Two new series of rare-earth organic frameworks involving two structural architectures: syntheses, structures and magnetic properties

Abstract

The preparation and properties of two new series of rare-earth organic frameworks, [Ln2(cam)2(NO3)2(MeOH)4]n (Ln = Gd (1·Gd), Tb (1·Tb), Dy (1·Dy), Ho (1·Ho) and Er (1·Er)) and [Ln(D-cam)(O2CH)]n (Ln = Tb (2·Tb), Dy (2·Dy), Ho (2·Ho) and Er (2·Er); D-H2cam = (+) D-camphoric acid) under solvothermal conditions is described. Single-crystal X-ray diffraction analyses revealed that the 1·Gd–1·Er compounds are isostructural and crystallize in the monoclinic space group P21/n with the chiral D-camphorate ligand racemized, while the 2·Tb–2·Er compounds are isostructural and crystallize as orthorhombic with the chiral space group P21212121. The structures of the 1·Gd–1·Er compounds consist of a dimeric sub-building unit (SUB) of [Ln2(O2CR)4(NO3)2(MeOH)4], which is covalently-linked by cam2− to a 2D grid layer and the layer is extended into a 3D supramolecular network by hydrogen bonding. Compounds 2·Tb–2·Er feature a three-dimensional homochiral framework involving one-dimensional lanthanide–carboxylate chains that are aligned parallel to the [100] direction. Direct current (dc) magnetic susceptibility data were collected for these two series of compounds. The findings indicate that compound 1·Gd shows a Gd⋯Gd antiferromagnetic interaction through carboxylate bridges, with a coupling constant of J = −0.034 cm−1. Compounds 1·Tb–1·Er, and 2·Dy–2·Er are dominated by the depopulation of Stark levels, while 2·Tb exhibits ferromagnetic interaction between the Tb3+ ions. Interestingly, compounds 1·Dy and 2·Dy exhibit frequency-dependent out-of-phase signals in alternating current (ac) magnetic susceptibility measurements indicating their slow magnetic relaxation characteristics.