Simona Galli

High thermal and chemical stability in pyrazolate-bridged metal–organic frameworks with exposed metal sites

Reactions between the tritopic pyrazole-based ligand 1,3,5-tris(1H-pyrazol-4-yl)benzene (H3BTP) and transition metal acetate salts in DMF afford microporous pyrazolate-bridged metal–organic frameworks of the type M3(BTP)2·xsolvent (M = Ni (1), Cu, (2), Zn (3), Co (4)). Ab-initioX-ray powder diffraction methods were employed in determining the crystal structures of these compounds, revealing 1 and 2 to exhibit an expanded sodalite-like framework with accessible metal cation sites, while 3 and 4 possess tetragonal frameworks with hydrophobic surfaces and narrower channel diameters. Compounds 1–4 can be desolvated without loss of crystallinity by heating under dynamic vacuum, giving rise to microporous solids with BET surface areas of 1650, 1860, 930 and 1027 m2 g−1, respectively. Thermogravimetric analyses and powder X-ray diffraction measurements demonstrate the exceptional thermal and chemical stability of these frameworks. In particular, 3 is stable to heating in air up to at least 510 °C, while 1 is stable to heating in air to 430 °C, as well as to treatment with boiling aqueous solutions of pH 2 to 14 for two weeks. Unexpectedly, 2 and 3 are converted into new crystalline metal–organic frameworks upon heating in boiling water. With the combination of stability under extreme conditions, high surface area, and exposed metal sites, it is anticipated that 1 may open the way to testing metal–organic frameworks for catalytic processes that currently employ zeolites.

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.

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.

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.

Synthesis and characterisation of new polynuclear copper(I) pyrazolate complexes and their catalytic activity in the cyclopropanation of olefins

Abstract The reaction of [Cu(CH3CN)4](BF4) with racemic pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3,5-dicarbo-sec-butoxypyrazole, Hdcsbpz) or with pyrazole-3,5-di-ter-butyl (3,5-di-ter-butylpyrazole, Hdtbpz) quantitatively yields the new [Cu(dcsbpz)]4 and [Cu(dtbpz)]4 complexes, respectively. Crystals of [Cu(dcsbpz)]4 are triclinic, P 1 , a=10.9748(7), b=11.8399(8), c=26.5575(17) A, α=100.605(2), β=90.783(2), γ=105.362(2)°; [Cu(dtbpz)]4·CH2Cl2 is monoclinic, P21/n, a=10.902(3), b=19.200(3), c=25.772(4) A, β=93.86(2)°. Both species contain cyclic tetrameric molecules, with the heterocyclic ligands binding in the common N,N′-exo-bidentate mode; however, the shape and geometry of the inner Cu4 moiety is remarkably different, as highlighted, for example, by the absolute values of the 1,2 and 1,3 (non-bonding) Cu⋯Cu interactions. These polynuclear copper(I) pyrazolate complexes catalyse the conversion of alkenes into the corresponding cyclopropane derivatives with interesting diastereomeric excesses. Aiming at the evaluation of their catalytic activities, a systematic study of the cyclopropanation reactions in the presence of ethyl diazoacetate has been performed.

Synthesis, X-ray structures and luminescence properties of three multidimensional metal–organic frameworks incorporating the versatile 5-(pyrimidyl)tetrazolato bridging ligand

The hydrated sodium salt of the novel and versatile 5-(pyrimidyl)tetrazolato ligand (pmtz(-)), Na(pmtz).H(2)O (1), has been prepared in very mild conditions from 2-cyanopyrimidine and NaN(3). Two coordination polymers [Cd(pmtz)(2)]n (2)and [Cd(pmtz)(micro-Cl)(0.5)(micro-N(3))(0.5)(H(2)O)](n)(3), , have been synthesized from (1)under conventional or hydrothermal conditions, respectively, and fully characterized by single-crystal or powder X-ray diffraction methods. Compounds and consist of mono-dimensional polymeric chains, further stabilized by interchain pi-pi stacking and hydrogen bond interactions. Compound , containing octacoordinated Cd ions of crystallographic D(2) symmetry, exhibits neutral (4, 4) layers formed by square units of the metallacalix[4]arene type in 1,3-alternate conformation. Species , and display intense, room temperature, photoluminescence in the solid state.

X-RAY POWDER DIFFRACTION CHARACTERIZATION OF POLYMERIC METAL DIAZOLATES

ABSTRACT Polymeric metal diazolates typically appear as insoluble and intractable powders, the structure of which could only be retrieved by the extensive use of ab-initio X-ray powder diffraction (XRPD) methods from conventional laboratory data. A number of selected examples from the metal pyrazolate, imidazolate, pyrimidin-2-olate and pyrimidin-4-olate classes are presented, highlighting the specific crystallochemical properties, material functionality and methodological aspects of the structure determination process. Linear and helical one-dimensional polymers, layered systems and three-dimensional networks are described, with particular emphasis on polymorphism and on the thermal, optical, magnetic and sorption properties. A brief outline of the method, as it has been tailored in our laboratories during the last decade, is also offered.

Ultrasensitive Piezoresistive All‐Organic Flexible Thin Films

[*] Prof. J. Veciana, Prof. V. Laukhin, Dr. E. Laukhina, Prof. C. Rovira, Dr. M. Mas-Torrent, R. Pfattner, L. R. Ferreras Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) Campus UAB, 08193 Bellaterra (Spain) E-mail: vladimir@icmab.es; laukhina@icmab.es; vecianaj@icmab.es Prof. J. Veciana, Prof. V. Laukhin, Dr. E. Laukhina, Prof. C. Rovira, Dr. M. Mas-Torrent, R. Pfattner, L. R. Ferreras Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN) ICMAB-CSIC, 08193 Bellaterra (Spain)