Vanadium(II) sulfide

On heating to between 1,700–2,000 K (1,430–1,730 °C; 2,600–3,140 °F) VS evaporates forming VS molecules as well as atomic sulfur S and atomic vanadium V. Some VS₂ and S₂ molecules also appear in the gas phase.^[2]

The ground state of the VS molecule is C⁴Σ⁻; it has a dipole moment of 2.38 D. The excited state X⁴Σ⁻ has a dipole moment of 5.16 D.^[3]

Bonding in VS is mostly covalent, and little charge is transferred from the vanadium atoms to the sulfur.^[4]

Vanadium monosulfide has two different crystal structures, exhibiting dimorphism. The NiAs type is hexagonal (space group P6₃/mmc) while the MnP type is orthorhombic (s.g. Pcmm). The crystal form and unit cell dimensions vary with the sulfur to vanadium ratio. At the stoichiometric ratio, the stable structure is orthorhombic.^[5] As the S:V ratio increases, the c parameter decreases linearly. Over about S:V = 1.03 the b parameter increases and the a parameter decreases, suddenly converging to each other on 3.34 Å at a S:V ratio of 1.06. The most sulfur deficient orthorhombic form has the composition S_0.93V.

The crystal structure accommodates variations in the sulfur to vanadium ratio, by including vacancies. This means that the densest form is VS with a density of 4.90 g/cm³ while non-stoichiometric forms are less dense.^[6] Stoichimetric VS has the unit cell dimensions a = 5.825, b = 3.310 and c = 5.854 Å.^[1]

Stoichiometric VS changes crystal form at 630 °C (903 K; 1,166 °F) to the hexagonal form.^[4]

Vanadium monosulfide can be made by heating a mixture of finely powdered sulfur and vanadium in the correct ratio.^[1]

In VS, vanadium can be substituted by titanium (V_xTi_1-xS) in solid solution. Also, sulfur can be substituted by selenium (VS_xSe_1-x).^[4]

Other vanadium sulfides include V₃S, V₅S₄, V₇S₈, V₃S₄, V₅S₈ V₂S₃, VS₂, VS₄.^[1]

Ternary sulfides containing vanadium in the +2 oxidation state include VSc₂S₄, VTi₂S₄ and VCr₂S₄.^[7][8]