Zero-field slow magnetic relaxation behavior of Zn2Dy in a family of trinuclear near-linear Zn2Ln complexes: synthesis, experimental and theoretical investigations

Abstract

We hereby report a series of near-linear trinuclear [Zn₂Ln^III(HL)₄(CH₃COO)]·(NO₃)₂ (where Ln^III = La (1_-La), Ce (2_-Ce), Nd (3_-Nd), Sm (4_-Sm), Tb (5_-Tb), and Dy (6_-Dy)) complexes with Schiff base ligand (H₂L). Magnetization relaxation dynamic studies on complexes 2_-Ce, 5_-Tb, and 6_-Dy reveal the existence of well resolved frequency dependent zero-field out-of-phase χ′′_M signals, which is an indicator of a typical single-ion magnet behavior observed only for complex 6_-Dy with U_eff = 43.7 K (τ₀ = 2.42 × 10⁻⁶ s). The presence of two Zn(II) ions near the coordination geometry of Dy(III) ion in 6_-Dy is likely to keep the first excited m_J levels significantly away from the ground state m_J level and is responsible for the observation of zero field slow magnetic relaxation behavior. The data collected in the presence of a magnetic field of H_dc = 2 kOe enhances the energy barrier by two-fold (88.63 K, τ₀ = 1.36 × 10⁻⁷ s) in 6_-Dy, suggesting the presence of QTM at zero field along with other under barrier relaxations, such as the Raman process. On the other hand, complex 2_-Ce shows field induced slow relaxation of magnetization behavior with an effective energy barrier of 12.24 K (τ₀ = 1.89 × 10⁻⁴ s). The CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations using MOLCAS 8.0 code further rationalized our experimentally observed magnetization dynamics.