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Two new rod‐packing metal–organic frameworks (RPMOF) are constructed by regulating the in situ formation of the capping agent. In CPM‐s7, carboxylate linkers extend 1D manganese‐oxide chains in four additional directions, forming 3D RPMOF. The substitution of Mn2+ with a stronger Lewis acidic Co2+, leads to an acceleration of the hydrolysis‐prone sulfonate linker, resulting in presence of sulfate ions to reduce two out of the four carboxylate‐extending directions, and thus forming a new 2D rod‐packing CPM‐s8. Density functional theory calculations and magnetization measurements reveal ferrimagnetic ordering of CPM‐s8, signifying the potential of exploring 2D RPMOF for effective low‐dimensional magnetic materials. [ABSTRACT FROM AUTHOR]

A new ternary phase, TiIrB, was synthesized by arc-melting of the elements and characterized by powder X-ray diffraction. The compound crystallizes in the orthorhombic Ti1+xRh2−x+yIr3−yB3 structure type, space group Pbam (no. 55) with the lattice parameters a = 8.655(2), b = 15.020(2), and c = 3.2271(4) Å. Density Functional Theory (DFT) calculations were carried out to understand the electronic structure, including a Bader charge analysis. The charge distribution of TiIrB in the Ti1+xRh2−x+yIr3−yB3-type phase has been evaluated for the first time, and the results indicate that more electron density is transferred to the boron atoms in the zigzag B4 units than to isolated boron atoms. [ABSTRACT FROM AUTHOR]

Metal‐rich borides with the Ti3Co5B2‐type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru‐rich quaternary borides with the general composition A2MRu5B2 (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr2FeRu5B2 and Hf2FeRu5B2 prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M‐chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr2MnRu5B2 and for FM in Hf2MnRu5B2. Magnetic property measurements show a field dependence of the AFM transition (TN): TN is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, TN is lowest for a Hf‐based phase (20 K) and highest for a Zr‐based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf‐based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru‐rich phases. [ABSTRACT FROM AUTHOR]

Abstract: We report on a structural distortion of kinetically stable B6‐based ferromagnetic Nb6FeIr6B8 that induces an unprecedented transformation of a ferromagnetic Fe chain into two ferrimagnetic Fe chains through superstructure formation. Density functional theory calculations showed that the ferromagnetic Fe–Fe intrachain interactions found in the undistorted structure become ferrimagnetic in the distorted superstructure, mainly because the two independent iron atoms building each chain interact antiferromagnetically and carry different magnetic moments. High‐temperature SQUID magnetometry confirmed ferrimagnetic ordering at 525 K with a high and negative Weiss constant of −972 K indicating the presence of strong antiferromagnetic interactions, as predicted. This finding paves the way for the development of low‐dimensional magnetic intermetallic systems based on Heisenberg ferrimagnetic chains, which have previously been studied only in molecular‐based compounds. [ABSTRACT FROM AUTHOR]

The novel composition – TiFe1.3Os3.9B2.8 – is the first quaternary phase of the NbRuB structure type. The layer‐like structure consists of boron (mixed with 8 % Fe) dumbbells in the same layer as osmium atoms, some sites with mixed occupancies. The second layer has isolated boron, osmium/titanium (51 % Os) and iron atoms. The presence of iron enables the study of magnetism as Fe‐chains are present, with intra‐ and interchain distances of 3.02 Å and 5.76 Å, respectively. Density functional theory (DFT) predicts magnetic ordering to be likely with the antiferromagnetic ground state only 13 meV more favorable than the ferromagnetic state. This discovery opens the possibilities of studying various quaternary compositions in the superconducting NbRuB structure type. [ABSTRACT FROM AUTHOR]

The structural parameters, chemical bonding and magnetic properties of the ternary boride series M1.5Rh5.5B3 (M = Cr, Mn, Fe, Co, Ni) were investigated by first principles DFT calculations. The calculated crystallographic lattice parameters corroborate well with the experimental results of the reported Fe1.3Rh5.7B3 single crystal. In the most stable structural model used, Fe-dumbbells as well as isolated Fe-atoms exist. From spin polarised calculations, ferromagnetism is found for the members with M = Fe, Co, while ferrimagnetism is more stable for Mn1.5Rh5.5B3 and Pauli paramagnetism is more stable for M = Cr, Ni. The total magnetic moment per formula unit for the M = Mn, Fe and Co phases is calculated to be 3.32, 5.00 and 3.26 μB, respectively. According to COHP chemical bonding analysis, Rh-B contacts are mainly responsible for the structural stability, while Rh-M interactions influence the magnetic behavior of these complex borides. [ABSTRACT FROM AUTHOR]

We present the first bulk synthesis of Ti3Co5B2, which was realized by arc-melting a Co-rich elemental mixture. Our X-ray diffraction studies revealed a Ti/Co mixed occupancy on one of two possible Ti sites suggesting a phase width with x = 0-0.52 in Ti3- xCo5+ xB2. Moreover, we studied experimentally and theoretically the isoelectronic substitution of Ti and Co by their respective higher homologues (Zr/Rh and Hf/Ir). Surprisingly, Ti3Co5B2-type phase was obtained only for the Hf/Ir combination (single crystal analysis of Hf3Ir5B2), whereas for Zr/Rh a perovskite-like phase (ZrRh3Bx) was discovered instead. We found that small but crucial differences (atomic radius ratio and electronegativity difference) between elements of the same group in the periodic Table are responsible for the unexpected trend deviation. This finding is supported by DFT calculations of the free energy of formation. [ABSTRACT FROM AUTHOR]

The prolific Ti3Co5B2 structure type has produced exciting materials with tunable magnetic properties, ranging from soft magnetic Ti2FeRh5B2, to semihard magnetic Ti2FeRu4RhB2 and hard magnetic Sc2FeRu3Ir2B2. Density functional theory (DFT) was employed to investigate their spin-orbit coupling effect, spin exchange, and magnetic dipole-dipole interactions in order to understand their magnetic anisotropy and relate it to their various coercivities, with the objective of being able to predict new materials with large magnetic anisotropy. Our calculations show that the contribution of magnetic dipole-dipole interactions to the magnetocrystalline anisotropy energy (MAE) in Ti3Co5B2-type compounds is much weaker than the spin-orbit coupling effect, and Sc2FeRu3Ir2B2 has, by far, the largest MAE and strong intrachain and interchain Fe-Fe spin exchange coupling, thus confirming its hard magnetic properties. We then targeted materials containing the more earth-abundant and less expensive Co, instead of Rh, Ru or Ir, so that our study started with Ti3Co5B2, which we found to be nonmagnetic. In the next step, substitutions on the Ti sites in Ti3Co5B2 led to new potential quaternary phases with the general formula T2T'Co5B2 (T = Ti, Hf; T' = Mn, Fe). For Hf2MnCo5B2, we found a large MAE (+0.96 meV/f.u.) but relatively weak interchain Mn-Mn spin exchange interactions, whereas for Hf2FeCo5B2, there is a relatively smaller MAE (+0.17 meV/f.u.) but strong Fe-Fe interchain and intrachain spin exchange interactions. Therefore, these two Co-rich phases are predicted to be new rare-earth-free, semihard to hard magnetic materials. [ABSTRACT FROM AUTHOR]

Recent research on van der Waals (vdW) metal chalcogenides electrocatalysts for the hydrogen evolution reaction (HER) has been devoted to finding new catalysts with active basal planes. Here, we report on experimental and theoretical investigations of the HER activity of a recently discovered iron‐rich vdW spintronic material, Fe5Ge2Te2 (FG2T) in alkaline media (1 M KOH). We show that a densified electrode of FG2T requires an overpotential of only −90.5 mV to drive a current density of 10 mA/cm2. Free energy calculations of hydrogen adsorption using density functional theory (DFT) proved that the numerous sites present on the hexagonal Te layer are more active than those found in the recently proposed Fe3GeTe2 (FGT) catalyst, supporting higher activity for the new Fe‐richer catalyst. Like in FGT, XPS analysis has found that a thin oxide layer covers the active FG2T layers, suggesting the real active surface to be a hybrid FG2T/oxide layer. These results strengthen the idea of continued screening of iron‐based vdW materials to replace the non‐abundant platinum group electrocatalysts toward HER and other electrocatalytic processes. [ABSTRACT FROM AUTHOR]

Abstract: We report on a structural distortion of kinetically stable B6‐based ferromagnetic Nb6FeIr6B8 that induces an unprecedented transformation of a ferromagnetic Fe chain into two ferrimagnetic Fe chains through superstructure formation. Density functional theory calculations showed that the ferromagnetic Fe–Fe intrachain interactions found in the undistorted structure become ferrimagnetic in the distorted superstructure, mainly because the two independent iron atoms building each chain interact antiferromagnetically and carry different magnetic moments. High‐temperature SQUID magnetometry confirmed ferrimagnetic ordering at 525 K with a high and negative Weiss constant of −972 K indicating the presence of strong antiferromagnetic interactions, as predicted. This finding paves the way for the development of low‐dimensional magnetic intermetallic systems based on Heisenberg ferrimagnetic chains, which have previously been studied only in molecular‐based compounds. [ABSTRACT FROM AUTHOR]

The title compound is prepared from the elements (Nb tube, 1073 K, 7 d) and characterized by powder XRD, XPS, 27Al MAS NMR spectroscopy, magnetic measurements, and DFT band structure calculations. [ABSTRACT FROM AUTHOR]