二吡啶萘啶二胺配基之直線型異金屬串錯合物合成與研究

Abstract

本論文主要是利用多吡啶萘啶胺系列中最短且對稱的2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany)為配基，以合成多核直線型異金屬串錯合物，並探討其結構與性質，期望未來能應用於電子元件中，使電子元件微小化，能實現在分子導線上。合成金屬串錯合物時，導入不同的金屬離子，形成混金屬的錯合物後，會造成金屬串錯合物的物理或化學性質改變，跟以往單一金屬離子的金屬串錯合物不同，而且這些相異的性質都值得探討，所以本實驗室對異金屬串錯合物有更深的研究。 首先利用本實驗室特有的萘燒合成方法，將配基(H2bpyany)、雙核金屬化合物[Mo2(OAc)4]、過渡金屬鹽類[Ni(OAc)2·4H2O]及LiCl作為軸向配基，以萘(naphthalene)作為溶劑，於高溫220 oC及氬氣(Ar)的條件進行萘燒反應，可得到直線型五核異金屬串錯合物[Ni3Mo2(μ5-bpyany)4Cl](BF4) (1)。透過單晶繞射儀鑑定，得知鉬-鉬鍵長為2.09 Å，鉬、鎳金屬離子皆為正二價，推測為四重鍵。配基(H2bpyany)最多可和六個金屬配位，形成六核金屬串錯合物，但錯合物(1)為五核異金屬串錯合物，六氮配基上只有五個位置的氮原子和五個金屬配位，金屬串的最末端會形成一個空配位。藉由Ni-N間距離及磁性量測分析推測末端鎳金屬離子(Ni1)及內部第三個鎳金屬離子(Ni3)皆為高自旋態的電子組態 (S = 1)，且Ni-N間距離皆大於2 Å，兩磁性中心會相互作用，呈現較強的反鐵磁作用力，J = -97 cm-1，內部第二個鎳金屬離子(Ni2)則為低自旋態的電子組態 (S = 0)，Ni-N間距離為1.90 Å。其電化學顯示在E1/2 (ox) = +0.41 V的氧化還原電位是由[Mo2]4+/5+單元所造成，而E1/2 (red) = -0.33 V 為鎳金屬離子所致的氧化還原電位。 接著利用錯合物(1)上的空配位，繼續與不同的第二列族過渡金屬起始物([Ru(COD)(CH3CN)2Cl2]、[Rh(COD)Cl]2) 進行萘燒反應，可成功合成出含三種不同金屬離子的新型直線型六核異金屬串錯合物[Ni3Mo2Ru(μ6-bpyany)4Cl2](BF4)2 (2) 、[Ni3Mo2Rh(μ6-bpyany)4Cl2](BF4)2 (3)，並透過單晶繞射儀鑑定其結構。將錯合物(2) 、(3)的鍵長與錯合物(1)比較，可以知道釕及銠金屬與鉬金屬間鍵結的不同。 另外，也試著將合成錯合物(1)的鎳金屬鹽類置換成CoCl2，以類似的反應條件，可成功合成出直線型五核異金屬串錯合物[Co3Mo2(μ5-bpyany)4Cl](ClO4) (4)，並透過單晶繞射儀鑑定，可知其結構與錯合物(1)相同。其電化學顯示在E1/2 (ox) = +0.55 V的氧化還原電位是由[Mo2]4+/5+單元所造成，E1/2 (red) = -0.05 V為鈷金屬離子所致的氧化還原電位。

In the past decades, molecular electronics have been widely researched in many fields and extended metal atom chains (EMACs) are of considerable significance for their potential applications in molecular wires and nanoelectronics. In order to develop new generation of metal string complexes, a heterometallic framework have been studied. Compared to homonuclear complexes, the structure, magnetic properties and resistance of mixed metal complexes are versatile. Therefore, the aim of this thesis is to synthesize linear oligo-nuclear metal string complexes with the shortest and symmetric ligand made up of pyridyl and naphthyridyl groups, 2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany), and investigate their structures, magnetic properties and electrochemistry. [Ni3Mo2(μ5-bpyany)4Cl](BF4) (1) was prepared from a reaction mixture containing Mo2(OAc)4, Ni(OAc)2·4H2O, LiCl and H2bpyany in refluxing naphthalene under an argon atmosphere. 2,7-Bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany) used in this thesis was a hexadentate ligand and hence could support a linear chain of six metal ions. However, the X-Ray structure showed that the complex (1) was a pentanuclear heterometal string complexes (HMSCs), and one of nitrogens on the pyridines didsn’t bond to any metals. The Ni-N distances with terminal nickel atoms (2.09 Å) were considerably different from those with inner nickel atoms (1.89 Å) in these homometallic Ni string complexs. However, the Ni3-Nny distances (2.02 Å) of the complex (1), which was inner nickel atom, were longer than Ni-N distances with terminal nickel atoms. The elongation of this Ni3-Nny bond might be attributed to the whole expansion of coordination environment by Mo Mo fragment with longer metal-ligand distances. A consequence of this elongation, a different spin state of the Ni2+ ion, was therefore proposed. This assumption was further supported by the magnetic measurement, and it was the reason that the complex (1) exhabited antiferromagnetic interaction (J = -97 cm-1) from magnetic studies. Then, the complex (1) was employed to react with other metal salts ([Ru(COD)(CH3CN)2Cl2]、[Rh(COD)Cl]2) to generate heterometallic EMACs, [Ni3Mo2Ru(μ6-bpyany)4Cl2](BF4)2 (2) and [Ni3Mo2Rh(μ6-bpyany)4Cl2](BF4)2 (3) , containing three kinds of metals. By the metallic bond lengths of the complex (2) and (3), there were different bondings between the Mo-Ru bond and the Mo-Rh bond. We replaced the nickel with the cobalt and used the similar synthesized way to get pentanuclear HMSCs, [Co3Mo2(μ5-bpyany)4Cl](ClO4) (4), whose structure was isostructural with the complex (1). The magnetic studies showed a spin crossover property in the complex (4).