Elisa Barea

Capture of Nerve Agents and Mustard Gas Analogues by Hydrophobic Robust MOF-5 Type Metal–Organic Frameworks

In this communication, a series of observations and data analyses coherently confirms the suitability of the novel metal-organic framework (MOF) [Zn(4)(μ(4)-O)(μ(4)-4-carboxy-3,5-dimethyl-4-carboxy-pyrazolato)(3)] (1) in the capture of harmful volatile organic compounds (VOCs). It is worthy of attention that 1, whose crystal structure resembles that of MOF-5, exhibits remarkable thermal, mechanical, and chemical stability, as required if practical applications are sought. In addition, it selectively captures harmful VOCs (including models of Sarin and mustard gas, which are chemical warfare agents), even in competition with ambient moisture (i.e., under conditions mimicking operative ones). The results can be rationalized on the basis of Henry constant and adsorption heat values for the different essayed adsorbates as well as H(2)O/VOC partition coefficients as obtained from variable-temperature reverse gas chromatography experiments. To further strengthen the importance of 1, its performance in the capture of harmful VOCs has been compared with those of well-known materials, namely, a MOF with coordinatively unsaturated metal sites, [Cu(3)(btc)(2)] and the molecular sieve active carbon Carboxen. The results of this comparison show that coordinatively unsaturated metal sites (preferential guest-binding sites) are ineffective for the capture of VOCs in the presence of ambient moisture. Consequently, we propose that the driving force of the VOC-MOF recognition process is mainly dictated by pore size and surface hydrophobicity.

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

Textile/Metal-Organic-Framework Composites as Self-Detoxifying Filters for Chemical-Warfare Agents**

The current technology of air-filtration materials for protection against highly toxic chemicals, that is, chemical-warfare agents, is mainly based on the broad and effective adsorptive properties of hydrophobic activated carbons. However, adsorption does not prevent these materials from behaving as secondary emitters once they are contaminated. Thus, the development of efficient self-cleaning filters is of high interest. Herein, we report how we can take advantage of the improved phosphotriesterase catalytic activity of lithium alkoxide doped zirconium(IV) metal-organic framework (MOF) materials to develop advanced self-detoxifying adsorbents of chemical-warfare agents containing hydrolysable P-F, P-O, and C-Cl bonds. Moreover, we also show that it is possible to integrate these materials onto textiles, thereby combining air-permeation properties of the textiles with the self-detoxifying properties of the MOF material.

Polymorphic coordination networks responsive to CO2, moisture, and thermal stimuli: porous cobalt(II) and zinc(II) fluoropyrimidinolates.

The novel porous [{M(F-pymo)(2)}(n)]2.5n H(2)O coordination networks (M=Co, Zn; F-pymo=5-fluoropyrimidin-2-olate), possessing sodalitic topology, have been synthesised and structurally characterised by means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three-dimensional dehydrated [{M(F-pymo)(2)}(n)] species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN(4) coordination sphere changes into an MN(3)O one. A mixed-metal phase, [{Co(x)Zn(1-x)(F-pymo)(2)}(n)]2.5n H(2)O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid-gas adsorption properties of the anhydrous 3D frameworks have been explored towards N(2), H(2) (77 K) and CH(4), CO(2) (273 K). These results show that these materials permit the diffusion of CO(2) molecules only. Remarkably, the CO(2) adsorption process for the [{Co(F-pymo)(2)}(n)] network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the [{Zn(F-pymo)(2)}(n)] network only permits CO(2) diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO(2) selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the Co(II) systems reveal that the as synthesised [{Co(F-pymo)(2)}(n)]2.5n H(2)O material behaves as an antiferromagnet with a T(N) of about 29 K. At variance, the [{Co(F-pymo)(2)}(n)] layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin-canting phenomenon.

Functionalisation of MOF open metal sites with pendant amines for CO2 capture

The present work deals with the study of the effect of functionalisation of open metal sites in [Cu3(btc)2] (btc = 1,3,5-benzenetricarboxylate) [HKUST-1] with bifunctional amines for CO2 adsorption under dry and humid conditions.

Nanoscaled Zinc Pyrazolate Metal–Organic Frameworks as Drug-Delivery Systems

This work describes synthesis at the nanoscale of the isoreticular metal-organic framework (MOF) series ZnBDP_X, based on the assembly of Zn(II) metal ions and the functionalized organic spacers 1,4-bis(1H-pyrazol-4-yl)-2-X-benzene (H2BDP_X; X = H, NO2, NH2, OH). The colloidal stability of these systems was evaluated under different relevant intravenous and oral-simulated physiological conditions, showing that ZnBDP_OH nanoparticles exhibit good structural and colloidal stability probably because of the formation of a protein corona on their surface that prevents their aggregation. Furthermore, two antitumor drugs (mitroxantrone and [Ru(p-cymene)Cl2(pta)] (RAPTA-C) where pta = 1,3,5-triaza-7-phospaadamantane) were encapsulated within the pores of the ZnBDP_X series in order to investigate the effect of the framework functionalization on the incorporation/delivery of bioactive molecules. Thus, the loading capacity of both drugs within the ZnBDP_X series seems to directly depend on the surface area of the solids. Moreover, ligand functionalization significantly affects both the delivery kinetics and the total amount of released drug. In particular, ZnBDP_OH and ZnBDP_NH2 matrixes show a slower rate of delivery and higher percentage of release than ZnBDP_NO2 and ZnBDP_H systems. Additionally, RAPTA-C delivery from ZnBDP_OH is accompanied by a concomitant and progressive matrix degradation due to the higher polarity of the BPD_OH ligand, highlighting the impact of functionalization of the MOF cavities over the kinetics of delivery.

In vitro and in vivo antiparasital activity against Trypanosoma cruzi of three novel 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one-based complexes.

Conventional reactions of the versatile multidentate ligand 5-methyl-1,2,4-triazolo[1,5-a] pyrimidin-7(4H)-one (HmtpO) with metallic(II) perchlorate salts lead to three novel multidimensional complexes [Cu(HmtpO)(2)(H(2)O)(3)](ClO(4))(2)·H(2)O (1), {[Cu(HmtpO)(2)(H(2)O)(2)](ClO(4))(2) ·2HmtpO}(n) (2) and {[Co(HmtpO)(H(2)O)(3)](ClO(4))(2)·2H(2)O}(n) (3). We have tested the antiparasital activity in vitro and in vivo of the three new complexes against Trypanosoma cruzi showing very promising results and overcoming clearly the reference drug commonly used for the Chagas disease treatment, benznidazole.

Borderline microporous-ultramicroporous palladium(II) coordination polymer networks. Effect of pore functionalisation on gas adsorption properties

PdII coordination polymer networks of the type [Pd(μ-X-pymo-N1,N3)2·(H2O)m]n (X = H, 2HHH; F, 2FFF; Br, 2BrBrBr; I, 2III), containing the X-pymo (X-Hpymo = 5-X-2-hydroxypyrimidine) ligands, have been obtained by refluxing aqueous suspensions of the monomeric trans-[Pd(X-Hpymo-N1)2Cl2] (1HH-1II) precursors with NaOH in a 1 : 1 ratio. While 2BrBrBr and 2III have been recovered as amorphous materials, the microcrystalline species 2HHH and 2FFF, in their hydrated and anhydrous forms, have been structurally characterised by ab initio XRPD methods: square planar PdII ions, symmetrically connected by exobidentate N1,N3-X-pymo bridges, give rise to neutral sodalite zeotypic frameworks (with H2O guest molecules eventually included in the pores). The thermal properties and porosity have been determined for all of the 2XXX systems. The H2, N2 and CO2 adsorption isotherms showed that the 2HHH and 2FFF materials possess permanent porosity, as opposed to the 2BrBrBr and 2III ones. Moreover, the isomorphic incorporation of fluorine in the framework causes important modifications in the gas-adsorption isotherms; stronger interactions at very low pressures (Henrys law region) appear in all of the probes studied (N2, CO2 and H2). Compounds 2HHH and 2FFF possess high H2 adsorption capacities at 77 K with respective values of 1.3 and 1.15 weight percentage, and storage densities of about 0.018 kg H2 L−1, which are combined with large isosteric adsorption heats (8–9 kJ mol−1).