Valentina Colombo

Cation‐Exchange Porosity Tuning in Anionic Metal–Organic Frameworks for the Selective Separation of Gases and Vapors and for Catalysis

The outperforming adsorptive properties of the so-called open metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) rely on their fully accessible porous structure and the easy tuning of the shape, size, and chemical nature of their pores. The ability of some of these systems to mimic the structure and properties of zeolites has also been realized. There are, however, unsolved problems related to the general lower thermal and chemical stability (hydrolysissensitive nature) of MOFs compared to their zeolite counterparts. Consequently, the search for highly robust MOFs capable of withstanding the working conditions typically found in industrial processes is a highly desirable challenge. In this regard, the robustness of the metal–nitrogen(heterocycle) coordinative bonds leads to the formation of MOF materials with enhanced chemical and thermal stabilities. It should also be noted that, in contrast to the wellknown cation-exchange features of zeolites, the zeomimetic coordination polymers generally possess neutral or cationic frameworks and consequently do not usually give rise to cation-exchange processes. Herein, we report the synthesis, structural characterization, thermal/chemical stability, and adsorptive, separation, and catalytic properties of the anionic MOF NH4[Cu3(m3-OH)(m3-4-carboxypyrazolato)3] (NH4@1). In addition, we have examined the plausible modulation of its porous network by means of ion-exchange processes of the extraframework cations. The results show that the ion-exchange processes on these systems lead to profound changes in the textural properties of their porous surface and in the adsorption selectivity of different separation processes of gases and vapors. The crystal structure of NH4@1 [10] is based on an anionic 3D porous framework built up of trinuclear Cu3(m3-OH) clusters connected to another six through m3-4-carboxypyrazolato bridges (Figure 1). In this way, tetrahedral cages with

Tuning the Adsorption Properties of Isoreticular Pyrazolate-Based Metal–Organic Frameworks through Ligand Modification

Two isoreticular series of pyrazolate-based 3D open metal-organic frameworks, MBDP_X, adopting the NiBDP and ZnBDP structure types [H(2)BDP = 1,4-bis(1H-pyrazol-4-yl)benzene], were synthesized with the new tagged organic linkers H(2)BDP_X (X = -NO(2), -NH(2), -OH). All of the MBDP_X materials have been characterized through a combination of techniques. IR spectroscopy proved the effective presence of tags, while X-ray powder diffraction (XRPD) witnessed their isoreticular nature. Simultaneous TG/DSC analyses (STA) demonstrated their remarkable thermal stability, while variable-temperature XRPD experiments highlighted their high degree of flexibility related to guest-induced fit processes of the solvent molecules included in the channels. A structural isomer of the parent NiBDP was obtained with a sulfonate tagged ligand, H(2)BDP_SO(3)H. Structure solution from powder diffraction data collected at three different temperatures (room temperature, 90, and 250 °C) allowed the determination of its structure and the comprehension of its solvent-related flexible behavior. Finally, the potential application of the tagged MOFs in selective adsorption processes for gas separation and purification purposes was investigated by conventional single component adsorption isotherms, as well as by advanced experiments of pulse gas chromatography and breakthrough curve measurements. Noteworthy, the results show that functionalization does not improve the adsorption selectivity (partition coefficients) for the resolution of gas mixtures characterized by similar high quadrupole moments (e.g., CO(2)/C(2)H(2)); however, the resolution of gas mixtures containing molecules with highly differentiated polarities (i.e., N(2)/CO(2) or CH(4)/CO(2)) is highly improved.

Highly Hydrophobic Isoreticular Porous Metal-Organic Frameworks for the Capture of Harmful Volatile Organic Compounds

The release of toxic pollutants into the environment, which includes oil spills, leaks of harmful industrial products, and the deliberate emission of chemical warfare agents is a risk of growing concern. Worthy of note, oil spill cleanups amount to over 10 billion dollars annually. Remediation of these environmental problems involves the use of large amounts of adsorbents such as sand, activated carbons, or zeolites. However, the effectiveness of such adsorbents is often limited by their affinity to moisture. Consequently, the search for highly hydrophobic porous materials to be used as suitable stopgap of harmful organics spills has become of paramount importance. In the past years, porous metal–organic frameworks (MOFs) have been extensively studied to explore their possible applications in near future technologies for the safe storage of energetically and environmentally relevant gases. The tunable nature of their pores might be beneficial also in cushioning environmental problems caused by the release of harmful volatile organic compounds (VOCs). A remarkable example of the design amenability of MOFs is the well-known isoreticular [Zn4OL3] series (L= arene-dicarboxylate), wherein the size and the functionality of the pores can be modulated in a highly rational and systematic way. Nevertheless, the advantageous structural features of this family of MOFs are readily hampered by its high sensitivity to moisture, which limits its practical applications. A similar size-scaling approach has been applied by Lillerud and coworkers on the isoreticular [Zr6O4(OH)4L6] series, [9] evidencing that a significant improvement in the stability of the material can be achieved with an appropriate combination of dicarboxylate linkers and oxophylic metal fragments. Alternately, it is possible to take advantage of the enhanced stability imparted by polyazolate-containing ligands in combination with borderline metal ions. Accordingly, we designed and isolated an isoreticular series of porous MOFs, the pore size and polarity of which was modulated by coupling stiff bi-pyrazolate or mixed pyrazolate/carboxylate linkers (Scheme 1) to Ni hydroxo clusters acting as 12-connected

Cubic Octanuclear Ni(II) Clusters in Highly Porous Polypyrazolyl-Based Materials

Two highly porous coordination polymers, containing rare octanuclear hydroxo-nickel clusters and long bis-pyrazolyl spacers, are shown to possess, after mild thermal treatment, lattice cavities up to 72% of the total crystal volume.

Probing hydrogen bond networks in half-sandwich Ru(II) building blocks by a combined 1H DQ CRAMPS solid-state NMR, XRPD, and DFT approach.

The hydrogen bond network of three polymorphs (1α, 1β, and 1γ) and one solvate form (1·H2O) arising from the hydration-dehydration process of the Ru(II) complex [(p-cymene)Ru(κN-INA)Cl2] (where INA is isonicotinic acid), has been ascertained by means of one-dimensional (1D) and two-dimensional (2D) double quantum (1)H CRAMPS (Combined Rotation and Multiple Pulses Sequences) and (13)C CPMAS solid-state NMR experiments. The resolution improvement provided by homonuclear decoupling pulse sequences, with respect to fast MAS experiments, has been highlighted. The solid-state structure of 1γ has been fully characterized by combining X-ray powder diffraction (XRPD), solid-state NMR, and periodic plane-wave first-principles calculations. None of the forms show the expected supramolecular cyclic dimerization of the carboxylic functions of INA, because of the presence of Cl atoms as strong hydrogen bond (HB) acceptors. The hydration-dehydration process of the complex has been discussed in terms of structure and HB rearrangements.

Crystal Chemistry of the Antibiotic Doripenem

Doripenem, an ultrabroad spectrum-injectable antibiotic belonging to the wide class of carbapenem beta-lactams, is commonly marketed as powders of a pure monohydrate phase. Here, we have selectively prepared another hydrated phase (a dihydrate) and determined the crystal structure of both forms by state-of-the art powder diffraction methods. Both phases crystallize in the monoclinic P21 space group, and, to some extent, are structurally related. Moreover, by using variable temperature diffractometric analyses, we also discovered a crystalline anhydrous form of doripenem, the structure of which (with two crystallographically independent molecules in the monoclinic P21 space group) remains so far unknown. The thermal interconversion among these phases was further studied by thermogravimetry, differential scanning calorimetry, and thermodiffractometric analyses, and their (metric or stereochemical) mutual relations fully analyzed. The complete structural characterization of the two hydrated phases allows the use of accurate whole pattern profile-fitting procedures for quantitative analyses of these drugs in polycrystalline, or even amorphous, matrices, opening the way to industrial process control and legal protection.

Two-component organic crystals without hydrogen bonding: structure and intermolecular interactions in bimolecular stacking

A survey of crystal structures including two organic compounds unable to form hydrogen bonding has been carried out using the Cambridge Structural Database. Such systems are common and numerous. Association modes mostly include stacking of flat systems, one of them usually being an aromatic hydrocarbon. “Alternate-ladder” (AL) and “slanted column” (SC) motifs occur most frequently; AL is somewhat prevalent in fluoroarene and pyromellitic dianhydride cocrystals, whereas SC occurs preferentially, but not exclusively, with quinones, nitrobenzene, TCNB and TCNQ coformers. Segregation of A and B chemical units in separate columns is very seldom observed, while A⋯B is the energetically dominating pair in a vast majority of the cases. A stable network of stacked A⋯B units seems to be a strict requirement for observing cocrystallization, even more than an overall higher stability of the cocrystal with respect to its coformers. This highlights the central role of kinetic factors in determining the drive to stacking hetero-recognition. Energy dissection using the PIXEL scheme shows that dispersion energies play a dominant but not exclusive role. The interaction between flat organic systems is found to be a viable synthetic approach for cocrystallization, on the same footing as the more popular O–H⋯O, O–H⋯N and N–H⋯O hydrogen bonding. Some practical suggestions for the choice of the best coformers are provided.

A phosphorescent copper(I) coordination polymer with sodium 3,5-dimethyl-4-sulfonate pyrazolate

A phosphorescent copper(I) coordination polymer with the sodium salt of 3,5-dimethyl-4-sulfonate pyrazole (HLNa) has been prepared and structurally characterized. The presence of the SO3Na substituent in position 4 of the pyrazole ring led to a 3D polymeric species in which an organic/inorganic/organic sandwich motif is observed and repeated along the a axis through zig-zag chains of linear coordinated Cu(I) ions. The inorganic core of the sandwich consists of a trapezoidal grid of Na-ions interconnected by μ-(κO;κ2-O′,O′′)-bridging sulfonates and bridging water molecules; H-bonds can be also found between water molecules and SO3− groups. In the solid state, the copper derivative showed an interesting phosphorescent behavior when irradiated with UV light, with a yellow emission (570 nm) and a good absolute quantum yield (ΦPL = 0.44), together with a remarkable Stokes shift of 2.50 eV.

Electron Density Analysis of Metal Clusters with Semi-Interstitial Main Group Atoms. Chemical Bonding in [Co6X(CO)16]− Species

In this work, we propose a careful and thorough analysis of the chemical bond nature in high nuclearity metal carbonyl clusters having semi-interstitial main group atoms. We investigated the species [Co6X(CO)16]- (X = As, P), known for a rather interesting conformational flexibility of the cluster (leading to open or closed cages) and a corresponding polymorphism in the solid state (observed at least for X = As). The factors that trigger the molecular isomerism and the nature of X-Co and Co-Co interactions emerge from theoretical calculations and high resolution X-ray diffraction. Both energy and charge density atomic partitioning (QTAIM, EDA, IQA) are employed for this analysis, with the aim of revealing the stabilizing/destabilizing factors of the interaction between the cage and the semi-interstitial atoms in the various conformations.