Bismuth trihalides (BiX₃, X = Cl, Br or I) reacted with a range of thio- and seleno-ether ligands L–L in anhydrous MeCN solution to yield compounds with either a 1∶1, 1∶2 or 2∶1 Bi∶L–L ratio. Structural studies on [BiBr₃{MeE(CH₂)₃EMe}] (E = S or Se) and [BiCl₃{MeSe(CH₂)₃SeMe}] revealed that all of these species adopt an infinite two-dimensional sheet array derived from planar Bi₂X₆ units linked by bridging dithio- or diseleno-ether ligands which occupy mutually trans co-ordination sites, giving a distorted octahedral geometry at Bi^III. The structure of [BiBr₃{MeS(CH₂)₂SMe}₂] reveals a discrete molecular compound which adopts a 7-co-ordinate distorted pentagonal bipyramidal geometry involving two chelating MeS(CH₂)₂SMe ligands. This arrangement is also found for the iodide analogue. Reaction of BiBr₃ with the Ph-substituted ligand PhS(CH₂)₂SPh generated a very different structural arrangement in which chains of almost mutually orthogonal Bi₂Br₂ ‘rectangles’ are cross-linked by bridging dithioether ligands to yield infinite sheets of formula [Bi₂Br₆{PhS(CH₂)₂SPh}]. With the tripodal ligands L³ (MeC(CH₂SMe)₃ or MeC(CH₂SeMe)₃) compounds of stoichiometry [BiX₃(L³)] were obtained. The crystal structure of [BiCl₃{MeC(CH₂SeMe)₃}] shows Bi₂Cl₆ subunits linked by bridging selenoether ligands to give a two-dimensional sheet. Each selenoether tripod functions as a bidentate chelate to Bi and bridges to an adjacent Bi via the third Se-donor, giving a distorted octahedral geometry at Bi^III. Although a rather poor quality structure, [Bi₂I₆{MeC(CH₂SeMe)₃}₂] is not isostructural with its chloro analogue, but shows discrete dimers formed via Bi₂I₆ subunits, with each Bi also co-ordinated to a bidentate Se tripod and two terminal I ligands. The third Se-donor on each ligand remains non-co-ordinating. The influence of the Bi-based lone pair on the structures adopted by these complexes is discussed.