Cl5Ta(μ-O)TaCl3{(i)PrS(CH2)2S(i)Pr}] and [(TaCl4)2(μ-O)(μ-Me2Se2)]: two chalcogenoether complexes of Ta2OCl8 with very different geometries

The title compounds, [1,2-bis(isopropylsulfanyl)ethane-2κ(2)S,S']octachlorido-1κ(5)Cl,2κ(3)Cl-μ-oxido-ditantalum(V), [Ta(2)Cl(8)O(C(8)H(18)S(2))], (I), and μ-dimethyldiselane-κ(2)Se:Se'-μ-oxido-bis[tetrachloridotantalum(V)], [Ta(2)Cl(8)O(C(2)H(6)Se(2))], (II), contain six-coordinate Ta(V) centres linked by a nonlinear oxide bridge. Compound (I) contains one Ta(V) centre bonded to a chelating dithioether and three terminal chloride ligands, with the second Ta(V) centre bonded to five terminal chloride ligands. In (II), two tetrachloridotantalum(V) residues are bridged by the diselenide, giving a puckered five-membered Ta/O/Ta/Se/Se ring. The Ta-O distances in the bridges are short in both compounds, indicating that significant multiple-bond character is retained despite the deviation from linearity, and the bond lengths reveal a clear trans influence order of O > Cl > S > Se on the hard Ta(V) centre. The structures are compared with the [Ta(2)Cl(10)O](2-) anion, which contains a linear oxide bridge.