The rational construction of diamond-like dysprosium–hexacyanometallate frameworks featuring dynamic magnetic behaviour

Abstract

Four novel isostructural heterometallic dysprosium–hexacyanometallate frameworks, namely {[Dy₄(L)₄(H₂O)₄(CH₃OH)₄M(CN)₆]·Cl·8H₂O}_n and {[Dy₄(L)₄(H₂O)₄(CH₃OH)₄M(CN)₆]·Br·4CH₃OH}_n (M = Fe for 1 and 3, Co for 2 and 4; H₂L = N′-(2-hydroxybenzylidene)picolinohydrazide) have been successfully assembled by a feasible approach employing a superparamagnetic dimeric unit as the building block and hexacyanometallates [M(CN)₆]³⁻ as bridges. Within these frameworks, hexacyanometallates serve as 4-way nodes and connect the adjacent dimeric building blocks to form a three-dimensional diamond-like structure with a Schlafli symbol of 6^6. Magnetic measurements indicate the ferromagnetic nature of intradimer Dy³⁺–Dy³⁺ interactions, the antiferromagnetic coupling between Dy³⁺ ions and adjacent [Fe(CN)₆]³⁻ units, as well as the dynamic magnetic behaviour under zero dc field with the effective energy barriers of 111(2), 283(8), 108(2), and 280(15) K for 1–4, respectively. Ab initio calculations and in-depth magneto-structural studies demonstrate that the magnetic anisotropy of Dy³⁺ ions and the intradimer ferromagnetic coupling are positive factors for slowing down the quantum tunnelling of magnetization (QTM), resulting in the highest effective energy barrier and the largest coercive field for 2 among all compounds, while the antiferromagnetic interaction between Dy³⁺ ions and [Fe(CN)₆]³⁻ units can accelerate the QTM and thus shut off the magnetic memory effect of 1 and 3 at low temperature.