Heterospin single-molecule magnet behaviors after irradiation of polymorphous 2:2 cyclic diazo-cobalt(II) complexes

摘要

Three kinds of crystals (crystals, alpha, beta and gamma) of 2: 2 cyclic cobalt complexes formulating as [Co(Br-hfpip)(2)-(D2py(2))] 2 X: X = 2CH(2)Cl(2) (1d alpha a), 4CH(2)Cl(2) (1d beta), and 4CH(2)Cl(2).4EtOH (1d gamma) and Br-hfpip = 1,1,1,5,5,5-hexafluoro- 4-(4-bromophenylimino)-2-pentanonate, were obtained and were determined to be polymorphous by X-ray crystallography, having the space groups of P (1) over bar for 1d alpha and 1d alpha, and P2(1) for (1d gamma') In three polymorphs, the local coordination structures of cobalt complex units in the molecule were the same; compressed octahedral. The molecular structure for 1d alpha was different from those for 1d beta and 1d alpha' The dihedral angles between the X-Y plane and the pyridine ring were 43 degrees and 44 degrees for 1da and 7080 for 1db and 1dc. In the crystal packings, 1d alpha had a short contact between the bromo substituent in hfpip ligand and the carbon at the b position of the pyridine ring in D2py(2), while 1d beta and 1d gamma had no short contact between the magnetically significant atoms. The powder X-ray diffraction (PXRD) patterns for the crushed samples of three polymorphs indicated that the crystal structures were changed by loosing crystal solvent and 1d alpha and 1db were microcrystals (1d alpha 0 and 1d beta 0), while 1d gamma became amorphous (1d gamma 0). In dc and ac magnetic measurements after irradiation of crushed samples (1d alpha 0, 1d beta 0, and 1d gamma 0), the photoproducts, 1c alpha 0, 1c beta 0, and 1c gamma 0 exhibited slow magnetic relaxation and magnetic hysteresis. 1c alpha 0 showed a single-molecule magnet (SMM) behavior with the effective activation barrier, Ueff/ kB = 98 K and coercive force, H-c = 2.9 kOe at 1.9 K affected by the intermolecular antiferromagnetic interaction. 1cb0 showed the magnetic behavior with Ueff/kB = 134 K and Hc = 13 kOe at 1.9 K typical of heterospin SMM. In 1cc0, weak v0m0 ol signals with frequency dependency and the temperature dependent hysteresis loop; Hc = 1.1 kOe at 1.9 K, were observed. (C) 2015 Elsevier B.V. All rights reserved.