CRYSTALLOGRAPHIC MECHANISM OF THE NbS//3 TO Nb//1//. //1//2S//2 TRANSITION.

Article abstract of DOI:10.1016/0038-1098(87)90745-9

An electron diffraction study has allowed the crystallographic mechanism to be established for the thermally-induced transition from NbS//3 to Nb//1//. //1//2S//2, which belongs to the NbS//2 structural type. For the trisulfide, the structural unit is a bicapped trigonal prism left bracket NbS(6 plus 2) right bracket (6 is for the prism, 2 is for the bicapping sulfur atoms). When heating NbS//3 one sulfur is removed from every (S//2) pair which leads to a (4 plus 2)**3 sulfur coordination for niobium. Atomic rearrangements are then needed for new left bracket NbS//6 right bracket prisms to be reconstructed, perpendicular to the original bicapped ones, and for the NbS//2 structural type to establish. The Van der Waals gap orientation remains unchanged through the transition; no strong bond is unnecessarily broken. The obtained disulfide is not stoichiometric (Nb//1//. //1//2S//2) due to the thermodynamic route followed.