微調二吡啶萘啶二胺配基及其直線型多核金屬串分子之合成與研究

Abstract

隨著人們對於電子產品精緻化與效能化的要求，將電子元件微小化甚至分子化是科學家們追求的目標，因此分子電子元件成為相當熱門的研究題材，在分子導線探討的領域中，金屬串分子是相當具有潛力的，我們實驗室致力於發展的金屬串分子中，包含兩個系列，一是以修飾配基上的官能基改變金屬串分子的特性，二是以改變金屬的組合合成不同的混金屬串分子。多吡啶胺與多萘啶胺皆已被廣泛地使用在金屬串的研究，而另外還有一個系列是將上述兩個部分做組合，形成一個新的系列，吡啶萘啶胺系列。在此系列中，最短且對稱的配基為2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany)，六核的鎳金屬串與鈷金屬串皆已發表，包含結構、電化學和磁性都有詳細的研究。 在我的研究部分，修飾已發表的H2bpyany配基，在兩末端吡啶的5號位上修飾苯基，以及將兩端吡啶以嘧啶或吡嗪做取代，藉此達到修飾的效果。因此合成出三個配基，H2bphpyany、H2bphpmany和 H2bphpzany，再以此三個配基合成出鎳金屬串與鈷金屬串。 在六核鎳金屬串的部分，利用H2bphpyany、H2bphpmany這兩個配基，成功的合成出5個化合物，[Ni6(bphpyany)4Cl2](PF6)2 (1)、[Ni6(bphpyany)4Cl2](PF6) (2)、[Ni6(bphpyany)4(NCS)2](PF6)2 (3)和[Ni6(bphpmany)4Cl2](PF6)2 (4)、[Ni6(bphpmany)4Cl2](PF6) (5)，經由X光單晶繞射鑑定，發現結構與已發表的[Ni6(bpyany)4X2](PF6)n (X = Cl, NCS; n = 2, 1)相同，且相關鍵長也幾乎一樣。在磁性方面，化合物1、3、4的兩末端五配位的Ni2+為高自旋，因此是屬於反鐵磁性。而2、5中間的萘啶單元具有Ni23+的磁性中心，所以由磁性表現來看是屬於順磁性物質。 在第二個部分為鈷金屬串的研究，利用修飾配基H2bphpyany和 H2bphpzany，成功合成出[Co6(bphpyany)4(NCS)2](PF6) (6)、[Co6(bphpyany)4(NCS)2](PF6)2 (7)、[Co5(bphpzany)4(NCS)2] (8)、[Co5(bphpzany)4(OTf)2] (9) 和 [Co6(bphpzany)4(NCS)2](PF6) (10) 五個化合物，從結構上可以分為兩個部分，化合物8和9為缺陷的五核鈷金屬串，左右兩端為燈籠型的雙核鈷單元，中間為一個罕見的八配位鈷離子，形成一個直線型的[Co2…Co…Co2]金屬串。磁性方面雙核鈷單元為逆磁性單元，中間八配位的鈷離子是屬於高自旋的電子組態。化合物6和10具有Co611+的結構，其磁性具有spin-crossover的現象。化合物7的結構與6相似，磁性是一個順磁性的表現。導電度方面，缺陷的五核鈷金屬串與全未定域化的六核鈷金屬串，其導電值並沒有明顯的差異。利用理論計算其化合物8與10，藉由分析分子軌域的組成與其鍵級分布，成功解釋其導電度的現象。

In the past several decades, 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. In order to develop new generation of metal string complexes, two series of them, which contain fine tuning of ligands or a heterometallic framework, have been studied. Ligands such as oligo-α-pyridylamines and oligo-naphthyridylamine are usually used in the linear metal string complex, and another series of ligands made up of pyridyl and naphthyridyl moieties, are designed and used for the development of metal-string complexes. For the series, the shortest symmetrical ligand, 2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany), has been used for the syntheses of a series of hexa-nuclear metal string complexes, [M6(μ6-bpyany)4X2](PF6)n (M = Ni, Co; X = Cl, NCS; n = 1, 2), and their structural characterizations, electrochemistry, and magnetic properties have been published. In the present work, we modified the published ligand, H2bpyany, replacing the 5-position hydrogen atom of pyridyl groups with phenyl groups and the pyridyl groups with pyrimidyl and pyrazine groups. Three fine-tune ligands, H2bphpyany, H2bphpmany, and H2bphpzany, were synthesized and used to synthesize nickel and cobalt metal-string complexes. In hexanickel metal-string complexes, four linear extended Ni chains complexes, [Ni6(bphpyany)4Cl2](PF6)2 (1), [Ni6(bphpyany)4Cl2](PF6) (2), [Ni6(bphpyany)4(NCS)2](PF6)2 (3), [Ni6(bphpmany)4Cl2](PF6)2 (4), and [Ni6(bphpmany)4Cl2](PF6) (5), have been synthesized using the modified H2bphpyany and H2bphpmany ligands, and their structures have been determined by single-crystal X-ray diffraction. The crystal structure of these complexes show that the Ni‒N and Ni‒Ni distances are similar with [Ni6(bpyany)4X2](PF6)n (X = Cl, NCS; n = 2, 1) in the literature. The temperature dependent magnetic measurements performed on two independent high-spin nickel(II) ions of 1, 3, and 4, demonstrating that metal strings are antiferromagnetic. Complexes 2 and 5 contain two independent high-spin nickel(II) ions like 1 and one mixed-valence Ni23+, displaying that it is paramagnetic. In the second part, five hexacobalt metal-string complexes, [Co6(bphpyany)4(NCS)2](PF6) (6), [Co6(bphpyany)4(NCS)2](PF6)2 (7), [Co5(bphpzany)4(NCS)2] (8), [Co5(bphpzany)4(OTf)2] (9), [Co6(bphpzany)4(NCS)2](PF6) (10), supported by four bphpyany2- or bphpzany2- ligands have been synthesized, and characterized. The structure of complexes 8 and 9 consist of two lantern-type dinuclear Co2 fragments at the terminal positions and one rare octacoordinated cobalt at the centre forming a linear [Co2…Co…Co2] chain. The magnetic susceptibility measurements show a quartet ground state with a significant spin-orbital contribution of the centre Co(II) ion. Complexes 6 and 10 consist of a linear Co611+ configuration wrapped by four ligands and their magnetic susceptibility measurement reveal a spin-crossover process (S = 1/2 ⇆ S = 3/2). The structure of 7 is similar with 6, and its magnetic behavior measurement reveals paramagnetism. In the study of single molecular conductance, defective pentacobalt and fully delocalized hexacobalt atom chains also do not show any difference. We use the theoretical calculation, Extended Hückel method, to analyze the consisting of molecular orbitals and the distributing of bond order about 8 and 10, and successfully explain the interesting phenomenon.