Syntheses and Studies of Modified Tripyridyl Diamine Ligand (H2dpqda) and the Linear Nickel String Complexes
Date Issued
2007
Date
2007
Author(s)
Chiu, Chun-Chieh
DOI
zh-TW
Abstract
The aim of this thesis is to investigate the synthesis, structures, and correlative magnetic properties of linear nickel metal string complexes, where the new ligand is 2-dipyridyl-2’-quionlinyl diamine (H2dpqda). The design of H2dpqda ligand which exists sterical hindrance is expected to block the axial ligand. Due to asymmetrical H2dpqda ligand, nickel metal string complexes may have several isomers, e.g. (4,0), (3,1), (2,2) cis, (2,2) trans head-tail isomers.
The H2dpqda ligand reacts with Ni(OAc)2•4H2O in high temperature of melt naphthalene, and the axial ligand is NCS- from NaSCN.
From FAB-MS data, it shows two apparent signals. One is the five
nickel metal string, [Ni5(μ5-dpqda)4(NCS)2] (1), and the other is [Ni4(μ4-dpqda)3(μ3-Hdpqda)(NCS)] (2). They can be separated by the different crystalline form. The reaction of LiCl with H2dpqda ligand and Ni(OAc)2•4H2O is expected to controll (4,0) form by using the chloride as axial ligand.
Three linear nickel complexes 1, 2 and [Ni4(μ4-Hdpqda)4(Cl)(F)](BF4)2 (3) have been characterized by X-ray crystallography. The crystal structure shows that complex 1 belongs to (4,0) form and at crowded NCS axial ligand, the bond distances have many differences compared to [Ni5(tpda)4(NCS)2]. For complex 2, it is supposed to have the same reaction as H2tpda ligand. Complex 3 is also (4,0) form because of the chloride axial ligand.
The magnetic results show complex 1 and 3 have two high spin nickel(II) atoms with antiferromagnetic coupling. The magnetic moment of complex 2 owning nonlinear crystal structure displays ferromagnetism.
From STM data, unsymmetrical complex 1 does not show rectification. The resistance of a single complex 1 is 27.5 MΩ, not much different from that of complex 3 (24.0 MΩ). In the future, it is to expected to design new ligands to synthesize metal string complexes having better conductance and rectification.
Subjects
金屬串
分子導線
metal string
metal-metal bonding
Type
thesis
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