Synthesis and Crystal Structure of >Bis(tetrapropylammonium) Hexabromotellurate(IV)‐bis{dibromoselenate(II)}, [N n Pr 4 ] 2 [TeBr 6 (SeBr 2 ) 2 ], the Salt of a Mixed‐valence Bromotellurate(IV)‐Selenate(II) Anion

Dark brown crystals of [N n Pr 4 ] 2 [TeBr 6 (SeBr 2 ) 2 ] ( 1 ) were obtained when selenium and bromine (1:1) were allowed to react in acetonitrile solution in the presence of tellurium(IV) bromide and tetrapropylammonium bromide. The salt 1 crystallizes in the monoclinic space group P2 1 / n with the cell dimensions a = 14.7870(3) Å, b = 9.5523(3) Å, c = 16.7325(3) Å, β = 110.56(10)° (at 123(2) K). In the solid state the [TeBr 6 (SeBr 2 ) 2 ] 2– anion contains a nearly regular [TeBr 6 ] octahedron in which the four equatorial bromo ligands have developed bonds to Se II atoms of the SeBr 2 molecules. The contacts between the bridging bromo and the Se II atoms of the SeBr 2 molecules are 3.0000(4) and 3.0561(4) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr 2 molecules as acceptors. The Te IV –Br distances are in the range 2.6816(3)–2.7131(3) Å and the Se II –Br bond lengths in the coordinated SeBr 2 molecules are 2.3548(4) and 2.3725(4) Å.