Metastable Ni₇B₃: A New Paramagnetic Boride from Solution Chemistry, Its Crystal Structure and Magnetic Properties

Abstract

We trapped an unknown metastable boride by applying low-temperature solution synthesis. Single-phase nickel boride, Ni7B3, was obtained as bulk samples of microcrystalline powders when annealing the amorphous, nanoscale precipitate that is formed in aqueous solution of nickel chloride upon reaction with sodium tetrahydridoborate. Its crystal structure was solved based on a disordered Th7Fe3-type model (hexagonal crystal system, space group P63mc, no. 186, a = 696.836(4) pm, c = 439.402(4) pm), using synchrotron X-ray powder data. Magnetic measurements reveal paramagnetism, which is in accordance with quantum chemical calculations. According to high-temperature X-ray diffraction and differential scanning calorimetry this nickel boride phase has a narrow stability window between 300 and 424 °C. It crystallizes at ca. 350 °C, then starts decomposing to form Ni3B and Ni2B above 375 °C, and shows an exothermic effect at 424 °C.

Th7Fe3‐Type Related Structures in Pd(Pt)‐Cu‐B Systems: Pd6CuB3—A New Structure Type for Borides

“…In contrast to transition-metal carbide systems, only few borides were found to crystallize in the Th 7 Fe 3 -type structure (M = Tc ,R e, Ru, Rh). [5,9] In addition, ad isordered varianto fT h 7 Fe 3 has been reported lately [10] [11] Comparative studies of the structures of Rh 7 B 3 ,R u 7 B 3 and Re 7 B 3 binaries in relation to M 7 C 3 carbides [12] elucidated the hexagonals ymmetry for M 7 B 3 and revealed the absence of either superstucture reflections or diffuse intensities thus confirming the structure of borides, as suggested by Aronsson. [5] Considering1 )the fact that boron and carbon tend to form homologues compounds at low non-metal contents( e.g.…”

“…In contrast to transition‐metal carbide systems, only few borides were found to crystallize in the Th 7 Fe 3 ‐type structure (M=Tc, Re, Ru, Rh) . In addition, a disordered variant of Th 7 Fe 3 has been reported lately for a metastable Ni 7 B 3 compound. M/M′ substitution has been investigated for Re 7 B 3 by Kuz′ma et al.…”

Synthesis and Magnetic Properties of the Boride Series MRh6–nRunB3 (M = Co, Ni; n = 1–5)

“…Therefore, for the new NiRh 6– n Ru n B 3 series no magnetic ordering is expected since no magnetic ordering was found in the Rh‐ and Ru‐based ternaries. Also, the binary metastable Ni‐based phase Ni 7 B 3 was recently reported as paramagnetic . Indeed, no magnetic ordering was found in the whole series (see Supporting Information, Figure S3).…”

“…In other words, the loss of valence electrons ( VE ) by substituting Ru for Rh for the Ru‐rich side of the series is compensated by increasing the amount of the VE ‐richer but smaller Ni. This scenario is very likely, given the fact that Ni 7 B 3 was recently discovered by Albert et al as a metastable paramagnetic phase …”

Nano-Metal Borides of Cobalt, Nickel and Copper

“…Lattice parameters are known from electron diffraction [3]. Katherine et al described that Ni 7 B 3 is the first binary boride of a 3d metal and proposed that a single-phase bulk synthesis of Ni 7 B 3 that crystallized with unknown disordered structure [7].…”