Categorization of plethora of transition metal chalcogenide nanowires M x X y constructed from the M₆ octahedral building block. (a) Trans-edge sharing to form M 4 X 6 nanowires. (b) Face-to-face to form M 6 X 9 or M 6 X 6 nanowires. (c) Vertex-to-vertex to form M 5 X 4 nanowires with the least X/M ratio so far. The upper structures in panels (a)–(c) are to show how possible nanowire geometry forms from M₆ building block, and the lower structures are to show the exemplary extended nanowires which have mostly been synthesized in experiment. M and X atoms are shown in silver grey and brown, respectively.