Abstract
A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N3O2] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H2DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H4DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C2H5OH)Cl] (1); [Er(DAPMBH)(H2O)Cl]·2C2H5OH (2); [Er(DAPMBH)(CH3OH)Cl] (3); [Er(DAPMBH)(CH3OH)(N3)] (4); [(Et3H)N]+[Er(H2DAPS)Cl2]− (5); and [(Et3H)N]+[Y0.95Er0.05(H2DAPS)Cl2]− (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, Ueff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.
Highlights
It has become obvious that magnetic anisotropy is the most critical factor for the development of high-performance single-molecule magnets (SMMs) [1,2,3]
An effective strategy for increasing the magnetization reversal barriers (Ueff) and the blocking temperature (TB) of molecular nanomagnets is based on the use of coordination metal centers with enhanced spin–orbit coupling [4,5,6,7,8], which are capable of producing strong uniaxial magnetic anisotropy, especially in the case of a suitable coordination environment [6,9,10,11,12,13,14,15]
To study the impact of the charge states of the axial ligands on the magnetic behavior of the Er+3 pentagonal-bipyramidal (PBP) complexes in an alternating magnetic field, we synthesized a series of six seven-coordinate PBP complexes, including a plane pentadentate ligand with a [N3 O2 ]2− binding node in the equatorial position, and various axial ligands
Summary
It has become obvious that magnetic anisotropy is the most critical factor for the development of high-performance single-molecule magnets (SMMs) [1,2,3]. An alternative way to achieve high SMM characteristics is to control the coordination geometry and the symmetry around the lanthanide ions with the aim of quenching the unwanted quantum tunneling of magnetization (QTM) through the use of appropriately designed molecules with higher-order symmetries [3]. These factors, taken together, ensure the unquenched angular orbital momentum of the metal center, resulting in strong uniaxial magnetic anisotropy. The PBP geometry in these complexes is largely random, since the Ln3+
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