Oxide-oxide galvanic displacement reactions: Effect of the concentration of the ions released by the sacrificial oxide

Abstract Galvanic displacement reactions between a solid oxide and a dissolved metal cation are interesting processes for the preparation of oxide nanoparticles or electrocatalytic layers consisting of secondary mixed oxides. Their mechanism is not yet fully clarified. The composition of the secondary mixed oxides and their growth rate depend on many physical and chemical variables. In the present study, we have focused on the effects of the concentration of the ions released from the sacrificial oxide to the solution, when they are intentionally added to reaction media. We have studied the displacement of sacrificial PbO2 by either Mn2+ or Co2+ cations in acetate solution that contained variable concentrations of Pb2+, using electrochemical methods, SEM-EDS and XPS. The evolution of the open circuit potential of the systems was monitored during the reactions. We have found that, for both divalent cations, increasing concentrations of Pb2+ ions in the acetate solutions caused the formation of mixed oxides richer in Pb. Effects on growth rate and equilibrium potential were different for Mn2+ and Co2+

Varying spin state composition by the choice of capping ligand in a family of molecular chains: detailed analysis of magnetic properties of chromium(III) horseshoes

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Origin of the unusual ground-state spin S = 9 in a Cr10 single-molecule magnet

The molecular wheel [Cr10(OMe)20(O2CCMe3)10], abbreviated {Cr10}, with an unusual intermediate total spin S = 9 and non-negligible cluster anisotropy, D/kB = −0.045(2) K, is a rare case among wheels based on an even number of 3d-metals, which usually present an antiferromagnetic (AF) ground state (S = 0). Herein, we unveil the origin of such a behavior. Angular magnetometry measurements performed on a single crystal confirmed the axial anisotropic behavior of {Cr10}. For powder samples, the temperature dependence of the susceptibility plotted as χT(T) showed an overall ferromagnetic (FM) behavior down to 1.8 K, whereas the magnetization curve M(H) did not saturate at the expected 30 μB/fu for 10 FM coupled 3/2 spin Cr3+ ions, but to a much lower value, corresponding to S = 9. In addition, the X-ray magnetic circular dichroism (XMCD) measured at high magnetic field (170 kOe) and 7.5 K showed the polarization of the cluster moment up to 23 μB/fu. The magnetic results can be rationalized within a model, including the cluster anisotropy, in which the {Cr10} wheel is formed by two semiwheels, each with four Cr3+ spins FM coupled (JFM/kB = 2.0 K), separated by two Cr3+ ions AF coupled asymmetrically (J23/kB = J78/kB = −2.0 K; J34/kB = J89/kB = −0.25 K). Inelastic neutron scattering and heat capacity allowed us to confirm this model leading to the S = 9 ground state and first excited S = 8. Single-molecule magnet behavior with an activation energy of U/kB = 4.0(5) K in the absence of applied field was observed through ac susceptibility measurements down to 0.1 K. The intriguing magnetic behavior of {Cr10} arises from the detailed asymmetry in the molecule interactions produced by small-angle distortions in the angles of the Cr–O–Cr alkoxy bridges coupling the Cr3+ ions, as demonstrated by ab initio and density functional theory calculations, while the cluster anisotropy can be correlated to the single-ion anisotropies calculated for each Cr3+ ion in the wheel.The authors acknowledge financial support from the Spanish Agencia Estatal de Investigación, through Projects MAT2017-83468-R (AEI/FEDER, UE) and PID2020-115159GB-I00/AEI/10.13039/501100011033, Aragonese Project RASMIA E12_20R (co-funded by Fondo Social Europeo) and of the European Union FEDER (ES). Also University of Padova Grants P-DISC#09BIRD2019-UNIPD SMOW.Peer reviewe

A new biogenerated Rh-based catalyst for aqueous biphasic hydroformylation

A new bio-generated rhodium based system embedded in a peculiar polysaccharide matrix (Rh-EPS), was obtained and purified from cultures of bacterial cells of Klebsiella oxytoca DSM 29614. The product was analyzed with different techniques to obtain information on its structure-property correlation. In order to determine its catalytic activity and selectivity in the aqueous biphasic hydroformylation some olefins were chosen as model substrates, obtaining fine-good results.A new bio-generated rhodium based system embedded in a peculiar polysaccharide matrix (Rh-EPS), was obtained and purified from cultures of bacterial cells of Klebsiella oxytoca DSM 29614. The product was analyzed with different techniques to obtain information on its structure-property correlation. In order to determine its catalytic activity and selectivity in the aqueous biphasic hydroformylation some olefins were chosen as model substrates, obtaining fine-good results

Complessi polinuclearim a catena di cromo (III): sintesi e proprietà magnetiche

The work carried out adresses the synthesis, the characterization and the interpretation of the magnetic properties of a new family of chromium (III) polinuclear complexes. The synthesis of chromium chains of different length, their supramolecular assemblies and their chemistry have been througly investigated. In particular, the possibility to template both the length and the supramolecular architecture, by changing the nature of only one reagent (the amine), has been demonstrated. This strategy has led to isolate some components of a larger family of chromium molecular chains described by the general formula: {[CrxFx+5(O2CR)2x-2][NH2R2]3}n. By investigating the chemistry of these systems, a route to produce isolated molecular finite chain has been found. The reaction occurs through a simple exchange reaction between terminal fluorides and ?-diketone ligands. The possibility to obtain finite molecular chains is very intriguing since the magnetic properties of these compounds are not yet fully explored and investigated. Real examples of onedimensional “spin segments” are still lacking in the literature. Furthermore, it has been demonstrated that the horseshoes systems can act as cluster ligands leading to new and unpredictable heteronuclear clusters. Magnetic susceptibility and Inelastic Neutron Scattering (INS) measures have revealed as in the finite molecular chains the special boundary conditions imposed at the terminations may strongly influence the isotropic exchange and the spin exitations. From these data the exchange costants and the single ion anisotropy parameter have been derived. INS spectra at low temeperature can be rationalize with the picture of L&E bands and spin waves can be observed. Moreover, EPR at different frequencies and temperature has shown rich spectra. EPR studies allow further characterisation of the spin Hamiltonian parameters of these chromium chains.Il lavoro qui presentato si è focalizzato sulla sintesi, la caratterizzazione e l’interpretazione delle prorprietà magnetiche di una nuova famiglia di complessi polinucleari di cromo (III). In partcolare, è stata attentamente studiata la sintesi di complessi di cromo a catena con diverse lunghezze, la loro aggregazione supramolecolare e la loro chimica ed è stato dimostrato come sia possibile controllare la lunghezza e l’aggregazione supramolecolare delle catene mediante sintesi templata. Questa strategia ha portato ad isolare alcuni componenti di una famiglia di complessi a catena di formula generale: {[CrxFx+5(O2CR)2x-2][NH2R2]3}n. Investigando la chimica di questi sistemi, è stata identificata una via sintetica, per produrre una seconda tipologia di catene molecolari di cromo (III), basata su una reazione di scambio tra leganti ?-dichetonati e i fluoruri terminali presenti sui complessi a catena. La possibilità di ottenere catene molecolari di dimensione finita è di notevole interesse poiché le proprietà magnetiche di questi sistemi non sono state ancora completamente esplorate. I composti sintetizzati rappresentano uno dei primi esempi, riportati in letteratura, di complessi a catena di dimensioni finite. Inoltre, è stato dimostrato come questi sistemi possono agire da leganti verso altri centri metallici e portare alla formazione di nuovi composti eteronucleari. Misure di suscettività magnetica e di scattering neutronico anelastico (INS) hanno rivelato come l’accopiamento isotropo e le eccitazioni di spin siano fortemente influenzati dalla struttura a catena aperta, specie se confrontati con gli analoghi ad anello. Da questi studi è stato anche possibile ricavare le costanti di scambio isotropo e i parametri di anisotropia dello ione cromo (III). Gli spettri INS a bassa temperatura sono stati interpretati con il modello delle bande L ed E e consentono di osservare eccitazioni di spin dovute alle cosiddette onde di spin. Infine, misure EPR multifrequenza, a basse temperature, hanno permesso un’ulteriore caratterizzazione dei parametri dell’Hamiltoniano di spin di questi complessi polinucleari a catena

A Zn(II) Metallocycle as Platform to Assemble a 1D + 1D → 1D Polyrotaxane via π···π Stacking of an Ancillary Ligand

A new [Zn2L2] metallocycle bearing two metal centers that can coordinate ancillary ligands and a pocket suitable to host guest molecules is reported. These two features are exploited by reacting the metallocycle with a pyridine ligand to self-assemble in the solid state an extended intertwined system with the rare 1D + 1D → 1D topology. This interpenetrated architecture is supported by π···π stacking between two pyridine units of two different metallocycles in the pocket of a third metallocycle

Helicate versus Mesocate in Quadruple-Stranded Lanthanide Cages: A Computational Insight

To drive the synthesis of metallo-supramolecular assemblies (MSAs) and to fully exploit their functional properties, robust computational tools are crucial. The capability to model and to rationalize different parameters that can influence the outcome is mandatory. Here, we report a computational insight on the factors that can determine the relative stability of the supramolecular isomers helicate and mesocate in lanthanide-based quadruple-stranded assemblies. The considered MSAs have the general formula [Ln2L4]2− and possess a cavity suitable to allocate guests. The analysis was focused on three different factors: the ligand rigidity and the steric hindrance, the presence of a guest inside the cavity, and the guest dimension. Three different quantum mechanical calculation set-ups (in vacuum, with the solvent, and with the solvent and the dispersion correction) were considered. Comparison between theoretical and experimental outcomes suggests that all calculations correctly estimated the most stable isomer, while the inclusion of the dispersion correction is mandatory to reproduce the geometrical parameters. General guidelines can be drawn: less rigid and less bulky is the ligand and less stable is the helicate, and the presence of a guest can strongly affect the isomerism leading to an inversion of the stability by increasing the guest size when the ligand is flexible