Varying anion coordination in new families of dinuclear Ni^IILn^III complexes: zero-field slow relaxation of magnetization and theoretical validations

Herein, we report the room-temperature synthesis, structural characterization, and magnetic performances of two new families of dinuclear Ni^II-Ln^III complexes, [NiLn(HL)₂(NO₃)₃]·<i>n</i>H₂O·CH₃CN (1a-1c) (<i>n</i> = 1 for Ln = Tb, and <i>n</i> = 1.5 for Dy and Ho) and [NiLn(HL)₂(OAc)₂(H₂O)]Cl·5H₂O (2a-2c) (Ln = Tb, Dy, and Ho), developed utilizing the ligand H₂L (2-methoxy-6-[(<i>E</i>)-2'-hydroxymethyl-phenyliminomethyl]-phenol). Partial deprotonation of H₂L in the reaction medium provided HL^-, ideally suited for trapping Ni^II and selected 4f ions in its two adjacent pockets. X-ray structural characterization of complexes 1a-2c showed the preferential pinning of the octahedral Ni^II center by the imine N-donor alongside Ln^III centers with a coordination number of nine in a muffin geometry. Both Dy analogs exhibited clear out-of-phase signals (1b and 2b; <i>U</i>_eff = 20 K and 18.7 K, respectively) in the absence of an external dc field in ac magnetic susceptibility measurements, whereas slow relaxation of magnetization was apparent under the optimal applied fields of 2 and 3 kOe for the Tb analogs (1a and 2a) and Ho analogs (1c and 2c), respectively. The analysis of static and dynamic magnetic properties was reinforced by thorough CASSCF-based computational analysis and density functional theory (DFT) calculations.