Does the real ReN2 have the MoS2 structure?

Rhenium nitride (ReN(2)) with the hexagonal MoS(2) structure was recently synthesized by metathesis reaction under high pressure. Here the calculated elastic and thermodynamic stabilities and chemical bonding show that the MoS(2) phase is unstable based on first-principles calculations. Meanwhile, the MoS(2)-type ReN(2) compound may be stabilized by nitrogen-vacancies from X-ray diffraction and supercell calculations. Structure searches identify a monoclinic C2/m phase for ReN(2), which is energetically more stable than previous predictions and MoS(2) structure over a wide range of pressures. Above 130 GPa, a tetragonal P4/mbm phase becomes favorable from enthalpy calculations. Both phases have superior mechanical properties, and their syntheses would have important applications fundamentally and technologically.

Excellent Magnetocaloric Performance of the Fe87Ce13-xBx (x = 5, 6, 7) Metallic Glasses and Their Composite.

The novel Fe87Ce13-xBx (x = 5, 6, 7) metallic glass (MG) ribbons were fabricated in this work. The compositional dependence of glass forming ability (GFA), magnetic and magnetocaloric properties of these ternary MGs, and the mechanism involved was investigated. The GFA and Curie temperature (Tc) of the MG ribbons were found to improve with the boron content, and the peak value of magnetic entropy change (-ΔSmpeak) reaches a maximum of 3.88 J/(kg × K) under 5 T when x = 6. Based on the three results, we designed an amorphous composite that exhibits a table-shape magnetic entropy change (-ΔSm) profile with a rather high average -ΔSm (-ΔSmaverage~3.29 J/(kg × K) under 5 T) from 282.5 K to 320 K, which makes it a potential candidate for the highly efficient refrigerant in a domestic magnetic refrigeration appliance.

Mechanism for Improved Curie Temperature and Magnetic Entropy Change in Sm-Doped Fe88Zr8B4 Amorphous Alloys.

In the present work, Fe88Zr8-xSmxB4 (x = 2, 4) amorphous alloys (AAs) were successfully synthesized into the shape of 40-micrometer-thick ribbons and their magnetic properties were measured. The Fe88Zr8-xSmxB4 (x = 2, 4) AAs exhibited a rather high maximum magnetic entropy change (-ΔSmpeak): ~3.53 J/(K × kg) near 317 K for x = 2 and ~3.79 J/(K × kg) near 348 K for x = 4 under 5 T. The effects of a Sm substitution for Zr on the Curie temperature (Tc) and -ΔSmpeak were studied and compared to those of Nd and Pr substitutions, for the purpose of revealing the mechanism involved in more detail.

Hexanuclear Co4 Dy2 , Zn4 Dy2 , and Co4 Y2 Complexes with Defect Tetracubane Cores: Syntheses, Structures, and Magnetic Properties.

A hexanuclear heterometallic cluster of composition [Dy2 Co4 (L)4 (NO3 )2 (OH)4 (C2 H5 OH)2 ] ⋅ 2 C2 H5 OH (1) was synthesized by employing a Schiff base 2-(((2-hydroxy-3-methoxybenzyl) imino)methyl)-4-methoxyphenol (H2 L) as ligand and utilizing Dy(NO3 )3 ⋅ 6H2 O and Co(NO3 )2 ⋅ 6H2 O as metal ion sources. X-ray single-crystal diffraction analysis indicated that complex 1 contains a defect tetracubane core and possesses central symmetric structure, with two DyIII ions being in the central body position of the molecule and four CoII ions being arranged at the outer sites. Magnetic studies reveal that complex 1 behaves as single-molecule magnet (SMM) with energy barrier of 27.50 K. To investigate the individual contribution of DyIII and CoII ions to the SMM behavior, another two complexes of formulae [Dy2 Zn4 (L)4 (NO3 )2 (OH)4 ] ⋅ 4CH3 OH (2) and [Y2 Co4 (L)4 (NO3 )2 (OH)4 (C2 H5 OH)2 ] ⋅ 2 C2 H5 OH (3) were prepared. Complexes 1 and 3 are isomorphous. The coordination geometries of DyIII ions in 1 and 2 are different. The DyIII ions are eight-coordinated in 2 and nine-coordinated in 1. Complex 2 exhibits SMM behavior with energy barrier of 69.67 K, but complex 3 does not display SMM property. These results reveal that the SMM behaviors of 1 and 2 are mainly originated from DyIII ions. It might be the higher symmetry of DyIII ions in 2 that results in the higher energy barrier.

Designing asymmetric Dy2 single-molecule magnets with two-step relaxation processes by the modification of the coordination environments of Dy(iii) ions.

The reaction of Dy(NO3)3·6H2O and an asymmetric Schiff-base linker 5-chloro-2-(((2-hydroxy-3-methoxybenzyl)imino)methyl) phenol (H2L) afforded a dinuclear compound [Dy2L2(HL)(NO3)(EtOH)]·0.5C2H5OH (1). Complex 1 features two inequivalent Dy(iii) sites, where three ligand sets (one HL- moiety and two L2- groups) are shared by two Dy(iii) ions. The strategic introduction of CH3COOH in the reaction system used for synthesizing 1 induces the replacement of the HL- ligand by the CH3COO- ion, consequently resulting in the generation of [Et3NH][Dy2L2(NO3)(CH3COO)2] (2). In complex 2, two Dy(iii) centers adopt NO7 (D2d geometry) and NO6 (C2v) coordination sphere, respectively. DC magnetic susceptibility studies for the two complexes indicate ferromagnetic interactions. Complexes 1 and 2 exhibit single-molecule magnet behavior with two-step slow relaxation processes due to the possession of inequivalent metal sites. The energy barriers of 69.19 and 45.73 K for 1, and 92.77 and 72.95 K for 2 are determined. Theoretical calculations reveal that the two-step relaxation processes in both 1 and 2 mainly originate from the single-ion magnetism of two distinct Dy(iii) ions with inequivalent coordination environments.