一系列同向排列不對稱四核鎳金屬串錯合物之合成與研究

Abstract

透過在萘啶吡啶胺配基上修飾甲基與苯基，成功地合成出一系列的鎳金屬串錯合物，並研究其結構、電化學、磁性、導電度等性質。從結果來說，在配基上修飾甲基或苯基造成金屬串具有較大的立體障礙，並利用文獻中四個萘啶配基可以穩定雙核鎳的選擇性，再以結晶純化而成功地以不對稱的四氮配基合成出一系列的同向排列的不對稱四核鎳金屬串錯合物。 在配基合成的部分，2-chloro-1,8-naphthyridine 和 2-amino-5-phenylpyridine 在鹼性環境下合成出 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine (Hphpyany) 配基，而 2-chloro-1,8-naphthyridine 和 2-amino-4-picoline 在鹼性環境下合成出 2-α-picolylamino-1,8-naphthyridine (Hpcany) 配基。利用 Hphpyany 配基，合成出[Ni4(phpyany)4(Cl)2](CF3SO3) 1, [Ni4(phpyany)4(Cl)2](BF4)2 2, [Ni4(phpyany)4(NCS)2](ClO4) 3, [Ni4(phpyany)4(NCS)2](CF3SO3)2 4，同時也利用 Hpcany 配基合成出 Ni4(pcany)4(Cl)2](ClO4) 5, [Ni4(pcany)4(Cl)2](PF6)2 6, [Ni4(pcany)4(NCS)2](PF6) 7 和 [Ni4(pcany)4(NCS)2](PF6)2 8。 這八個錯合物皆是以四片不對稱脫氫配基螺旋纏繞在直線排列的鎳金屬串上，四片配基皆是以(4,0)異構物的型式排列。在錯合物1、3、5、7中，皆為還原一個電子的的金屬串，其配位在萘啶環上的鎳鎳距離約為 2.33 Å，較其氧化一個電子的產物2、4、6、8來的短。從磁性測量結果可以發現，在錯合物1、3、5、7中，末端的Ni2+ 與Ni23+ 混價單元具有反鐵磁作用力 (錯合物1為 J = -42 cm-1、錯合物3為 J = -46 cm-1、錯合物5為 J = -42 cm-1、錯合物7為 J = -43 cm-1)，而在錯合物2、4、6、8中，末端的兩個Ni2+也具有反鐵磁性作用力 (錯合物2為 J = -33 cm-1、錯合物4為 J = -35 cm-1、錯合物6為 J = -32 cm-1、錯合物8為 J = -35 cm-1)。在循環伏安電位測量中，錯合物1具有E1/2(1) = 0.12 V與E1/2(2) = -0.65 V，錯合物3具有 E1/2(1) = 0.10 V與E1/2(2) = -0.72 V，錯合物5具有E1/2(1) = 0.10 V與 E1/2(2) = -0.71 V，錯合物7具有E1/2(1) = 0.13 V與E1/2(2) = -0.65 V。電子吸收光譜中，還原一個電子的錯合物1、3、5、7 在 600-700 nm 之間會有一個平緩的吸收峰。我們也利用NMR來鑑定錯合物1-8中配基是否皆為同向排列的。此系列四核鎳金屬串是第一個可以利用STM break-junction方式量測單分子導電度，其導電值錯合物3為8.36 (±1.88)×10-4 G0、錯合物4為7.95 (±2.47)×10-4 G0、錯合物7為 (7.66 (±2.50)×10-4 G0、錯合物8為 (7.62 (±3.28)×10-4 G0。

A series of tetranickel metal chains supported by the fine-tuning ligand, Hphpyany and Hpcany, were synthesized successfully. Their structures, magnetic property, electrochemistry, absorption spectra, NMR spectra and single-molecule conductance were investigated. The isomeric issue of the asymmetric tetranickel metal chains has been overcome successfully by means of the fine-tuning moieties of phenyl group and methyl group and further crystallization. The new ligand, 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine (Hphpyany), was synthesized by the reaction of 2-chloro-1,8-naphthyridine with 2-amino-5-phenylpyridine in the presence of potassium tert-butoxide under palladium(0)-catalyzed condition, and 2-α-picolylamino-1,8-naphthyridine (Hpcany) was synthesized by the reaction of 2-chloro-1,8-naphthyridine with 2-amino-4-picoline in the presence of potassium tert-butoxide under palladium(0)-catalyzed condition. The linear tetranickel metal complexes, [Ni4(phpyany)4(Cl)2](CF3SO3) 1, [Ni4(phpyany)4(Cl)2](BF4)2 2, [Ni4(phpyany)4(NCS)2](ClO4) 3, [Ni4(phpyany)4(NCS)2](CF3SO3)2 4, [Ni4(pcany)4(Cl)2](ClO4) 5, [Ni4(pcany)4(Cl)2](PF6)2 6, [Ni4(pcany)4(NCS)2](PF6) 7 and [Ni4(pcany)4(NCS)2](PF6)2 8 were synthesized and have been crystallographically characterized. All of the complexes consist of four phpyany- ligands or pcany- ligands wrapped around a linear tetranickel core, in the same orientation. The remarkably short Ni-Ni distances (ca. 2.33 Å) for compounds 1, 3, 5 and 7 indicate partial metal-metal bonding, which can be viewed as each complexes containing one mixed-valence Ni23+ unit. Magnetic susceptibility measurements reveal that the Ni47+ core complexes 1, 3, 5 and 7 exhibit antiferromagnetic interaction (J = -42 cm-1 for 1, J = -46 cm-1 for 3, J = -42 cm-1 for 5 and J = -43 cm-1 for 7) between the terminal Ni2+ ion and the Ni23+ unit, while the Ni48+ core complexes 2, 4, 6 and 8 exhibit antiferromagnetic interaction (J = -33 cm-1 for 2, J = -35 cm-1 for 4, J = -32 cm-1 for 6 and J = -35 cm-1 for 8) between the two terminal Ni2+ ions. The results of the cyclic voltammetry indicate the presence two reversible redox couples at E1/2(1) = 0.12 V, E1/2(2) = -0.65 V for 1, at E1/2(1) = 0.10 V, E1/2(2) = -0.72 V for 3, at E1/2(1) = 0.10 V, at E1/2(2) = -0.71 V for 5 and at E1/2(1) = 0.13 V, E1/2(2) = -0.65 V for 7. The products of the oxidation process E1/2(1) of 1 and 3 are the corresponding oxidized species 2 and 4 respectively, and the products of the oxidation process E1/2(1) of 5 and 7 are the corresponding oxidized species 6 and 8 respectively. The absorption spectra of compounds 1, 3, 5 and 7 are shown a broad peak in the 630-650 nm regions while no significant absorption in the 600-700 nm for compounds 2, 4, 6 and 8. The NMR spectrum was utilized to investigate the isomeric issue for compounds 1-8. The values of conductance (8.36 (±1.88)×10-4 G0 for 3, 7.95 (±2.47)×10-4 G0 for 4, (7.66 (±2.50)×10-4 G0 for 7 and (7.62 (±3.28)×10-4 G0 for 8) and resistance (15.4 (±3.46) MΩ for 3, 16.2 (±5.04) MΩ for 4, 16.8 (±5.51) MΩ for 7 and 16.9 (±7.29) MΩ for 8) were determined by STM break-junction measurements. These represent the first conductance measurements of linear tetranickel chain.