Synthesis, Crystal Structures, and Magnetic Properties of Lanthanide (III) Amino-Phosphonate Complexes

Abstract

Both compounds have been characterized with elemental analysis, single-crystal X-ray diffraction methods, and magnetic measurements. The molecular structure of compounds 1 and 2 reveal two highly unsymmetrical complexes comprising ten lanthanide metal centers, where the lanthanide metal ion centers in the cages are linked through pivalate units and further interconnected by CPO 3 tetrahedra to build the crystal structure. The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K, the magnetic measurements for compound 1 suggests antiferromagnetic interactions between the Gd(III) metal ion centers at low temperatures. The large number of isotropic Gd(III) ions comprising 1 makes it a candidate for magnetocaloric applications, thus the magnetocaloric properties of this molecular cage were investigated indirectly through isothermal magnetisation curves. The magnetic entropy change was found to be 34.5 J kg −1 K −1 , making 1 a plausible candidate in magnetic cooling applications.

Phosphonated Podand Type Ligand for the Complexation of Lanthanide CationsPhosphonated Podand Type Ligand for the Complexation of Lanthanide Cations

“…The coordination chemistry of phosphonate functions with Ln cations can be quite complicated by the various binding modes which can be adopted . It is not rare to see that the three oxygen atoms of the function can take part into coordination of numerous Ln cations in the solid state, such as the pentadentate coordination observed in some structures of aminophosphonate complexes of Gd, or the bridging mono‐ or bidentate modes of Ln helical structures . However, phosphonate functions are also bringing numerous advantages, replacing favourably their carboxylate counterparts on a thermodynamic point of view with a larger steric hindrance that may allow to exclude water molecules from the first coordination sphere such as in the DOTP complexes, having a double negative charge around neutral pH, and bringing very important second sphere interactions, which can be advantageously used for MRI contrast agents for example .…”