Aufbau <em>vs.</em> non-Aufbau ground states in two-coordinate d⁷ single-molecule magnets

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>Single-molecule magnets (SMMs) with d⁷ electronic configurations often require designer ligands to satisfy the metals electronic conditions to achieve large angular momentum. Herein, the slow relaxation of the magnetization in two d⁷ metal complexes in near identical ligand fields is achieved from divergent origins. The two compounds, [Co^II{N(SiMePh₂)₂}₂] and [K(2,2,2-crypt)][Fe^I{N(SiMePh₂)₂}₂] (2,2,2-crypt = 2,2,2-cryptand), display unusual electronic configurations giving rise to SMM behavior originating either from 3d–4s orbital mixing or a non-Aufbau ground state. The chracteristics contributing to the rare non-Aufbau ground state configurations are illuminated by the use of a highly donating amido-ligand, which would be expected to significantly split the respective orbitals. Magnetic circular dichroism provides experimental support for <em>ab initio</em> determined electronic structures. Moreover, computational models reveal that the relative electronic configurations are largely retained independently of coordination geometry, provided that some degree of pseudo-linearity is retained. Thus, providing generalized design principles in the pursuit of linear d⁷ SMMs.</p></div>