The first tetradentate μ-1η ~2:2η ~2-Sn _2Se _6 ligand to a lanthanide(III) center: Solvothermal syntheses and characterizations of lanthanide selenidostannate polymers with tetraethylenepentamine as a second ligand

摘要

Novel lanthanide selenidostannate polymers containing the soft-base Sn _2Se _6 ligand, (H _3O) _n[La(tepa)(μ- 1η ~2:2η ~2-Sn _2Se _6)] _n (1), [{Nd(tepa)(μ-OH)} _2(μ-1η:2η-Sn _2Se _6)] _n (2), and [{Gd(tepa)(μ-OH)} _2(μ-1η:2η-Sn _2Se _6)] _n·nH _2O (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 _2Se _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-1η ~2:2η ~2-Sn _2Se _6) ~-] _n. The μ- 1η ~2Se ~1,Se ~2:2η ~2Se ~5,Se ~6 bridging mode in 1 is a new coordination mode for the Sn _2Se _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 _2Se _6 ligand with the trans-terminal Se atoms, the Sn _2Se _6 units connect the [{Ln(tepa)(μ-OH)} _2] ~(4+) cations into neutral coordination polymers [{Ln(tepa)(μ-OH)} _2(μ-Sn _2Se _6)] _n. The coordination modes μ-1η ~2Se ~1,Se ~2:2η ~2Se ~5,Se ~6 in 1 and μ-1ηSe ~1:2ηSe ~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.