The Synthesis and Crystal Structure of NpSe 3

Neptunium triselenide, NpSe 3 , was synthesized in high yield by the reaction of the elements in a Sb 2 Se 3 flux at 1223 K. Its structure has been determined by single‐crystal X‐ray diffraction methods. Thecompound crystallizes with two formula units in space group C $\rm^{2}_{2h}$ –P 2 1 / m of the monoclinic system in the TiS 3 structure type with cell constants at 100 K of a = 5.592(3) Å, b = 4.002(2) Å, c = 9.422(5) Å, β = 97.40(1) °. The asymmetric unit comprises one neptunium and three selenium atoms, each with site symmetry m . Np–Se interatomic distances range from 2.859(2) to 2.927(3) Å; the Se–Se bond length of 2.340(3) Å is typical of a single bond. The compound may thus be charge‐balanced and formulated as Np 4+ Se 2– Se 2 2– .