Sreerama Subramanya Gupta, Pal Samudranil
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
Inorg Chem. 2005 Sep 5;44(18):6299-307. doi: 10.1021/ic050704f.
A series of dinuclear complexes of Mn(III), Fe(III), and Co(III) with two diazine Schiff bases, H2salhn and H2mesalhn, is reported. The Schiff bases are prepared by condensation reactions of hydrazine with salicylaldehyde (H2salhn) and with 2-hydroxyacetophenone (H2mesalhn) in 1:2 mol ratio. X-ray crystallographic characterization reveals triple helical structures of [Co2(salhn)3], [Co2(mesalhn)3], and [Fe2(mesalhn)3]. In each complex, three dinucleating O,N,N,O donor ligands provide three diazine (=N-N=) bridges between the metal ions and facial O3N3 coordination spheres around them. The ligands are twisted about the N-N single bond and coordinate to the two metal ions in a helical fashion to generate the triple helical structure. The dicobalt(III) complex of mesalhn2- is D3-symmetric, while the diiron(III) analogue is very close to being of this symmetry. On the other hand, the dicobalt(III) complex of salhn2- significantly deviates from the ideal D3-symmetry due to the large range covered by the twist angles of the three ligands. In the crystal lattice of these complexes, intermolecular C-H...O, C-H...N, O-H...O, C-H...Cl, and pi-pi interactions involving the complex and the solvent molecules lead to one- and two-dimensional supramolecular structures. The complexes [Fe2(mesalhn)3] and [Co2(mesalhn)3] are redox active and display two successive metal-centered reductions on the cathodic side of Ag/AgCl reference electrode. Weak antiferromagnetic spin-coupling is operative between the two metal ions in [Mn2(salhn)3] (J = -0.57(1) cm(-1)) and in [Fe2(mesalhn)3] (J = -2.82(4) cm(-1)).
报道了一系列锰（III）、铁（III）和钴（III）与两种二嗪席夫碱H2salhn和H2mesalhn形成的双核配合物。席夫碱通过肼与水杨醛（H2salhn）以及与2-羟基苯乙酮（H2mesalhn）以1:2摩尔比进行缩合反应制备。X射线晶体学表征揭示了[Co2(salhn)3]、[Co2(mesalhn)3]和[Fe2(mesalhn)3]的三螺旋结构。在每个配合物中，三个双齿O,N,N,O供体配体在金属离子及其周围的面式O3N3配位球之间提供三个二嗪（=N-N=）桥。配体围绕N-N单键扭曲，并以螺旋方式与两个金属离子配位以生成三螺旋结构。mesalhn2-的二钴（III）配合物具有D3对称性，而二铁（III）类似物非常接近这种对称性。另一方面，salhn2-的二钴（III）配合物由于三个配体的扭转角覆盖范围较大，显著偏离理想的D3对称性。在这些配合物的晶格中，涉及配合物和溶剂分子的分子间C-H...O、C-H...N、O-H...O、C-H...Cl和π-π相互作用导致一维和二维超分子结构。配合物[Fe2(mesalhn)3]和[Co2(mesalhn)3]具有氧化还原活性，并且在Ag/AgCl参比电极的阴极侧显示出两个连续的以金属为中心的还原。[Mn2(salhn)3]（J = -0.57(1) cm(-1)）和[Fe2(mesalhn)3]（J = -2.82(4) cm(-1)）中的两个金属离子之间存在弱反铁磁自旋耦合。
