Department of Chemistry, University of Calcutta, Kolkata, India.
J Chem Phys. 2011 May 7;134(17):174507. doi: 10.1063/1.3581028.
The magnetic, electronic, and Mössbauer spectral properties of [Fe(2)L(μ-OAc)(2)]ClO(4), 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H(2)L, indicate that 1 is a class III mixed valence iron(II∕III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a Fe(2) cationic configuration with a S(t) = 9∕2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm(-1) for an electron transfer parameter, B, of 950 cm(-1), a zero-field uniaxial D(9∕2) parameter of -0.9(1) cm(-1), and g = 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U(eff), of 9.8 cm(-1). At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 × 10(-8) s. A fit of the temperature dependence of the average effective hyperfine field yields |D(9∕2)| = 0.9 cm(-1). An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm(-1).
[Fe(2)L(μ-OAc)(2)]ClO(4)，1 的磁性、电子和穆斯堡尔谱性质表明，1 是一类 III 型混合价铁(II∕III)配合物，其中一个电子完全离域在两个晶相不等价的铁位点之间，产生具有 S(t) = 9∕2 基态的 Fe(2)阳离子构型。2 至 300 K 之间的直流磁化率和 1 的等磁场变温磁化率的拟合结果得出，电子转移参数 B 为 950 cm(-1)时，各向同性磁交换参数 J 为-32(2) cm(-1)，零场单轴 D(9∕2)参数为-0.9(1) cm(-1)，g = 1.95(5)。与单轴各向异性磁各向异性的存在一致，交流磁化率测量表明，1 是一种低温下的单分子磁铁，具有 9.8 cm(-1)的单分子磁有效弛豫势垒。在 5.25 K 时，1 的穆斯堡尔光谱表现出两个谱分量，分配给两个晶相不等价的铁位点，具有静态有效超精细场；随着温度从 7 升高到 310 K，光谱表现出铁-57 拉莫尔进动时间为 5×10(-8) s 的超精细场的快速弛豫。平均有效超精细场的温度依赖性拟合得到 |D(9∕2)| = 0.9 cm(-1)。5 至 85 K 之间的弛豫频率的对数的 Arrhenius 图得到弛豫势垒为 17 cm(-1)。
