Magnetic effects of lanthanide bonding Lanthanide coordination compounds have attracted attention for their persistent magnetic properties near liquid nitrogen temperature, well above alternative molecular magnets. Gould et al . report that introducing metal-metal bonding can enhance coercivity. Reduction of iodide-bridged terbium or dysprosium dimers resulted in a single electron bond between the metals, which enforced alignment of the other valence electrons. The resultant coercive fields exceeded 14 tesla below 50 and 60 kelvin for the terbium and dysprosium compounds, respectively. —JSY

download file view on ChemRxiv Long_Layfield.docx (1.12 MiB) download file view on ChemRxiv Long_Layfield_SI.docx (5.82 MiB) Ab initio prediction of high-temperature magnetic relaxation rates in single-molecule magnets

Single-molecule magnets (SMMs) could potentially store binary information in future ultra-high-density information storage devices. The current challenge to improve performance is understanding and preventing memory loss via molecular vibrations. In this work, we synthesize an improved SMM over a previous design and use a computational approach to probe how molecular vibrations contribute to memory loss.

Vibronic coupling, the interaction between molecular vibrations and electronic states, is a fundamental effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to directly probe vibronic transitions in [Yb(trensal)] (where H3trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, which we calculate fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C3 symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.

Magnetisation decay measurements are commonly being used to characterise very slow relaxation in single-molecule magnets. We explore measurement protocol and data analysis to define the best practise.

Isolated dysprosocenium cations, [Dy(CpR)2]+ (CpR = substituted cyclopentadienyl), have recently been shown to exhibit superior single-molecule magnet (SMM) properties over closely related complexes with equatorially-bound ligands. However, gauging the crossover point at which the CpR substituents are large enough to prevent equatorial ligand binding, but small enough to approach the metal closely and generate strong crystal field splitting, has required laborious synthetic optimization. We therefore created the computer program, AtomAccess, to predict the accessibility of a metal binding site and its ability to accommodate additional ligands. Here we apply AtomAccess to rapidly screen a series of derivatized dysprosium metallocene fragments of varying steric bulk in silico, allowing us to identify the crossover point for equatorial coordination in [Dy(CpR)2]+ cations, and hence predict a cation that is at the cusp of stability without equatorial interactions, viz. [Dy(Cpttt)(Cp*)]+ (Cpttt = C5H2tBu3-1,2,4, Cp* = C5Me5). Upon synthesizing this cation we found it crystallizes as either a contact ion-pair, [Dy(Cpttt)(Cp*){Al[OC(CF3)3]4-k-F}], or separated ion-pair polymorph, [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4]C6H6. These complexes, together with their precursors and yttrium analogs, have been characterized by NMR and ATR-IR spectroscopy, elemental analysis, powder and single crystal X-ray diffraction, SQUID magnetometry and ab initio calculations. We find that the contact ion-pair shows inferior SMM properties to the separated ion-pair, as expected, due to faster Raman and quantum tunneling of magnetization relaxation processes. The experimental verification of the predicted crossover point for equatorial coordination in this work indicates that programs like AtomAccess have significant potential to boost efficiency in exploratory synthetic chemistry.

Electron–phonon coupling underlies many physical phenomena, but its microscopic origins are nuanced. This Review derives the spin–phonon interactions in molecules from first principles, and describes an implementation for molecular spin dynamics calculations.

The novel series of heteroleptic Sm(iii) halide complexes provides the backdrop for a fluorescence-detected Lα1 X-ray absorption spectroscopic study.