Syntheses and Studies of Geometric Isomers of Tetranickel Strings with 2-α-Pyridylamino-1,8-Naphthyridine Ligand
Date Issued
2007
Date
2007
Author(s)
Wang, Rui-Ren
DOI
zh-TW
Abstract
The goal of this thesis is to study isomer effect to the influence of the metal string complexes. Here we presented the design and preparation of new unsymmetrical tetradentate ligands and the investigation of their linear tetranickel string complexes. X-ray structures, electrochemistry and magnetism of the linear tetranickel string complexes were studied.
(1) Three new ligands, 2-α-pyridylamino-1,8-naphthyridine (Hpyany), 2-α-pyrazaylylamino-1,8-naphthyridine (Hpzany), 2-α-picodylamino-1,8-naphthyridine (Hpcany), were synthesized by the palladium-catalyzed cross-coupling of 2-chloro-1,8-naphthyridine with the corresponding amine. The crystal structures of Hpyany, Hpzany and Hpcany were studied, and extensive hydrogen bonding between the amindo group and nitrogen atoms of naphthyridine and pi-pi interaction between pyridine and naphthyridine rings were observed.
(2)The linear tetranickel string complexes were synthesized through reacting of ligand with NiCl2. Owing to the asymmetry of the ligands, there are four possible geometrical isomers of the tetranickel string complexes resulting from the orientations of the ligands, abbreviated as (4,0), (3,1) and (2,2-cis) forms. The isomers of tetranickel string complexes were successfully synthesized and isolated. For instance, complex [Ni4(pyany)4(NCS)2]2+ exhibits the major products (4,0) and (3,1) isomers, and [Ni4(pzany)4(Cl)2]n+ (n=1,0) was successfully synthesized and isolated as (4,0)、(3,1) and (2,2-cis) geometric isomers. The electrochemical study showed that different oxidation states are accessible. Through redox
reaction, three oxidation states of linear tetranickelstring complexes, eg, complexes with one-electron reduced and two-electron reduced species, [Ni4(L)4X2]n+ (n=0, 1, 2), were successfully obtained and structurally characterized, and their electrochemistry and magnetism were studied. Using our pyrazine-modulated ligand, Hpzany, the tetranickel string [Ni4(pzany)4(Cl)2]n+ (n=2,1,0) were successfully synthesized and isolated as (4,0)、(3,1) and (2,2-cis) geometric isomers. two isomers (4,0) and (3,1) conformation with one-electron reduction occurred on position corresponding to naphthyridine rings; the other is (2,2-cis) form of two-electron reduction products. Therefore, we got further understanding of isomer effect for metal string complexes.
(3)The magnetism of linear tetranickel string complexes of different isomers with different oxidation states were studied. The two terminal nickel atoms in [Ni4(pyany)4(NCS)2]2+ existed in high spin state of S = 1 and showed an antiferromagnetic coupling (J = - 36 cm-1 ). However, after one-electron reduction that occurred in the two nickel atoms at the position of naphthyridine rings, the spin state of the two nickel atoms is S =3/2. The antiferromagnetic coupling between two spin states increased to J = - 83cm-1 after one-electron reduction of tetranickel string complexes.
(4) A new series of tetranickel string complexes with ligands (H2N-(-)-camdapa), (H2Tsdapa) and (H2Msdapa) were synthesized to study the bulky steric effect. Due to the strong electron-attract effect and bulky steric effect of solfonyl group, mixed-ligand tetranickel string complexes were obtained. The tetranickel string complexes underwent one-electron reduction, producing two complexes with one compound containing an axial ligand Cl– and another no axial ligand. The one-electron reduction occurred in dinickel unit on naphthyridine of compound without axial ligand, generating a strong antiferromagnetic coupling between two spin state of S = 3/2 and S = 1. J = - 89cm-1.
Subjects
萘
啶
吡
胺胺
幾何異構物
naphthyridine
pyridine
geometric isomer
Type
thesis
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