Zero-Field Single Molecular Magnet Behavior of Selenotungstate-Encapsulated Dy(III) Tetramers
来源：ACS Publications
Two tartaric acid-bridged organic–inorganic hybrid Dy(III)-substituted selenotungstates [HN(CH3)2]2K8Na14[(α-SeW9O33)4Dy4(H2O)4W6(tart)4O12]·33H2O (1) and K16[(α-SeW9O33)4Dy4(H2O)12W6(tart)2O12]·42H2O (2) are synthesized by controlling the reaction parameters such as counter cations and pH. Tetrameric polyoxoanions 1 and 2 consist of four trivacant Keggin [α-SeW9O33]8– fragments, which encapsulate the heterometallic clusters [Dy4(H2O)4W6(tart)4O12]12+ and [Dy4(H2O)12W6(tart)2O12]20+, respectively. The heterometallic cluster of complexes 1 and 2 contains highly coordinated flexible tartaric acid ligands, which act as linkers connecting two POM units, where tart4– ligands chelate both W(VI) and Dy(III) centers in complex 1 and only W(VI) centers in complex 2. Magnetic studies reveal zero-field single-molecule magnet behavior for both complexes. The magnetic relaxation of complex 1 follows an energy barrier (Ueff) of 52.68 K, whereas complex 2 follows the QTM relaxation process. Further, we analyze the electronic nature of both complexes to correlate their energy state distributions with magnetic properties. Additionally, the ab initio calculation results confirm the high axial ground states with minimum transverse anisotropy due to the local symmetry C2v and D2d (a subgroup of D4d) around the Dy(III) metal centers, which further helps in the stabilization of the pure highest mJ state (mJ = ±15/2) in complex 1. Notably, complex 1 is the first example of tartaric acid-bridged Dy-selenotungstates that exhibits a zero-field single-molecule magnet with a high energy barrier.