Magnetic Excitations in Polyoxotungstate-Supported Lanthanoid Single-Molecule Magnets: An Inelastic Neutron Scattering and ab Initio Study

Abstract

Inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) magnetic excitations of the analogs of the most representative lanthanoid-polyoxometalate single-molecule magnet family: Na[Ln(WO)] (Ln = Nd, Tb, Ho, Er). Ab initio complete active space self-consistent field/restricted active space state interaction calculations, extended also to the Dy analog, show good agreement with the experimentally determined low-lying CF levels, with accuracy better in most cases than that reported for approaches based only on simultaneous fitting to CF models of magnetic or spectroscopic data for isostructural Ln families. In this work we demonstrate the power of a combined spectroscopic and computational approach. Inelastic neutron scattering has provided direct access to CF levels, which together with the magnetometry data, were employed to benchmark the ab initio results. The ab initio determined wave functions corresponding to the CF levels were in turn employed to assign the INS transitions allowed by selection rules and interpret the observed relative intensities of the INS peaks. Ultimately, we have been able to establish the relationship between the wave function composition of the CF split Ln ground multiplets and the experimentally measured magnetic and spectroscopic properties for the various analogs of the Na[Ln(WO)] family.

Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet

“…INS experiments allowed for the high-resolution investigation of the CF excitations 39 – 41 . Since neutrons carry a magnetic moment (giving rise to the selection rule Δ m J = ±1) and show direct interaction with both nuclear and magnetic degrees of freedom, assignment of CF excitations depend on analysis of momentum transfer ( Q ).…”

Inelastic Neutron Scattering of Lanthanoid Complexes and Single‐Molecule Magnets

“…The trivalent rare‐earth ions have similar ionic radii thus it is often possible to synthesise isomorphous diamagnetic analogues with a similar phonon spectrum. This allows the phononic background to be measured with a good degree of accuracy, thus a common strategy is to measure the diamagnetic Y, La or Lu analogue , , , , . The paramagnetic spectrum of interest can then be presented following subtraction of the diamagnetic “phonon” spectrum.…”

“…An added advantage is the steric bulk of many polyoxometalates, helping to minimise undesirable intermolecular interactions. We have employed INS to investigate two families of polyoxometalate‐based Ln‐SMMs . The first compound studied was the SMM‐analogue Na 9 [Tb(W 5 O 18 ) 2 ] ( 3‐Tb ) which was investigated on the PELICAN TOF beamline at the Australian Centre for Neutron Scattering (ACNS), Australia .…”

“…A pure sample of one polymorph of 3‐Tb was later investigated (Figure ), together with pure polymorphs of the Nd, Ho and Er analogues on PELICAN, providing a systematic study of the family of SMMs . All analogues exhibit CF transitions within the energy range measured, with well‐defined transitions observed.…”

“…Magnetic transitions are labelled with Roman numerals; a spurious peak is indicated with an asterisk. Adapted with permission from ref . Copyright 2017 American Chemical Society.…”