Synthesis and Structure of Quasi-One-Dimensional Niobium Tetrasulfide NbS₄

The binary niobium sulfide NbS₄ was synthesized as a crystalline phase. We showed that NbS₄ can be formed from Nb metal, from defect niobium sulfide Nb_1.14S₂, or from some other niobium dichalcogenides in reactions with excess sulfur in an evacuated ampule at 440 °C. The crystal structure of NbS₄ (monoclinic space group C2/c, a = 13.126(2) Å, b = 10.454(1) Å, c = 6.951(1) Å, β = 111.939(5)°) is a packing of infinite chains {NbS₄}_1∞, analogous to VS₄. In the chains, Nb atoms are in a tetragonal-antiprismatic coordination of sulfur atoms of disulfide groups (S₂)^2-; short Nb···Nb contacts (2.896 Å) alternating with longer ones (3.278 Å) appear within the chains at 150 K. According to density functional theory calculations, NbS₄ is a thermodynamically stable compound, a nonmagnetic semiconductor. NbS₄ is a new member of the family of quazi-one-dimensional compounds, group 5 metal polychalcogenides, well-known for their interesting electrophysical properties. The synthesis and crystal structure as well as the thermal stability and lattice dynamics of NbS₄ are discussed here.