Heterospin single-molecule magnets with extra-large anisotropic barrier

The mixtures of Co(X-hfpip)2; X = I and H, and bisdiazo-dipyridine ligands, D2py2(TBA), in 1:1 ratios gave the discrete cobalt complexes, 1 and 2, respectively. The molecular structures for 1 and 2 revealed by X-ray crystallography were cyclic 2:2 cobalt complexes formulated as [(Co(X-hfpip)2)2(D2py2(TBA))2], in which the cobalt units were compressed octahedra. After irradiation of the microcrystalline samples, the resulting Co–carbene complexes, 1c and 2c, showed SMM behaviors exhibiting slow magnetic relaxations. In dc and ac magnetic susceptibility experiments, the activation barrier, Ueff, for reorientation of the magnetic moment were estimated to be 139 and 135 K for 1c and 2c, respectively, and the hysteresis loops of the magnetization (the coercive force, Hc, and 26 and 15 kOe at 1.9 K for 1c and 2c, respectively) were observed. In addition, the values of the quantum tunneling time, τQ, were determined to be 1.1 × 105 and 5.4 × 105 s (t1/2 = 21 and 104 h) for 1c and 2c, respectively, below 2.5 K.

Cyclic 2:2 Co complexes, [(Co(X-hfpip)2)2(D2py2(TBA))2]; X = H and I, bridged with photoresponsive magnetic couplers were prepared. After irradiation of the microcrystal of [(Co(I-hfpip)2)2(D2py2(TBA))2], the complex behaved as a single-molecule magnet with Ueff = 139 K, Hc = 26 kOe at 1.9 K, and τQ = 1.1 × 105 s.Figure optionsDownload as PowerPoint slideHighlights
► Preparations and structures of cyclic Co complexes bridged with photoresponsive magnetic couplers.
► Formation of heterospin single-molecule magnets with extra-large anisotropic barrier after photolysis.
► Resonant spin-quantum tunneling times were also determined by dc magnetization decay.