Peripheral site modification in a family of dinuclear [Dy2(hynad)2–6(NO3)0–6(sol)0–2]0/2− single-molecule magnets bearing a {Dy2(μ-OR)2}4+ diamond-shaped core and exhibiting dissimilar magnetic dynamics

Abstract

The first use of the organic chelate N-hydroxy-1,8-naphthalimide (hynadH) in Dy^III chemistry has unveiled access to a synthetic ‘playground’ composed of four new dinuclear complexes, all of which possess the same planar {Dy₂(μ-OR)₂}⁴⁺ diamond-shaped core, resulting from the bridging and chelating capacity of the hynad⁻ groups. The structural stability of the central {Dy₂} core has allowed for the modulation of the peripheral coordination sites of the metal ions, and specifically the NO₃⁻/hynad⁻ ratio of capping groups, thus affording the compounds [Dy₂(hynad)₂(NO₃)₄(DMF)₂] (1), (Me₄N)₂[Dy₂(hynad)₂(NO₃)₆] (2), [Dy₂(hynad)₄(NO₃)₂(H₂O)₂] (3), and [Dy₂(hynad)₆(H₂O)₂] (4). Because of the chemical and structural modifications in the series 1–4, the Dy^III coordination polyhedra are also dissimilar, comprising the muffin (1 and 3), tetradecahedral (2), and spherical tricapped trigonal prismatic (4) geometries. Complexes 1, 2, and 4 exhibit a ferromagnetic response at low temperatures, while 3 is antiferromagnetically coupled. All compounds exhibit out-of-phase (χ′′_M) ac signals as a function of ac frequency and temperature, thus behaving as single-molecule magnets (SMMs), in the absence or presence of applied dc fields. Interestingly, the hynad⁻-rich and nitrato-free complex 4, demonstrates the largest energy barrier (U_eff = 69.62(1) K) for the magnetization reversal which is attributed to the presence of the two axial triangular faces of the spherical tricapped trigonal prism by the negatively charged O-atoms of the hynad⁻ ligands.