The First Tetradentate μ‐1κ²:2κ²‐Sn₂Se₆ Ligand to a Lanthanide(III) Center: Solvothermal Syntheses and Characterizations of Lanthanide Selenidostannate Polymers with Tetraethylenepentamine as a Second Ligand

Abstract

Novel lanthanide selenidostannate polymers containing the soft‐base Sn2Se6 ligand, (H3O)n[La(tepa)(μ‐1κ2:2κ2‐Sn2Se6)]n (1), [{Nd(tepa)(μ‐OH)}2(μ‐1κ:2κ‐Sn2Se6)]n (2), and [{Gd(tepa)(μ‐OH)}2(μ‐1κ:2κ‐Sn2Se6)]n·nH2O (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 La3+ ion is coordinated by a tepa ligand to form an unsaturated [La(tepa)]3+ unit, and the [Sn2Se6]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‐1κ2:2κ2‐Sn2Se6)–]n. The μ‐1κ2Se1,Se2:2κ2Se5,Se6 bridging mode in 1 is a new coordination mode for the Sn2Se6 unit to LnIII 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‐Sn2Se6 ligand with the trans‐terminal Se atoms, the Sn2Se6 units connect the [{Ln(tepa)(μ‐OH)}2]4+ cations into neutral coordination polymers [{Ln(tepa)(μ‐OH)}2(μ‐Sn2Se6)]n. The coordination modes μ‐1κ2Se1,Se2:2κ2Se5,Se6 in 1 and μ‐1κSe1:2κSe5 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.