samples were lightly ground with a mortar and pestle to reduce the amount of sample decomposition, but we note that some effects due to polycrystallinity remain in the spectra below. The presence of a very sharp resonance at g = 2.00 is attributed to an impurity in the quartz EPR tubes, and serves as an internal reference for comparing relative intensities. The spectra were simulated, using EasySpin 6.0.0-dev.48 using the pepper function. The OpenMolcas 71 (version v19.11-d14be45) quantum chemistry package was used to perform CASSCF-SO calculations on 1-Ln, 3-Sm, 3-Eu, 4-Sm and 4-Eu to determine the electronic structures. The molecular geometry from a single crystal XRD structure was used by selecting a single molecule from the asymmetric unit and taking the largest disorder component only. Electron integrals were calculated using basis sets from the ANO-RCC library with VTZP quality on the metal atom, VDZP quality on the P and O atoms and VDZ quality on all other atoms, employing the second-order DKH Hamiltonian for scalar relativistic effects. Resolution of identity Cholesky decomposition (RICD) of the two-electron integrals with atomic compact Cholesky decomposition (acCD) auxiliary basis sets was employed to reduce computational demand. The molecular orbitals (MOs) for 1-Ln, 3-Sm, 3-Eu, 4-Sm and 4-Eu were optimized using state-averaged CASSCF (SA-CASSCF) wave functions; the active space taken was the valence 4f electrons and seven 4f orbitals. For 1-Eu, one Eu(II) ion was replaced with Sr(II), a diamagnetic equivalent, to determine the electronic structure and magnetic properties of one spin center at a time. The SA-CASSCF wavefunctions included 1 octet, 48 sextets, 392 quartets, and 560 doublets; a subset of these