1,721,134 research outputs found
Porosity and crystal morphology of heterometallic coordination networks from β-diketonate ligands
Full text linkPorous coordination polymers (PCPs) or metal-organic-frameworks (MOFs) are considered very promising porous materials that can be exploited in many different technological fields such as gas storage, heterogeneous catalysis and separation of mixtures. In the field of MOF materials, many efforts are devoted to the search of rational synthetic procedures. Among others, a useful synthetic strategy is the so-called Metalloligand (MLs) approach. MLs are coordination complexes containing suitably oriented exo donor-groups that, used in place of organic linkers, can orient the formation of desired homo and heterometallic polymeric architectures [1]. Functionalized chelating ligands suited to obtain useful MLs are -diketonate molecules.[2]
We report the synthesis and the structural characterization of two families of coordination frameworks obtained through the use of different -diketonate ligands with copper salts of several counter-ions. The first family of polymers have a two-dimensional layered structure whereas the members of the second family adopt a three-dimensional flexible framework structure.
We have focused our attention to the correlations between the crystal structure, the dimensionality, the topology and porosity of the networks and the crystal morphologies, as well as to the investigation of the surface phenomena during the crystal growing process. Moreover, we have mapped a continuous set of crystal morphologies by controlling experimental variables such as the solvent system, the metal-ligand molar ratio and the nature of the counter-anion. The aim is to develop a method to tune the crystal habit according to the specific requirement of some important applications.[3]
[1] S. Kitagawa, R. Kitaura, S. Noro Angew. Chem., Int. Ed., 43 (2004) 2334.
[2] L. Carlucci, G. Ciani, S. Maggini, D.M. Proserpio, M. Visconti, Chem. Eur. J, 16 (2010) 12328.
[3] L. Carlucci, G. Ciani, J. M. Garcìa-Ruiz, M. Moret, D. M. Proserpio and S. Rizzato , Cryst. Growth Des., 2009, 9(12), 5024-5034
Molecular recognition and crystal energy landscapes : an X-ray and computational study of caffeine and other methylxanthines
No full textWe introduce a new approach to crystal-packing anal., based on the study of mutual recognition modes of entire mols. or of mol. moieties, rather than a search for selected atom-atom contacts, and on the study of crystal energy landscapes over many computer-generated polymorphs, rather than a quest for the one most stable crystal structure. The computational tools for this task are a polymorph generator and the PIXEL d. sums method for the calcn. of intermol. energies. From this perspective, the mol. recognition, crystal packing, and solid-state phase behavior of caffeine and several methylxanthines (purine-2,6-diones) have been analyzed. Many possible crystal structures for anhyd. caffeine have been generated by computer simulation, and the most stable among them is a thermodn., ordered equiv. of the disordered phase, revealed by powder X-ray crystallog. Mol. recognition energies between two caffeine mols. or between caffeine and water have been calcd., and the results reveal the largely predominant mode to be the stacking of parallel caffeine mols., an intermediately favorable caffeine-water interaction, and many other equiv. energy min. for lateral interactions of much less stabilization power. This last indetn. helps to explain why caffeine does not crystallize easily into an ordered anhyd. structure. In contrast, the mono- and dimethylxanthines (theophylline, theobromine, and the 1,7-isomer, for which we present a single-crystal X-ray study and a lattice energy landscape) do crystallize in anhyd. form thanks to the formation of lateral hydrogen bonds
Parallel and inclined (1D -> 2D) interlacing modes in new polyrotaxane frameworks [M-2(bix)(3)(SO4)(2)] [M = Zn(II), Cd(II); Bix=1,4-bis(imidazol-1-ylmethyl)benzene]
No full textThe reactions of M-II sulfates (M = Zn, Cd) with the flexible ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix) yield the novel interesting coordination networks [M-2(bix)(3)(SO4)(2)], containing 1D polymeric motifs of alternating rings and rods, which show extended rotaxane-like mechanical links producing 2D sheets via unprecedented parallel (M = Zn) or inclined (M = Cd) interlacing modes of the chains
Borromean links and other non-conventional links in 'polycatenated' coordination polymers: re-examination of some puzzling networks
No full textA number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the 'polycatenanes' class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion.A number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the 'polycatenanes' class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion
A new type of supramolecular entanglement in the silver(I) coordination polymer [Ag-2(bpethy)(5)](BF4)(2) [bpethy = 1,2-bis(4-pyridyl)ethyne]
No full textThe polymeric compound [Ag-2(bpethy)(5)](BF4)(2), obtained from AgBF4 and 1,2-bis(4-pyridyl)ethyne (bpethy) in molar ratio 1:3, contains infinite molecular ladder motifs with monodentate ligands as sidearms on both sides, that are threaded through the squares of adjacent polymeric units in a mutual relationship, to give infinite 'polythreaded' bidimensional layers
Growth of HKUST-1 on functionalized graphene layers
No full textMetal Organic Frameworks (MOFs) are porous crystalline materials showing 1, 2 and 3 dimensional extended frameworks that are sustained by coordinative chemical bonds between organic ligands and metal cations/clusters. Among all the characterized MOFs, HKUST-1 or [Cu3(BTC)2(H2O)3]n (H3BTC = benzene-1,3,5-tricarboxylic acid) is one of the most studied [1]. Recently it has been noticed that HKUST-1 is also a good system for methane storage [2].
Even MOFs can act as gas storage on their own, they have been also combined with other materials to create composites in order to improve their properties. These composites have been mainly prepared with other materials such as silica, carbon nanotubes, graphite oxide or other carbon types [3]. Graphene is a single layer (2D) of sp2 carbon atoms arranged with a honeycomb structure. Due to its properties (high-resistance, high thermal and electrical conductivity) it has gained a lot of interest in recent years. In particular, the development of composite materials with improved properties as well as the organic functionalization of the graphene layers are of increasing interest. Here we report our results on the growth of HKUST-1 in the presence of benzoic acid functionalized graphene. [4]
Authors acknowledge financial support from Regione Lombardia (Project: NASEMS, Concert_EN-046).
[1] S. S.-Y. Chui et al. Science, 1999, 283, 1148-1150.
[2] J. A. Mason et al. Chem. Sci., 2014, 5, 32-35.
[3] Y. Zhao et. al RSC Advances, 2013, 3, 9932-9941.
[4] M. Jahan et al. J.Am.Chem.Soc. 2010, 132, 14487–1449
A new type of entanglement involving one-dimensional ribbons of rings catenated to a three-dimensional network in the nanoporous structure of [Co(bix)2(H2O)2](SO4)·7H2O [bix = 1,4-bis(imidazol-1-ylmethyl)benzene]
No full textCoII sulfate reacts with the flexible ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix) to yield the coordination network [Co(bix)2(H2O)2](SO4)·7H2O, containing polymeric ribbons of
rings which penetrate and catenate a 3D single frame of the CdSO4 topology, to produce an open-channel entangled architecture with nanoporous behaviour
1,2-eq,eq-[Re-2(CO)(8)(THF)(2)]: A reactive Re-2(CO)(8) fragment that easily activates H-H and C-H bonds
No full textThe reaction of [Re-2(mu-H)(2)(CO)(8)] (1) with diazomethane at 193 K in THF-d(8) gives the unstable [Re-2(mu-H)(mu-CH3)(CO)(8)] derivative (2) containing a methyl group arising from the insertion of CH2 into a Re-H-Re bond. Isotopic perturbation of the equilibria by partial deuteration demonstrated that the methyl bridges the Re-Re bond in an unsymmetrical way, with a fast exchange between one agostic and two terminal C-H bonds. At temperatures higher than 253 K, 2 decomposes, in THF solution, with CH4 elimination to give the novel red complex 1,2-eq,eq-[Re-2(CO)(8)(THF)(2)] (3), which was characterized by NMR spectroscopy and X-ray analysis. In the solid form a staggered conformer of Ca symmetry was found. C-13 NMR analysis revealed the presence, in wet THF, of the aquo complexes [Re-2(CO)(8)(THF)(H2O)] (4) and [Re-2(CO)(8)(H2O)(2)] (5), whose formation is favored at low temperature (Delta H degrees for the formation of 5 from 4: -14.4(2) kJ mol(-1)). In solution, due to the lability of the THF ligands, 3 behaves as a "lightly stabilized" Re-2(CO)(8) fragment, capable of activating different E-H bonds. Reaction with HCl in THF leads to [Re-2(mu-H)(mu-Cl)(CO)(8)], while with H-2 the unsaturated starting material [Re-2(mu-H)(2)(CO)(8)] is obtained. In THF solution, at room temperature, reactions with phenylacetylene, styrene, and acetaldehyde give the derivatives of C-H activation [Re-2(mu-H)(mu-C drop CPh)(CO)(8)], [Re-2(mu-H)(mu-CH=C(H)Ph)(CO)(8)], and [Re-2(mu-H)(mu-eta(2)-C(Me)O)(CO)(8)]. Moreover, the activation of an sp(3) C-H bond in ethyl acetate occurs slowly when 3 is dissolved in the reactant itself, the resultant product being [Re-2(mu-H)(mu-eta(2)-CH2C(O)OEt)(CO)(8)]
A polythreaded three-dimensional architecture of undulated layers originated by the contribution of different supramolecular interactions
No full textThe structure of compound [Cd2(NDC)2(L)2(H2O)] 0.5DMF (1) (NDC = 1,4-naphthalenedicarboxylate,
L = pyrazino[2,3-f][1,10]phenanthroline and DMF = N,N0-dimethylformamide) is reported. Two independent
Cd(II) atoms in a distorted [CdO4N2] octahedral environment and three unique NDC ligands showing
different coordination modes give strongly undulated two-dimensional grid motifs. Dangling L ligands
are chelated to every Cd(II) atom decorating both sides of the layers. Due to the marked undulation of
the layers, the large open windows are threaded by the dangling ligands of other layers producing a
three-dimensional polythreaded supramolecular array that can be also described as a single threedimensional
framework if the extended columnar face-to-face p–p interactions are considered
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