Steric Control of Polynuclear Manganese Complexes by the Use of Tripodal Tetradentate Ligands
作者:Masakazu Hirotsu、Masaaki Kojima、Wasuke Mori、Yuzo Yoshikawa
DOI:10.1246/bcsj.71.2873
日期:1998.12
Tripodal tetradentate ligands (H2L1: N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L2: N-(3,5-di-t-butyl-2-hydroxybenzyl)-N-(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L3: N,N-bis(3,5-di-t-butyl-2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L4: N,N-bis(2-hydroxy-3-methoxybenzyl)-N′,N′-dimethylethylenediamine, H2L5: N-(3,5-di-t-butyl-2-hydroxybenzyl)-N-(2-hydroxy-3-methoxybenzyl)-N′,N′-dimethylethylenediamine) made it possible to prepare sterically controlled polynuclear manganese complexes. In the presence of carboxylate ligands, in contrast to the L3 ligand which gave mononuclear MnIII complexes, the other ligands afforded mixed-valence trinuclear complexes with an MnIII–MnII–MnIII arrangement. In methanol, the general formula of the products is [Mn3(L)2(carboxylato)2(OCH3)2]. While preparations in acetonitrile generated [Mn3(L1)2(ba)4] (ba = benzoate(1−)) and [Mn3(L2)2(ba)2(OH)2]. The structure of [Mn3(L1)2(ba)4] was determined by X-ray analysis. The three manganese cores are arranged linearly, and the central and terminal ions are bridged by a phenolate and two carboxylate groups. In the case of the L5 ligand, dinuclear and tetranuclear complexes were also obtained and structurally characterized. In the dinuclear complex, [Mn(L5)(CH3OH)(OCH3)MnCl2], a distorted octahedral MnIII and a five-coordinated MnII site are bridged by a phenolate and an alkoxo oxygen donor. The tetranuclear complex, [Mn4(L5)2(ba)6], including an MnIII–MnII–MnII–MnIII arrangement, is regarded as a carboxylato bridged dimer of a dinuclear unit, [Mn(L5)(ba)2Mn]+. Because the bulkiness of the L5 ligand lies between the L2 and L3 ligands, the dinuclear unit is favorable. Variable-temperature magnetic susceptibility measurements showed the ferromagnetic spin-exchange coupling for [Mn(L5)(CH3OH)(OCH3)MnCl2] and the antiferromagnetic one for [Mn3(L1)2(ba)4]. The phenolato and alkoxo bridges give rise to the ferromagnetic exchange interactions between MnIIIand MnII ions. On the other hand, the antiferromagnetic interactions stem from carboxylato bridges.
三齿四齿配体(H2L1:N,N-双(2-羟基苯甲基)-N',N'-二甲基乙二胺,H2L2:N-(3,5-二叔丁基-2-羟基苯甲基)-N-(2-羟基苯甲基)-N',N'-二甲基乙二胺,H2L3:N,N-双(3,5-二叔丁基-2-羟基苯甲基)-N',N'-二甲基乙二胺,H2L4:N,N-双( 2-羟基-3-甲氧基苯甲基)-N',N'-二甲基乙二胺,H2L5:N-(3,5-二叔丁基-2-羟基苯甲基)-N-(2-羟基-3-甲氧基苯甲基)-N ',N'-二甲基乙二胺)使得制备空间控制的多核锰配合物成为可能。在羧酸配体存在下,与产生单核 MnIII 配合物的 L3 配体相反,其他配体提供具有 MnIII-MnII-MnIII 排列的混合价三核配合物。在甲醇中,产物的通式为[Mn3(L)2(羧基)2(OCH3)2]。而在乙腈中制备则生成 [Mn3(L1)2(ba)4](ba = 苯甲酸盐(1−))和 [Mn3(L2)2(ba)2(OH)2]。 [Mn3(L1)2(ba)4]的结构通过X射线分析确定。三个锰核呈线性排列,中心离子和末端离子通过一个酚盐基团和两个羧酸盐基团桥联。对于 L5 配体,还获得了双核和四核配合物并进行了结构表征。在双核配合物 [Mn(L5)(CH3OH)(OCH3)MnCl2] 中,扭曲的八面体 MnIII 和五配位 MnII 位点通过酚盐和烷氧基氧供体桥接。四核配合物 [Mn4(L5)2(ba)6],包括 MnIII-MnII-MnII-MnIII 排列,被视为双核单元 [Mn(L5)(ba)2Mn]+ 的羧基桥联二聚体。由于 L5 配体的体积位于 L2 和 L3 配体之间,因此双核单元是有利的。变温磁化率测量显示了 [Mn(L5)(CH3OH)(OCH3)MnCl2] 的铁磁自旋交换耦合和 [Mn3(L1)2(ba)4] 的反铁磁自旋交换耦合。酚桥和烷氧基桥引起 MnIII 和 MnII 离子之间的铁磁交换相互作用。另一方面,反铁磁相互作用源于羧基桥。