Adsorptive separation of olefin/paraffin mixtures by porous solids can greatly reduce the energy consumption associated with the currently employed cryogenic distillation technique. Here, the ...complete separation of propane and propylene by a designer microporous metal–organic framework material is reported. The compound, Y6(OH)8(abtc)3(H2O)6(DMA)2 (Y‐abtc, abtc = 3,3′,5,5′‐azobenzene‐tetracarboxylates; DMA = dimethylammonium), is rationally designed through topology‐guided replacement of inorganic building units. Y‐abtc is both thermally and hydrothermally robust, and possesses optimal pore window size for propane/propylene separation. It adsorbs propylene with fast kinetics under ambient temperature and pressure, but fully excludes propane, as a result of selective size exclusion. Multicomponent column breakthrough experiments confirm that polymer‐grade propylene (99.5%) can be obtained by this process, demonstrating its true potential as an alternative sorbent for efficient separation of propane/propylene mixtures.
A tailor‐made microporous metal–organic framework designed through a topologically guided secondary building unit (SBU) replacement strategy exhibits the highest selectivity for fast and efficient separation of propane and propylene via a size‐exclusion adsorption mechanism. This material, with excellent thermal and hydrothermal stability, and facile and scalable synthesis, is capable of producing polymer‐grade propylene (99.5%) from a typical propane/propylene mixture of cracking products.
A novel ultramicroporous coordination polymer, namely Cu(F-pymo)2(H2O)1.25n (1, F-pymo = 5-fluoropyrimidin-2-olate), has been prepared and structurally characterized. 1 displays a zeolitic gismondine ...(GIS) topology, with ca. 2.9 A wide helical channels which, in the thermally activated counterpart (1'), account for a 13% void volume and are responsible for the observed selective solid-gas adsorption properties toward H2, N2, and CO2. At 77 K 1' behaves as a molecular sieve, selectively adsorbing H2 over N2, possibly due to size-exclusion reasons. At variance, although CO2 molecules are slightly larger than the pore size, they are readily incorporated by 1' at temperatures as high as 433 K. Variable-temperature X-ray powder diffraction (TXRPD) studies, in the temperature range 303-473 K, show that dehydration is reversible and has almost negligible effects on the network. At variance, the uptake of CO2 occurs through a transient phase and channels expansion. While the gas storage capacity of 1' is not very high-H2, 0.56 wt % and 0.010 kg H2/L at 90 K and 900 Torr, and CO2, 7.6 wt % at 273 K and 900 Torr-the guest molecules achieve very high densities, comparable to that of the liquid for H2 (0.023 vs 0.021 molecules A-3) and to that of the solid for CO2 (0.014 vs 0.022 molecules A-3). In addition, we have also studied the effect of the perturbation exerted by the guest molecules on its magnetic properties. The results show that while dehydration of 1 has negligible effect on its spin-canted antiferromagnetic behavior, CO2 incorporation in the pores is responsible for an increment of the transition temperature at which the weak ferromagnetic ordering takes place from 22 to 29 K.
Carboxylate‐bridged chain complexes of CoII (the diaquacobalt(II) mono‐ and α,ω‐dialkanoates) form two homologous series of layered compounds which have been fully characterised both structurally and ...magnetically. The crystal structures of two selected members, Co{CH3(CH2)10COO}2(H2O)2 and Co{CH3(CH2)18COO}2(H2O)2, have been solved by X‐ray powder diffraction and selected‐area electron diffraction methods, and refined by the Rietveld technique. Crystal data: monoclinic, P 21/a; a=9.688(1), b=7.5495(9), c=37.281(5) Å, β=96.70(3)°, Z=4; and monoclinic, P 21/a; a=9.7260(7), b=7.5477(7), c=57.53(1) Å, β=94.66(4)°, Z=4, respectively. Their isomorphous structures contain layers of octahedral diaquacobalt(II) ions bonded to two chemically inequivalent alkanoates, one chelating and one bridging two Co atoms about 6.3 Å apart, thus confirming the rare anti–anti conformation mode of the μ‐RCOO groups recently proposed for diaquacobalt(II) α,ω‐dodecanedioate. Extensive magnetic characterisation allowed estimation of the feeble antiferromagnetic coupling, which is weaker in the mono‐ than in the dialkanoate series.
The rare anti–anti conformation mode of μ‐RCOO groups is confirmed for two examples of carboxylate‐bridged chain complexes of CoII. These complexes exist as homologous series that form layered compounds (the figure shows one such unit cell), which we have fully characterised, both magnetically and structurally. For the first time the complete three‐dimensional structure of transition metal soaps containing long‐chain alkanoates has been determined with the use of X‐ray powder diffraction.
The crystal structure of pirfenidone, C
H
NO alternative name: 5-methyl-1-phenyl-pyridin-2(1
)-one, an active pharmaceutical ingredient (API) approved in Europe and Japan for the treatment of ...Idiopathic pulmonary fibrosis (IPF), is reported here for the first time. It was crystallized from toluene by the temperature gradient technique, and crystallizes in the chiral monoclinic space group
2
. The phenyl and pyridone rings are inclined to each other by 50.30 (11)°. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds involving the same acceptor atom, forming undulating layers lying parallel to the
plane.
The novel porous {M(F‐pymo)2}n⋅2.5n H2O 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 MN4 coordination sphere changes into an MN3O one. A mixed‐metal phase, {CoxZn1−x(F‐pymo)2}n⋅2.5n H2O, 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 N2, H2 (77 K) and CH4, CO2 (273 K). These results show that these materials permit the diffusion of CO2 molecules only. Remarkably, the CO2 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 CO2 diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO2 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 CoII systems reveal that the as synthesised {Co(F‐pymo)2}n⋅2.5n H2O material behaves as an antiferromagnet with a TN 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.
Flexible MOFs! Application of high‐pressure CO2 or exposure to moisture of a zeomimetic coordination network induces a reversible structural change from a non‐porous β‐phase to a porous α‐phase (see figure). An additional structural transformation into a layered γ‐phase is promoted by thermal treatment implying a concomitant modification of the physicochemical properties.
Synthesis and Characterization of Some Aza[5]helicenes Bazzini, Cristina; Brovelli, Sergio; Caronna, Tullio ...
European Journal of Organic Chemistry,
April 2005, Letnik:
2005, Številka:
7
Book Review, Journal Article
In the last few years, the quantum theory of atoms in molecules has become the paradigm for interpreting theoretical and experimental electron density distributions. Within this framework, the link ...between bonding modes and topological properties has been fully achieved for ‘light atom’ molecules. However, the derived correspondence rules cannot be extended straightforwardly to organometallic compounds since bonds to a transition metal display a different and much narrower spectrum of topological indexes. The complementary usage of theoretical computations on a set of prototype transition metal molecules and experimental determinations of the electron density in transition metal carbonyl clusters are discussed. Since these compounds are characterised by weakly bound metal cages and fluxional carbonyl ligands, the focus is on the nature of metal–metal and metal–carbonyl interactions as well as on the evolution of three-centre-four-electron M(μ-CO)M bonds along the (CO)M–M↔M(μ-CO)M↔M–M(CO) conversion path. The interpretation of the electron density distribution here proposed could be extended reasonably to a wider class of organometallic compounds.
In this account, we describe the use of simple pyrimidine derivatives in combination with metal ions to build highly structured molecular architectures containing functional nanoenvironments, ...cavities and surfaces that can interact with additional species. The supramolecular structure of these systems can be rationally controlled by metal fragment geometry, reaction conditions and presence of templating agents. Thus, the use of transition metals with low coordination numbers or blocked bonding positions in combination with pyrimidines (e.g. 2-hydroxypyrimidine, 4-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimidine) leads to the formation of either discrete assemblies, 1D polymers or helixes. When metal ions with higher coordination possibilities are applied instead, 2D and 3D networks are generated. Some of the assemblies built in this way possess functional cavities, pores and surfaces that can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to recognition processes. The latter range from molecular recognition in homogeneous phase as well as clathrate formation, to heterogeneous solid–gas and solid–liquid adsorption phenomena. It should be noted that these materials are not rigid but able to undergo guest-induced reorganisation processes even in the solid state. Finally, some of these materials also combine additional interesting magneto-optical properties. Thus, dual systems can be envisaged in which two or more of these properties are present in the same material.
Combination of metal ions with pyrimidines leads to a great variety of flexible polynuclear assemblies. These systems can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to guest induced conformational changes in solution and in the solid state as well.
The cluster Co
As
(CO)
was obtained by pyrolysis of Co
As(CO)
. The metal cage features a closed-packed core inside a Co/As shell that progressively deforms from a cubic face-centered symmetry. The ...redox and acid-base reactivities were determined by cyclic voltammetry and spectrophotometric titrations. The calculated electron density revealed the shell-constrained distribution of the atomic charges, induced by the presence of arsenic.
PDF
