Maximizing the magnetic anisotropy of Dy complexes by fine tuning organic ligands: A systematic multireference high-throughput exploration of over 30k molecules

Abstract

The design of the coordination environment of magnetic ions is key to achieving properties such as large magnetic anisotropy and slow magnetic relaxation, but a systematic exploration of the relevant chemical space for these compounds is missing. Here, we automatically extract all entries of mononuclear Dy coordination complexes from crystallographic databases and use multireference ab initio methods to compute their magnetic anisotropy. In addition, we generate and simulate magnetic anisotropy for 25k new molecules with the general formula [Dy(H$_2$O)$_5$L$_2$]$^{n-}$ and pentagonal bipyramidal coordination geometry, a motif selected as very promising. While no molecule with record magnetic anisotropy is serendipitously identified in crystallography databases, molecules with crystal field splittings over 1600 cm$^{-1}$ are identified by systematically exploring new organic ligands. This corresponds to a ~100% increase of magnetic anisotropy over the reference compound, ~30% over any known pentagonal bipyramidal Dy complex, and approaching record values of pseudo bi-coordinated Dy ions. This study demonstrates that the fine-tuning of Dy's second coordination sphere by organic ligands design can significantly improve magnetic anisotropy and that automated computational screening is key to accelerating this chemically non-intuitive process.

Figures (8)

• Figure 1: Dysprosocenium energy levels. The computed energy levels for [Dy(Cp$^{ttt}$)$_2$]$^{+}$ (Cp$^{ttt}$=C$_5$H$_2^t$Bu$_3$-1,2,4 and $^t$Bu=C(CH$_3$)$_3$) goodwin2017molecular are plotted as a function of the reference $\hat{J}_z$ expectation value. Arrows indicate the energy gaps between the ground state and the first and last KDs.
• Figure 2: Electronic properties of screened compounds. Electronic properties of compounds deposited in the COD, CCSD, and SIMDAVIS databases, computed at the CASSCF level of theory. (a) Population distribution of the screened compounds with respect to the computed energy of the first electronic excited state. (b) Population distribution of the screened compounds with respect to the computed energy of the seventh electronic excited state, i.e., the highest electronic state of the fundamental multiplet $J = 15/2$. (c) Each panel shows the eigenvalues of the projected effective $S = 1/2$$g$-tensor for the first eight KDs. The $g_z$ component is reported on the y-axis, while the x-axis represents the average value of the $g_x$ and $g_y$ components. The colour map of the points corresponds to the value of $\Delta E_{01}$ for each compound. The red dashed line shows the $g_z$ value for a perfect setup of axially aligned KD levels.
• Figure 3: First coordination shell symmetry analysis. First ($\Delta E_{01}$, left) and last ($\Delta E_{07}$, right) excited KDs energies computed at the CASSCF level for each symmetry detected in the database. The color bar shows the CShM score of each compound, where smaller values indicate a closer match to the reference symmetry. Compounds containing hapticity-defined ligands bound to the magnetic center could not be assigned a reference symmetry with the SHAPE software and are shown as black dots and labeled as "$\eta$".
• Figure 4: Reference pentagonal bi-pyramidal compound and PCA. Panel a) shows the three-dimensional structure of the compound [($^t$BuPO(NH$^i$Pr)$_2$)$_2$Dy(H$_2$O)$_5$]$^{3+}$Air-stable_2016, where the central Dy(III) atom is surrounded by five water molecules in plane, and two $^t$BuPO(NH$^i$Pr)$_2$ ligands as the axial ligands. Panel b) shows the reduced structure of the Dy(III) core with the planar water ligands used to assemble new pentagonal bi-pyramidal compounds by inserting new axial ligands (L). Cyan: Dy, Red: O, Blue: N, Grey: C, White: H, Yellow: P. Panel c) shows the distribution of the principal components of the ligands' bispectrum components, sorted in colour by their different connecting atom species.
• Figure 5: Distribution of compounds in the database. We first show the distribution of first (a) and last (b) KD energies compared to the best known reference compounds(Compound 1:Sourav_2022, Compound 2: Air-stable_2016, Compound 3-6: Qian-Cheng_2025. Panel c) shows the relationship between the eight KDs $g_x, g_y$ and $g_z$ values, with their corresponding first KD gap visualized by colour. The inset zooms on the regime between 19.9 and 20 for $g_z$ and 0 and 0.01 for $g_x+g_y$. The red dashed line shows the $g_z$ value for a perfect setup of axially aligned KD levels.