Ferrocene-Modified Polyacrylonitrile-Containing Block Copolymers as Preceramic Materials.

In the pursuit of fabricating functional ceramic nanostructures, the design of preceramic functional polymers has garnered significant interest. With their easily adaptable chemical composition, molecular structure, and processing versatility, these polymers hold immense potential in this field. Our study succeeded in focusing on synthesizing ferrocene-containing block copolymers (BCPs) based on polyacrylonitrile (PAN). The synthesis is accomplished via different poly(acrylonitrile-block-methacrylate)s via atom transfer radical polymerization (ATRP) and activators regenerated by electron transfer ATRP (ARGET ATRP) for the PAN macroinitiators. The molecular weights of the BCPs range from 44 to 82 kDa with dispersities between 1.19 and 1.5 as determined by SEC measurements. The volume fraction of the PMMA block ranges from 0.16 to 0.75 as determined by NMR. The post-modification of the BCPs using 3-ferrocenyl propylamine has led to the creation of redox-responsive preceramic polymers. The thermal stabilization of the polymer film has resulted in stabilized morphologies based on the oxidative PAN chemistry. The final pyrolysis of the sacrificial block segment and conversion of the metallopolymer has led to the formation of a porous carbon network with an iron oxide functionalized surface, investigated by scanning electron microscopy (SEM), energy dispersive X-ray mapping (EDX), and powder X-ray diffraction (PXRD). These findings could have significant implications in various applications, demonstrating the practical value of our research in convenient ceramic material design.

Synthesis, magnetic and NMR spectroscopic properties of the MAl5Pt3 series (M = Ca, Y, La-Nd, Sm-Er).

Following recent investigation in the ternary system Sr-Al-Pt led to the discovery of SrAl5Pt3 which crystallizes in the orthorhombic YNi5Si3 type (Pnma) structure. Interestingly, only two more aluminum representatives, CeAl5Pt3 and EuAl5Pt3, have been reported to adopt this structure type. Therefore, we decided to investigate the existence range of compounds adopting the YNi5Si3 type structure. Besides the already known Sr, Ce and Eu members, the series could be extended to Ca, Y and La-Nd as well as Sm-Er. All compounds were synthesized from the elements and characterized by powder X-ray diffraction. While for CaAl5Pt3 and LaAl5Pt3 also the respective M2Al16Pt9 members were observed, the other compounds could be obtained either as X-ray pure materials or with small amounts of Al3Pt2 as a side phase. The structure of ErAl5Pt3 could be refined from single crystal data, verifying that also the small rare-earth elements adopt the YNi5Si3 type structure. Selected members of the series were furthermore characterized by magnetization and susceptibility measurements. Since YAl5Pt3 could be obtained as a phase pure material and exhibits no paramagnetic behaviour it was investigated by 27Al MAS NMR investigations. Also, XPS measurements were conducted on this compound to gain an insight into the charge distribution. Finally, quantum-chemical calculations supported the NMR measurements and gave an insight into the chemical bonding and the charge distribution.

Synthesis, Physical, and Magnetocaloric Properties of MgZn2-Type Gd2Al3Rh.

Gd2Al3Rh was synthesized from the elements using arc-melting techniques, along with subsequent annealing. The title compound adopts the hexagonal MgZn2 type structure (space group P63/mmc, hP12, Wyckoff sequence hfa) with the Gd atoms found on the Mg positions (4f), the Rh (2a) and Al (6h) atoms occupying the two Zn sites of the prototype. In addition, mixing of Rh and Al on both crystallographic positions is observed. The magnetic susceptibility and magnetization experiments were conducted indicating ferromagnetic ordering below the Curie temperature of TC = 51.3(1) K and very high magnetization of 6.96(1) µB at 3 K and 70 kOe. In addition, heat capacity and electrical resistivity measurements were conducted. The magnetocaloric properties of ferromagnetic Gd2Al3Rh have been determined by means of magnetization measurements. For a field change of ΔH = 0 → 50 kOe the magnetic entropy change equals ΔSMmax = -4.8 J kg-1 K-1, leading to a relative cooling power of RCP = 283 J kg-1 for the same field change. The adiabatic temperature change was estimated to be ΔTadmax = 2.1 K using the heat capacity data.

One-pot Functionalization for the Preparation of Cobaltocene-Modified Redox-Responsive Porous Microparticles.

Porous organic cobaltocenium-containing particles are scarce in literature but highly interesting for their electrochemical properties and reusability in, for example, catalysis or magnetic systems. In this work, we present a scalable one-pot strategy to introduce tailorable amounts of cobaltocenium on a porous substrate, adjusting the electrochemical switching capability. For this purpose, 3-(triethoxysilyl)propan-1-amine (APTES) and ethynyl cobaltocenium hexafluorophosphate is used as functionalization agents for in-situ catalyst-free hydroamination, followed by silane condensation at the particles' surface. Functionalized particles are characterized by attenuated total reflection infrared spectroscopy (ATR-IR), thermogravimetric analysis (TGA), laser scanning confocal microscopy (LSCM), scanning electron microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), powder X-ray diffraction (PXRD) and cyclic voltammetry (CV) showing excellent control over the degree of functionalization, i.e., the added cobaltocenium reagents. The electrochemical stability and good addressability while preserving the porous structure are shown. By utilizing higher amounts of APTES, the overall cobaltocenium amount can be reduced in favor of additional amine groups, strongly affecting the electrochemical behavior, making this functionalization strategy a good platform for metallopolymer immobilization and tailored functionalization. Additionally, thermal treatment of the synthesized metallopolymer microparticles paves the way to magnetic properties with tailorable microporous architectures for end-of-life and upcycling aspects.

On the Ytterbium Valence and the Physical Properties in Selected Intermetallic Phases.

The present review summarizes important aspects of the crystal chemistry of ytterbium-based intermetallic compounds along with a selection of their outstanding physical properties. These originate in many cases from the ytterbium valence. Different valence states are possible here, divalent (4f14), intermediate-valent, or trivalent (4f13) ytterbium, resulting in simple diamagnetic, Pauli or Curie-Weiss paramagnetic, or valence fluctuating behavior. Especially, some of the Yb3+ intermetallics have gained deep interest due to their Kondo or heavy Fermion ground states. We have summarized their property investigations using magnetic and transport measurements, specific heat data, NMR, ESR, and Mössbauer spectroscopy, elastic and inelastic neutron scattering, and XAS data as well as detailed thermoelectric measurements.

Searching for Laves Phase Superstructures: Structural and 27Al NMR Spectroscopic Investigations in the Hf-V-Al System.

Laves phases exhibit a plethora of different structures and a multitude of physical properties. Investigations in the ternary system Hf-V-Al led to the discovery of numerous members of the solid solution Hf(V1-xAlx)2, which adopt the hexagonal MgZn2 type (C14) for medium to high amounts of Al (x = 0.2-1) and the cubic MgCu2 type (C15) for small Al amounts (x = 0.05-0.1). While all members exhibit Pauli-paramagnetic behavior due to the absence of localized magnetic moments, the V-rich cubic member Hf(V0.95Al0.05)2 additionally exhibits a superconducting state below TC = 7.6(1) K. All synthesized compounds were characterized by powder X-ray diffraction, and selected samples were furthermore investigated by 27Al solid-state magic-angle spinning (MAS) NMR. HfAl2 exhibits two Al resonances, one rather sharp and one significantly broadened signal, in line with the crystal structure and respective coordination environments. The members of the solid solution exhibit extremely broadened resonances due to the mixing of V and Al on the same crystallographic sites. For nominal Hf(V0.125Al0.875)2, however, two distinct sharp NMR signals were observed. This contrasts with the description of a solid solution. Therefore, single-crystal X-ray studies were conducted, showing that Hf(V0.125Al0.875)2 really is an ordered compound with the sum formula Hf4VAl7 (P3̅m1), which exhibits an, thus far, unknown superstructure of MgZn2.

Oligo-Condensation Reactions of Silanediols with Conservation of Solid-State-Structural Features.

Oligo- and polysiloxanes are usually prepared by condensation reactions in solvents without control of stereochemistry. Here we present a solventless thermal condensation of stable organosilanols. We investigated the condensation reactions of organosilanediols with different organic substituents, having in common at least one aromatic group. The condensation kinetics of the precursors observed by NMR spectroscopy revealed a strong dependence on temperature, time, and substitution pattern at the silicon atom. SEC measurements showed that chain length increases with increasing condensation temperature and time and lower steric demand of the substituents, which also influences the glass transition temperatures (Tg) of the resulting oligo- or polymers. X-ray diffraction studies of the crystalline silanediols and their condensation products revealed a structural correlation between the substituent location in the crystalline precursors and the formed macromolecules induced by the hydrogen bonding pattern. In certain cases, it is possible to carry out topotactic polymerization in the solid-state, which has its origin in the crystal structure.