Luminescence and Single-Molecule Magnet Properties in Ideal Symmetry Compounds: Example of a Near-Planar Tricoordinate Ytterbium(III) Amide

Abstract

We are reporting on the use of a low-coordinate Yb^III amide with near-ideal planar trigonal [Yb{N(SiMe₃)₂}₃] (1) and on a bipyramidal trigonal derivative [Yb{N(SiMe₂H)₂}₃ ⋅ (thf)₂] (2) that constitute quintessential cases to investigate luminescent and magnetic properties otherwise usually blurred on less symmetrical compounds. These compounds represent the first experimental objects that allow for the confirmation of the recent conjecture about best-performing SMM built on the archetypal prolate lanthanide ion. We have performed a combined theoretical, luminescent, and magnetic study on these molecules. For 1, a spectacular split of the ²F_7/2 ground state of 1312 cm⁻¹ is measured by low-temperature near-infra-red luminescence as well as the calculated pure wavefunction composition of the low-lying Kramers doublets, making this complex a textbook example of a prolate SMM. These results are corroborated by comparison with 2, that exhibits as expected a 50 % decrease of the ground state splitting compared to 1. Yet, we show that these remarkable features are insufficient to promote SMM behavior, and Orbach relaxation is unlikely to occur even on such an ideal low-coordinate SMM without control of spin-phonon coupling.