Figure 7.

Simplified qualitative depiction of proposed exchange-coupled states in 1-X generated using the Ising model. Differences between pairs of uranium ions are assumed to be negligible, leading to three quasi-degenerate antiferromagnetic states separated in energy from the excited, doubly degenerate, ferromagnetic state by 2J_z, _avg (≈ 2J_avg; −2J formalism). Here, J_avg is the average exchange interaction (see Section 6.4 of the Supporting Information for more details). As discussed in the text, this model was used to estimate J_avg for 1-Cl and 1-Br based on their U_eff values. Weaker exchange in the case of 1-I is proposed to give rise to the diagram depicted in Figure S124, wherein there is thermal population of the exchange-coupled excited state, and relaxation of individual uranium centers occurs via a Raman mechanism.