Bernardo Monteiro

Magnetic Properties of the Layered Lanthanide Hydroxide Series YxDy8-x(OH)20Cl4·6H2O: From Single Ion Magnets to 2D and 3D Interaction Effects

The magnetic properties of layered dysprosium hydroxides, both diluted in the diamagnetic yttrium analogous matrix (LYH:0.04Dy), and intercalated with 2,6-naphthalene dicarboxylate anions (LDyH-2,6-NDC), were studied and compared with the recently reported undiluted compound (LDyH = Dy8(OH)20Cl4·6H2O). The Y diluted compound reveals a single-molecule magnet (SMM) behavior of single Dy ions, with two distinct slow relaxation processes of the magnetization at low temperatures associated with the two main types of Dy sites, 8- and 9-fold coordinated. Only one relaxation process is observed in both undiluted LDyH and intercalated compounds as a consequence of dominant ferromagnetic Dy-Dy interactions, both intra- and interlayer. Semiempirical calculations using a radial effect charge (REC) model for the crystal field splitting of the Dy levels are used to explain data in terms of contributions from the different Dy sites. The dominant ferromagnetic interactions are explained in terms of orientations of easy magnetization axes obtained by REC calculations together with the sign of the superexchange expected from the Dy-O-Dy angles.

Investigation of Layered Double Hydroxides Intercalated by Oxomolybdenum Catecholate Complexes

Oxomolybdenum(VI) complexes of 3,4-dihydroxybenzoic acid (3,4-H 2dhb) have been incorporated into layered double hydroxides (LDHs) by treatment of the LDH-nitrate (Zn-Al, Mg-Al) or LDH-chloride (Li-Al) precursors with aqueous or water/ethanol solutions of the complex (NMe 4) 2[MoO 2(3,4-dhb) 2].2H 2O at 50 or 100 degrees C. The texture and chemical composition of the products were investigated by elemental analysis and scanning electron microscopy (SEM) with coupled energy dispersive spectroscopy (EDS). Microanalysis for N and EDS analysis for Cl showed that at least 90% of nitrate or chloride ions were replaced during the ion exchange reactions. The final Mo content in the materials varied between 6.5 and 11.6 wt %. Mo K-edge EXAFS analysis, supported by IR, Raman, UV-vis, and (13)C{ (1)H} CP/MAS NMR spectroscopic studies, showed the presence of cointercalated [MoO 2(3,4-dhb) 2] ( m- ) and [Mo 2O 5(3,4-dhb) 2] ( m- ) complexes in proportions that depend on the type of LDH support and the reaction conditions. The binuclear bis(catecholate) complex, with a Mo...Mo separation of 3.16 A, was the major species intercalated in the Zn-Al and Li-Al products prepared using only water as solvent. The X-ray powder diffraction (XRPD) patterns of all the Mo-containing LDHs showed the formation of an expanded phase with a basal spacing around 15.4 A. High-resolution synchrotron XRPD patterns were indexed with hexagonal unit cells with a c-axis of either 30.7 (for Li-Al-Mo LDHs) or 45.9 A (for a Zn-Al-Mo LDH). Fourier maps ( F obs) calculated from the integrated intensities extracted from Le Bail profile decompositions indicated that the binuclear guest species are positioned such that the Mo --> Mo vector is parallel to the host layers, and the overall orientation of the complex is perpendicular to the same layers. The thermal behavior of selected materials was studied by variable-temperature XRPD, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).

Metal-organic frameworks based on uranyl and phosphonate ligands

Three new crystalline metal-organic frameworks have been prepared from the reaction of uranyl nitrate with nitrilotris(methylphosphonic acid) [H6nmp, N(CH2PO3H2)3], 1,4-phenylenebis(methylene)diphosphonic acid [H4pmd, C6H4(PO3H2)2], and (benzene-1,3,5-triyltris(methylene))triphosphonic acid [H6bmt, C6H3(PO3H2)3]. Compound [(UO2)2F(H3nmp)(H2O)]·4H2O (I) crystallizes in space group C2/c, showing two crystallographically independent uranyl centres with pentagonal bipyramidal coordination geometries. While one metal centre is composed of a {(UO2)O3(μ-F)}2 dimer, the other comprises an isolated {(UO2)O5} polyhedron. Compound [(UO2)(H2pmd)] (II) crystallizes in space group P21/c, showing a centrosymmetric uranyl centre with an octahedral {(UO2)O4} coordination geometry. Compound [(UO2)3(H3bmt)2(H2O)2]·14H2O (III) crystallizes in space group P\bar 1, showing two crystallographically independent uranyl centres. One uranyl centre is a {(UO2)O5} pentagonal bipyramid similar to that in (I), while the other is a {(UO2)O4} centrosymmetric octahedron similar to that in (II). Compounds (I) and (III) contain solvent-accessible volumes accounting for ca 23.6 and 26.9% of their unit-cell volume, respectively. In (I) the cavity has a columnar shape and is occupied by disordered water molecules, while in (III) the cavity is a two-dimensional layer with more ordered water molecules. All compounds have been studied in the solid state using FT-IR spectroscopy. Topological studies show that compounds (I) and (III) are trinodal, with 3,6,6- and 4,4,6-connected networks, respectively. Compound (II) is instead a 4-connected uninodal network of the type cds.

Heterometallic 3d-4f SMMs

Abstract Single-molecule magnetism (SMM) is considered nowadays to be an open, challenging research topic not only due to the fundamental physics and chemistry involved but also due to the unique potential of SMMs in molecule-based information storage, quantum computing, and spin-based electronic devices. After a brief introduction to the SMM research field, the advantages of combining transition metals with lanthanides in order to design 3d-4f SMMs with high anisotropy barriers will be emphasized. Their characteristics as SMMs depend on the combination of the single-ion anisotropies of all the paramagnetic metal centers involved and on the presence of the 3d-4f exchange interactions. In a tutorial style, intended for a general chemistry audience, the synthetic strategies and the resulting magnetic behavior of these compounds will be highlighted, taking into account the intrinsic properties of the d metal ions involved and the role played by the contributions of both d and f electrons to tune the orbitals of the trivalent lanthanide ions involved. The reported systems will mainly be discussed in terms of the contributions of the intrinsic properties of the 3d paramagnetic manganese, copper, and iron, followed by the contributions of 4f ions.

Ln(III)-based SIMs

Abstract Single-ion magnets (SIMs) are molecular compounds that have gained increasing relevance due to their potential applications in spintronics, quantum computing, and high-density information storage. Slow magnetic relaxation in a mononuclear lanthanide (Ln) complex was first reported in 2003. The fact that these compounds present the highest relaxation energy barriers for the reversal of the magnetization and blocking temperatures up to date makes them the most studied family of SIMs. Their unquenched orbital moment and strong spin-orbit coupling promote anisotropic magnetic properties in a ligand field, allowing the occurrence of slow relaxation of the magnetization. In this chapter, a brief state of the art concerning this class of molecular magnets will be presented, followed by the reasons that led to the switch of strategy from large spins to large anisotropies that accompanied the arising of SIMs as the second generation of single-molecule magnets (SMMs). This advent arrived with the introduction of f elements, mainly lanthanides, associated with the notion of mononuclearity. Additionally, the electronic configuration of some Ln 3+ ions offers advantages due to their very well-defined emission wavelengths that cover a large spectroscopic range. When linked to selected organic ligands, they can be useful in practical applications as bifunctional magnetic luminescent materials.

Impact on CO2/N2 and CO2/CH4 Separation Performance Using Cu-BTC with Supported Ionic Liquids-Based Mixed Matrix Membranes

The efficient separation of gases has industrial, economic, and environmental importance. Here, we report the improvement in gas separation performance of a polyimide-based matrix (Matrimid®5218) filled with a Cu-based metal organic framework [MOF, Cu3(BTC)2] with two different ionic liquids (ILs) confined within the pores. The chosen ILs are commonly used in gas solubilization, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]), and the incorporation of the [EMIM][BF4]@Cu-BTC and [EMIM][OTf]@Cu-BTC composites in Matrimid®5218 proved to be an efficient strategy to improve the permeability and selectivity toward CO2/N2 and CO2/CH4 mixtures.

Redetermination of dipotassium μ-oxo-bis­[aqua­(oxalato-κ2O,O′)dioxomolybdate(VI)] at 150 K

The crystal structure of title compound, K2[Mo2O5(C2O4)2(H2O)2], originally determined by Cotton, Morehouse & Wood [(1964). Inorg. Chem. pp. 1603–1608], has been redetermined to higher precision and the hydrogen-bonding network elucidated. The anionic [Mo2O5(C2O4)2(H2O)2]2− complex ion is centrosymmetric with the μ2-bridging O atom located at the inversion centre.