An alkoxyborate-bridging Dy2 single-molecule magnet with ferromagnetic coupling

Abstract

Non-radical bridges capable of coupling Ising-type magnetic anisotropy in a collinear manner are rather limited in the construction of dinuclear single-molecule magnets (SMMs). Here, we report the first alkoxyborate-bridging SMM [Dy₂(B(OMe)₄)(Hdapp)₂(^tBu-DDTP)₂](BPh₄)·3MeOH (1, where H₂dapp = (2,6-diacetylpyridine)-bis(2-pyridyl-hydrazone) and H^tBu-DDTP = 4-(tert-butyl)-2,6-di(1,3-dithiolan-2-yl)phenol) obtained by either in situ alcoholysis of tetraphenylborate or addition of tetramethoxyborate. The alkoxyborate bridge chelates two anisotropic Dy(III) ions in a μ₂-κ²:κ² coordination fashion, and the axial anisotropy axes of Dy(III) sites approach collinearity with a ferromagnetic coupling constant of +1.38 cm⁻¹. Magnetic studies and ab initio calculations indicate that 1 and the Y(III)-diluted analogue (1@Y) both exhibit slow magnetic relaxation behaviour dominated by the Raman-like mechanism. However, magnetic dilution of 1 in a yttrium matrix proves that 4f–4f ferromagnetic coupling plays an important role in the inhibition of zero-field fast quantum tunneling of magnetization (QTM), since the zero-field relaxation time for 1 is two orders of magnitude longer than that of 1@Y at 2 K. These findings demonstrate an alternative and effective approach for achieving axially ferromagnetically coupled SMMs using alkoxyborate bridges.