Strong uranium-phosphorus antiferromagnetic exchange coupling in a crystalline diphosphorus radical trianion actinide complex

Abstract

The dominant form of elemental nitrogen on Earth is dinitrogen, but elemental phosphorus is found predominantly as white phosphorus or other singly bonded allotropes. Thus, there is interest in studying diphosphorus derivatives, most notably trapping between metal ions affording diphosphorus in +2, +1⋅, 0, 1−⋅, 2−, and 4− charge states. However, the diphosphorus radical trianion form had previously remained elusive due to the instability of main-group diatomics with large, odd negative charges. Here, we disclose a crystalline diuranium diphosphorus radical trianion complex with strong antiferromagnetic uranium-phosphorus magnetic exchange coupling parameters of up to −731 cm⁻¹. This value is over five times greater than that of lanthanide analogues and is comparable to or exceeds d-block metal-metal and metal-ligand exchange couplings, despite being based on a 5f metal, which is typically regarded as possessing contracted valence orbitals compared with d-block ions. This highlights exchange-coupled f-element-p-block radical bridged character that can be engendered in molecular magnetism.