Magnetic properties of 1 : 4 complexes of CoCl2 and pyridines carrying carbenes (S0 = 4/2, 6/2, and 8/2) in diluted frozen solution; influence of carbene multiplicity on heterospin single-molecule magnets
作者:Satoru Karasawa、Kimihiro Nakano、Jun-ichi Tanokashira、Noriko Yamamoto、Takahito Yoshizaki、Noboru Koga
DOI:10.1039/c2dt31288c
日期:——
The microcrystalline sample of a parent complex, [CoCl2(py)4], showed a single-molecule magnet (SMM) behavior with an effective activation barrier, Ueff/kB, of 16 K for reversal of the magnetism in the presence of a dc field of 3 kOe. Pyridine ligands having 2â4 diazo moieties, DYpy; Y = 2, 3l, 3b, and 4, were prepared and confirmed to be quintet, septet, septet, and nonet in the ground state, respectively, after irradiation. The 1â:â4 complexes, CoCl2(DYpy)4; Y = 2, 3l, 3b, and 4 in frozen solutions after irradiation showed the magnetic behaviors of SMMs with total spin multiplicity, Stotal = 17/2, 25/2, 25/2, and 33/2, respectively. Hysteresis loops depending on the temperature were observed and the values of coercive force, Hc, at 1.9 K were 12, 8.4, 11, and 8.1 kOe for CoCl2(CYpy)4; Y = 2, 3l, 3b, and 4, respectively. In dynamic magnetic susceptibility experiments, ac magnetic susceptibility data obeyed the Arrhenius law to give Ueff/kB values of 94, 92, 93, and 87 K for CoCl2(CYpy)4; Y = 2, 3l, 3b, and 4, respectively, while the relaxation times for CoCl2(CYpy)4; Y = 2 and 3l, obtained by dc magnetization decay in the range of 3.5â1.9 K slightly deviated downward from Arrhenius plots on cooling. The dynamic magnetic behaviors for CoCl2(CYpy)4 including [CoCl2(py)4] and CoCl2(C1py)4 suggested that the generated carbenes interacted with the cobalt ion to increase the relaxation time, Ïq, due to the spin quantum tunneling magnetization, which became larger with increasing Stotal of the complex.
母体复合物[CoCl2(py)4]的微晶样品显示了单分子磁(SMM)行为,在 3 kOe 直流电场存在下,磁性反转的有效激活势垒 Ueff/kB 为 16 K。我们制备了具有 2â4 重氮分子(DYpy;Y = 2、3l、3b 和 4)的吡啶配体,并在辐照后确认其基态分别为五元、七元、七元和壬元。1â:â4 复合物 CoCl2(DYpy)4; Y = 2、3l、3b 和 4 在冷冻溶液中经辐照后显示出 SMM 的磁性行为,总自旋倍率分别为 Stotal = 17/2、25/2、25/2 和 33/2。在 1.9 K 时,CoCl2(CYpy)4;Y = 2、3l、3b 和 4 的矫顽力 Hc 值分别为 12、8.4、11 和 8.1 kOe。在动态磁感应强度实验中,交流磁感应强度数据符合阿伦尼乌斯定律,CoCl2(CYpy)4; Y = 2、3l、3b 和 4 的 Ueff/kB 值分别为 94、92、93 和 87 K,而 CoCl2(CYpy)4; Y = 2 和 3l 在 3.5â1.9 K 范围内通过直流磁化衰减获得的弛豫时间在冷却时略微向下偏离阿伦尼乌斯图。CoCl2(CYpy)4(包括 [CoCl2(py)4] 和 CoCl2(C1py)4)的动态磁性行为表明,由于自旋量子隧道磁化,生成的碳烯与钴离子相互作用,增加了弛豫时间 Ïq,而弛豫时间随着复合物 Stotal 的增加而变大。