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Molecular Design of Asymmetric Metal Dinuclear Complexes towards Molecular Switching of Intramolecular Electron Transfer

不对称金属双核配合物分子内电子转移分子开关的分子设计

基本信息

批准号：
02640474
负责人：
HAGA Masa-aki
金额：
$ 1.41万
依托单位：
Mie University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

Supramolecular assemblies composing of oligonuclear metal complexes with bridging ligands can be considered to have a potential as a building block for synthesizing a molecular level chip such as molecular size "wires, " and "rectifiers". We focus our attention on the "molecular switching" by proton transfer in metal complexes, since the proton transfer can be regarded as a trigger signal to change the metal-metal interaction or the structure of the complex. In order to get the basic information for the design of molecular-level devices such as a molecular switch, new mononuclear and hetero-dinuclear complexes, [M(L)_2(bpbimH_2)]^<2+> and [M(L^1)_2(bpbimH_2)M'(L^2)_2]^<4+> (M and M' = Ru, Rh, and/or Os ; L^1 or L^2 = 2, 2'-bipyridine (bpy), 1, 10-phenanthroline (phen), or 4.4'-dimethylbipyridine (dmbpy)), containing dinucleating ligand 2, 2'-bis- (2-pyridyl)-bibenzimidazole (bpbimH_2) have been prepared. Both absorption spectra and oxidation potential are strongly dependent on the solu … More tion pH, which is responsible for the N-H deprotonation on the coordinated bpbimH_2 ligand. The mononuclear Ru and Os complexes act not only as a basic acid but also as a diacidic base, while hetero-dinuclear complexes essentially act as a dibasic acid. The proton-tcoupled electron transfer reaction is proved by E_<1/2> - pH plot (Pourbaix diagram). The number of electron participated in the proton- coupled electron transfer reaction essentially depends on the redox activity on the second metal site. The pK_a values of the complexes reflect on both metal and its oxidation states, M (II) and M (III). The pK_a values of the mixed-valence dinuclear complexes are quite close to those of each M (II) and M (III) component, which suggests that the mixed-valence complexes have a localized valence structure. The mixed-valence complexes bridged by the protonated ligand bpbimH_2 exhibit the intervalence (IT) band at 7300 cm^<-1> for M = Ru, and at 9100 cm^<-1> for M = Os, respectively. When the bridging ligand is deprotonated, this IT band is shifted to the lower energy at 5880 cm^<-1> for M = Ru, and 7700 cm^<-1> for M = Os, and intensified. The degree of metal-metal interaction of the deprotonated dinuclear complexes becomes 4-6 times larger than that of the protonated complexes. This proton-induced change of metal-metal interaction can be rationalized by change of HOMO energy levels on deprotonation or protonation in the bridging ligands. Thus, the proton transfer in the bpbimH_2 bridging dinuclear complexes can be elucidated to serve as a trigger signal for switching the metal-metal minteraction. Less

由具有桥连配体的寡金属络合物组成的超分子组装体可以被认为具有作为用于合成分子水平芯片（诸如分子大小的“线“和“整流器”）的构建块的潜力。我们的注意力集中在金属配合物中的质子转移的“分子开关”，因为质子转移可以被看作是一个触发信号，改变金属-金属相互作用或配合物的结构。为了获得分子开关、新型单核和异双核配合物等分子水平器件设计的基础信息，[M（L）_2（bpbimH_2）]^<2+>和[M（L^1）_2（bpbimH_2）M'（L^2）_2]^<4+>（M和M' = Ru、Rh和/或Os ; L^1或L^2 = 2，2 ′-联吡啶（bpy）、1，10-菲咯啉（phen）或4，4 ′-二甲基联吡啶（dmbpy）），含有双核配体2，合成了2 ′-二-（2-吡啶基）-联苯并咪唑（bpbimH_2）。吸收光谱和氧化电位都强烈依赖于溶液的性质。 ...更多信息 pH值对bpbimH_2配体上的N-H去质子化起重要作用。单核Ru和Os配合物不仅作为碱性酸，而且作为二元酸碱，而异双核配合物基本上作为二元酸。用E_（1/2）- pH图（Pourbaix图）证明了质子-电子转移反应。参与质子偶联电子转移反应的电子数主要取决于第二金属位上的氧化还原活性。配合物的pK_a值反映了金属及其氧化态M（II）和M（III）。混合价双核配合物的pK_a值与M（II）和M（III）组分的pK_a值非常接近，表明混合价双核配合物具有定域价结构。由质子化配体bpbimH_2桥连的混合价配合物分别在7300 cm^<-1>（M = Ru）和9100 cm^<-1>（M = Os）处显示出价间（IT）带。当桥连配体被去质子化时，该IT带被移动到较低的能量，<-1>对于M = Ru在5880 cm^处，对于M = Os在7700 cm^<-1>处，并且被增强。去质子化的双核配合物的金属-金属相互作用程度比质子化的配合物大4-6倍。这种质子引起的金属-金属相互作用的变化可以通过桥连配体中去质子化或质子化的HOMO能级的变化来合理化。因此，bpbimH_2桥联双核配合物中的质子转移可作为金属-金属相互作用的触发信号。少