Magnetic Ordering in Tetragonal 3d Metal Arsenides M2As (M = Cr, Mn, Fe): An Ab Initio Investigation

The electronic and magnetic structures of the tetragonal Cu2Sb-type 3d metal arsenides (M2As, M = Cr, Mn, Fe) were examined using density functional theory to identify chemical influences on their respective patterns of magnetic order. Each compound adopts a different antiferromagnetic (AFM) ordering of local moments associated with the 3d metal sites, but every one involves a doubled crystallographic c-axis. These AFM ordering patterns are rationalized by the results of VASP calculations on several magnetically ordered models using a × a × 2c supercell. Effective exchange parameters obtained from SPRKKR calculations indicate that both direct and indirect exchange couplings play essential roles in understanding the different magnetic orderings observed. The nature of nearest-neighbor direct exchange couplings, that is, either ferromagnetic (FM) or AFM, were predicted by analysis of the corresponding crystal orbital Hamilton population (COHP) curves obtained by TB-LMTO calculations. Interestingly, the magnetic structures of Fe2As and Mn2As show tetragonal symmetry, but a magnetostrictive tetragonal-to-orthorhombic distortion could occur in Cr2As through AFM Cr1–Cr2 coupling between symmetry inequivalent Cr atoms along the a-axis, but FM coupling along the b-axis. A LSDA+U approach is required to achieve magnetic moment values for Mn2As in better agreement with experimental values, although computations always predict the moment at the M1 site to be lower than that at the M2 site. Finally, a rigid-band model applied to the calculated DOS curve of Mn2As correctly assesses the magnetic ordering patterns in Cr2As and Fe2As

Identifying a Structural Preference in Reduced Rare-Earth Metal Halides by Combining Experimental and Computational Techniques

The structures of two new cubic {TnLa3}Br3 (Tn = Ru, Ir; I4132, Z = 8; Tn = Ru: a = 12.1247(16) Å, V = 1782.4(4) Å3; Tn = Ir: a = 12.1738(19) Å, V = 1804.2(5) Å3) compounds belonging to a family of reduced rare-earth metal halides were determined by single-crystal X-ray diffraction. Interestingly, the isoelectronic compound {RuLa3}I3 crystallizes in the monoclinic modification of the {TnR3}X3 family, while {IrLa3}I3 was found to be isomorphous with cubic {PtPr3}I3. Using electronic structure calculations, a pseudogap was identified at the Fermi level of {IrLa3}Br3 in the new cubic structure. Additionally, the structure attempts to optimize (chemical) bonding as determined through the crystal orbital Hamilton populations (COHP) curves. The Fermi level of the isostructural {RuLa3}Br3 falls below the pseudogap, yet the cubic structure is still formed. In this context, a close inspection of the distinct bond frequencies reveals the subtleness of the structure determining factors

СЛОВО ПРО ПРОФЕСОРА В. В. КРУТІКОВА

The electronic structures of “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), in connection to the recently synthesized Ti9-nFe2+nRu18B8 (n = 1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Through a combination of calculations on specific models and using the rigid band approximation, which is validated by the DOS curves for “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), mixing of Fe and Ti is anticipated at both the 2b- and 4h-chain sites. The model “Ti8.5Fe2.5Ru18B8” (n = 0.5) revealed that both Brewer-type Ti−Ru interactions as well as ligand field splitting of the Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using “Ti6Fe5Ru18B8” (n = 3). A rigid band analysis of the LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ≤ 0.75) and ferrimagnetic ordering at higher Fe content (n \u3e 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fe1-ladder and 4h-chain sites

C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate

C–H insertion reactions between different substrates and diazo reagents were catalyzed by tetratolylporphyrinato methyliridium (Ir(TTP)CH3). The highest yields were achieved for reactions between the bulky diazo reagent methyl 2-phenyldiazoacetate (MPDA) and substrates containing electron-rich C–H bonds. An intermediate metalloporphyrin complex was identified as a metal–carbene complex, Ir(TTP)(═C[Ph]CO2CH3)(CH3) (4), using 1H NMR and UV/vis absorption spectroscopy. The presence of 4 was further supported by computationally modeling the absorption spectra with time-dependent DFT (6-31G(d,p)/SBKJC basis set, PBE0 functional). Kinetic studies for C–H insertion reactions using different substrates showed substantial differences in the rate of MPDA consumption, suggesting that carbene transfer is rate-limiting. Furthermore, primary kinetic isotope effects of 3.7 ± 0.3 and 2.7 ± 0.4 were measured using toluene and cyclohexane, respectively. These data are consistent with a mechanism that involves direct C–H insertion rather than a radical rebound pathway

Impact of Early Sport Specialization on Interscholastic Athletes and Programs

Early sport specialization (ESS) is a popular pathway for athletic development with implications for enhanced skill acquisition but also adverse mental and physical outcomes (LaPrade et al., 2016). As such, adolescent athletes may face a dilemma regarding whether to play multiple sports or immediately narrow the focus to one. Coaches are positioned to influence motivational climates and sport-specific skill development (Amorose & Anderson-Butcher, 2007), making it important to understand their perceptions of ESS. Interviews were conducted with thirteen coaches of girls’ volleyball and basketball teams to gain an understanding of ESS as it pertains to athletes and programs at the interscholastic level. Participants identified influences and impacts of ESS, specifically how it can affect participation and competitiveness of interscholastic sports.        &nbsp

Impact of Early Sport Specialization on Interscholastic Athletes and Programs

Early sport specialization (ESS) is a popular pathway for athletic development with implications for enhanced skill acquisition but also adverse mental and physical outcomes (LaPrade et al., 2016). As such, adolescent athletes may face a dilemma regarding whether to play multiple sports or immediately narrow the focus to one. Coaches are positioned to influence motivational climates and sport-specific skill development (Amorose & Anderson-Butcher, 2007), making it important to understand their perceptions of ESS. Interviews were conducted with thirteen coaches of girls’ volleyball and basketball teams to gain an understanding of ESS as it pertains to athletes and programs at the interscholastic level. Participants identified influences and impacts of ESS, specifically how it can affect participation and competitiveness of interscholastic sports.        &nbsp