Chiral Silver-Lanthanide Metal-Organic Frameworks Comprised of One-Dimensional Triple Right-Handed Helical Chains Based on [Ln 7 (μ 3 -OH) 8 ] 13+ Clusters.

Three new isostructural chiral silver-lanthanide heterometal-organic frameworks [Ag ₃ Ln ₇ (μ ₃ -OH) ₈ (bpdc) ₆ (NO ₃ ) ₃ (H ₂ O) ₆ ](NO ₃ )·2H ₂ O [Ln = Eu (1), Tb (2, Sm (3); H ₂ bpdc = 2,2'-bipyridine-3,3'-dicarboxylic acid] based on heptanuclear lanthanide clusters [Ln ₇ (μ ₃ -OH) ₈ ] ¹³⁺ comprised of one-dimensional triple right-handed helical chains were hydrothermally synthesized. Various means such as UV-vis spectroscopy, IR spectroscopy, elemental analysis, powder X-ray diffraction, and thermogravimetric/differential thermal analysis were used to characterize the compounds, wherein compound 3 was crystallographically characterized. In the structure of compound 3, eight μ ₃ -OH ^- groups link seven Sm ³⁺ ions, forming a heptanuclear cluster, [Sm ₇ (μ ₃ -OH) ₈ ] ¹³⁺ , and the adjacent [Sm ₇ (μ ₃ -OH) ₈ ] ¹³⁺ clusters are linked by the carboxylic groups of bpdc ^2- ligands, leading to the formation of a one-dimensional triple right-handed helical chain. The adjacent triple right-handed helical chains are further joined together by coordinating the pyridyl N atoms of the bpdc ^2- ligands with Ag ⁺ , resulting in a chiral three-dimensional silver(I)-lanthanide(III) heterometal-organic framework with one-dimensional channels wherein NO ₃ ^- anions and crystal lattice H ₂ O molecules are trapped. The compounds were studied systematically with respect to their photoluminescence properties and energy-transfer mechanism, and it was found that H ₂ bpdc (the energy level for the triplet states of the ligand H ₂ bpdc is 21505 cm ^-1 ) can sensitize Eu ³⁺ luminescence more effectively than Tb ³⁺ and Sm ³⁺ luminescence because of effective energy transfer from bpdc ^2- to Eu ³⁺ under excitation in compound 1.