Rectangle versus Square Oxalate-Connective Tetralanthanide Cluster Anchored in Lacunary Lindqvist Isopolytungstates: Syntheses, Structures, and Properties

Two types of unique oxalate-connective lanthanide-substituted isopolyoxotungstates, Na₁₀[Ln₂(C₂O₄)­(H₂O)₄(OH)­W₄O₁₆]₂·30H₂O (<b>1</b>) and K₄Na₁₆[Ln­(C₂O₄)­W₅O₁₈]₄·60H₂O (<b>2</b>) (Ln = Eu^III, Ho^III, Er^III, or Tb^III), have been synthesized under conventional aqueous solution conditions and structurally characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, and thermogravimetric analyses. It should be pointed out that the utilization of different alkaline cations leads to the formation of two structural types. When only Na⁺ ions are present in the system, type <b>1</b> was obtained, while when Na⁺ and K⁺ ions are used, type <b>2</b> was found. Complex <b>1</b> is a double-oxalate-bridging di-Ln substituted Lindqvist dimer with a rectangle tetra-Ln cluster, whereas <b>2</b> is a single-oxalate-connective mono-Ln^III Lindqvist tetramer with square tetra-Ln cluster. As far as we know, such di-Ln substituted Lindqvist fragment in <b>1</b> is observed for the first time. Moreover, <b>2</b> represents the first organic–inorganic hybrid square Ln-substituted isopolyoxotungstate. The solid-state luminescent properties of <b>1-Eu</b>, <b>1-Tb</b>, <b>2-Eu</b>, and <b>2-Tb</b> have been measured. <b>1-Eu</b> and <b>2-Eu</b> display intense, sharp, and narrow emission bands in the orange visible region that originate from the characteristic ⁵D₀ → ⁷F_<i>J</i> transitions, and their fluorescence lifetimes are 1.18 and 1.20 ms, respectively. <b>1-Tb</b> and <b>2-Tb</b> exhibit green photoluminescence mainly derived from ⁵D₄ → ⁷F₅ transitions. The decay behavior of <b>1-Tb</b> can be fitted to a biexponential function with lifetimes of τ₁ = 0.43 ms and τ₂ = 1.25 ms, whereas the decay behavior of <b>2-Tb</b> can be fitted to single exponential function with the lifetime of 1.03 ms. Magnetic susceptibilities of <b>1</b> and <b>2</b> have been measured, and the decline of χ_M<i>T</i> upon cooling for <b>1</b> and <b>2</b> is mostly related to the progressive thermal depopulation of the excited state of Ln cations

Rectangle versus Square Oxalate-Connective Tetralanthanide Cluster Anchored in Lacunary Lindqvist Isopolytungstates: Syntheses, Structures, and Properties

Two types of unique oxalate-connective lanthanide-substituted isopolyoxotungstates, Na₁₀[Ln₂(C₂O₄)­(H₂O)₄(OH)­W₄O₁₆]₂·30H₂O (<b>1</b>) and K₄Na₁₆[Ln­(C₂O₄)­W₅O₁₈]₄·60H₂O (<b>2</b>) (Ln = Eu^III, Ho^III, Er^III, or Tb^III), have been synthesized under conventional aqueous solution conditions and structurally characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, and thermogravimetric analyses. It should be pointed out that the utilization of different alkaline cations leads to the formation of two structural types. When only Na⁺ ions are present in the system, type <b>1</b> was obtained, while when Na⁺ and K⁺ ions are used, type <b>2</b> was found. Complex <b>1</b> is a double-oxalate-bridging di-Ln substituted Lindqvist dimer with a rectangle tetra-Ln cluster, whereas <b>2</b> is a single-oxalate-connective mono-Ln^III Lindqvist tetramer with square tetra-Ln cluster. As far as we know, such di-Ln substituted Lindqvist fragment in <b>1</b> is observed for the first time. Moreover, <b>2</b> represents the first organic–inorganic hybrid square Ln-substituted isopolyoxotungstate. The solid-state luminescent properties of <b>1-Eu</b>, <b>1-Tb</b>, <b>2-Eu</b>, and <b>2-Tb</b> have been measured. <b>1-Eu</b> and <b>2-Eu</b> display intense, sharp, and narrow emission bands in the orange visible region that originate from the characteristic ⁵D₀ → ⁷F_<i>J</i> transitions, and their fluorescence lifetimes are 1.18 and 1.20 ms, respectively. <b>1-Tb</b> and <b>2-Tb</b> exhibit green photoluminescence mainly derived from ⁵D₄ → ⁷F₅ transitions. The decay behavior of <b>1-Tb</b> can be fitted to a biexponential function with lifetimes of τ₁ = 0.43 ms and τ₂ = 1.25 ms, whereas the decay behavior of <b>2-Tb</b> can be fitted to single exponential function with the lifetime of 1.03 ms. Magnetic susceptibilities of <b>1</b> and <b>2</b> have been measured, and the decline of χ_M<i>T</i> upon cooling for <b>1</b> and <b>2</b> is mostly related to the progressive thermal depopulation of the excited state of Ln cations