Search results for "Framework"
showing 10 items of 942 documents
Novel bimetallic MOF phosphors with an imidazolium cation: structure, phonons, high- pressure phase transitions and optical response
2018
We report the synthesis, crystal structure, phonons and luminescence properties of three novel heterometallic metal organic frameworks (MOFs) with perovskite-like topology of the following formulas: [C3H5N2]Na0.5Cr0.5(HCOO)3 (ImNaCr), [C3H5N2]Na0.5Al0.5(HCOO)3 (ImNaAl) and [C3H5N2]Na0.5Al0.475Cr0.025(HCOO)3 (ImNaAlCr with 5 mol% of Cr3+). ImNaCr crystallizes in a monoclinic system (P2/n space group) with one imidazolium cation (Im+) in an asymmetric unit forming six N–H⋯O and four C–H⋯O hydrogen bonds. In contrast to other known heterometallic MOFs, the complete substitution of Cr3+ ions with smaller Al3+ ions leads to a change of the crystal symmetry. ImNaAl adopts a monoclinic P21/n space…
Confined crystallization of a HKUST-1 metal–organic framework within mesostructured silica with enhanced structural resistance towards water
2017
A HKUST-1 metal–organic framework was crystallized in the NH2-modified mesostructured silica FDU-12 in order to improve its structural stability upon water exposure. In-depth structural characterization studies of the designed composite confirmed successful formation of the MOF phase within the ordered spherical mesopores of the silica matrix. In spite of the confinement within the cavities, MOF exhibits full accessibility for the adsorbed gas molecules. In contrast to the bulk HKUST-1, which undergoes slow phase transition in a humid environment, the structural integrity of the HKUST-1 in the humid-protective matrix remains unchanged even after immersion and stirring in water at elevated t…
Multitechnique Analysis of the Hydration in Three Different Copper Paddle-Wheel Metal-Organic Frameworks
2019
The structural instability in a humid environment of the majority of metal-organic frameworks (MOFs) is a challenging obstacle for their industrial-scale development. Recently, two water-resistant MOFs have been synthetized, STAM-1 and STAM-17-OEt. They both contain copper paddle wheels, like the well-known water-sensitive HKUST-1, but different organic linkers. The crystal lattice of both the MOFs undergoes a phase transition upon interaction with water molecules. Their unusual flexibility allows the controlled breaking of some interpaddle wheel Cu-O interactions in the so-called crumple zones, with a mechanism called hemilability, which is considered to have a crucial role for the stabili…
Guest Modulation of Spin-Crossover Transition Temperature in a Porous Iron(II) Metal Organic Framework: Experimental and Periodic DFT Studies
2014
The synthesis, structure, and magnetic properties of three clathrate derivatives of the spin-crossover porous coordination polymer {Fe(pyrazine)[Pt(CN)(4)]} (1) with five-membered aromatic molecules furan, pyrrole, and thiophene is reported. The three derivatives have a cooperative spin-crossover transition with hysteresis loops 14-29 K wide and average critical temperatures T-c=201 K (1.fur), 167 K (1.pyr), and 114.6 K (1.thio) well below that of the parent compound 1 (T-c=295 K), confirming stabilization of the HS state. The transition is complete and takes place in two steps for 1.fur, while 1.pyr and 1.thio show 50% spin transition. For 1.fur the transformation between the HS and IS (mi…
Mechanism of water adsorption in the large pore form of the gallium-based MIL-53 metal-organic framework
2016
Abstract Water adsorption in the large pore ( lp_empty ) form of Ga-MIL-53 was studied by TGA, DSC and in situ XRD and FTIR at 298 K. The large pore form can be stabilized at room temperature after activation under vacuum at 553 K. The isotherm of water adsorption in this large pore form (pore dimensions: 1.67 × 1.33 nm) is very similar to that measured on the narrow pore ( np_empty ) form (pore dimensions: 1.97 × 0.76 nm). Such a similarity is rather unusual given that the pore sizes of these two phases are very different. In order to understand the origin of this effect in situ XRD and FTIR measurements were particularly helpful. It was found that the adsorption of even small amount of wa…
Meeting the Discipline-Culture Framework of Physics Knowledge: A Teaching Experience in Italian Secondary School
2014
The paper deals with physics teaching/learning in high school. An investigation in three upper secondary school classes in Italy explored the reactions of students to a structuring lecture on optics within the discipline-culture (DC) framework that organises physics knowledge around four interrelated fundamental theories of light. The lecture presented optics as an unfolding conceptual discourse of physicists regarding the nature of light. Along with the knowledge constructed in a school course of a scientific lyceum, the students provided epistemological comments, displaying their perception of physics knowledge presented in the classroom. Students’ views and knowledge were investigated by…
Eugenesia y autoría moral. Lectura de una tesis habermasiana
2017
El objetivo de esta comunicación es ahondar en la visión que ha mantenido Jürgen Habermas a propósito de la manipulación genética; en concreto, se pretende abordar críticamente su hipótesis de una pérdida de autoría del sujeto manipulado. A juicio del autor, la intervención genética positiva —aquélla que tiene por objeto la introducción de virtuales mejoras en el sujeto— alcanzaría a violar la conciencia de autoría de dicho sujeto, así como su autocomprensión en tanto agente moral. En este sentido, se pretende investigar críticamente dos aspectos diferentes de la cuestión: en primer lugar, la corrección o no de la tesis habermasiana; en segundo lugar, la pertinencia o no de dicha tesis a la…
Crystallisation of H3BTC, H3TPO or H2SDA with MII (M = Co, Mn or Zn) and 2,2′-bipyridyl: design and control of co-ordination architecture, and magnet…
1999
The hydrothermal reaction of benzene-1,3,5-tricarboxylic acid (H3BTC) with MII (M = Mn, Co or Zn), tris(4-carboxyphenyl)phosphine oxide (H3TPO) or cis-stilbene-4,4′-dicarboxylic acid (H2SDA) with CoII and 2,2′-bipyridyl (BIPY) gave 1-D co-ordination networks formulated as: [M(HBTC)(BIPY)(H2O)] (M = Mn 1, Co 2, or Zn 3; [Co3(BTC)2(BIPY)2(H2O)6]·4H2O 4, [Co3(TPO)2(BIPY)2(H2O)6]·xH2O 5 and [Co(SDA)(BIPY)(H2O)] 6. Structures 1 and 2 consist of double stranded chains of alternating HBTC dianions and dimeric units MII–MII linked by two µ-(1,1) bridging carboxylates. Magnetic properties of 1 and 2 indicate the presence of ferromagnetic exchange interactions within the dimers. Structures 4 and 5 co…
Clathration of Five-Membered Aromatic Rings in the Bimetallic Spin Crossover Metal–Organic Framework [Fe(TPT)2/3{MI(CN)2}2]·G (MI = Ag, Au)
2014
Six clathrate compounds of the three-dimensional spin crossover metal−organic framework formulated [Fe(TPT)2/3{MI (CN)2}2]· nG, where TPT is 2,4,6-tris(4-pyridyl)-1,3,5-triazine, MI = Ag or Au and G represent the guest molecules furan, pyrrole and thiophene, were synthesized using slow diffusion techniques. The clathrate compounds were characterized by single-crystal X-ray diffraction at 120 and 300 K, thermogravimetric analysis and thermal dependence of the magnetic susceptibility. All compounds crystallize in the R3̅ m trigonal space group. The FeII defines a unique [FeN6] crystallographic site with the equatorial positions occupied by four dicyanometallate ligands while the axial positio…
Novel metal–organic frameworks based on 5-bromonicotinic acid: Multifunctional materials with H2 purification capabilities
2012
Two new metal–organic frameworks based on 5-bromonicotinic acid complexes [Cd(5-BrNic)2]n (1) and [Co(5-BrNic)2(H2O)]n (2) have been synthesized by hydrothermal reactions of this ligand with cadmium and cobalt metallic(II) salts in the presence of water. Compound 1 displays intense photoluminescence properties in the solid state at room temperature, while 2 exhibits an antiferromagnetic interaction between Co(II) ions with a J value of −4.1 cm−1. Experimental studies, backed up by Monte Carlo simulations about adsorption, pore size distribution and accessible surface area reveal the capability of 2 for H2 purification applications.