Unravelling the electronic structure, bonding, and magnetic properties of inorganic dysprosocene analogues [Dy(E4)2]− (E = N, P, As, CH)

Abstract

Organometallic sandwich complexes of Dy(III) ion are ubiquitous for designing high-temperature single-ion magnets with blocking temperatures close to the liquid nitrogen boiling point. Magnetic bistability at the molecular level makes them potential candidates for nano-scale information storage materials. In the present contribution, we have thoroughly investigated the electronic structure, bonding, covalency, and magnetic anisotropy of inorganic dysprosocene complexes with a general formula of [Dy(E₄)₂]⁻ (where E = N, P, As, CH) using state-of-the-art scalar relativistic density functional theory (SR-DFT), and a multiconfigurational complete active space self-consistent field (CASSCF) method with the N-electron valence perturbation theory (NEVPT2). Geometry optimization calculations predict stabilization of the [Dy(E₄)₂]⁻ complexes with a linear geometry and D_4h local symmetry Dy(III) ion in [Dy(N₄)₂]⁻ (1) and [Dy(P₄)₂]⁻ (2) complexes, while a bent geometry has been observed for the [Dy(As₄)₂]⁻ (3), [Dy(P₂(CH)₂)₂]⁻ (4), and [Dy(As₂(CH)₂)₂]⁻ (5) complexes. Energy decomposition analysis (EDA) and natural bonding orbital (NBO) calculations reveal sizable 5d–ligand covalency followed by 6s/6p and weak 4f–ligand covalency in complexes 1–5. Both the natural localized molecular orbitals (NLMOs) at the DFT level and ab initio-based ligand field theory (AILFT) at the NEVPT2 level of theory predict an increase in the Dy–ligand covalency as we move from N to As. Spin-Hamiltonian parameter analysis of complexes 1–5 reveals stabilization of the m_J |±15/2〉 as the ground state with highly axial g values (g_xx ∼ g_yy ∼ 0 and g_zz ∼ 20) and the barrier height of 2902, 1214, 1104, 1845, and 1509 K for 1–5, respectively. The Orbach effective demagnetization barrier (U_eff) for complexes 1–5 ranges between 2416–1175 K, with a record U_eff value of 2416 K observed for 1. In addition, we have explored the role of heavy element effects on the magnetic anisotropy by turning off the spin–orbit coupling of the pnictogens (N, P, and As), and our calculations clearly predict that heavy atoms in the first coordination sphere help in increasing the barrier height for magnetic relaxation. Heavy elements like P and As significantly enhance the SOC contributions, thereby providing a platform for designing and optimizing Dy(III) complexes with tailored magnetic behaviors.