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  • 學位論文

具有內消旋構型之新穎異五核金屬串錯合物[Mo2NiMo2(tpda)4(NCS)2]之合成與研究

Heteropentanuclear Metal String Complex [Mo2NiMo2(tpda)4(NCS)2] with a meso-Configuration of the Complex

指導教授 : 彭旭明

摘要


本論文研究方向主要為合成五核直線型異金屬串錯合物並探討其結構與性質。並希望未來可以應用到電子元件上,使未來科技趨勢在尺度上有更大的突破。本實驗室團隊於2014 年在Chemistry-A European Journal 期刊上發表第一個異五核金屬串錯合物[NiRu2Ni2(tpda)4(NCS)2],並且在導電度上具有特別的NDR (negative differential resistance)效應,使得本實驗室對於異金屬串有更多的發展性。由於導入兩種不同的金屬離子,造成金屬串的物理/化學性質改變,產生許多和以往不同的性質,相當值得探討。 首先利用本實驗室特有的萘燒合成方法,將配基三吡啶二胺(Tripyridyldiamine, H2tpda)與金屬起始物[Mo2(OAc)4 與Ni(OAc)2]以萘做為溶劑下高溫反應,並再加入LiCl 或NaSCN 作為軸向配基,將可成功合成出目標產物五核異金屬直線型金屬串分子[Mo2NiMo2(tpda)4(NCS)2]和[Mo2NiMo2(tpda)4Cl2]。利用單晶繞射儀鑑定其結構,可以發現兩個金屬串錯合物皆具有兩種不同構型結構,分別為helical 和meso 構型的金屬串錯合物。Helical 構型的金屬串錯合物分子與本實驗室以往傳統的金屬串分子一樣,四片配基以螺旋的方式圍繞中間金屬;而meso 構型的金屬串則是四片配基呈現微V 字型的形狀與中間金屬配位,整體結構為一個meso 的組態,和以往實驗室所合成的金屬串分子有很大的不同,是個很特別的發現。錯合物中的鉬、鎳金屬離子皆為正二價,兩邊末端為鉬鉬雙核金屬單元,鉬-鉬鍵長為2.09~2.14 Å是鉬鉬四重鍵;而中間為鎳金屬離子,整體為一個對稱的金屬串錯合物。再經由磁性量測分析為順磁磁性行為,末端兩個[Mo2]4+為S = 0 的磁矩,所以磁矩的主要貢獻來自中間的鎳金屬離子,為S = 1 的高自旋電子組態;再透過L-edge 的X-ray吸收光譜測量其錯合物的鎳金屬離子的配位環境,並與不同配位環境的鎳金屬離子比較,更確定錯合物中的鎳為高自旋的電子組態。因為以往鎳金屬四方配位皆為低自旋電子組態,但在此分子中為高自旋電子組態。第二部份我們嘗試將中間的鎳金屬換成鈷金屬離子,利用相同的合成方法,將起始物換成CoCl2 並調控適當比例,即可得到[Mo2CoMo2(tpda)4(Cl)2]。而此錯合物經由X-ray 儀器鑑定解析為一個helical 構型的金屬串分子,整體結構與Mo2NiMo2(tpda)4Cl2 相似,為一個isostructural 的關係。末端兩邊為雙核鉬金屬單元,中間為鈷金屬離子,外圍有四片配基以螺旋的方式圍繞中間金屬,整體為中性的金屬串分子。但因晶體晶形不好和產率很低,所以對於此化合物還未有更完善的討論。而測量其磁性,為一順磁磁性物質,推測鈷金屬離子為一個高自旋 S =3/2 的電子組態。在300 K 有效磁矩為2.53 B.M.,與spin only 的理論值3.87 B.M. 還有段差距;但因為此錯合物的產量很低還有晶體的晶型品質不好,所以對這錯合物的還需要更多的探討及研究。

並列摘要


During the past few years, molecular electronics have been widely discussed in many fields and extended metal atom chains (EMACs) are of considerable significance for their potential applications as molecular wires. The typical conformation of extended metal atom chains (EMACs) consists of a 1D polymetallic core surrounded and supported by multidentate oligo-α-pyridylamido organic ligands. Recently, novel results obtained from single-molecule conductance experiments performed on the first pentanuclear heterometal string complex, [NiRu2Ni2(tpda)4(NCS)2], showed unique negative differential resistance characteristics. In order to develop the new generation of heterometal string complex, we chose the molybdenum with the nickel or cobalt to synthesize the novel symmetric heteropentanuclear metal string complex. In the first part, A dimeric molybdenum precursor and nickel ions are used to synthesize a symmetric heteropentanuclear complex, [Mo2NiMo2(tpda)4X2], (X = Cl, NCS). Interestingly, we can get the two configuration of this structure in this two metal string complexes. One is helical configuration and other is meso configuration, the meso configuration is a distinction from other metal chains previously reported. The linear metal chain core is wrapped by four syn–syn–syn–syn type tpda2- ligands in a meso configuration, with torsion angles Npy–M–M–Npy of 10.51° and -11.31°. Additionally, the Mo Mo distance (2.09-2.14 Å) of the Mo2NiMo2 complexes within the normal observed distance range for Mo Mo quadruple bonds (2.06-2.17 Å). The Nicentral–Npy distance (2.06-2.10 A) of Mo2NiMo2 complexes, however, are slightly longer in comparison with these homometallic Ni strings. The elongation of this Nicentral–Npy bond may be attributed to the whole expansion of the coordination environment by considering the incorporation of two Mo Mo fragments with relatively longer metal ligand distances at both termini. A consequence of this elongation, a different spin state of the Ni2+ ion, is therefore proposed. This assumption is further supported by the magnetic measurement and X-ray absorption of L-edge. In the second part, we change the nickel metal to cobalt ion and use the same synthesized way to get symmetric heterometal string complexes, [Mo2CoMo2(tpda)4X2], (X = Cl, NCS). This structure is only the helical configuration. Unfortunately we didn’t get the meso configuration structure. From the bad quality crystal and low yield, we could not study these complexes very well.

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