Rizzi Alberto C, Brondino Carlos D, Calvo Rafael, Baggio Ricardo, Garland María T, Rapp Raul E
Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, Güemes 3450, 3000 Santa Fe, Argentina.
Inorg Chem. 2003 Jul 14;42(14):4409-16. doi: 10.1021/ic026111b.
We report the structure and the magnetic properties of a cobalt(II) compound with the amino acid l-threonine, Co(C(4)H(8)NO(3))(2)(H(2)O)(2). It crystallizes in the orthorhombic chiral space group C222(1), with a = 5.843(5) A, b = 10.120(10) A, c = 22.36(3) A, and Z = 4. The Co(II) ion is in a deformed octahedral environment on a 2-fold symmetry axis parallel to the crystallographic axis b. It is bonded to two threonine molecules in a bidentate fashion, via one oxygen from the carboxylate end and the alpha-amino nitrogen. A water molecule occupies the third independent site. The Co(II) ions are arranged in layers with intralayer and interlayer distances of 5.84 and 11.18 A, respectively. Magnetic measurements data reflect the molecular character of a compound with weak exchange interactions. EPR measurements in polycrystalline and single-crystal samples indicate a distorted axial symmetry around the Co(II) ion, as expected from the structural results. Eigenvalues and eigenvectors of the g tensor are determined. The measured principal g values (5.81, 4.56, and 2.23) reflect a high-spin Co(II) ion, as suggested by the type of ligands and the molecular symmetry. From the incomplete collapse of the hyperfine structure we estimate 0.25 < |J| < 1.2 cm(-1) between neighboring Co(II) ions within a layer, transmitted through H-bonds. A higher limit |J'| < 0.07 cm(-1) is estimated for the exchange interactions between Co(II) ions in neighboring layers. From a global fit of a spin Hamiltonian with spin (3)/(2) to magnetization and EPR data we obtain a zero field splitting delta approximately 231 cm(-1) between the two lowest doublet states. The results are discussed in terms of the molecular and electronic structure of the compound.
我们报道了一种钴（II）与氨基酸L-苏氨酸形成的化合物Co(C₄H₈NO₃)₂(H₂O)₂的结构和磁性。它结晶于正交手性空间群C222(1)，a = 5.843(5) Å，b = 10.120(10) Å，c = 22.36(3) Å，Z = 4。Co(II)离子处于平行于晶体学轴b的二重对称轴上的变形八面体环境中。它通过来自羧基端的一个氧原子和α-氨基氮原子以双齿方式与两个苏氨酸分子键合。一个水分子占据第三个独立位点。Co(II)离子排列成层，层内和层间距离分别为5.84 Å和11.18 Å。磁性测量数据反映了具有弱交换相互作用的化合物的分子特性。多晶和单晶样品的EPR测量表明，正如结构结果所预期的那样，Co(II)离子周围存在扭曲的轴向对称性。确定了g张量的本征值和本征向量。测量得到的主g值（5.81、4.56和2.23）反映了一个高自旋Co(II)离子，这与配体类型和分子对称性相符。从超精细结构的不完全崩塌，我们估计层内相邻Co(II)离子之间通过氢键传递的交换相互作用|J|在0.25 < |J| < 1.2 cm⁻¹之间。对于相邻层中Co(II)离子之间的交换相互作用，估计其上限|J'| < 0.07 cm⁻¹。通过将自旋为(3)/(2)的自旋哈密顿量全局拟合到磁化和EPR数据，我们得到两个最低双重态之间的零场分裂δ约为231 cm⁻¹。根据化合物的分子和电子结构对结果进行了讨论。
