Attainment of Pentagonal-Bipyramidal LnIII Complexes from a Planar Pentadentate Ligand

Abstract

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 an axial symmetry, as they could maximize the anisotropy of complexes of oblate lanthanoid ions, such as dysprosium(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 SIMs. 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 LnIII complexes (these being Ln: Dy and Er, oblate and prolate, respectively), in order to compare their structures. Thus, the reaction of H4daps with (CH3)4NOH·5H2O and the corresponding LnCl3·hexahydrate has yielded heptacoordinate [(CH3)4N][LnIII(H2daps)Cl2] complexes, where the tetramethylammonium cation is acting as the counterion of pentagonal–bipyramidal LnIII complexes, which are bearing two chloride atoms in apical positions. As both complexes could be crystallized as single crystals, we can compare their crystal structures, as well as with some other related complexes in the literature, which contain different counterions, trying to see their influence on other properties of the compounds, such as their magnetic behavior.

A Series of Novel Pentagonal-Bipyramidal Erbium(III) Complexes with Acyclic Chelating N3O2 Schiff-Base Ligands: Synthesis, Structure, and Magnetism

“…05 (H 2 DAPS)Cl 2 ] − (6), do not display the frequency dependence of the χ (ν) and χ"(ν) signals in the zero/nonzero DC applied field, opposite to the similar isostructural Dy complexes, which are field-induced SMMs [53]. A similar behavior was observed in the case of erbium and dysprosium anionic complexes, [Er(Dy)(H 2 DAPS)Cl 2 ] − , with the counterion, [(CH 3 ) 4 N] + [54]. Such a difference in the magnetic properties of these isostructural dysprosium and erbium complexes can be easily understood in terms of the difference in the form of the 4f electron density for the Dy 3+ and Er 3+ ions: oblate and prolate (equatorially or axially elongated f -electron charge clouds), respectively [35].…”

“…The interaction of ErCl 3 with H 4 DAPS in absolute ethanol in the presence of the deprotonating agent, Et 3 N, leads, as we have shown, to the desired erbium complex, [(Et 3 H)N] + [Er(H 2 DAPS)Cl 2 ] − (5) (Figure 4). An analogous anionic Er complex was recently synthesized, but with a different counterion, [(CH 3 ) 4 N] + arising from the use of the deprotonating agent, (CH 3 ) 4 NOH [54]. Note that Compound 5 is an erbium analogue of the dysprosium complex, as has been described in [53].…”

“…For a Dy analog containing 95% of diamagnetic Y, the value of the magnetization barrier is 70 K under a low DC field, equal to 500 Oe. Despite the fact that the seven-coordinated PBP Dy complexes are being actively studied [33,34], we are aware of only three works in which the PBP Er complexes with pseudo-D 5h symmetry have been described [32,54,55]. Considering that Dy and Er have fundamentally different distributions of 4f electron density, oblate and prolate, respectively [35], it is of interest to synthesize PBP erbium complexes with acyclic pentadentate (N 3 O 2 ) ligands and to perform a comparative study of their SMM properties, depending on the nature of the axial ligands.…”