Syntheses, structures, and properties of lanthanide-organic frameworks with flexible disulfide derivative of carboxylate

Reaction of disulfide-containing ligand 6,6′-dithiodinicotinic acid (H₂cpds) with lanthanide metal salts led to three compounds {[Ln₂(cpds)₃(H₂O)₅]·7H₂O}_n (Ln = Gd, 1; Tb, 2; Er, 3) under hydrothermal conditions. The single-crystal X-ray diffraction analysis revealed that complexes 1-3 are isostructural. Two eight-coordinated metal centers are connected with carboxylate groups of H₂cpds to give a binuclear [Ln₂(CO₂)₄] unit. H₂cpds discloses two independent binding modes resulting in the two types of 1-D chains by the connection of [Ln₂(CO₂)₄] unit. Finally, the 1-D chains are linked by H₂cpds to construct a 3-D network with an uncommon twofold interpenetrating 4-connected CdSO₄ structure type (6⁵,8 topology). It is worth noting that polyrotaxane-like motif is also exhibited in the 3-D network. The Tb(III) compound exhibits strong green photoluminescence in the visible region. Furthermore, the magnetic property of the Gd(III) compound has been investigated in the temperature range of 2-300 K. The thermal behaviors and XPRD patterns of three compounds have also been discussed.