Attainment of Pentagonal-Bipyramidal Ln^III Complexes from a planar pentadentate ligand

The search for mononuclear lanthanoid-based single-ion magnets (SIMs) has increased the interest in some coordination environments with low coordination numbers, in combination with uniaxial symmetry, as they could maximize the anisotropy of complexes of oblate lanthanoid ions, as disprosium(III). ions as disprosium(III). In this sense, the pentagonal-bipyramid geometry can have ground-state doublets with perfect axiality, and therefore such complexes can be good candidates for SIM. In our particular case, we have used a well-known open planar pentadentate chelating Schiff base ligand as 2,6-bis(1-salicyloylhydrazonoethyl)pyridine) (H₄daps) for the synthesis of air-stable pentagonal-bipyramidal Ln^III complexes (being Ln: Dy and Er, oblate and prolate, respectively), in order to compare their structures. Thus, reaction of H₄daps with (CH₃)₄N·5H₂O, and the corresponding LnCl₃·hexahydrate has yielded heptacoordinate [(CH₃)₄N][Ln^III(H₂daps)Cl₂] complexes, where the tetramethylammonium cation is acting as counterion of pentagonal-bipyramidal Ln^III complexes, which are bearing two chloride atoms in apical positions. As both complexes crystallized as single crystals, we can compare their crystal structures as well as with other related complexes in literature, but containing different counterions, trying to see their influence on other properties of the compounds, as their magnetic behavior.