Forment-Aliaga Alicia, Coronado Eugenio, Feliz Marta, Gaita-Ariño Alejandro, Llusar Rosa, Romero Francisco M
Instituto de Ciencia Molecular, Universitat de València, 46100-Burjassot, Spain.
Inorg Chem. 2003 Dec 1;42(24):8019-27. doi: 10.1021/ic034407r.
A carboxy-substituted alkylammonium salt, namely, (4-carboxybenzyl)tributylammonium hexafluorophosphate, ZHPF(6), was prepared and used as incoming carboxylate ligand in a ligand-exchange reaction with [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)] (1) to afford a new Mn(12) single-molecule magnet (SMM), [Mn(12)O(12)(Z)(16)(H(2)O)(4)]PF(6) (2), bearing 16 cationic units appended in the periphery. This compound behaves as a single-molecule magnet, exhibiting an out-of-phase ac magnetic susceptibility chi' '(M) signal that shows a single maximum in the 3.1-5.4 K temperature range. The frequency dependence of the maximum follows an Arrhenius law, with an effective energy barrier for reorientation of the spins U(eff) = 53 K. The reduced magnetization versus H/T data at different temperatures were fitted by using a Hamiltonian containing Zeeman, axial, and quartic zero-field splitting terms. The expected spin ground state S = 10 was found, and the least-squares fit afforded the following zero-field-splitting parameters: D = -0.44 cm(-1); B(4)(0) = 0.12 x 10(-4) cm(-1). Magnetization hysteresis loops were observed for 2, with a coercive field H(c) = 0.34 T. Complex 2 has been used as countercation in the preparation of a family of hybrid salts containing different polyoxometalate anions, [Mn(12)O(12)(Z)(16)(H(2)O)(4)]W(6)O(19) (3), [Mn(12)O(12)(Z)(16)(H(2)O)(4)]PW(12)O(40) (4), [Mn(12)O(12)(Z)(16)(H(2)O)(4)](H(3)O)PW(11)O(39)Ni (5), and [Mn(12)O(12)(Z)(16)(H(2)O)(4)](H(3)O)PW(11)O(39)Co (6). 3-6 exhibit typical magnetic hysteresis loops with higher coercive fields for the complexes containing diamagnetic polyanions: H(c) = 0.075 T (3), 0.046 T (4), 0.016 T (5), and 0.0075 T (6). However, the dynamics of the magnetic behavior below the blocking temperature is similar in all compounds. Broad frequency-dependent out-of-phase ac susceptibility signals are observed, presumably due to mixtures of different Jahn-Teller isomers. Their temperature dependence is also typical of an activated-energy process, with effective energy barriers in the 50 K range, irrespective of the nature of the polyoxoanion (diamagnetic, as in 3 and 4, or paramagnetic, as in 5 and 6). These findings seem to discard any influence of the polyoxometalate in the magnetic properties of the SMM.
制备了一种羧基取代的烷基铵盐，即（4 - 羧基苄基）三丁基铵六氟磷酸盐（ZHPF₆），并将其用作与[Mn₁₂O₁₂(O₂CCH₃)₁₆(H₂O)₄]（1）进行配体交换反应时引入的羧酸盐配体，从而得到一种新的Mn₁₂单分子磁体（SMM），[Mn₁₂O₁₂(Z)₁₆(H₂O)₄][PF₆]₁₆（2），其外围带有16个阳离子单元。该化合物表现为单分子磁体，在3.1 - 5.4 K温度范围内呈现出一个异相交流磁化率χ″(M)信号，该信号有一个单一的最大值。最大值的频率依赖性遵循阿仑尼乌斯定律，自旋重取向的有效能垒U(eff) = 53 K。在不同温度下，将约化磁化强度与H/T数据用包含塞曼、轴向和四次零场分裂项的哈密顿量进行拟合。发现预期的自旋基态S = 10，最小二乘法拟合得到以下零场分裂参数：D = -0.44 cm⁻¹；B₄(0) = 0.12×10⁻⁴ cm⁻¹。观察到2的磁化滞后回线，矫顽场H(c) = 0.34 T。配合物2已被用作抗衡阳离子，用于制备一系列含有不同多金属氧酸盐阴离子的杂化盐，[Mn₁₂O₁₂(Z)₁₆(H₂O)₄][W₆O₁₉]₈（3）、[Mn₁₂O₁₂(Z)₁₆(H₂O)₄][PW₁₂O₄₀]₁₆/₃（4）、[Mn₁₂O₁₂(Z)₁₆(H₂O)₄][(H₃O)PW₁₁O₃₉Ni]₄（5）和[Mn₁₂O₁₂(Z)₁₆(H₂O)₄][(H₃O)PW₁₁O₃₉Co]₄（6）。对于含有抗磁性聚阴离子的配合物，3 - 6表现出典型的磁滞回线，且矫顽场更高：H(c) = 0.075 T（3）、0.046 T（4）、0.016 T（5）和0.0075 T（6）。然而，在所有化合物中，低于阻塞温度时磁行为的动力学是相似的。观察到宽的频率依赖性异相交流磁化率信号，可能是由于不同的 Jahn - Teller异构体的混合。它们的温度依赖性也是典型的活化能过程，有效能垒在50 K范围内，与多金属氧阴离子的性质无关（抗磁性的，如在3和4中；或顺磁性的，如在5和6中）。这些发现似乎排除了多金属氧酸盐对单分子磁体磁性质的任何影响。
