Authors: Ibtesham Tarannum | Shruti Moorthy | Saurabh Kumar Singh
Source: Dalton Transactions (article, 2023-01-01)
Field: Materials Science — Electronic, Optical and Magnetic Materials

Understanding electrostatics and covalency effects in highly anisotropic organometallic sandwich dysprosium complexes [Dy(C<sub><i>m</i></sub>R<sub><i>m</i></sub>)<sub>2</sub>] (where R = H, SiH<sub>3</sub>, CH<sub>3</sub> and <i>m</i> = 4 to 9): a computational perspective In this article, we have thoroughly studied the electronic structure and 4f-ligand covalency of six mononuclear dysprosium organometallic sandwich complexes [Dy(C<sub><i>m</i></sub>R<sub><i>m</i></sub>)<sub>2</sub>]<sup><i>n</i>+/-</sup> (where R = H, SiH<sub>3</sub>, CH<sub>3</sub>; <i>m</i> = 4 to 9; <i>n</i> = 1, 3) using both the scalar relativistic density functional and complete active space self-consistent field (CASSCF) and N-electron valence perturbation theory (NEVPT2) method to shed light on the ligand field effects in fine-tuning the magnetic anisotropy of these complexes. Energy decomposition analysis (EDA) and <i>ab initio</i>-based ligand field theory AILFT calculations predict the sizable 4f-ligand covalency in all these complexes. The analysis of CASSCF/NEVPT2 computed spin-Hamiltonian (SH) parameters indicates the stabilization of <i>m</i><sub><i>J</i></sub> |±15/2〉 for [Dy(C<sub>4</sub>(SiH<sub>3</sub>)<sub>4</sub>)<sub>2</sub>]<sup>-</sup> (1), [Dy(C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>)<sub>2</sub>]<sup>+</sup> (2) and [Dy(C<sub>6</sub>H<sub>6</sub>)<sub>2</sub>]<sup>3+</sup> (3) complexes with the <i>U</i><sub>cal</sub> value of 1867.5, 1621.5 and 1070.8 cm<sup>-1</sup>, respectively. On the other hand, we observed <i>m</i><sub><i>J</i></sub> |±9/2〉 as the ground state for [Dy(C<sub>7</sub>H<sub>7</sub>)<sub>2</sub>]<sup>3-</sup> (4) and [Dy(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>]<sup>-</sup> (5) complexes with significantly smaller <i>U</i><sub>cal</sub> values of 237.1 and 38.6 cm<sup>-1</sup> respectively. For the nine-membered ring [Dy(C<sub>9</sub>H<sub>9</sub>)<sub>2</sub>]<sup>+</sup> (6) complex, we observed the stabilization of the <i>m</i><sub><i>J</i></sub> |±1/2〉 ground state, with the first excited state being located ∼29 cm<sup>-1</sup> higher in energy. AILFT-NEVPT2 ligand field splitting analysis indicates that the presence of π-type 4f-ligand interactions in complexes 1-3 help generate the axial-ligand field, while the δ-type interactions in complexes 4-5 generate the equatorial ligand field despite the ligands approaching from the axial direction. As the ring size increases, φ-type interactions dominate, generating a pure equatorial ligand field stabilising <i>m</i><sub><i>J</i></sub> |±1/2〉 as the ground state for 6. Calculations suggest that the nature of the ligand field mainly governs the <i>U</i><sub>cal</sub> values in the following order: 4f-L<sub>σ</sub> > 4f-L<sub>π</sub> > 4f-L<sub>δ</sub> > 4f-L<sub>φ</sub>. Calculations were performed by replacing ligands with CHELPG charges to access the crystal field (CF) effects which suggests the stabilization of pure <i>m</i><sub><i>J</i></sub> |±15/2〉 in all the charge-embedded models (1Q-6Q). Our findings point out that the crystal field and ligand field effects complement each other and generate a giant barrier for magnetic relaxation in the small ring complexes 1-3, while a relatively weak crystal field and adverse 4f-L<sub>δ</sub>/4f-L<sub>φ</sub> interactions diminish the SMM behaviour in the large ring complexes 4-6. Chemistry ; Dysprosium ; Complete active space ; Crystallography ; Ligand (biochemistry) ; Ligand field theory ; Valence (chemistry) ; Ab initio ; Ground state ; Excited state ; Density functional theory ; Computational chemistry ; Atomic physics ; Ion ; Physics ; Inorganic chemistry Magnetism in coordination complexes ; Lanthanide and Transition Metal Complexes ; Metal complexes synthesis and properties