Antal Peter, Drahoš Bohuslav, Herchel Radovan, Trávníček Zdeněk
Department of Inorganic Chemistry, Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palacký University , 17. listopadu 12, CZ-771 46 Olomouc, Czech Republic.
Inorg Chem. 2016 Jun 20;55(12):5957-72. doi: 10.1021/acs.inorgchem.6b00415. Epub 2016 Jun 1.
The 2-pyridylmethyl N-pendant-armed heptadentate macrocyclic ligand {3,12-bis(2-methylpyridine)-3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1,14,16-triene = L} and M(L)2 complexes, where M = Mn(II) (1), Fe(II) (2), Co(II) (3), Ni(II) (4), and Cu(II) (5), were prepared and thoroughly characterized, including elucidation of X-ray structures of all the compounds studied. The complexes 1-5 crystallize in non-centrosymmetric Sohncke space groups as racemic compounds. The coordination numbers of 7, 6 + 1, and 5 were found in complexes 1-3, 4, and 5, respectively, with a distorted pentagonal bipyramidal (1-4) or square pyramidal (5) geometry. On the basis of the magnetic susceptibility experiments, a large axial zero-field splitting (ZFS) was found for 2, 3, and 4 (D(Fe) = -7.4(2) cm(-1), D(Co) = 34(1) cm(-1), and D(Ni) = -12.8(1) cm(-1), respectively) together with a rhombic ZFS (E/D = 0.136(3)) for 4. Despite the easy plane anisotropy (D > 0, E/D = 0) in 3, the slow relaxation of the magnetization below 8 K was observed and analyzed either with Orbach relaxation mechanism (the relaxation time τ0 = 9.90 × 10(-10) s and spin reversal barrier Ueff = 24.3 K (16.9 cm(-1))) or with Raman relaxation mechanism (C = 2.12 × 10(-5) and n = 2.84). Therefore, compound 3 enlarges the small family of field-induced single-molecule magnets with pentagonal-bipyramidal chromophore. The cyclic voltammetry in acetonitrile revealed reversible redox processes in 1-3 and 5, except for the Ni(II) complex 4, where a quasi-reversible process was dominantly observed. Presence of the two 2-pyridylmethyl pendant arms in L with a stronger σ-donor/π-acceptor ability had a great impact on the properties of all the complexes (1-5), concretely: (i) strong pyridine-metal bonds provided slight axial compression of the coordination sphere, (ii) substantial changes in magnetic anisotropy, and (iii) stabilization of lower oxidation states.
制备并全面表征了2-吡啶甲基N-侧臂七齿大环配体{3,12-双(2-甲基吡啶)-3,12,18-三氮杂-6,9-二氧杂双环[12.3.1]十八碳-1,14,16-三烯 = L}以及M(L)2配合物，其中M = Mn(II) (1)、Fe(II) (2)、Co(II) (3)、Ni(II) (4)和Cu(II) (5)，包括对所有研究化合物的X射线结构进行解析。配合物1 - 5以非中心对称的 Sohncke 空间群结晶为外消旋化合物。配合物1 - 3、4和5中分别发现配位数为7、6 + 1和5，具有扭曲的五角双锥(1 - 4)或四方锥(5)几何构型。基于磁化率实验，发现2、3和4存在较大的轴向零场分裂(ZFS)(D(Fe) = -7.4(2) cm(-1)、D(Co) = 34(1) cm(-1)和D(Ni) = -12.8(1) cm(-1))，4还存在菱形ZFS(E/D = 0.136(3))。尽管3中存在易平面各向异性(D > 0，E/D = 0)，但在8 K以下观察到了磁化强度的缓慢弛豫，并分别用奥尔巴赫弛豫机制(弛豫时间τ0 = 9.90 × 10(-10) s，自旋反转势垒Ueff = 24.3 K (16.9 cm(-1)))或拉曼弛豫机制(C = 2.12 × 10(-5)，n = 2.84)进行了分析。因此，化合物3扩大了具有五角双锥发色团的场致单分子磁体的小家族。乙腈中的循环伏安法显示1 - 3和5中存在可逆的氧化还原过程，除了Ni(II)配合物4，在4中主要观察到准可逆过程。L中两个具有较强σ-供体/π-受体能力的2-吡啶甲基侧臂的存在对所有配合物(1 - 5)的性质有很大影响，具体表现为：(i) 强吡啶-金属键导致配位球轻微轴向压缩；(ii) 磁各向异性发生显著变化；(iii) 较低氧化态得以稳定。
