Syntheses and Characterization of Metal Strings and Cluster Complexes with the Modified Asymmetrical Ligands
Date Issued
2011
Date
2011
Author(s)
Dai, Pin-Ren
Abstract
The aim of this research is to investigate the synthesis, structure, and properties of the pentanickel metal string complexes and the tetranuclear cluster which the ligands are 2-pyridylamino-7-acetylamino- 1,8-naphthyridine (H2pan) and 2-(5-phenylpyridyl) -amino-7-acetylamino-1,8-naphthyridine(H2ppan).
The novel asymmetrical ligands were synthesized by palladium-catalyzed reaction which was proposed by S. L. Buchwald27, and the product was characterized by NMR and FAB-MS.
First of all, we reacted these ligands with Ni(OAc)2．4H2O at high temperature of melt naphthalene, we successfully obtained two novel pentanickel metal string compounds, [Ni5(pan)4(OAc)2] and [Ni5(ppan)4Cl2]. The X-ray structure studies of [Ni5(pan)4(OAc)2] reveals the crystal system is triclinic and the space group is P-1. In the structure of [Ni5(pan)4(OAc)2], the terminal nickel ions (Ni5, Ni4) are octahedral. In the metal string, the outer nickel ions (Ni1, Ni3) are square pyramidal and the central nickel ion (Ni2) is square planar. The axial ligand is acetate ion. There are two forms for ligands binding: one uses the nitrogen atom from amide group to bind terminal nickel ions, and another uses oxygen atom from amide to connect with two outer nickel ions as a bridge. Compared to traditional metal string, the middle part of this complex is similar to trinickel string complexes. The average metal distance from inside to outside is 2.414 and 3.30 A. Through the bond length of Ni-N, we know that Ni(2) is LS, and other Nickel ions are HS. The magnetic properties shows that the pentanickel complex [Ni5(pan)4(OAc)2] is antiferromagnetic. The μeff value for [Ni5(pan)4(OAc)2] is 5.16 B.M at 300K. The CV of [Ni5(pan)4(OAc)2] complex show one reversible reduction at -0.78 V.
The structure of [Ni5(ppan)4Cl2] is monoclinic, and the space group is P21/c. The major structure is similar to that of [Ni5(pan)4(OAc)2]. The main difference is that the outer nickel ions are square pyramidal. The magnetic properties show that the pentanickel complex [Ni5(ppan)4Cl2] is antiferromagnetic. The μeff for [Ni5(ppan)4Cl2] is 5.01 B.M at 300 K. The CV of [Ni5(ppan)4Cl2], one reversible reduction at -0.70 V for [Ni5(ppan)4Cl2].
Eventually, we study the coordination chemistry by using H2pan ligand to react separately with cobalt, copper and zinc ions to get tetranuclear clusters; among this, copper and zinc metal clusters all formed [2×2] structure. We also study its structure and magnetic properties.
Subjects
Nickel Metal String
Coordination chemistry
Metal Cluster
Type
thesis
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