# Geometry-Driven Field-Induced Single-Ion Magnetism in Hexagonal Bipyramidal Tb3+ and Ho3+ Complexes

## TL;DR

This paper reports the first Tb3+ and Ho3+ complexes with a hexagonal bipyramidal shape that act as single-ion magnets under a magnetic field.

## Contribution

First field-induced Tb3+ and Ho3+ single-ion magnets with hexagonal bipyramidal geometry and macrocyclic ligands in nonsandwich topology.

## Key findings

- Hexagonal bipyramidal Tb3+ and Ho3+ complexes exhibit single-ion magnet behavior under 2000 Oe field.
- Applied field partially suppresses quantum tunneling of magnetization in these complexes.
- Magnetic relaxation at higher temperatures is dominated by the Raman process, supported by ab initio calculations.

## Abstract

The synthesis of the precursors [Ln­(LN6en)­(CH3COO)2]­(BPh4)·nH2O (Ln = Tb, n = 0, 1;
Ln = Ho, n = 1, 2·H2O), followed by
a ligand exchange reaction with triphenylsilanolate, results in the
isolation of the complexes {[Ln­(LN6en)­(OSiPh3)2]­(BPh4)}·2CH2Cl2 (Ln = Tb, 3·2CH2Cl2; Ln
= Ho, 4·2CH2Cl2). Single-crystal
X-ray diffraction studies of 3·2CH2Cl2 and 4·2CH2Cl2 revealed
that both compounds adopt a hexagonal bipyramidal geometry. Magnetic
characterization shows that the complexes behave as single-ion magnets
(SIMs) under an optimal applied field of 2000 Oe. Notable, these are
the first reported Tb3+ and Ho3+ complexes with
a hexagonal bipyramidal coordination geometry to exhibit such magnet-like
behavior. Furthermore, they constitute the first field-induced Tb3+ and Ho3+ SIMs incorporating a macrocyclic ligand
in a nonsandwich topology. Magnetic measurements indicate that the
applied field only partially suppresses quantum tunneling of magnetization
(QTM) and that at higher temperatures magnetic relaxation is dominated
by the Raman process rather than the Orbach mechanism. These experimental
observations are supported by ab initio calculations, which provide
detailed insights into the electronic structure, including the splitting
of f-orbital energy levels, thereby elucidating the origin of the
observed magnetic behavior in both cases.