Synthesis and structures of bismuth(III) complexes involving thio- and seleno-ether ligands

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)(3)EMe}] (E = S or Se) and [BiCl3{MeSe(CH2)(3)SeMe}] 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)(2)SMe}(2)] reveals a discrete molecular compound which adopts a 7-co-ordinate distorted pentagonal bipyramidal geometry involving two chelating MeS(CH2)(2)SMe ligands. This arrangement is also found for the iodide analogue. Reaction of BiBr3 with the Ph-substituted ligand PhS(CH2)(2)SPh generated a very different structural arrangement in which chains of almost mutually orthogonal Bi2Br2 'rectangles' are crosslinked by bridging dithioether ligands to yield infinite sheets of formula [Bi2Br6{PhS(CH2)(2)SPh}]. With the tripodal ligands L-3 (MeC(CH2SMe)(3) or MeC(CH2SeMe)(3)) compounds of stoichiometry [BiX3(L-3)] 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.