Joaquim Marçalo

University of Lisbon, Lisboa, Lisbon, Portugal

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Publications (98)310.32 Total impact

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    ABSTRACT: The reaction of the hexadentate dianionic 1,4,8,11-tetraazacyclotetradecane-based bis(phenolate) ligand, (tBu2ArO)2Me2-cyclam2-, with [SmI2(thf)2] in thf resulted in the formation of the divalent samarium complex [Sm(κ6-{(tBu2ArO)2Me2-cyclam})] (1). X-ray diffraction studies revealed that after recrystallization from n-hexane/thf complex 1 has a monomeric structure and does not contain thf molecules coordinated to the Sm(II) center. However, UV-vis and 1H NMR spectroscopy of 1 evidenced the formation of thf-solvated complexes in neat thf. Reductive studies show that complex 1 can act as a single electron-transfer reagent and form well-defined Sm(III) species. The reaction of 1 with several substrates, namely, TlBPh4, pyridine N-oxide, OPPh3, SPPh3 and bipyridines, are reported. Spectroscopic studies, including NMR, and single crystal X-ray diffraction data are in agreement with the formation of cationic Sm(III) species, monochalcogenide bridged Sm(III) complexes and Sm(III) complexes with bipyridine radical ligand, respectively.
    No preview · Article · Jan 2016 · Dalton Transactions
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    ABSTRACT: A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2 NPh)3 -tacn}U(IV) (η(2) -N2 Ph2 (.) )] (2), was obtained by one-electron reduction of azobenzene by the trivalent uranium compound [U(III) {(SiMe2 NPh)3 -tacn}] (1). Compound 2 was characterized by single-crystal X-ray diffraction and (1) H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single-molecule magnet behaviour for the first time in a mononuclear U(IV) compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single-ion Hamiltonian.
    Full-text · Article · Nov 2015 · Chemistry - A European Journal
  • Leonor Maria · Isabel C. Santos · Vânia R. Sousa · Joaquim Marçalo
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    ABSTRACT: A new monoiodide U(III) complex anchored on a hexadentate dianionic 1,4,8,11-tetraazacyclotetradecane-based bis(phenolate) ligand, [U(κ(6)-{((tBu2)ArO)2Me2-cyclam})I] (1), was synthesized from the reaction of [UI3(THF)4] (THF = tetrahydrofuran) and the respective potassium salt K2((tBu2)ArO)2Me2-cyclam and structurally characterized. Reactivity of 1 toward one-, two-, and four-electron oxidants was studied to explore the reductive chemistry of this new U(III) complex. Complex 1 reacts with one-electron oxidizers, such as iodine and TlBPh4, to form the seven-coordinate cationic uranium(IV) complexes [U(κ(6)-{((tBu2)ArO)2Me2-cyclam})I][X] (X = I (2-I), BPh4 (2-BPh4)). The new uranium(III) complex reacts with inorganic azides to yield the pseudohalide uranium(IV) complex [U(κ(6)-{((tBu2)ArO)2Me2-cyclam})(N3)2] (4) and the nitride-bridged diuranium(IV/IV) complex [(κ(4)-{((tBu2)ArO)2Me2-cyclam})(N3)U(μ-N)U(κ(5)-{((tBu2)ArO)2Me2-cyclam})] (5). Two equivalents of [U(κ(6)-{((tBu2)ArO)2Me2-cyclam})I] (1) effect the four-electron reduction of 1 equiv of PhN═NPh to form the bis(imido) complex [U(κ(4)-{((tBu2)ArO)2Me2-cyclam})(NPh)2] (6) and the U(IV) species 2-I. Moreover, the hemilability of the hexadentate ancillary ligand ((tBu2)ArO)2Me2-cyclam(2-) allows to perform the reductive cleavage of azobenzene with an unprecedented formation of a trans-bis(imido) complex. The complexes were characterized by NMR spectroscopy, and all the new uranium complexes were structurally authenticated by single-crystal X-ray diffraction.
    No preview · Article · Sep 2015 · Inorganic Chemistry
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    ABSTRACT: The gas-phase complexes AnO2(CH3CO2)2(-) are actinyl(V) cores, An(V)O2(+) (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O2 to U(V)O2(CH3CO2)2(-) exothermically produces the superoxide complex U(VI)O2(O2)(CH3CO2)2(-), this oxidation does not occur for Np(V)O2(CH3CO2)2(-) or Pu(V)O2(CH3CO2)2(-) because of the higher reduction potentials for Np(V) and Pu(V). It is demonstrated that NO2 is a more effective electron-withdrawing oxidant than O2, with the result that all three An(V)O2(CH3CO2)2(-) exothermically react with NO2 to form nitrite complexes, An(VI)O2(CH3CO2)2(NO2)(-). The assignment of the NO2(-) anion ligand in these complexes, resulting in oxidation from An(V) to An(VI), is substantiated by the replacement of the acetate ligands in AnO2(CH3CO2)2(NO2)(-) and AnO2(CH3CO2)3(-) by nitrites, to produce the tris(nitrite) complexes AnO2(NO2)3(-). The key chemistry of oxidation of An(V) to An(VI) by the addition of neutral NO2 is established by the substitution of acetate by nitrite. The replacement of acetate ligands by NO2(-) is attributed to a metathesis reaction with nitrous acid to produce acetic acid and nitrite.
    No preview · Article · Aug 2015 · Inorganic Chemistry
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    ABSTRACT: Gas-phase complexes of uranyl(V) ligated to anions X– (X = F, Cl, Br, I, OH, NO3, ClO4, HCO2, CH3CO2, CF3CO2, CH3COS, NCS, N3), [UO2X2]−, were produced by electrospray ionization and reacted with O2 in a quadrupole ion trap mass spectrometer to form uranyl(VI) anionic complexes, [UO2X2(O2)]−, comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO2(OH)2]− to slow [UO2I2]−. The reaction rates of [UO2X2]− ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O2-association complexes. The effect of the basicity of the X– ligands was also apparent in the relative rates for O2 addition, with a general correlation between increasing ligand basicity and O2-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O2 to form the [UO2X2]− anions, indicating weaker binding of the O2– ligand compared to the X– ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations.
    No preview · Article · Mar 2015 · The Journal of Physical Chemistry A
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    ABSTRACT: Several lanthanide and actinide tetranitrate ions, MIII(NO3)4-, were produced by electrospray ionization and subjected to collision induced dissociation in quadrupole ion trap mass spectrometers. The nature of the MO(NO3)3- products that result from NO2 elimination was evaluated by measuring the relative hydrolysis rates under thermalized conditions. Based on the experimental results it is inferred that the hydrolysis rates relate to the intrinsic stability of the MIV oxidation states, which correlate with both the solution IV/III reduction potentials and the fourth ionization energies. Density functional theory computations of the energetics of hydrolysis and atoms-in-molecules bonding analysis of the structures of representative oxide and hydroxide nitrates substantiate the interpretations. The results allow differentiation between those MO(NO3)3- that comprise an O2- ligand with oxidation to MIV and those that comprise a radical O- ligand with retention of the MIII oxidation state. In the particular cases of MO(NO3)3- for M = Pr, Nd and Tb it is proposed that the oxidation states are intermediate between M(III) and M(IV).
    Full-text · Article · Mar 2015 · Physical Chemistry Chemical Physics
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    ABSTRACT: 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.
    Full-text · Article · Feb 2015 · Inorganic Chemistry
  • J. M. Carretas · J. Cui · A. Cruz · I. C. Santos · J. Marçalo
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    ABSTRACT: The X-ray diffraction study of a single crystal with the composition [H2C(3,5-Me2pz)(3,5-Me2pzH)]2[UCl6] (1) is performed. This compound is the product of an attempted synthesis of a bis(pyrazolyl)methane complex of uranium(IV) obtained by the reaction of UCl4 with bis(3,5-dimethylpyrazol-1-yl)methane in THF. 1 crystallizes in the space group P-1 of the triclinic system: a = 9.6616(2) Å, b = 9.6946(2) Å, c = 10.7314(2) Å, α = 107.6210(10)°, β = 115.5600(10)°, γ = 99.6710(10)°, V = 810.45(3) Å3, Z = 1, d calc = 1.765 g/cm3, μ = 5.528 mm-1, R 1 = 0.0249. The structural unit consists of two separated [H2C(3,5-Me2pz)(3,5-Me2pzH)]+ cations and a UCl 62- anion. In the solid state structure of 1 several short intermolecular N-H⋯N and C-H⋯Cl contacts are identified suggesting the presence of hydrogen bonds.
    No preview · Article · Jan 2015 · Journal of Structural Chemistry
  • Joaquim Marçalo · John K. Gibson
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    ABSTRACT: Gas-phase chemistry studies of atomic and molecular rare earth and actinide ions have a well-founded history of more than three decades. In the gas phase, physical and chemical properties of elementary species can be studied in the absence of external perturbations. Due to the relative simplicity of gas-phase systems, compared to condensed-phase systems, solution or solid, it is possible to probe in detail the relationships between electronic structure, reactivity, and energetics, and the information obtained can be compared directly with results from theoretical models. Most of this research involves the use of a variety of mass spectrometry techniques, which provide the capacity to exert precise control over reactants and products. Many new rare earth and actinide molecular and cluster species have been identified that have expanded knowledge of the basic chemistry of these elements and provided links to condensed-phase processes. Several key thermodynamic values have been obtained for numerous elementary molecules. Such fundamental physicochemical studies have provided opportunities for the refinement and validation of computational methods as applied to the particularly challenging 4f lanthanides and 5f actinides. Among other applications, the roles of ligands, solvent molecules, and counterions have been examined at a molecular level. A deeper understanding of plasma chemistry, flame chemistry, radiolysis, and interstellar chemistry has relied on these types of studies. Important applications in analytical and biomedical mass spectrometry have also benefited from discoveries in this area.
    No preview · Article · Dec 2014 · Handbook on the Physics and Chemistry of Rare Earths
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    ABSTRACT: [U(Tp(Me2))2(bipy˙)], a uranium(iii) complex with a radical bipyridine ligand which has magnetic properties with contributions from both the ligand and the metal, presents slow relaxation of the magnetisation at low temperatures, already under zero static magnetic field, and energy barriers slightly above the non-radical analogues.
    Full-text · Article · Jul 2014 · Chemical Communications
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    ABSTRACT: Complementary experimental and computational methods for evaluating relative charge densities of metal cations in gas-phase clusters are presented. Collision induced dissociation (CID) and/or density functional theory computations were performed on anion clusters of composition MM'A(m+n+1)(-), where the two metal ions have formal charge states M(m+) and M'(n+), and A is an anion, NO3(-), Cl(-) or F(-) in this work. Results for alkaline earth and lanthanide metal ions reveal that cluster CID generally preferentially produces MA(m+1)(-) and neutral M'An if the surface charge density of M is greater than that of M': the metal ion with the higher charge density takes the extra anion. Computed dissociation energies corroborate that dissociation occurs via the lowest energy process. CID of clusters in which one of the two metal ions is uranyl, UO2(2+), show that the effective charge density of uranyl is greater than that of alkaline earths and comparable to that of the late trivalent lanthanides; this is in accord with previous solution results for uranyl, from which an effective charge of 3.2+ was derived.
    No preview · Article · Feb 2014 · The Journal of Physical Chemistry A
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    ABSTRACT: 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.
    Full-text · Article · Feb 2014 · Acta Crystallographica Section B: Structural Science
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    ABSTRACT: A challenge in actinide chemistry is activation of the strong bonds in the actinyl ions, AnO2(+) and AnO2(2+), where An = U, Np, or Pu. Actinyl activation in oxo-exchange with water in solution is well established, but the exchange mechanisms are unknown. Gas-phase actinyl oxo-exchange is a means to probe these processes in detail for simple systems, which are amenable to computational modeling. Gas-phase exchange reactions of UO2(+), NpO2(+), PuO2(+), and UO2(2+) with water and methanol were studied by experiment and density functional theory (DFT); reported for the first time are experimental results for UO2(2+) and for methanol exchange, as well as exchange rate constants. Key findings are faster exchange of UO2(2+) versus UO2(+) and faster exchange with methanol versus water; faster exchange of UO2(+) versus PuO2(+) was quantified. Computed potential energy profiles (PEPs) are in accord with the observed kinetics, validating the utility of DFT to model these exchange processes. The seemingly enigmatic result of faster exchange for uranyl, which has the strongest oxo-bonds, may reflect reduced covalency in uranyl as compared with plutonyl.
    No preview · Article · Jan 2014 · Inorganic Chemistry
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    ABSTRACT: The title compound is characterized by magnetic susceptibility measurements.
    No preview · Article · Dec 2013 · ChemInform
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    ABSTRACT: Atomic uranium cations, U(+) and U(2+), reacted with the facile sulfur-atom donor OCS to produce several monopositive and dipositive uranium sulfide species containing up to four sulfur atoms. Sequential abstraction of two sulfur atoms by U(2+) resulted in US2(2+); density functional theory computations indicate that the ground-state structure for this species is side-on η(2)-S2 triangular US2(2+), with the linear thiouranyl isomer, {S═U(VI)═S}(2+), some 171 kJ mol(-1) higher in energy. The result that the linear thiouranyl structure is a local minimum at a moderate energy suggests that it should be feasible to stabilize this moiety in molecular compounds.
    No preview · Article · Nov 2013 · Inorganic Chemistry
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    ABSTRACT: Invited for the cover of this issue is the group of Manuel Almeida at the University of Lisbon. The cover image illustrates the unit cell of a layered dysprosium hydroxide material that is the first example of a layered lanthanide compound showing single-molecule-magnet behavior.
    No preview · Article · Oct 2013 · European Journal of Inorganic Chemistry
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    ABSTRACT: Laser ionization of AnC4 alloys (An = Th, U) yielded gas-phase molecular thorium and uranium carbide cluster cations of composition AnmCn(+), with m = 1, n = 2-14, and m = 2, n = 3-18, as detected by Fourier transform ion-cyclotron-resonance mass spectrometry. In the case of thorium, ThmCn(+) cluster ions with m = 3-13 and n = 5-30 were also produced, with an intriguing high intensity of Th13Cn(+) cations. The AnC13(+) ions also exhibited an unexpectedly high abundance, in contrast to the gradual decrease in the intensity of other AnCn(+) ions with increasing values of n. High abundances of AnC2(+) and AnC4(+) ions are consistent with enhanced stability due to strong metal-C2 bonds. Among the most abundant bimetallic ions was Th2C3(+) for thorium; in contrast, U2C4(+) was the most intense bimetallic for uranium, with essentially no U2C3(+) appearing. Density functional theory computations were performed to illuminate this distinction between thorium and uranium. The computational results revealed structural and energetic disparities for the An2C3(+) and An2C4(+) cluster ions, which elucidate the observed differing abundances of the bimetallic carbide ions. Particularly noteworthy is that the Th atoms are essentially equivalent in Th2C3(+), whereas there is a large asymmetry between the U atoms in U2C3(+).
    No preview · Article · Sep 2013 · Inorganic Chemistry
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    ABSTRACT: The magnetic properties of the layered lanthanide hydroxide Dy 8(OH)20Cl4·6H2O were studied. Below 5 K, slow magnetic relaxation was observed even in the absence of an external field, with a blocking temperature of 3 K and an energy barrier of 36.1 K, a behavior characteristic of single-molecule magnets. Dy8(OH) 20Cl4·6H2O, a layered lanthanide hydroxide, shows slow magnetic relaxation at low temperatures with a blocking temperature of 3 K and an energy barrier of 36.1 K, a behavior characteristic of single-molecule magnets. This is the first example of a layered rare earth compound with such behavior.
    No preview · Article · Sep 2013 · European Journal of Inorganic Chemistry
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    ABSTRACT: Dense 13C pellets were prepared using the spark plasma sintering (SPS) technique. 13C material was used as starting powders with fibre-like shape and heterogeneous fibre diameters of few nanometres to few hundred nanometres. Graphite die and punches were used as a container, and the 13C powder was isolated from both die and punches with pure flexible graphite papyex. Results show that densification starts at 1900°C when the pressure overpasses 60 MPa, and maximum effect has been obtained at the same temperature <80 MPa. The powders were densified to more than ∼90% of the theoretical density by the SPS process. Such 13C pellets are of special interest to prepare actinide or lanthanide carbide intermetallics for spectroscopy studies.
    No preview · Article · Jun 2013 · Material Research Innovations
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    ABSTRACT: The iodouranium(iii) complex with two hydrotris(3,5-dimethylpyrazolyl)borate ligands is shown to adopt three closely related forms in the solid state. In addition to the previously reported structure for [U(Tp(Me2))2I], in which one of the pyrazolyl rings coordinates side-on to the U atom, another structure incorporating solvent molecules presents undistorted pyrazol rings, and a third one is the ionic compound [U(Tp(Me2))2]I. The implications of this structural diversity for the recently reported single ion magnet behaviour in this complex are discussed, namely on the basis of quantum chemistry calculations. The main effect of the bonding of the iodine atom to uranium is the increase of the size of the first coordination sphere and lowering of the symmetry of the molecule, resulting in a smaller crystal field splitting.
    No preview · Article · May 2013 · Dalton Transactions

Publication Stats

1k Citations
310.32 Total Impact Points


  • 2013-2015
    • University of Lisbon
      Lisboa, Lisbon, Portugal
  • 2012-2013
    • Technical University of Lisbon
      • Centro de Química Estrutural (CQE)
      Lisbon, Lisbon, Portugal
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 2001
    • The Immune Tolerance Network
      Seattle, Washington, United States