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Abstract:
The lanthanum-rich antimonide La2NiSb was synthesized by annealing a
cold-pressed pellet of the elements in a sealed silica glas tube at
1120K. La2NiSb was characterized by powder and single-crystal X-ray
diffraction: ordered Bi3Ni type, Pnma, Z = 4, a = 825.6(3), b =
452.2(2), c = 1195.5(4) pm, wR= 0.0695, 856 F-2 values, 26 variables.
The nickel atoms form infinite zig-zag chains (259 pm Ni-Ni) with
trigonal-prismatic lanthanum coordination for each nickel atom. The
antimony atoms cap the rectangular faces of the lanthanum prisms (336 pm
La-Sb) and thereby coordinate also the nickel atoms (271 pm Ni-Sb).
These rods run parallel to the b axis and form a herringbone pattern,
similar to the FeB-type structure of GdNi. Although metallic
conductivity is expected for La2NiSb from DFT-based band structure
calculations, the real-space bonding analysis shows prominent
localization of electrons on antimonide anions and positively charged
lanthanum cations. The chain substructure is strongly bonded by polar
covalent Ni-Sb and multicenter Ni-Ni interactions. The nickel atoms,
which are involved in multicenter bonding with adjacent nickel and
lanthanum atoms, provide a conductivity pathway along the prismatic
strands. Sb-121 Mossbauer spectroscopic data at 78 K show a single
signal at an isomer shift of -7.62(3) mm s(-1), supporting the
antimonide character. La2NiSb shows weak paramagnetism with a
susceptibility of 2.5 x 10(-3) emu mol(-1) at room temperature.
