High pressure synthesis and the valence state of vanadium ions for the novel transition metal pernitride, CuAl₂-type VN₂

Abstract

We report the first synthesis of CuAl2-type VN2 and experimental investigation of the valence state for vanadium ions in VN2.

High-pressure synthesis and crystal structures of molybdenum nitride Mo3N5 with anisotropic compressibility by a nitrogen dimer

“…The N–N distance for the pernitride with a single-bonded [N 2 ] 4− dimer has been reported to be approximately 1.4 Å, for example, TiN 2 (1.38 Å), 10 PtN 2 (1.42 Å), 50 and VN 2 (1.403(3) Å). 11 Thus, the N–N dimer in Mo 3 N 5 is also inferred to be a single bond, and Mo 3 N 5 is classified as molybdenum nitride pernitride represented by the chemical formula Mo 3 (N 2 )(N) 3 in the same way as rhenium nitride pernitride Re 2 (N 2 )(N) 2 . Mo 3 N 5 was exposed to air before the measurement, indicating that it is stable against oxygen and moisture.…”

“…The compressibility of each axis corresponds to the elastic stiffness constant ( C 11 , C 22 , and C 33 ), as shown in Table S4 †. In general, the pernitrides with the N–N dimer have low compressibility in the bonding direction of the dimer, for example, CuAl 2 -type VN 2 11 and anti-NiAs-type CrN 2 . 12 The binding direction of the nitrogen dimer for Mo 3 N 5 is tilted at about 4.6 degrees from the b -axis to the c -axis.…”

“…These highpressure phases have not only been discovered experimentally but have also been synthesized through prediction by theoretical calculations, for example, U 2 S 3 -type Nb 2 N 3 14,21 and CuAl 2 -type VN 2 . 11,22 Recently, however, we have synthesized U 7 Te 12 -type W 7 N 12 16 that was not predicted by theoretical calculations, indicating the importance of experimental structural exploration and the determination of the high-pressure phase.…”

“…[1][2][3][4][5][6][7][8][9] In contrast, early transition-metal nitrides and pernitrides crystallize in diverse structures. In 3d early transition-metal pernitrides, TiN 2 10 and VN 2 11 are CuAl 2 -type structures with an antiprismatic MN 8 polyhedron and N-N dimer, and CrN 2 12 is an anti-NiAs-type structure with a trigonal prismatic MN 6 poly-hedron and N-N dimer. On the other hand, 4d and 5d early transition-metal nitrides, unlike late and 3d early transitionmetal dinitrides, have non-simple compositions, e.g., Zr 3 N 4 and Hf 3 N 4 for Th 3 P 4 -type, 13 Nb 2 N 3 14 and Ta 2 N 3 15 for U 2 S 3type, and W 7 N 12 for U 7 Te 12 -type.…”

“…In addition, Mo 3 N 5 has an N-N dimer with bond lengths (N1-N1) of 1.412(6) Å in the Rietveld refinement and 1.406 Å in the DFT optimization. The N-N distance for the pernitride with a single-bonded [N 2 ] 4− dimer has been reported to be approximately 1.4 Å, for example, TiN 2 (1.38 Å),10 PtN 2 (1.42 Å),50 and VN 2 (1.403(3) Å) 11. Thus, the N-N dimer in Mo 3 N 5 is also inferred to be a single bond, and Mo 3 N 5 is classified as molybdenum nitride pernitride represented by the chemical formula Mo 3 (N 2 )(N) 3 in the same way as rhenium nitride pernitride Re 2 (N 2 )(N) 2 .…”