Multicore Iron Oxide Mesocrystals Stabilized by a Poly(phenylenepyridyl) Dendron and Dendrimer: Role of the Dendron/Dendrimer Self-Assembly

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change

Cap. 12 L'imposta sulle società

La giustificazione dell'imposta sulle società. Un primo aspetto da chiarire con riguardo dell'imposta sulle società ruota attorno all'ampo dibattito sui motivi che ne giustificano l'introduzione. Perchè esiste l'imposta sulle società

Functionalization of Monodisperse Iron Oxide NPs and Their Properties as Magnetically Recoverable Catalysts

Here we report the functionalization of monodisperse iron oxide nanoparticles (NPs) with commercially available functional acids containing multiple double bonds such as linolenic (LLA) and linoleic (LEA) acids or pyridine moieties such as 6-methylpyridine-2-carboxylic acid, isonicotinic acid, 3-hydroxypicolinic acid, and 6-(1-piperidinyl)­pyridine-3-carboxlic acid (PPCA). Both double bonds and pyridine groups can be reacted with noble metal compounds to form catalytically active species in the exterior of magnetic NPs, thus making them promising magnetically recoverable catalysts. We determined that both LLA and LEA stabilize magnetic iron oxide NPs, allowing the formation of π-complexes with bis­(acetonitrile)­dichloropalladium­(II) in the NP shells. In both cases, this leads to the formation of NP aggregates because of interparticle complexation. In the case of pyridine-containing ligands, only PPCA with two N-containing rings is able to provide NP stabilization and functionalization whereas other pyridine-containing acids did now allow sufficient steric stabilization. The interaction of PPCA-based particles with Pd acetate also leads to aggregation because of interparticle interactions, but the aggregates that are formed are much smaller. Nevertheless, the catalytic properties in the selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol were the best for the catalyst based on LLA, demonstrating that the NP aggregates in all cases are penetrable for DMEC. Easy magnetic separation of this catalyst from the reaction solution makes it promising as a magnetically recoverable catalyst

Multicore Iron Oxide Mesocrystals Stabilized by a Poly(phenylenepyridyl) Dendron and Dendrimer: Role of the Dendron/Dendrimer Self-Assembly

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly­(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change

Multicore Iron Oxide Mesocrystals Stabilized by a Poly(phenylenepyridyl) Dendron and Dendrimer: Role of the Dendron/Dendrimer Self-Assembly

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly­(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change

Zinc-Containing Magnetic Oxides Stabilized by a Polymer: One Phase or Two?

Here we developed a new family of Zn-containing magnetic oxides of different structures by thermal decomposition of Zn­(acac)₂ in the reaction solution of preformed magnetite nanoparticles (NPs) stabilized by polyphenylquinoxaline. Upon an increase of the Zn­(acac)₂ loading from 0.15 to 0.40 mmol (vs 1 mmol of Fe­(acac)₃), the Zn content increases, and the Zn-containing magnetic oxide NPs preserve a spinel structure of magnetite and an initial, predominantly multicore NP morphology. X-ray photoelectron spectroscopy (XPS) of these samples revealed that the surface of iron oxide NPs is enriched with Zn, although Zn species were also found deep under the iron oxide NP surface. For all the samples, XPS also demonstrates the atom ratio of Fe³⁺/Fe²⁺ = 2:1, perfectly matching Fe₃O₄, but not ZnFe₂O₄, where Fe²⁺ ions are replaced with Zn²⁺. The combination of XPS with other physicochemical methods allowed us to propose that ZnO forms an ultrathin amorphous layer on the surface of iron oxide NPs and also diffuses inside the magnetite crystals. At higher Zn­(acac)₂ loading, cubic ZnO nanocrystals coexist with magnetite NPs, indicating a homogeneous nucleation of the former. The catalytic testing in syngas conversion to methanol demonstrated outstanding catalytic properties of Zn-containing magnetic oxides, whose activities are dependent on the Zn loading. Repeat experiments carried out with the best catalyst after magnetic separation showed remarkable catalyst stability even after five consecutive catalytic runs

Polyphenylenepyridyl Dendrons with Functional Periphery and Focal Points: Syntheses and Applications

For the first time we report syntheses of a family of functional polyphenylenepyridyl dendrons with different generations and structures such as focal groups, periphery, and a combination of phenylene and pyridyl moieties in the dendron interior using a Diels–Alder approach and a divergent method. The dendron structure and composition were confirmed using NMR spectroscopy, MALDI-TOF mass spectrometry, FTIR, and elemental analysis. As a proof of concept that these dendrons can be successfully used for the development of nanocomposites, synthesis of iron oxide nanoparticles was carried out in the presence of thermally stable dendrons as capping molecules followed by formation of Pd NPs in the dendron shells. This resulted in magnetically recoverable catalysts exhibiting exceptional performance in selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol (DMVC)