Chiral Silver-Lanthanide Metal-Organic Frameworks Comprised of One-Dimensional Triple Right-Handed Helical Chains Based on [Ln7(μ3-OH)8]13+ Clusters

Three new isostructural chiral silver-lanthanide heterometal-organic frameworks [Ag(3)Ln(7)(mu(3)-OH)(8)(bpdc)(6)(NO3)(3)(H2O)(6)](NO3)center dot 2H2O [Ln = Eu (1), Tb (2, Sm (3); H(2)bpdc = 2,2'-bipyridine-3,3'-dicarboxylic acid] based on heptanuclear lanthanide clusters [Ln(7)(mu(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 mu(3)-OH- groups link seven Sm3+ ions, forming a heptanuclear cluster, [Sm-7(mu(3)-OH)(8)](13+), and the adjacent [Sm-7(mu(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 NO3- anions and crystal lattice H2O 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 Eu3+ luminescence more effectively than Tb3+ and Sm3+ luminescence because of effective energy transfer from bpdc(2-) to Eu3+ under excitation in compound 1.