A series of lanthanide germanate cluster organic frameworks

Abstract

Six new lanthanide (Ln) germanate cluster organic frameworks (LnGeCOFs) derived from {Ln₈Ge₁₂} cage cluster units {[Nd(pza)₂(H₂O)] [Nd₈Ge₁₂(μ₃-O)₂₄E₁₂(pza)(H₂O)₁₂]}·3H₂O (1), {[Dy(CH₃COO)(CO₃)(H₂O)]₂[Dy₈Ge₁₂(μ₃-O)₂₄E₁₂(H₂O)₁₂]}·11H₂O (2), {[TbGeE(HO)₂O(pza) (H₂O)]₂[Tb₈Ge₁₂(μ₃-O)₂₄E₁₂(H₂O)₆]}·18H₂O (3), {[DyGeE(HO)₂O(C₃H₅NO₂)(H₂O)]₂[Dy₈Ge₁₂(μ₃-O)₂₄E₁₂(H₂O)₈]}·8H₂O (4), {[Tb(pca)₂ (H₂O)]₃[Tb₈Ge₁₂(μ₃-O)₂₄E₁₂(H₂O)₄]}·(OH)₃·10H₂O (5) and {[Dy(pza)₂(H₂O)][Dy(pza)₂(H₂O)₂][Dy(pza)₃(H₂O)][Dy₈Ge₁₂(μ₃-O)₂₄E₁₂(pza)(HCOO) (H₂O)₆]}·5H₂O (6) have been hydrothermally synthesized and structurally characterized. Increasing the amount of the second ligands can induce not only the assembly from 1 to 5, 6 based on Ln oxides as the starting sources, but also the assembly from 2 to 3, 4 based on Ln salts as the starting sources. The successful preparation of these LnGeCOFs suggests the importance of the second ligands in the structural construction of 1–6. To our knowledge, 1 is the first example that includes right- and left-handed helical chains among LnGeCOFs based on bis(carboxyethylgermanium)sesquioxide. 2, 4 and 6 are the first dysprosium incorporated organogermanates based on bis(carboxyethylgermanium)sesquioxide. 4 and 5 display very open framework structures with a solvent-accessible volume of 34.6% for 4 and 35.0% for 5. Moreover, the solid-state photoluminescence properties of 1, 3 and 5 have been investigated at room temperature and they exhibit the characteristic emission bands derived from Ln cations.