Heterometallic clusters [CuSn₃S₉]⁵⁻ and [Cu₆Sn₆S₂₀]¹⁰⁻: solvothermal synthesis and characterization of 4f-3d...

Two types of 4f-3d thiostannates with general formula [Hen]₂[Ln(en)₄(CuSn₃S₉)]∙0.5 en (Ln1; Ln=La, 1; Ce, 2) and [Hen]₄[Ln(en)₄]₂[Cu₆Sn₆S₂₀]∙3 en (Ln2; Ln=Nd, 3; Gd, 4; Er, 5) were prepared by reactions of Ln₂O₃, Cu, Sn, and S in ethylenediamine (en) under solvothermal conditions between 160 and 190 °C. However, reactions performed in the range from 120 to 140 °C resulted in crystallization of [Sn₂S₆]⁴⁻) compounds and CuS powder. In 1 and 2, three SnS₄ tetrahedra and one CuS₃ triangle are joined by sharing sulfur atoms to form a novel [CuSn₃S₉]⁵⁻ cluster that coordinates to the Ln(3+) ion of [Ln(en)₄]³⁺ (Ln=La, Ce) as a monodentate ligand. The [CuSn₃S₉]⁵⁻ unit is the first thio-based heterometallic adamantane-like cluster coordinating to a lanthanide center. In 3-5, six SnS₄ tetrahedra and six CuS₃ triangles are connected by sharing common sulfur atoms to form the ternary [Cu₆Sn₆S₂₀ ]¹⁰⁻ cluster, in which a Cu₆ core is enclosed by two Sn₃S₁₀ fragments. The topological structure of the novel Cu₆ core can be regarded as two Cu₄ tetrahedra joined by a common edge. The Ln³⁺ ions in Ln1 and Ln2 are in nine- and eightfold coordination, respectively, which leads to the formation of the [CuSn₃S9]⁵⁻ and [Cu₆Sn₆S₂₀]¹⁰⁻ clusters under identical synthetic conditions. The syntheses of Ln1 and Ln2 show the influence of the lanthanide contraction on the quaternary Ln/Cu/Sn/S system in ethylenediamine. Compounds 1-5 exhibit bandgaps in the range of 2.09-2.48 eV depending on the two different types of clusters in the compounds. Compounds 1, 3, and 4 lost their organic components in the temperature range of 110-350 °C by multistep processes.