Dinuclear Manganese(II) Complexes with Bridging Selenidodiarsenate Anions [As 2 Se 4 ] 4− , [As 2 Se 5 ] 4− and [As 2 Se 6 ] 2−

Solvothermal reaction of [MnCl 2 (amine)] (amine = terpy and tren) with elemental As and Se at a 1:1:2 molar ratio in H 2 O/tren (10:1) affords the dimanganese(II) complexes [{Mn(terpy)} 2 (μ‐As 2 Se 4 )] ( 1 ) and [{Mn(tren)} 2 (μ‐As 2 Se 5 )] ( 2 ) respectively. The tetradentate [As 2 Se 4 ] 4− bridging ligands in 1 contain a central As–As bond and exhibit approximately C 2h symmetry. Pairs of gauche sited Se atoms participate in five‐membered As 2 Se 2 Mn chelate rings. In contrast, two AsSe 3 pyramids share a common corner in the [As 2 Se 5 ] 4− ligands of 2 and each coordinates an [Mn(tren)] 2+ fragment through a single terminal Se atom. Such dinuclear complexes are linked into tetranuclear moieties through weak Se···Mn interactions of length 3.026(3) Å involving one of these terminal Se atoms. At a 1:3:6 molar ratio, solvothermal reaction of [MnCl 2 (tren)] with As and Se leads to formation of a second dinuclear complex [{Mn(tren)} 2 (μ‐As 2 Se 6 ) 2 ] ( 3 ), which contains two bridging bidentate [As 2 Se 6 ] 2− ligands. These are cyclic with an As 2 Se 4 ring and can be regarded as being derived from [As 2 Se 5 ] 4− anions by formation of two Se‐Se bonds to an additional Se atom.