Coordination-driven assembly of dysprosium layers into a framework featuring enhanced energy barriers and quantum tunneling of magnetization

Abstract

An orchestrated reaction of Dy(ClO₄)₃·6H₂O with the organic ligand of N′-(2-hydroxybenzylidene)pyrazine-N-oxide-carbohydrazide (H₂L) affords a layered building block, denoted as {[Dy(L)(H₂O)(CH₃OH)]ClO₄·2CH₃OH}_n (1). Subsequently, the coordinated water and methanol molecules in 1 are efficaciously substituted by a di-topic ligand of 4,4′-bipyridine-N,N′-dioxide (bpdo), producing a unique three-dimensional framework labeled as {[Dy(L)(bpdo)]ClO₄·2H₂O}_n (2). Magnetic measurements demonstrate the ferromagnetic interaction between the dysprosium ions, as well as the slow magnetic relaxation under a zero dc field with the effective spin-reversal barriers of 161(7) K and 203(6) K for 1 and 2, respectively. Further ab initio calculations indicate that the enhanced energy barrier of 2 is associated with the alteration of coordination environment around the Dy³⁺ ion, while the introduction of the bpdo bridging ligand leads to the stronger magnetic anisotropy of the Dy³⁺ ion and thus the magnetic relaxation pathway through the second excited state. Furthermore, the bpdo ligand also introduces stronger equatorial charge and may result in faster quantum tunneling of magnetization in 2.