Our theoretical treatment of electronic structure in coordination complexes often rests on assumptions of symmetry. Experiments rarely provide fully symmetric systems to study. In solution, fluctuation in solvation, variations in...
Lanthanides are found in critical applications from display technology to renewable energy. Often these rare earth elements are used as alloys or functional materials, yet the access to them are...
The structure and solid-state luminescence properties of an EuIII compound with two different lanthanide sites, [Eu(μ-O)5(OH)(H2O)2][Eu(DOTA)(H2O)]2 (DOTA is 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetate, C16H24N4O8), were determined. The compound crystallizes in a laminar structure in the triclinic space group P\overline{1}, where the two sites are a free europium(III) ion and an [Eu(DOTA)(H2O)]− complex. The crystal structure was determined using complex data treatment due to nonmerohedral twinning. Experimental data sets were recorded with large redundancy and separated according to scattering domains in order to obtain a reliable structure. In the first site, the [Eu(DOTA)(H2O)]− complex was found to adopt a capped twisted square-antiprismatic (cTSAP) conformation, where a capping water molecule increased the coordination number of the europium(III) site to nine (CN = 9). In the second site, the europium(III) ion was found to be coordinated by two water molecules, one hydroxide group and five oxide groups from neighbouring [Eu(DOTA)(H2O)]− complexes. The coordination geometry of this site was found to be a compressed square antiprism (SAP) and the coordination number of the europium(III) ion was found to be eight (CN = 8). A large increase in the rate constant of luminescence was observed for EuIII in [Eu(DOTA)(H2O)]− in solid-state luminescence spectroscopy measurements compared to in solution, which led to investigations of single crystals in deuterated media to exclude additional effects of quenching. We conclude that the most probable cause of the decrease in the observed luminescence lifetimes is the high asymmetry of the coordination environment of [Eu(DOTA)(D2O)]− in the [Eu(μ-O)5(OD)(D2O)2][Eu(DOTA)(D2O)]2 crystals.
Despite significant effort, the complexity of europium(III) luminescence in general -and sample composition in particular -has precluded the publication of standard spectra of specific complexes in aqueous solution. Further, low spectral resolution, weighted averages with contributions from several species, as well as poor reproduction hampers the use of literature data, with the note that high quality data from e. g. Bünzli, Latva, Carnall, Parker, Heller, Balzani and Sabatini is from the preelectronic era. Here, luminescence spectra of Eu.DOTA, Eu.EDTA, Eu.DPA 1 , Eu.DPA 2 . Eu.DPA 3 , Eu.DTPA and the Eu(III) aqua ion was determined in samples with known pH and conductivity. The ligand concentrations were varied in a buffered medium (MES) with a significant salt background. In this manner, full complexation could be ensured, while pH and ionic strength were monitored. The spectra corresponding to the complexes were extracted, and the electronic structure of the ground state 7 F J manifold was investigated and contrasted to literature data. All spectroscopic data is made available and we suggest this becomes part of the standard procedure when investigating lanthanide(III) complexes.
surface sites. Each metal has a specific binding affinity toward the adsorbates involved in each catalytic reaction, which allows for selective tuning and optimization of catalytic processes via consideration of the incorporated metals. [1] In a binary disordered alloy, two metals randomly occupy symmetry equivalent sites in the crystal lattice, while the metals in an intermetallic structure occupy the crystallographic sites in the structure in a nonrandom arrangement at a specific atomic stoichiometry. [2] Alloys and intermetallics are known to have very different properties for catalysis. For example, intermetallic NPs composed of Pd and Cu have been observed to display superior catalytic activities in the CO 2 reduction reaction and oxygen reduction reaction over disordered face-centered cubic (fcc) alloys of the same composition, which has been attributed to changes in the electronic surface structure owing to the differences in local atomic arrangements. [3,4] In order to explore and implement the improved catalytic properties accessible in intermetallic NPs, it is crucial that the NP structure is controlled to promote only the most catalytically active structure. This degree of control can be obtained only if we understand how intermetallic NPs are formed, and which synthetic conditions dictate the resulting structure. Previous studies have indicated that the formation of intermetallic PdCu NPs proceeds through a disorder-order transformation, Intermetallic nanoparticles (NPs) have shown enhanced catalytic properties as compared to their disordered alloy counterparts. To advance their use in green energy, it is crucial to understand what controls the formation of intermetallic NPs over alloy structures. By carefully selecting the additives used in NP synthesis, it is here shown that monodisperse, intermetallic PdCuNPs can be synthesized in a controllable manner. Introducing the additives iron(III) chloride and ascorbic acid, both morphological and structural control can be achieved. Combined, these additives provide a synergetic effect resulting in precursor reduction and defect-free growth; ultimately leading to monodisperse, single-crystalline, intermetallic PdCu NPs. Using in situ X-ray total scattering, a hitherto unknown transformation pathway is reported that diverges from the commonly reported coreduction disorder-order transformation. A Cu-rich structure initially forms, which upon the incorporation of Pd(0) and atomic ordering forms intermetallic PdCu NPs. These findings underpin that formation of stoichiometric intermetallic NPs is not limited by standard reduction potential matching and coreduction mechanisms, but is instead driven by changes in the local chemistry. Ultimately, using the local chemistry as a handle to tune the NP structure might open new opportunities to expand the library of intermetallic NPs by exploiting synthesis by design.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smtd.202200420.
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