Two [Ln(4)] molecular rings folded as compact tetrahedra

Abstract

The design of photoactive ligands may provide access to multifunctional molecular nanomagnets. Wereport here the design and synthesis of a new multitopic chelating ligand, 1,2-bis-(5-(N'-(pyridine-2-yl-methylene)-carbohydrazide)-3-methyl-thien-3-yl)-cyclopentene (H2L), bearing a photoswitchablespacer and demonstrate that it undergoes reversible photoisomerization in solution. In the presence ofthe base NaH, H2L reacts with LnCl3salts (Ln = Dy, Tb) to form the supramolecular assemblies H2O@[Ln4L4Cl4(H2O)4] (Ln = Dy,1; Tb,2). The single crystal X-ray diffraction data of1and2reveal that bothcompounds consist of highly symmetric molecular rings efficiently folded through intramolecular weakinteractions in the form of tetrahedra. This arrangement imparts a conformation to the photochromicspacer of the ligand which inhibits its photoswitching activity. Despite the low symmetry of the coordi-nation geometry around the Ln ions, the Dy analog exhibits slow relaxation of the magnetization. Therelaxation rate under various conditions has been investigated, allowing us to elucidate the mechanismsinvolved in this relaxation.