The First Tetradentate μ‐1κ 2 :2κ 2 ‐Sn 2 Se 6 Ligand to a Lanthanide(III) Center: Solvothermal Syntheses and Characterizations of Lanthanide Selenidostannate Polymers with Tetraethylenepentamine as a Second Ligand

Novel lanthanide selenidostannate polymers containing the soft‐base Sn 2 Se 6 ligand, (H 3 O) n [La(tepa)(μ‐1κ 2 :2κ 2 ‐Sn 2 Se 6 )] n ( 1 ), [{Nd(tepa)(μ‐OH)} 2 (μ‐1κ:2κ‐Sn 2 Se 6 )] n ( 2 ), and [{Gd(tepa)(μ‐OH)} 2 (μ‐1κ:2κ‐Sn 2 Se 6 )] n · n H 2 O ( 3 ) (tepa = tetraethylenepentamine) were prepared by treating lanthanide oxides with Sn and Se using pentadentate polyamine tepa as a second ligand under solvothermal conditions. In 1 , the La 3+ ion is coordinated by a tepa ligand to form an unsaturated [La(tepa)] 3+ unit, and the [Sn 2 Se 6 ] 4– anion acts as a tetradentate bridging ligand with four terminal Se atoms to connect the [La(tepa)] 3+ units into a coordination polymeric anion [La(tepa)(μ‐1κ 2 :2κ 2 ‐Sn 2 Se 6 ) – ] n . The μ‐1κ 2 Se 1 , Se 2 :2κ 2 Se 5 , Se 6 bridging mode in 1 is a new coordination mode for the Sn 2 Se 6 unit to Ln III centers. In 2 and 3 , the lanthanide ion is coordinated by a tepa ligand, and two [Ln(tepa)] 3+ (Ln = Nd, Gd) ions are joined by two μ‐OH bridges to form dinuclear cations. Behaving as a bidentate μ‐Sn 2 Se 6 ligand with the trans ‐terminal Se atoms, the Sn 2 Se 6 units connect the [{Ln(tepa)(μ‐OH)} 2 ] 4+ cations into neutral coordination polymers [{Ln(tepa)(μ‐OH)} 2 (μ‐Sn 2 Se 6 )] n . The coordination modes μ‐1κ 2 Se 1 , Se 2 :2κ 2 Se 5 , Se 6 in 1 and μ‐1κ Se 1 :2κ Se 5 in 2 and 3 are related to the metal size of the lanthanide(III) ions. In addition, as an ethylenepolyamine with higher denticity, the pentadentate tepa exhibits a significantly different influence on the structures of the solvothermally synthesized Ln selenidostannates compared to the bidentate ethylenediamine and tridentate diethylenetriamine. Compounds 1 – 3 are semiconductors with well‐defined band gaps of 1.95–2.34 eV.