the datasets on which it was tested, and the smaller the number of labeled instances, the better the Ant-Labeler performance