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QEf achievements

PROBING HIGH OXIDATION STATES IN THE LANTHANIDE SERIES

G5 1

 

Lanthanide (Ln) chemistry is dominated by the +3 oxidation state, although some Ln show significant +2 and +4 chemistry. Recently, the synthesis of molecular Pr(V) species, in the gas phase and/or in noble-gas matrices, was reported. We have previously demonstrated that [Ln(NO3)4]- complexes, produced by ESI-QIT-MS, yield [LnO(NO3)3]- species by collision-induced dissociation (CID) after NO2 elimination, and that their relative hydrolysis behavior is related to the stability of the Ln +4 oxidation states. For Ce, Pr and Nd, it was possible to form [LnO2(NO3)2]- ions by subsequent CID of [LnO(NO3)3]-, and these anions revealed different reactivities with water, namely, hydrolysis for Ce, hydration for Nd and no reactivity for Pr. These differences seem to indicate that Pr is in a stable +5 oxidation state, which was confirmed by ab initio computations. Pr(V) is clearly accessible and higher oxidation state lanthanide chemistry could be richer than previously supposed.

NANOSTRUCTURED BIMETALLIC OXIDES AND INTERMETALLIC COMPOUNDS CONTAINING F-BLOCK ELEMENTS

G5 2aG5 2b

We continued our work on the preparation by electrospinning and characterization of nanoparticles and nanofibers of intermetallic compounds and bimetallic oxides containing f-block elements (lanthanides, Th and U), copper or nickel. The preparation and characterization of thermoelectric materials such as metal borides, pnictides and chalcogenides was also undertaken. Electrospinning is a reproducible and low cost route that enables the production of nanostructured materials, which expected high surface areas and tunable surface properties bring benefits to their properties. Applications of these compounds were studied: i) studies in heterogeneous phase catalysis for the production of value added products, such as methane, using primary pollutants, such as CO2 as feedstock, Figure a, and ii) for the generation and storage of energy, application as thermoelectric materials (CuxSy) and hydrogen absorbers (important for the development of fuel cells), Figure b.

CO2 AS RAW MATERIAL FOR THE PRODUCTION OF METHANE

G5 3

The use of CO2 as chemical feedstock is limited to a few processes: synthesis of urea (for nitrogen fertilizers and plastics), salicylic acid (a pharmaceutical ingredient), and polycarbonates (for plastics). In this context, the hydrogenation of CO2 to methane is a major catalytic goal. The methanation of carbon dioxide has a range of applications including: i) the purification of synthesis gas for the production of ammonia, ii) the production of syngas or iii) their use to convert the Martian CO2 atmosphere into CH4 and H2O for fuel and astronaut life support systems. In this work, production of methane was achieved in a continuous atmospheric pressure flow reactor using carbon dioxide and hydrogen as reagents (250 - 500 oC, GHSV=15000 mLCO2/g.h and H2/CO2=4 mol:mol). The results confirm the potentialities of the bimetallic oxides and intermetallic compounds containing f-block elements as catalysts, especially when compared with the behavior of a commercial rhodium hydrogenation catalyst (5%Rh/Al2O3) used as reference. The Figure shows the results of methane synthesis over nanoparticles of nickel bimetallic oxides containing f block elements at 400 oC.

EU(III)-BASED IONIC LIQUIDS:  A THERMOCHROMIC AND SELF-ORGANIZATION CASES IN A FAMILY OF HIGHLY EMISSIVE EU(III) TETRAKIS-Β-DIKETONATE IONIC LIQUIDS WITH AN ALKYLPHOSPHONIUM AS COUNTER-ION

G5 5

This work identified the first example of an observable and reversible case of thermochromism of an Eu(III) room temperature ionic liquid, [P6,6,6,14][Eu(fod)4] (1). This thermochromism is characterized by the conversion from light yellow (room temperature) to a reddish hue (ca. 80 ºC) due to an unusual interaction between one fod ligand and the phosphonium counter-ion. The reversibility of this optical effect presents applicability as an alcohol sensor adressing the “Food security, (…)” societal challenge (Backcover Picture - Chem. Commun., 2017, 53, 850-853). By changing the β-diketonate of the Eu(II) complex we extended the studies to the self-organization of the family 1, [P6,6,6,14][Eu(fod)3(dbm)] (2) and [P6,6,6,14][Eu(dbm)4] (3) highlighting the role of the cation [P6,6,6,14]+. The luminescence quantum yields determined for 1, 2, and 3 are 34%, 59%, and 64%, respectively, with the highest values being comparable with the maximum values previously reported for complexes of the same type.

U…H-B AGOSTIC INTERACTIONS IN HOMOLEPTIC URANIUM(IV) BIS(MERCAPTOIMIDAZOLYL)BORATE COMPLEXES

G5 4

The choice of the ancillary ligand is crucial for the stabilization of metal complexes in various oxidation states and in promoting innovative reactivity. In a previous work in our lab, monoanionic hydrobis(mercaptoimidazolyl)borate ligands showed their ability to stabilize trivalent uranium complexes. Studies were pursued in order to access complexes with uranium in other oxidation states. Oxidation reactions of the trivalent uranium complex [UI(k3-{H(Ph)B(timMe)2})2] provided access to the new homoleptic cationic uranium(IV) complexes [U(k3-{H(Ph)B(timMe)2})3][X] (X = BPh4, I; timMe = 2-mercapto-1-methylimidazolyl). Multinuclear NMR and IR spectroscopies and X-ray diffraction analysis were consistent with a k3-H,S,S coordination mode for the three hydrobis(mercaptoimidazolyl)borate ligands, favoring nine-coordinated U(IV) complexes in tricapped trigonal prismatic geometries. These recent results expand the field of non-aqueous uranium chemistry with soft donor ligands and demonstrate that hydrobis(mercaptoimidazolyl)borate ligands can also form robust complexes with U4+ ions.

LAYERED EUROPIUM HYDROXIDE SYSTEM FOR PHOSPHOROUS SENSING AND REMEDIATION

G5 6

Addressing the societal challenge “Climate action, environment, resource efficiency and raw materials”, we performed an experimental study of a dual-channel sensor towards anions formed by a LEuH material intercalated with 2,6-naphtalene dicarboxilate (LEuH-2,6-NDC). The sensor was tested with several biological relevant anions and the changes in NDC and europium emission intensities, upon excitation of NDC, were studied. Phosphate was found to have the highest degree of intercalation and displayed a strong increase (400%) on the fluorescence intensity of NDC. Intercalation of phosphate was further confirmed with Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES). Taking advantage of LEuH selectivity towards phosphate, its applicability in phosphorus remediation was studied presenting high sequestration capacity followed by controlled release of phosphate in three consecutive cycles and improved stability of the LEuH host material. These results highlight the significant potential of LLHs as new scavenging agents for inorganic phosphate.

  1. MEMBRANES WITH A LOW LOADING OF METAL–ORGANIC FRAMEWORK-SUPPORTED IONIC LIQUIDS FOR CO2/N2 SEPARATION IN CO2 CAPTURE
  2. MOLECULAR ENERGETICS
  3. RARE EARTH RECOVERY AND VALORISATION AND PROTECTION OF ENVIRONMENT
  4. Rare Earth Recovery and Valorisation and Protection of Environment