Heterometallic Titanium-Organic Frameworks as Dual Metal Catalysts for Synergistic Non-Buffered Hydrolysis of Nerve Agent Simulants

Heterometallic metal-organic frameworks (MOFs) can offer important advantages over their homometallic counterparts to enable targeted modification of their adsorption, structural response, electronic structure, or chemical reactivity. However, controlling metal distribution in these solids still remains a challenge. The family of mesoporous titanium-organic frameworks, MUV-101(M), displays heterometallic TiM2 nodes assembled from direct reaction of Ti(IV) and M(II) salts. We use the degradation of nerve agent simulants to demonstrate that only TiFe2 nodes are capable of catalytic degradation in non-buffered conditions. By using an integrative experimental-computational approach, we rationalize how the two metals influence each other, in this case, for a synergistic mechanism reminiscent of bimetallic enzymes. Our results highlight the importance of controlling metal distribution at an atomic level to span the interest of heterometallic MOFs to a broad scope of cascade or tandem reactions. Summary Mixed-metal or heterometallic metal-organic frameworks (MOFs) are gaining importance as a route to produce materials with increasing chemical and functional complexities. We report a family of heterometallic titanium frameworks, MUV-101(M), and use them to exemplify the advantages of controlling metal distribution across the framework in heterogeneous catalysis by exploring their activity toward the degradation of a nerve agent simulant of Sarin gas. MUV-101(Fe) is the only pristine MOF capable of catalytic degradation of diisopropyl-fluorophosphate (DIFP) in non-buffered aqueous media. This activity cannot be explained only by the association of two metals, but to their synergistic cooperation, to create a whole that is more efficient than the simple sum of its parts. Our simulations suggest a dual-metal mechanism reminiscent of bimetallic enzymes, where the combination of Ti(IV) Lewis acid and Fe(III)–OH Brönsted base sites leads to a lower energy barrier for more efficient degradation of DIFP in absence of a base.Financial support for this work was provided by the Marie Skłodowska-Curie Global Fellowships (749359-EnanSET, N.M.P) within the European Union research and innovation framework programme (2014-2020

Mossbauer spectroscopy analysis of Fe-57-doped YBaCo4O7+delta: effects of oxygen intercalation.

Mossbauer spectroscopy of layered YBaCo3.96Fe0.04O7+delta (delta=0.02 and 0.80), where 1% cobalt is substituted With 57 Fe isotope, revealed no evidence of charge ordering at 4-293 K. The predominant state of iron cations was found trivalent, irrespective of their coordination and oxygen stoichiometry variations determined by thermogravimetric analysis. The extremely slow kinetics of isothermal oxidation at 598 K in air, and the changes of Fe3+ fractions in the alternating triangular and Kagome layers in oxidized YBaCo3.96Fe0.04O7.80, may suggest that oxygen intercalation is accompanied with a substantial structural reconstruction stagnated due to sluggish cation diffusion. Decreasing temperature below 75-80 K leads to gradual freezing of the iron magnetic moments in inverse correlation with the content of extra oxygen. The formation of metal-oxygen octahedra and resultant structural distortions extend the temperature range where the paramagnetic and frozen states co-exist, down to 45-50 K. © 2008, Elsevier Ltd

Structural characterization of cobalt(III), nickel(II), copper(II) and iron(III) complexes of tetraazamacrocycles with N-carboxymethyl arms

The single crystal structures of complexes [CoL1]Br-0.5.[NO3](0.5). 5H(2)O 1, [Ni(HL1)]Br . 4H(2)O 2, Ca[CuL3]NO3. CH3CN . 2H(2)O 3 and [CoL3]. 2H(2)O 4 were determined, where H2L1 is 3,11-bis(carboxymethyl)-7-methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene and H3L3 is 3,7,11-tris(carboxymethyl)-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene. In all these complexes the metal centre is encapsulated by the macrocycle in a distorted octahedral environment, the four nitrogen atoms of the tetraaza ring defining the equatorial planes. In the complexes of H2L1 the axial positions are occupied by the two carboxymethyl groups which are adjacent to the pyridine ring, while in the complexes of H3L3 one of these positions is occupied by one of the carboxymethyl arms adjacent to the pyridine ring and the other by the group opposite to the pyridine moiety. The remaining carboxymethyl arm adjacent to the pyridine ring is further away from the metal centre and plays an important role in the crystal structures of both complexes. Crystals of 3 display a three-dimensional polymeric structure derived from the Ca-O bonds. In the lattice the Ca2+ ions are surrounded by eight oxygen atoms, with two calcium ions bridged by two oxygen atoms of carboxylate groups bonded to the copper centres. This large spherical molecule has a centrosymmetric structure with the centre of the core, Ca2O2, localised on a crystallographic inversion centre. Additionally, the complexes of H3L3 (3 and 4) have interesting superstructures based on several C=O ... HO hydrogen interactions between the carboxylate pendant arms and water molecules. The Fe3+ complexes of H2L2 (3,11-bis(carboxymethyl)-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene) and of H3L3 were characterised by EPR and Mossbauer spectroscopy. Both techniques revealed that the complexes of the bis(carboxymethyl) derivative appear as an equilibrium of high- and low-spin state species, the relative amount of the latter increasing with decrease of temperature, and that the complex of the tris(carboxymethyl) derivative appears practically as a high-spin state species. Molecular mechanics studies have provided data to explain the different behaviour of the iron(III) complexes of both ligands

Mixed conductivity and stability of CaFe2O4−δ.

The total conductivity of CaFe2O4-delta, studied in the oxygen partial pressure range from 10(-17) to 0.5 atm at 1023-1223 K, is predominantly p-type electronic under oxidizing conditions. The oxygen ion transference numbers determined by the steady-state oxygen permeation and faradaic efficiency measurements vary in the range of 0.2 to 7.2 x 10(-4) at 1123-1273 K, increasing with temperature. No evidence of any significant cationic contribution to the conductivity was found. The Mossbauer spectroscopy, thermogravimetry, and X-ray diffraction (XRD) showed that the orthorhombic lattice of calcium ferrite is essentially intolerant to the oxygen vacancy formation and to doping with lower-valence cations, such as Co and Ni. The oxygen nonstoichiometry (delta) is almost negligible, 0.0046-0.0059 at 973-1223 K and p(O-2) = 10(-5)-0.21 atm, providing a substantial dimensional stability of CaFe2O4-delta ceramics. The average linear thermal expansion coefficients, calculated from the controlled-atmosphere dilatometry and high-temperature XRD data, are (9.6-13.9) x 10(-6) K-1 in the oxygen pressure range from 10(-8) to 0.21 atm at 873-1373 K. Decreasing P(02) results in a modest lattice contraction and in the p-n transition indicated by the conductivity and Seebeck coefficient variations. The phase decomposition of CaFe2O4-delta occurs at oxygen chemical potentials between the low-p(O-2) stability limit of Ca2Fe2O5-delta brownmillerite and the hematite/magnetite boundary in binary Fe-O system. © 2008, Electrochemical Society Inc

Magnetic properties of the U1-xLaxPd2Ga3 series of compounds

Magnetization and specific heat results are reported for the U1-xLaxPd2Ga3 series of compounds. The results show an antiferromagnetic state for 0 <= x <= 0.4; with a structural change occurring around x = 0.15 where T-N shows a jump. For 0.5 <= x <= 0.6 the magnetic state is not clearly defined. For x = 0.7 and 0.8 the system does not order magnetically and exhibit a non-Fermi-liquid behavior. (C) 2003 Published by Elsevier B.V.2721E1E

Microdomain texture and microstructures of Fe⁴⁺-containing CaTi_0.4Fe_0.6O_3-δ

A study of the structure of Fe-1V CaTi0.4Fe0.6O3-delta is presented and compared to data on the Fe-III counterparts. The powder XRD pattern was dominated by a simple cubic perovskite unit cell;, however, some small peaks indicated an orthorhombic distortion. All peaks could be indexed using a space group analogous to the Fe-III phase Ca3TiFe2O8. From HRTEM the strong cubic peaks are well explained by the Superposition of three equivalent and mutually perpendicular orthorhombic unit cells. TEM analysis further revealed a microdomain structure consisting of disordered intergrowths of CaTiO3- and Ca3TiFe2O8-like phases. Mossbauer spectra show that ca. 4% of the Fe cations are in the 4+ oxidation state. Results suggest that the Fe 4+ cations are associated with octahedral coordination and hence are associated with the CaTiO3-like regions, transition regions between the CaTiO3- and Ca3TiFe2O8 intergrown phases and the domain boundaries. Structural models for the intergrowths are proposed based on HRTEM image simulations. (C) 2004 Elsevier Inc. All rights reserved.</p

Transport and magnetic properties of Ce2NiIn3

We report results on transport and magnetic properties for the title compound. Spin-glass (SG) features arise below the temperature of T-f = 2.8 K for Ce2NiIn3, as determined from ac and dc magnetic susceptibility. The low temperature specific heat presents an anomaly with a maximum located near T-f which is unusual when compared with other compounds of the type Ce2TX3 (where T = transition metal and X = Si, Ge) and canonical SG systems. The anisotropic SG behavior or inhomogeneous magnetic ordering have been proposed as the possible causes for the arising magnetic ground state. The results for Ce2NiIn3 are compared with those obtained for Ce2NiGe3, isotypic compound. (c) 2006 Elsevier B.V. All rights reserved.43241671343