Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química, Universitat de València, Avenida Dr. Moliner 50, 46100 Burjassot, València, Spain.
Inorg Chem. 2011 Jun 20;50(12):5731-9. doi: 10.1021/ic200531s. Epub 2011 May 25.
Four heterotrinuclear Re(IV)(2)M(II) compounds of general formula (NBu(4))(2)[{Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2)] [NBu(4)(+) = tetra-n-butylammonium cation, ox = oxalate, Him = imidazole; M = Mn (1), Co (2), Ni (3), and Cu (4)] have been synthesized by using the novel mononuclear complex Re(IV)Br(4)(ox) as a ligand toward divalent first-row transition metal ions in the presence of imidazole. Compounds 1-4 are isostructural complexes whose structure contains discrete trinuclear {Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2) anions and bulky NBu(4)(+) cations. The Re and M atoms are six-coordinated: four peripheral bromo and two oxalate-oxygens (at Re), and two cis-coordinated imidazole molecules and four oxygen atoms from two oxalate ligands (at M), build distorted octahedral surroundings. Two peripheral ReBr(4)(ox) units act as bidentate ligands through the oxalate group toward the central [M(II)(Him)(2)] fragment affording the trinuclear entities. The values of the intramolecular Re···M separation are 5.62(1) (1), 5.51(1) (2), 5.46(1) (3), and 5.55(1) Å (4). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range of 1.9-300 K show the occurrence of intramolecular antiferro- [J = -1.1 cm(-1) (1)] and ferromagnetic interactions [J = +3.9 (2), +19.7 (3), and +14.4 cm(-1) (4)], the Hamiltonian being defined as Ĥ = -J [Ŝ(M)(Ŝ(Re1) + Ŝ(Re2))]. The larger spin delocalization on the oxalato bridge in 1-4 when compared to the trinuclear Re(IV)(2)M(II) complexes with chloro instead of bromo as peripheral ligands (1'-4') accounts for the strengthening of the magnetic interactions in 1-4 [J = -0.35 (1'), +14.2 (3'), and +7.7 cm(-1) (4')]. An incipient frequency dependence of the out-of-phase ac signals of 3 at very low temperatures is reminiscent of a system with slow relaxation of the magnetization, a phenomenon characteristic of single-molecule magnet behavior.
四种异核 Re(IV)(2)M(II)化合物的通式为 (NBu(4))(2)[{Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2)] [NBu(4)(+) = 四丁基铵阳离子，ox = 草酸盐，Him = 咪唑；M = Mn (1)，Co (2)，Ni (3)，和 Cu (4)]，是通过使用新型单核配合物 Re(IV)Br(4)(ox) 作为配体，在存在咪唑的情况下，向二价第一过渡金属离子合成的。化合物 1-4 是结构相同的配合物，其结构包含离散的三核 {Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2) 阴离子和庞大的 NBu(4)(+) 阳离子。Re 和 M 原子都是六配位的：四个外围的溴和两个草酸盐-氧（在 Re 处），以及两个顺式配位的咪唑分子和四个来自两个草酸盐配体的氧原子（在 M 处），形成扭曲的八面体环境。两个外围的 ReBr(4)(ox) 单元通过草酸盐基团作为双齿配体，朝向中心的 [M(II)(Him)(2)] 片段，提供三核实体。分子内 Re···M 分离的数值为 5.62(1) (1)、5.51(1) (2)、5.46(1) (3)和 5.55(1) Å (4)。在 1-4 的多晶样品中，在 1.9-300 K 的温度范围内进行的磁化率测量表明存在分子内反铁磁 [J = -1.1 cm(-1) (1)] 和铁磁相互作用 [J = +3.9 (2)、+19.7 (3)和 +14.4 cm(-1) (4)]，哈密顿量定义为 Ĥ = -J [Ŝ(M)(Ŝ(Re1) + Ŝ(Re2))]。与氯代而非溴代作为外围配体的三核 Re(IV)(2)M(II)配合物 (1'-4') 相比，1-4 中草酸盐桥的更大自旋离域导致了磁性相互作用的增强 [J = -0.35 (1')、+14.2 (3')和 +7.7 cm(-1) (4')]。在非常低的温度下，3 的反相交流信号的初始频率依赖性让人想起磁化弛豫缓慢的系统，这是单分子磁体行为的特征现象。
